Bonneville engine

VAP

Registered User
Biulding SC engine for Bonneville salt flats

Hi All, first post here, great forum!

I'm looking at building a full on 3.8 SC engine for fitting into a (under) 260 CI class in Bonneville. I have done some research and as far as I can see the SC engine is certainly the choice to start with given the forged crank and good block.

The car will be a '90 Thunderbird that I have already, nice ride at present if I do say so myself :)

Without having an engine on the stand in front of me (which I am looking for by the way), I have some rather, umm, unconventional questions:

Another site says that the 3.8 is essentially a 5.0 configuration minus 2 cylinders and some parts interchange. Hmmmm, (lightbulb moment) are the bore spacings and head bolt locations the same between the 3.8 and the 5.0L? How about this; has anybody tried to cut off and weld a set of new tech 5.0 aluminum heads?

How much can I bore the 3.8L SC block and keep the strength. Or, how much closer can I get to my 260CI target?

How much HP will the stock crank and block hold up to? (Given proper ballancing and all the correct prep and oiling work?)

Remember, If I do this I EXPECT to build a radical racing engine, and I have many years of experience doing this. I have just never built a 3.8 engine this way.
 
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How do you plan to get air into the motor? N/A, turbo, supercharger, nitro, etc.

That makes a big difference in what direction you go with this motor.
 
XR7 Dave said:
How do you plan to get air into the motor? N/A, turbo, supercharger, nitro, etc.

That makes a big difference in what direction you go with this motor.
Yes and no. Initially I'm planning to run N.A. carbed with ram air, and then the next year go to a turbo set up with a pile of boost.The only things I will have to change in between are pistons and cam grind. The bottom end and heads just need to be as stout as is humanly possible for either.......
 
darkstar_one said:
ummm.... pontiac bonneville? why dont u just pop in a V6 3800 engine from a FIREBIRD?
ummm.... no, that would be the Bonneville Salt flats, the the big flat white thing all over the western part of Utah. The plan is to break 200 MPH with this thing. This is what the named that tanker Pontiac AFTER....... :)
 
OK, new stuff

Bought another '90 standard Thunderbird today. Drove it home for $50. N.A. 3.8 knocks and one 1/4 panel is banged. I will use this one for my project instead of tearing up my sweet one.

Does anybody want to trade your core SC engine for some of the other parts I'm going to strip out of this one? No blow-up's please.

http://members.tripod.com/~COSA4U/wannaride.html
 
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VAP said:
Bought another '90 standard Thunderbird today. Drove it home for $50. N.A. 3.8 knocks and one 1/4 panel is banged. I will use this one for my project instead of tearing up my sweet one.

Does anybody want to trade your core SC engine for some of the other parts I'm going to strip out of this one? No blow-up's please.

http://members.tripod.com/~COSA4U/wannaride.html

Ok, that helps a lot. Have you calculated the HP level you need to run the speed you want?

The 3.8 follows the 5.0 in basic layout, but all dimensions are off. The 4.5L SVO engine was closer to the 5.0.

For displacement you are looking for 4.2L which Ford already makes in the F150's from 97 up. From what I understand the cyl walls are kind of thin so you can't really bore it all that much. The 4.2 is a stroker version with 3.75" stroke vrs 3.39" on the 3.8.

The problem comes into basic design of the motor.

1) crank. The 90 deg motor with 60 deg even firing strategy requires that the crank have the paired journals offset. You will see this when you take one apart. This results in a relatively small eliptical section joining the paired cylinders which results in many broken cranks. This does not mean that the crank will not hold a ton of HP, but it does mean that random cranks seem to have a flaw in them that does not show up in testing but can still break at the most innopportune time.

Having said that, the cranks from the SC and NA 3.8 are totally different and the SC is not only internally balanced vrs external on the NA motor, but it also has heavy counter weights on all cylinders where as the NA crank does not. This makes about a 20lb difference on the crank weight. Not sure if that concerns you or not.

