Ported Head & Cam rwhp gain

[Randy N Connie]

How much RWHP did you gain after installing ported heads & cam?

Thanks Randy

[SilverCasket]

About 60-80.

Anthony

[David Neibert]

How much RWHP did you gain after installing ported heads & cam?

Thanks Randy

Randy,

Only around 25-30 but the car went from running 13.8 to 13.3.....then I upgraded the blower & plenum and gained another 50.

David

[Slysc]

My first set of ported heads and cam gave me about -30 hp:rolleyes:

My second set of heads with the same cam put me at 289 hp compared with the stock hp.

[XR7 Dave]

My heads/cam package got me 30rwhp at peak, but extended the range significantly. Torque went up only about 10rwtq. That was with a stock 90 blower. I went from running 14.50 @ 95mph to running 14.20 @ 98mph. Problem was that I went from seeing in increase from 12-14psi through the rpm range to seeing drop from 11-10psi through the same range.

I think it is possible to pickup 100rwhp with the right combination.

[JStudrawa]

My heads/cam package got me 30rwhp at peak, but extended the range significantly. Torque went up only about 10rwtq. That was with a stock 90 blower. I went from running 14.50 @ 95mph to running 14.20 @ 98mph. Problem was that I went from seeing in increase from 12-14psi through the rpm range to seeing drop from 11-10psi through the same range.

I think it is possible to pickup 100rwhp with the right combination.

Uhm, call me ignorant but... you're saying I put a nice cam and 3 way ported heads into the bored-30-over engine I have sitting there, and I can gain up to 100 rwhp?

Without what other mods, since I am stock right now.

[DamonSlowpokeBaumann]

I dont think 100rwhp will be happening with a bone stock motor with just mildly ported heads and a cam.

[shotbirdsc]

My Car gained 34 RWHP I upgraded to Steig III and cam. Ran 99-100 mph traps before now runs 104-106 mph traps. Et's are terrible but that's not the engines fault. ;)

[XR7 Dave]

Uhm, call me ignorant but... you're saying I put a nice cam and 3 way ported heads into the bored-30-over engine I have sitting there, and I can gain up to 100 rwhp?

Without what other mods, since I am stock right now.

No, I was saying that my car with a crap blower and nothing else in it's favor picked up 30rwhp with no other changes. I said "with the right combination" you can pick up as much as 100rwhp. Back when the Stiegemeier heads/cam package first came out they got 70rwhp on a mildly modded 95 SC. If you have all the right parts bolted to a stock motor and then upgraded heads and cam afterwards I think 100rwhp is quite possible.

My 89 SC made 295rwhp with a FMIC and an AR blower. With good heads and cam in place the same combination makes over 400rwhp. That's not speculation.

[DamonSlowpokeBaumann]

My disclaimer is mildly.

And yes heads and cam will make a large difference once they become the main restriction of an engine

[Randy N Connie]

My disclaimer is mildly.

And yes heads and cam will make a large difference once they become the main restriction of an engine

Mine, you might say would be mild. I used a peice of sandpaper wraped
around my finger to do the port work. ;) Melted some lead in the
ports with a bick-lighter.:p

Randy

[83GT460]

How much RWHP did you gain after installing ported heads & cam?

Thanks Randy

Randy if you aren't in a big hurrry I will send you dyno sheets from before and after as soon as I am done with mine. I think my only changes for the next set of dyno runs are going to be heads, cam, and injectors. The heads I will be using should be about the same as what you showed me in the trunk of your car at the Hotel in Oklahoma.

Charles

[seawalkersee]

I guess thats a NO on needing to borrow some parts:D

Chris

[DamonSlowpokeBaumann]

The heads I will be using should be about the same as what you showed me in the trunk of your car at the Hotel in Oklahoma.


Is this secret code for welded exhaust ports? lmao

[seawalkersee]

I must not have been near that car. I would have liked to look at those heads too. I can not picture Charles or his car....Now I am sad.:(

Chris

[Mansier]

I ported the heads on our road race myself. Took about 6 hours on each head. Did a short job on the intake, then another 6 hours or so on the stock blower housing. The engine was a 110,000 mile engine. Other mods included 3.8 mustang MAC headers and ford powerstroke intercooler. A 5% pulley was added along with lightweight pulleys for the accessories. I am pretty sure everything else was stock, and the cam sensor was off (WAY off) when we dynoed. RW numbers were 242rwhp, 333rwtq. Pretty good for an engine with no bottom end work at all.

