lost power with big intake

[Slysc]

Last year I was running a double intercooler with stock IC tubes and a raised top. With that setup, I ran a 12.45 @ 109.7 mph in the 1/4. Then, I put on a custom top that exits out the front, and ran 3" aluminum mandrel bent tubing to a big 3" X 12" X 24" core bar and plate intercooler and 3" back to the intake. I ran that setup at the shootout and my best time was a 12.70. At the shootout, I dynoed 350 whp with slightly bent valves and a leaking headgasket. So, over the winter, I had the valves ground straight, and put on better valve springs, I ported the front of the exit of the blower very nicely and had the sound ports welded up, I removed the power steering and made a custom upper and lower intake. My intake was expanded by 20mm and a divider was added to direct the flow into the lower intake. It was very nicely done and just about doubled the flow of the intake which I thought would match the 3" IC tubing better. After that, I dynoed again at 342 whp. So I'm figuring that losing the power steering is about 10 hp so I actually lost about 18 hp from last year. This year, my best 1/4 mile is 12.99 @ 108.3 mph. Losing a bit from wheelspin but still significantly slower.

The trend I'm seeing is that every time I open up the intake air volume, it's losing velocity. The 3" IC tubing slowed me, then the larger intake slowed me further. So I'm wondering if I increased my boost somehow, if the larger intake would be better than stock or if I just need to go back to the stock intake and a smaller IC tube?

[David Neibert]

Dan,

What cam are you using ?

David

[J57ltr]

I guess you dynoed on the same one for both pulls?

You made a lot of changes at once and some seem a little experimental. Maybe something you did may be hurting the combination?

Your MPH is a difference of .54 MPH what does that translate to

Your dyno HP is 8 hp less.

It's hot and humid down here and It's hot all over. I was in Denver and it was "The hottest since 1978 and, expected to hit 108 today" I think the paper said.

Do you think it could bad air?

What else changed?

Just some thoughts.

Jeff

[Slysc]

I'm running a .520 lift Dr. Fred cam. I'm not sure the duration but it's not crazy big. (if anyone knows the duration of the Dr. Fred .520 lift cam, I would be interested in knowing). I've run this same cam for 4 years now.

My dyno pulls were only 8 hp difference yes, but taking off the power steering will increase wheel horse power by 8-10 and freshening up the valves and fixing the headgasket leak should be worth something too. I would expect about 20 hp more than last year even if the bigger intake did nothing. To see 8 hp less means that something I did took me backwards.

Also, My boost is around 13 max. I was running 14-15 when I ran the 12.45 but I wasn't surprised when the boost went down because of the increased volume in the intake and the bigger IC tubes. I don't think I'm running less air, it's just not under as much pressure. (?)

[seawalkersee]

This is something that I have been pondering for A LONG time. I asked the question to fastsc92 when he was building his intercooler. He used a 2 1/2 return after his ic and a 3" primary. I would push the guess the EXACT same as you are doing. I would only have the question of your CUSTOM intake. What is it? I understand you ported it but is there a possibility that you have created a pressured area in the intake that causes a bad swirl or something like that? If you do a post for Intakes, you will see some that Randy has built. I would pick his brain if I were you. He has given me some good hints on what to do with my car when I had problems.

Chris

[Randy N Connie]

Sinking the valves farther into the valve seat you can
loose flow.Air has more turbulance between valve &
valve seat.Plus you now have less lift of valve from
seat radius

AlsoThe valve job lowered your cranking
pressures by making the combustion chamber CC's
larger.Valve face is farther away from piston top.

If your boost has dropped I would try a smaller pulley.
Or a different jackshaft pulley.

The manifold-plenum mod ,if shaped right.Will extend
RPM power range, & help motor to turn on faster, &
will compliment power adders.Manifold don't make
power on there own.The biggest reason for this mod
is to change RPM power levels,HP OR & TORQUE curves,
And the speed of both curves.You do this buy adding
to the mod more fuel, air, lower temp & raise octane
with alky injection.

I would think your doing just fine except keeping the
old valveseats & valves,That now have wider seat
cut margins cut on them causing air drag.Your just
not done adding to your mods and tuning yet.
I would try a smaller pulley and a snow injection.