The SC block is very solid overall and will most likely hold as much power as you can put through it. For the crank however, I'd look at having a billet one made. It's been done and that should be indestructible.

2) Heads. The heads need a lot of work. The bore spacing is different than a 5.0 so forget that idea. The 3.8 has some of the typical Ford issues regarding cylinder sealing. With only 4 bolts in an aluminum head, keeping the head down on the cylinder is an issue at high boost. We lifted the head repeatedly at about 23psi even with MLS gaskets, orings, and 1/2" head studs. Sealing is going to be an issue, especially at the bottom where the plug is at.

3) My recommendation is to stay with 3.8L and about 20psi and then ratio up the rpms until you get the HP level you need. :D
 
SC heads are machined to accept the injectors instead of placing them in the intake manifold like a 5.0 does, so using a carb may be difficult.

David
 
I have a core engine if you are still in need. Spun bearing, but ran when I pulled it out. I need to get it outta my garage since I'm moving soon. San Diego. JJ
A few months back there was a bonneville t-bird on the home page, maybe you can get in touch with the owner for some input.
 
Thanks Dave for the excellent info. That's the kind of stuff I need to make a proper plan for this engine.

So, the SC block is definately the right choice.

The 4.2L crank is cast (as I understand it), and I wouldn't trust it at RPM. I'd rather go with the 3.8 SC crank Sonic checked and Magnifluxed, and then ballanced. As far as the billet crank, one made at SCAT for a SBF is about $1,700. That's one they do all the time, I'm sure a totally new set up (4.2 stroke) would add at least 1K to that. If I was going to go there, honestly, I'd just have a de-stroked billet made for a SBF.

Intake manifold I'll just weld up myself for what I need for the head of choice running a Holley 780DP/DF. Ram air will be run and actually works at those speeds.

HP required to achieve any certain MPH is reletive to the aerodynamic drag on the car plus slippage on traction. Armchair engeneering puts me at about 425 to reach 180MPH which is my first year goal. That depends on a bunch of factors that are dynamic like winds, and salt conditions. What I do need to plug in here is the RPM that the engine makes max HP at.

Which brings me to; how fast can I twist a SC bottom end that is built totally right? Can I get 7K, 8K? Remember, it only needs to run at power for about 3 minutes, and then do it again once more. That's it for the year:)

Any idea what is critical HP at 20PSI turbo'd on a SC crank?






XR7 Dave said:
Ok, that helps a lot. Have you calculated the HP level you need to run the speed you want?

The 3.8 follows the 5.0 in basic layout, but all dimensions are off. The 4.5L SVO engine was closer to the 5.0.

For displacement you are looking for 4.2L which Ford already makes in the F150's from 97 up. From what I understand the cyl walls are kind of thin so you can't really bore it all that much. The 4.2 is a stroker version with 3.75" stroke vrs 3.39" on the 3.8.

The problem comes into basic design of the motor.

1) crank. The 90 deg motor with 60 deg even firing strategy requires that the crank have the paired journals offset. You will see this when you take one apart. This results in a relatively small eliptical section joining the paired cylinders which results in many broken cranks. This does not mean that the crank will not hold a ton of HP, but it does mean that random cranks seem to have a flaw in them that does not show up in testing but can still break at the most innopportune time.

Having said that, the cranks from the SC and NA 3.8 are totally different and the SC is not only internally balanced vrs external on the NA motor, but it also has heavy counter weights on all cylinders where as the NA crank does not. This makes about a 20lb difference on the crank weight. Not sure if that concerns you or not.

The SC block is very solid overall and will most likely hold as much power as you can put through it. For the crank however, I'd look at having a billet one made. It's been done and that should be indestructible.