Now we have a new cam, the right timing, and the bigger injectors/MAF, etc. Should be more like 275-285 rwhp. (I'M HOPING!).

LM

[83GT460]

Is this secret code for welded exhaust ports? lmao

No not really secret code, I said that because he & I were discussing the heads because we both purchased from David Dalke what started as the last three sets of Steigmeirs and yes they are the version with welded exhust ports. I really don't have any secret mods on my car, I will gladly tell anyone what I have done to it.

Charles

[CMac89]

I ported the heads on our road race myself. Took about 6 hours on each head. Did a short job on the intake, then another 6 hours or so on the stock blower housing. The engine was a 110,000 mile engine. Other mods included 3.8 mustang MAC headers and ford powerstroke intercooler. A 5% pulley was added along with lightweight pulleys for the accessories. I am pretty sure everything else was stock, and the cam sensor was off (WAY off) when we dynoed. RW numbers were 242rwhp, 333rwtq. Pretty good for an engine with no bottom end work at all.

Now we have a new cam, the right timing, and the bigger injectors/MAF, etc. Should be more like 275-285 rwhp. (I'M HOPING!).

LM
Is this with a late or early model blower?

[Mansier]

The car is a 1992, so I guess that is early model

[CMac89]

Well, you can put late model blowers on any SC........

[DamonSlowpokeBaumann]

Charles it was a joke. I actually have those same heads except I had a lil more work done to em and a crapload of highperformance coatings.

[Mansier]

The car was stock when I got it. So the blower was circa 1992.

[83GT460]

Charles it was a joke. I actually have those same heads except I had a lil more work done to em and a crapload of highperformance coatings.

I realize that it was a joke, I get your NYC humor! Now back to the question in hand, only a 30 HP gain from a set of heads and a cam, I am afraid I am going to be a very unhappy camper if I don't see better results

Charles.

[David Neibert]

I realize that it was a joke, I get your NYC humor! Now back to the question in hand, only a 30 HP gain from a set of heads and a cam, I am afraid I am going to be a very unhappy camper if I don't see better results

Charles.

Charles,

How much you gain, depends on what order you do your supporting mods. I didn't gain much because the blower I had wasn't moving enough air.

David

[83GT460]

Charles,

How much you gain, depends on what order you do your supporting mods. I didn't gain much because the blower I had wasn't moving enough air.

David

David that is something that is good to point out so that those who would be considering mods such as this will have a better understanding of what it take to make more power. I as well as others have said many times it is not always the number of mods that you have but how well they work together. Oddly enough whenever I dynoed my car last, it made peak power all the way out to 5600 RPM which it shouldn't be able to do with stock heads, cam, and my own porting on the blower. I think it would still make more power but it is out of injector and I have the alcohol turn all the way up and am using the largest nozzel I have. I am definately shooting for good numbers with the new heads, cam and big injectors and once that is done it's time for a nice new twin screw.

Charles

[CMac89]

I think that 30rwhp gain from a ported stock valve head and a cam with MPI/II sounds fair. If you have stock IC atleast.

[83GT460]

I think that 30rwhp gain from a ported stock valve head and a cam with MPI/II sounds fair. If you have stock IC atleast.

Mine won't be stock valve and at some point I won't be using the stock IC. Who knows maybe my head and cam change will show a 20-30 HP gain and then when I change IC it may show a 40HP gain. It's all about parts working together.

Charles

[CMac89]

It's all about parts working together.
This is more than true. If you have oversized valves and a FMIC I wouldn't be surprised if you made a 50-60rwhp gain.

[XR7 Dave]

Charles, if you do some *quality* software dyno simulations, you will see that the data doesn't suggest that the motor should just fall over and die at 4500rpm. There are some non-mechanical factors that are causing the motor to lay down.

[83GT460]

Charles, if you do some *quality* software dyno simulations, you will see that the data doesn't suggest that the motor should just fall over and die at 4500rpm. There are some non-mechanical factors that are causing the motor to lay down.