Hope to get to see ya race again this year good luck Randy

[blue94sc]

I was reading your post on your power loss and I have an observation.
Since you have increased the IC tube and intercooler sizes wouldn't that increase the volume of the system? Now unless I am all wet, wouldn't that possibly cause a decrease in pressure OR a lagging in pressure build up?
The M90 can only put out a certain amount of volume and if the volume it needs to fill is too great, could that could possibly cause an actual power loss?
There is probably an air flow rate at a certain pressure based on the cross sectional diameter of a tube.
Just a thought.
: - |
Bill

[MySCRocket1203]

what about tuning and fuel upgrades that much more air maybe a few more drops of gasoline would livin things up a bit

[seawalkersee]

The only thing I could see as far as the system not making enough boost would be to drill and install vacuum ports throughout the system to see what the pressures are. However I believe the 3"is not too big but that is what allowed the loss in boost. I think Randy is correct about the boost but I dont know how much of a problem these heads are in the combustion area. I DO know that he would not have mentioned it if there was not a problem that could be related to it though. Good luck dan.

Chris

[Slysc]

I've attached some pictures of how the intake was modified. Randy, let me know if you see any problems with it.

I dynoed this setup and the air fuel was at 12.5 until past 5500 then it dropped to 11.5 (richer). I figure that's good. I guess it was the added volume that makes me think that the decrease in intake velocity might be hurting me. How much material does a valve grind displace? I never thought that it was enough to hurt performance.

I next step is going to be more boost. Custom 25% OD jackshaft setup. We'll see what happens.

[David Neibert]

Originally Posted by Slysc

I've attached some pictures of how the intake was modified. Randy, let me know if you see any problems with it.

I dynoed this setup and the air fuel was at 12.5 until past 5500 then it dropped to 11.5 (richer). I figure that's good. I guess it was the added volume that makes me think that the decrease in intake velocity might be hurting me. How much material does a valve grind displace? I never thought that it was enough to hurt performance.

I next step is going to be more boost. Custom 25% OD jackshaft setup. We'll see what happens.

Dan,

Have you checked to make sure the bypass valve is closing all the way ?

David

[XR7 Dave]

Nothing you have done should have cost you more than 1psi of boost. I suspect you have some other issues. Also, your manifold will raise your rpm range. This means you must rev the motor higher than before to get more average power. I didnt' see an increase in HP with manifold mods but I did see the rpm range extended significantly and the average power increased. This made the car faster at the track but I had to adjust my driving style before I saw any of it.

Now that I have made the mistake of going to 3.27 gears, on average my car is slower than before. I need 3.73's to run this motor in the 1/4 mile.

[Randy N Connie]

I can't say much without seeing the inside of the plenum.
The tube welded to the plenum,looks to have a pretty
sharp radius from the outside veiw.

The 3'' outside diameter tube is not to big.The inside
diameter is the important part,it should be 2.750.

I have not studied the blower tube size going from the
blower hat to the intercooler.I have given it some thought
of why Charles of MP uses a smaller tube from the
blower to intercooler,and then steps it up in size from
the intercooler to the intake manifold plenum.I beleive
this to increase the cool air plenum effect size of the
system.

I would add a little more boost.And talk to XRDave to cool
the air more.Then check timing and add.You got what you
got,now talk to a tuner.

I will send you a PM on plenum shape design later,I have
to go back to work,don't have enough time right now.

Randy

[Slysc]

I'm pretty sure that my bypass valve is closing correctly. I adjusted it and watched it close. I should probably try blocking off both ends and seeing if there is any difference in boost.

The modifications I did to the blower were that I welded the sound ports shut which I was told would give me a smidge more boost, and I reworked the front of the exit to eliminate the ledge in the front of the case. I figured that would let the air out into the front exit top that I have better than having to flow up and around the restriction. Maybe one of those mods robbed me.

The car feels like it pulls through 6500 rpm but on the dyno, it was dropping torque sharply after 5500. I'm going through the traps at 5100 rpm (according to my 25.5 diameter tires and 3.55 gears) and that should be right in my power band.

[Randy N Connie]

Not to freak ya out but,Food for thought on using bent valves.

To save money, manufactures make 2 peice valves.
They machine the valve head and the stem .Then
they put them in a machine that spins the two peice
while pressing the head and stem together.This
produces heat and the valve head and stem are
the welded or melted together.Then finish ground.

The two part valves can easily fracture after being bent.
This is why its a good insurance to use machine one peice
valves in performance engines with high spring pressures.

On valve jobs, sinking the valves after the second or thrird
valve job. Causes valve shrouding from the seats diameter.

And if you cut the valve seat for the valve.And you do not
make a cut before and after the valveseat valve cut.The
valveseat valves margin gets to wide and cause the air to
drag.You can loose as much as 20 CFMs.For a race motor
the valveseat cut for the valve should not be over .060
I like .050.The cuts before and after the valveseat cut
for the valve should be even narrower.

And this is true for the back side of the valve.If you cut
the back of the valve to get it back true after bending.
The magin will be to wide and cause air drag.You also need
to do a muti cut on the backside of valve.