2) Heads. The heads need a lot of work. The bore spacing is different than a 5.0 so forget that idea. The 3.8 has some of the typical Ford issues regarding cylinder sealing. With only 4 bolts in an aluminum head, keeping the head down on the cylinder is an issue at high boost. We lifted the head repeatedly at about 23psi even with MLS gaskets, orings, and 1/2" head studs. Sealing is going to be an issue, especially at the bottom where the plug is at.

3) My recommendation is to stay with 3.8L and about 20psi and then ratio up the rpms until you get the HP level you need. :D
 
VAP wrote;

Armchair engeneering puts me at about 425 to reach 180MPH which is my first year goal

i'm not experienced at building purpose built race engines (or any engine for that matter), but what i will say is that if this is a contest for top speed rather than an acceleration contest, then the higher rpms 7k on up are not necessarily needed on this engine. 425hp at the crank minus 15% driveline losses is a net of 361 wheel hp. An SC engine's stroke wasn't by design to rev safely above 6,500 rpms i would think. And if you generated only 361 hp at the wheels with that engine at 8k rpms, you're not going to be generating a whole lot of torque in that range either (if that is your objective). you would have to give that thing some serious leverage if your setting up for 8k rpms- gear ratios would be the key to bring out the big torque with that setup. the gears selected would have to enable the engine to leverage out a certain amount of wheel torque necessary at a determined rpm (peak engine output) to support 180 mph. I think you can get a better setup to generate much more power to the wheels safely and consistently if you stay below 7k with that crank-IMO. but you did say you're using a turbo setup- in that case you may be able to get a little more rpms reliably.
 
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hytorksc said:
VAP wrote;



i'm not experienced at building purpose built race engines (or any engine for that matter), but what i will say is that if this is a contest for top speed rather than an acceleration contest, then the higher rpms 7k on up are not necessarily needed on this engine. 425hp at the crank minus 15% driveline losses is a net of 361 wheel hp. An SC engine's stroke wasn't by design to rev safely above 6,500 rpms i would think. And if you generated only 361 hp at the wheels with that engine at 8k rpms, you're not going to be generating a whole lot of torque in that range either (if that is your objective). you would have to give that thing some serious leverage if your setting up for 8k rpms- gear ratios would be the key to bring out the big torque with that setup. the gears selected would have to enable the engine to leverage out a certain amount of wheel torque necessary at a determined rpm (peak engine output) to support 180 mph. I think you can get a better setup to generate much more power to the wheels safely and consistently if you stay below 7k with that crank-IMO. but you did say you're using a turbo setup- in that case you may be able to get a little more rpms reliably.



get a 5 speed SC , it already goes 145 stock. get some heads cam and AR blower and youll be going pretty fast.
 
VAP said:
Which brings me to; how fast can I twist a SC bottom end that is built totally right? Can I get 7K, 8K? Remember, it only needs to run at power for about 3 minutes, and then do it again once more. That's it for the year:)

Any idea what is critical HP at 20PSI turbo'd on a SC crank?
I don't think anyone knows. I don't know of anyone spinning an SC motor that high because the blower won't do it. The block itself is much better than a production 5.0 if that means anything. The motor will make about 500ftlbs of torque at those boost levels, so it's just a matter of how high you want to go. 7000 rpm would net 650HP. I don't think the heads will breath at 8000rpm.
 
XR7 Dave said:
I don't think anyone knows. I don't know of anyone spinning an SC motor that high because the blower won't do it. The block itself is much better than a production 5.0 if that means anything. The motor will make about 500ftlbs of torque at those boost levels, so it's just a matter of how high you want to go. 7000 rpm would net 650HP. I don't think the heads will breath at 8000rpm.
Alright, now we're getting down to it!

So I should be able to twist it to 7K with 20 LBS and have it stay together for the runs. (Given a proper build of the engine).

The heads seem to be the weak point. Are there substancial differences in flow between stock heads as per year/model? Or, which heads are the best ones to start with - I will port them in-house.

What is the max bore I can go with on the block and keep the integrety?
 
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