David I haven't used any software to do any simulations but was just basiclly going with the common consensus that a stock headed and cammed motor is usually done by 4500-4800. I also realize that much of this has to do with the overly safe factory A/F ratios and timing tables.

Charles

[XR7 Dave]

David I haven't used any software to do any simulations but was just basiclly going with the common consensus that a stock headed and cammed motor is usually done by 4500-4800. I also realize that much of this has to do with the overly safe factory A/F ratios and timing tables.

Charles

Yes, people also say that my cam should be all done by 5500rpm. And there was a time when it was....

[turbospeed]

well in my mostly stock SC im expecting a 15RWHP gain wih a camand a 3 angle valve job....is that expecting too much?

im expecting to hit 250rwhp with my mods , 94/95 blower and a tune.

and according to my desktop dyno software i should expect like a 3hp gain from my .20 pistons lol

[DamonSlowpokeBaumann]

.20 pistons will increase compression and unshroud ya valves a bit I believe...Mayeb more then that!

[DamonSlowpokeBaumann]

I like to post things twice at times hahaha

[XR7 Dave]

.20 pistons will increase compression and unshroud ya valves a bit I believe...Maybe more then that!

I'm not sure why you are so stuck on this idea. Do you have data which supports your assertion that a larger bore will make a significant impact on port flow in this case? I ask because I have studied the valve/cylinder bore interaction and it is my opinion that even a .060" increase in bore size is of very minimimal if not even inconsequential consequence, particularly if one stays with a valve which will seal on the stock seats.

Of much greater consequence is the fact that most SC blocks are well above spec in height which means that most SC's have nowhere near 8.4:1 compression in the first place.

[CMac89]

A larger bore always has had a positive influence on port flow from what I've ever experienced. I went from a 4.180 bore to a 4.210 bore on my SSer and got 12 more cfm. They do unshroud the valves more and compensates for the lack of steep seat angle on any application.

I've always seen that the lower the valve angle then the air runs into the side of the cylinder wall on a continued angle. The steeper the seat angle the less prone the air is to hitting the cylinder wall resulting in a proper flow path into the cylinder. I have my valves on the race motors all at 57*.

The relevance of this is that the larger the bore, the straighter and farther down the air runs into the cylinder, the more flow you are going to pick up.

[DamonSlowpokeBaumann]

Dave,

I did say a bit! So what is it that I am exactly stuck on? Opening up a bore generally helps in the unshrouding of valves...I did say I believe it will help unshroud valves..Not that it definately will..Or oh my god you wouldnt believe how much this will unshroud yoru valves..

Soo..

Exactly what is it I'm stuck on?

I dont think there is any argument that increasing the bore increases compression however:O) And I didnt say OH MY GOD LOOK HOW MUCH MORE COMPRESSION YOU WILL GET FROM THAT EITHER!

I did however imply that youde probably makwe more then 3hp from it :O)

MERRY XMASS DAVE!

PS Thanks to CMAC for explaining this in laymans terms:O)

[DamonSlowpokeBaumann]

Just in case.............

The swept volume of the cylinder indicates how much air the piston displaces as it moves from BDC to TDC. Increasing the cylinder volume without making any other changes will increase the compression ratio because it enlarges the cylinder volume without increasing the combustion chamber volume. In other words, the piston will have to cram more air into the same amount of space. Cylinder volume is calculated using the bore and stroke of the engine with this formula: Cylinder volume = 0.7853982 x bore2 x stroke

On a standard 350 Chevy, the bore is 4.00 inches and the stroke is 3.48. Apply the formula, and you'll find that one cylinder is 43.730 ci (multiply this times eight cylinders and you get 349.84, which is rounded to 350 for total engine displacement).

If you overbore our sample 350 from 4.00 inches to 4.020 inches and make no other changes, the compression ratio will increase from 8.84:1 to 8.90:1 because the volume of the cylinder has increased. When overboring an engine, the percentage of gain in compression ratio decreases as you add clearance volume and increases as you remove clearance volume.

[XR7 Dave]

Sorry for coming across that way. I was referring to the fact that you have brought up the airflow advantage of cylinder overbore several times in the past and in each case I feel that it is minutia rather than something of real relevance.

For example, in CMac's case, while he picked up 12cfm, my question is two fold. 1) how close do the valves actually come to the cylinder wall in your case? and 2) what % of increase in flow does that 12cfm represent? and 3) do your cylinder heads employ canted valves?

Regarding compression, my point was very valid and totally glossed over. In the case of the 3.8L engine in question, a change in bore from 3.811 to 3.831 results in a change of compression ratio from the theoretical 8.4:1 to 8.48:1. However, decking the block to 0.000" (OE spec) from a more typical 0.015" will raise compression from an actual 8.16:1 to OE specified 8.4:1. If you've ever wondered how SC's run with 28-29 deg timing and 15psi boost, now you know. I've measured some SC motors as low as 7.9:1. Simply blueprinting the stock motor to the tight side of factory tolerance can get you as high as 8.8:1 on an early deep dish piston. How about them apples?

This is why I get frustrated some times when people labor over minutia until people toss up their hands and walk away when the big issues go on unaddressed.

Same thing goes for harmonic balancers, but we won't go there. :p

[DamonSlowpokeBaumann]

Dave,

Kinda like the long rod discussion :O) There is no substitution to making sure a motor is at the min reaching factory specs however that wasnt the discussion

Damon

[DamonSlowpokeBaumann]

And clearence Volume

Clearance volume is determined by the distance from the cylinder block deck to the top of the piston flat (not counting any dishes or domes) when the piston is at TDC. In many engines, especially 350 Chevys found in cars, the pistons don't come all the way up to the height of the deck--they can be anywhere from 0.003 to 0.020 inch below it. This amount is known as the piston deck height, and it affects compression ratio because it affects the volume of air in the combustion area when the piston is at TDC. If the piston is farther below the deck, then clearance volume is increased and the compression ratio is reduced. If the piston is closer to the deck, clearance volume is reduced and compression ratio is increased.

Here's how to calculate the clearance volume once you know the piston deck height: Clearance volume = 0.7853982 x bore2 x deck height

In our sample 350 with a deck height of 0.015 inch (meaning the top of the piston is 0.015 inch below the deck of the block), the clearance volume is 0.188 ci.

If the deck height of our sample engine was increased to 0.020, compression would drop from 8.84:1 to 8.75:1. If the deck height of our sample engine was decreased to 0.003, compression would increase from 8.84:1 to 9.05:1.

[DamonSlowpokeBaumann]

And what about Piston Dome?

Note that clearance volume does not take into account any pop-up domes or sunken-in dishes on the head of the piston. These configurations also increase or decrease volume in the combustion chamber and affect the compression ratio. The manufacturer's catalog will list the displacement in cubic centimeters of the dishes or domes on the piston, but we've found that it's not consistent whether they express the cc's of a dish as a positive or a negative number. For the purposes of calculating compression, we prefer to view the cc's of a dish as a positive number because a dish adds volume to the cylinder (and reduces the compression ratio); a dome is a negative number because it subtracts volume from the cylinder (and increases the compression ratio).

Another confusion with piston designations is that they're listed in cubic centimeters, but we use cubic inches to calculate compression ratio. You can convert to cubic inches with this formula: Piston dome or dish in cubic inches = cc's x 0.0610237

Since our sample engine uses pistons that have 4.5cc dished valve reliefs in them, then they increase the volume of each cylinder by 0.275 ci. If we changed to pistons with a dish of 22 cc (1.34 ci) and made no other changes, then the compression ratio would drop from 8.84:1 to 7.58:1. If we used pistons with a dome of 12 cc (0.73 ci), then the compression would increase from 8.84:1 to 10.56:1.

[DamonSlowpokeBaumann]

HEad gaskets?

Head-gasket volume is determined by the compressed thickness of the gasket. A thicker gasket adds volume and reduces compression; a thinner gasket reduces volume and increases compression.

A gasket's compressed thickness is listed in the manufacturer's catalog and ranges from 0.051 inch to 0.015 inch. Also, the gasket bore is often larger than the engine bore; a 4.100-inch gasket is common. In our example, we assumed a head gasket with a 4.000-inch bore. Once you know the compressed thickness and gasket bore, here's how to calculate the volume that the gasket will add to the combustion area: Head-gasket volume = 0.7853982 x gasket bore2 x compressed thickness

In our example with a 0.038-inch thickness and 4.000-inch bore, the gasket adds 0.478 ci to the volume of the cylinder. If we used a thinner 0.015-inch gasket and made no other changes, the compression ratio would increase from 8.84:1 to 9.27:1.

[DamonSlowpokeBaumann]

Chamber Volume

The volume of the combustion chambers is the final factor in determining compression ratio. The larger the chamber, the more volume is added to the cylinder and the lower the compression ratio; smaller chambers reduce volume and increase the compression ratio.

For small-block Chevys, chamber sizes range from around 58 cc to 78 cc. However, the volume of the chambers can vary greatly depending on the type of heads and valves used, the amount the heads may have been milled, the number of valve jobs that have been performed, and any custom chamber grinding that has been done. Manufacturers of cylinder heads will tell you the range of sizes of the chambers in their heads, but for any used or custom-machined heads, the only way to know the size of the chambers is to have a machine shop check. Once this number is known, here's how to convert it from cubic centimeters to cubic inches: Chamber volume in inches = cc's x 0.0610237

Therefore, the 76cc chambers in our 350 have a volume of 4.638 ci. If we were to use cylinder heads with 58cc chambers and make no other changes, the compression ratio would increase from 8.84:1 to 10.72:1.

If you add up descrepencies in all 5 aspects that result in compression ratio well as you said Dave....It can be wayyyyyyyyyyyyyy off. And No I dont have the patience to write this crap. I pulled it from my archive of already written junk:O)

[CMac89]

For example, in CMac's case, while he picked up 12cfm, my question is two fold. 1) how close do the valves actually come to the cylinder wall in your case? and 2) what % of increase in flow does that 12cfm represent? and 3) do your cylinder heads employ canted valves?
That's about a 3.6% increase in peak flow. At .600 lift it picked up 6cfm, but at .900 it was 12cfm. 20cfm for me is about 40hp. I got 17 hp with the increase of bore size combined with the head flow.

The valves on our motors are about .035" since the intake and exhaust valve is only about .050" away from eachother closed. They are not canted. I noticed the SC valves are canted, which helps, but doesn't necessarily cancel out the plausibility of bigger bore and seat angle improvements in terms of headflow. I have a friend that runs a 454 bbc in SSer and gained 20cfm with going .060" over and 45* seat angle from a 30* seat angle. These valves are canted. Air still runs into the back of the valve and is thrown wherever the seat angle takes it to. It still is all relative.

Not sayin the increase on the SC flow numbers will be great with .020, but it does help. Whether or not it is significant can only be tested.

[seawalkersee]

WOW....THIS IS WHAT I am talking about. A serious technical discussion. Look what happens when I sleep. Ok, Damon all of your formulas appear to be correct, in fact, you have gone in to the rhelm of exact specs for building space ship tollerances. .061 is fine for ccs to inches and .7854 has always been good for PI. However, I think Dave has a valid point with his "How close are the valves to the wall" comment. Dave, it has been shown on a 4.6 that improving the bore GREATLY improves the flow. A LOT more then improving the stroke. But, there is an eywbrow in those heads that kinda kills the flow from the intake. The bore increase is a relevant arguement but I think with these heads, you would yeild a greater gain by lowering/raising the valve on its seat inside the chamber as Dave N. (I believe) did. I think the MAC touched on that but I am pressed for time this morning so I have to go back and read it later.

Chris

[XR7 Dave]

That's what I thought. :)

1) Our valves are canted 11 deg, so the further the valve opens, the further it pulls away from the cylinder walls.

2) As CMac pointed out, significant flow increases begin when flow exceeds .600". Since most mild SC's run at .550" lift or less (mine runs @ .513") a swag will tell you that we are in the "minimal impact" lift zone. Truth in fact is that at .500" lift the valve just barely clears the chamber wall meaning that chamber wall contour is much more critical than cylinder wall clearance.

3) Once the valve makes it past the chamber wall and begins to interact with the cylinder wall, the clearance in our motors (stock valve-stock bore, has grown to .155" vs. .050" in the above example motor. So an increase in bore size of .010" will result in less than a 10% change in the clearance to the cylinder wall. Keep in mind that this interaction is only relevant in about a 10% range of the radius of the valve. IMO the effect just keeps getting less and less the more we consider the factors involved.


Then while every thing Damon has posted is correct, my original point stands. Deck height is a much bigger factor in HP and compression than cylinder bore could ever be. I have seen that Ford is no better than Chevy in maintaining accurate deck heights as I've seen as much as .020" below deck on motors I've dissasembled. The advantages of a proper blueprint here are huge.

Typically the only way you can get the specified 8.2:1 compression ratio in these motors is to at least do a partial blueprint. A standard rebuild will often have 8.2:1 compression due to the overbore but I've never seen a stock motor that was close.

This is something to think about when considering how some people claim they never get detonation, others complain about pinging continually, and some cars run great with the stock tune and some don't.

Rather than yak about theory, lets look at some facts ok?

OE specs:

Chamber volume: 61.5/64.5cc (nominal = 63)
Deck height: -.027/.025 (nominal = -0.002)

Measured value:

Piston dish: 18cc

So static compression if the engine is entirely at nominal would be 8.10:1.
Worst case scenario - 7.64:1 :eek:
Best - 8.67:1
Best OE with .030" overbore - 8.79:1

As you can see the OE spec allows just over a full point of compression ratio variation all while staying within spec, while a .030" overbore can change ratio by 0.22 which will in some cases not even get you back to OE spec. I have found that most SC's run around 7.9-8.0:1.

People wanting to to run Super Stock at the SC Shootout might want to be taking notes. ;)

[CMac89]

The valves on the Pontiac heads are NOT canted so the contour, cylinder wall distance to the valve, and valve seat angle are the only things you can do about flow. The larger the bore you go the farther away the valve is from the cylinder wall and the radius from the valve to the contour of the cylinder wall increases.

Low lift on a canted valve in our SC motors makes everything worse because this is when the valve is closest to the cylinder wall. If we ran .900" lift then cylinder wall to valve distance wouldn't be as much of a concern flow wise. I would be willing to bet that our heads ported with oversized valves flow numbers will still be climbing to .700-.800 lift. This lift needs to be tried if possible for the reason the valves are canted 11*.

I agree, however, to compression being more influenced by deck height than increase in cylinder size. Overbore slightly helps, but deck height makes the huge differences. I went from .001" out of the hole, on my SSer, and had to machine the piston .002" in the hole and lost 15lbs of compression. This resulted in a loss of a tenth in ET, ouch.

Another reason deck height would have more of an influence on the SC motor is because of the aluminum head. Thermal efficiency is ALOT lower on an aluminum head than a cast iron. Static compression is the same, but when the cylinder is heated up then energy and heat is dispersed from the aluminum head resulting in lower compression as one aspect of the situation. I know soooo many stories of guys losing great amount of hp going from cast iron heads to aluminum. The reason being that compression and heat is lost during combustion. Coatings help, but it still isn't exactly close to what a cast iron head can do.

[XR7 Dave]

Low lift on a canted valve in our SC motors makes everything worse because this is when the valve is closest to the cylinder wall. If we ran .900" lift then cylinder wall to valve distance wouldn't be as much of a concern flow wise. I would be willing to bet that our heads ported with oversized valves flow numbers will still be climbing to .700-.800 lift. This lift needs to be tried if possible for the reason the valves are canted 11*.


No, your thinking is backwards. When closed the SC valves are no closer to the cylinder wall than any other motor. Once they open, they immediately start heading towards the center of the chamber, away from the wall. This means that when the valve starts to open, that is the only time the valve has anything in common with an inline valve setup.

It would be more accurate to say that with these heads, at low lift wall proximity is more critical than at higher lift. However, when you consider that it takes about .400" to clear the chamber wall, you can see that cylinder bore diameter isn't likely to be a significant flow determining factor at low lift.

Furthermore, testing has shown that the ports start to flatline really bad after as little as .500" lift in stock condition, and even in highly ported condition they start to flatline around .600" lift. SWAG would tell you that by .800 lift turbulence would have set in and flow would have begun to actually decrease.

:)

[DamonSlowpokeBaumann]

.800 lift..WHat happened to being realistic! :O)

[turbospeed]

so by .20 over bore and milling the head .010 i should expect my compression to be about 8:5:1 ??

[XR7 Dave]

Yes, although I would be more concerned with deck height than milling the heads to gain compression. Raising compression without eliminating the dead spot caused by a low deck height will make the motor more susceptible to detonation.

When you are having the motor decked (a MUST DO when rebuilding) make sure they take it to .000" clearance. You will need to know how much was taken off because you'll need to have the intake face of the intake manifold milled to match. If you do that, then your compression ratio will be closer to the OE claim of 8.2. Then once you have that, you can mill the heads if you want. .010 will raise you to about 8.5 in most cases. However, if your motor sits .020" in the hole, then you will lose significant compression as well as detonation resistance. Because all SC motors vary, there is not a specific amount that I can tell you to remove.

[turbospeed]

Yes, although I would be more concerned with deck height than milling the heads to gain compression. Raising compression without eliminating the dead spot caused by a low deck height will make the motor more susceptible to detonation.

When you are having the motor decked (a MUST DO when rebuilding) make sure they take it to .000" clearance. You will need to know how much was taken off because you'll need to have the intake face of the intake manifold milled to match. If you do that, then your compression ratio will be closer to the OE claim of 8.2. Then once you have that, you can mill the heads if you want. .010 will raise you to about 8.5 in most cases. However, if your motor sits .020" in the hole, then you will lose significant compression as well as detonation resistance. Because all SC motors vary, there is not a specific amount that I can tell you to remove.

well i didnt have my block decked altough i did use a torque plate to cut it.
:( i hope everything runs rigth once im done.

rigth now im just waiting for my clutch.

btw im thinking of breaking in my engine by running it a lil hard on it not bashing the engine but running it a lil hard.
also once its broken in its safe to race it and stuff or should i wait until i have it tuned.
the only important mod is the cam.

[DamonSlowpokeBaumann]

There are many theories on breaking in an engine. I perfer to drive normal but vary the engine RPM's often never going past 4,000 RPM's for the first couple of hundred miles..I also use synthetic motor oil. Which is perfectly acceptable

[seawalkersee]

Why would you ever mill a SC head unless it was warped? The deck is sooo short on them now.

Since we are talking about that, what about the CC in the head could we change, not lose any compression, and improve flow?

Chris

[89SCK@t]

Oh jesus....i need to get back to school for a math class...I have never been so lost...I feel ignant....:confused:

[DamonSlowpokeBaumann]

I feel lost everyday!

[seawalkersee]

I feel lost everyday!
Awww geezzz...and YOU are the one posting the formulas...You prolly have a Chevrolet hiding somewhere amongst your birds dont you?....

Chris

[CMac89]

There are many theories on breaking in an engine. I perfer to drive normal but vary the engine RPM's often never going past 4,000 RPM's for the first couple of hundred miles..I also use synthetic motor oil. Which is perfectly acceptable
A couple trips down the track with regular multi-grade oil has worked good for me.

[David Neibert]

Furthermore, testing has shown that the ports start to flatline really bad after as little as .500" lift in stock condition, and even in highly ported condition they start to flatline around .600" lift. SWAG would tell you that by .800 lift turbulence would have set in and flow would have begun to actually decrease.


Dave,

You are correct...I've had my heads flow tested several times and in their current form, they peak right about .600 and at .650 lift they must be getting turbulance because they flow considerably less (about the same as .550 lift).

David

[DamonSlowpokeBaumann]

Awww geezzz...and YOU are the one posting the formulas...You prolly have a Chevrolet hiding somewhere amongst your birds dont you?....

Chris

I had a CHebby sitting in my driveway once :O). Truth be told I have little patience for explaining these things and would rather someone else did and I just nitpick;O)

Even if Dave knew nothing about the airflow characteristics of an engine I would let him build my shortblock knowing full well he'd check every minute detail. (Knowing full well I would recheck everything when I got it back) :O)

Most typical engine builders will just rebuild. Very few actually :blueprint: an engine.

My stock blocked 302 V8 turbo motor makes the power it does and stays together due to the fact that it was indeed fully blueprinted. Same with my SC motor.

I would love to see what a blueprinted SC motor with stock cam, 5 angle valve job, cleanup of the ports (not true porting) would make power wise. I even have a feeling Dave has that up his sleeve

[Scott Long]

Whats so special about the 5 angle valve job. They cut the vavle seats in the head I know, but does the valve itself get cut? Or is it just hoping to get a little more air in and out around the edges of the valve hole in the chamber and make it seal up tighter when its closed?

[CMac89]

Whats so special about the 5 angle valve job. They cut the vavle seats in the head I know, but does the valve itself get cut? Or is it just hoping to get a little more air in and out around the edges of the valve hole in the chamber and make it seal up tighter when its closed?
three angles on the seat and two cut into the valve is 5angle. It creates a better flow path which increases flow a bit.

[turbospeed]

soa 3 angle valve job is one on the seat and 2 in the valves?

and a regular valve job is ?? one on the valves?

[Scott Long]

Years ago in high school shop class I did a valve job on a small block 350. But I forgot what we cut and where.

When I did my SC head gaskets, I removed all the valves out of the head and then after it was milled I put the valves in with a little bit of valve grinding compound grit paste and then used my cordless drill to lap the valves. I assume they sealed better but I wouldn't say I increased the flow potential. I also traced the exhaust manifold gaskets on the head with a permanent marker and used a die grinder to open them up slightly and then I used a polishing stone to smooth out the port a bit. I think I took the bumps out but I don't remember and I'm not going to tear it down just to look and see.

[seawalkersee]

Nope...three angle is ALL three in the seat. The five angle is five in the seat. The process is for higher compression and strong spring engines. I can not remember what angles go where but it makes the angle of the seat that contacts the valve much tighter. It allows better flow into the head because it cuts out the inside of the seat.

Chris

[turbospeed]

i have a software called dyno 2000 and another called cartest if anybody wants them PM me.

[DamonSlowpokeBaumann]

Scott you lapped the valves which will help with valve seatment

[seawalkersee]

Actually, there are two schools of thought on that. Up until about three weeks ago, I though it was unheard of to lap valves in the engine after a vavle job. The thinking behind that is, YOU HAVE ALREADY CUT THE VALVES. Why do you want to lap them now? The seat is already there. It is a razor sharp seat that if you did the job properly, does not need to be lapped. Now, all of a sudden, I see some threads here on this site, and another article in a magazine, and was talking to a guy building an engine, all three have wasted time on a lap and possibly widened their seats. What gives?

Chris

[Randy N Connie]

I put 5 angles on the seat.And make two back cuts on the valve.
this gives the valves 4 angles.So I have a total of 9 angles on
seat and valve.street heads.

about all the room there is to cut on the seat is 7 angles.

For my performance heads .I have used a total of 11
angles on the seat and valve combined.

Randy

[seawalkersee]

If I had the tools to do that I too would do that on all of my stuff. But...just the bits for that cost a LOT of cash.

Chris

[XR7 Dave]

Actually, there are two schools of thought on that. Up until about three weeks ago, I though it was unheard of to lap valves in the engine after a vavle job. The thinking behind that is, YOU HAVE ALREADY CUT THE VALVES. Why do you want to lap them now? The seat is already there. It is a razor sharp seat that if you did the job properly, does not need to be lapped. Now, all of a sudden, I see some threads here on this site, and another article in a magazine, and was talking to a guy building an engine, all three have wasted time on a lap and possibly widened their seats. What gives?

Chris

The process of lapping valves is the same, but the purpose for doing so is different depending on what you want to accomplish.

The old school process of lapping valves to achieve a seal is counterproductive because while it mates the two surfaces, it creates a ditch which hampers flow.

However, when a valve job has been done properly, hand lapping the valves can be helpful. I would never power lap any valve, but a light lapping can actually improve seal without creating a ditch or widening the seat at all.

I made the suggestion on another thread that lightly lapping the valves will show you exactly where the seat is and verify matching concentricity. You can use other methods to mark the seats, but a light lapping works good too. After they have been lapped, then you have your margin lines from which to cut your next angles.

[seawalkersee]

Ok...I can see that. But a LIGHT lapping would have to be done by hand for five or so revolutions. I guess if you have done it enough times you could be okay if you knew how. I have NOT done it more then a total of five times or so, so I would need some practice.

Chris

[Toms-SC]

Dave D;

Does having the heads decked change the compression ratio at all? :confused:

[DamonSlowpokeBaumann]

Any material you take of the deck surface of the heads will increase compression.