[taff2]

An inline 4 cylinder engine is much easier on the block with high cylinder pressures (boost) than a V8 engine. Look at how the V8 pistons downward force transfers to the block- the left bank of cylinders try to push the right pan rail apart, and the right bank of cylinders try to push the left pan rail apart. This 'spreading' of the pan rails is what cracks V8 blocks up through the mains oil holes, and it's only the mains caps that stop this. Hence why splayed main caps work well,they pull the pan rails in towards the main saddles, and cross bolted blocks work even better. A 4 pot has a straight downward push on the main caps ,and stronger caps or cap straps and better bolts/studs will do the job. Yes I know the Pontiac half a V8 doesn't push straight down on the mains,but it pushes in one direction on the mains, so in theory it would be less likely to crack up through the mains.
This means Charlie, that you can shoot for a 1000hp with out a care in the world!

[Boostedbird]

The engine that's in my car is a stock 2 bolt block with the stock caps and bolts. It has a cast Eagle crank, forged Scat rods, Ross pistons, and a flat tappet cam. On 7.5-8psi I went 9.45@145mph weighing 3,770lbs. Calculator says that's between 850-930hp. Now I'm running around on 14psi. It's pretty rowdy. I'm not saying that it's not gonna blow up tomorrow, but I've been beating on it for a few years now. I'm guessing with open exhaust it's around 850whp now. The last time that I dynoed it put 744whp down through the full exhaust on 12psi and low air in the drag radials. Anyway, that's my stock block experience.

I forgot to add that I have E heads that flow 308 cfm at my cam's lift.

[charlie66]

I know the whole theory about the 4 cylinder . I agree with you 100%. But i still think 100 - 125 hp per cylinder with a turbo is safe to have . especially being a street driven car... Im building a 400 4 bolt main 9.5 to 1 steel headed motor with twin 6870's . So ill be finding out how right or wrong im am. I believe ill be fine....

[Boostedbird]

I would love to have a reason to build a turbo 400". I like 400's a lot anyway, just haven't had one in fourteen years. Sounds like a long time!

[charlie66]

Why you need a reason? Just do it .. Would make a better street motor for traction.....

[ponjohn]

Originally Posted by charlie66

Are you building something?

Deciding on N/A 463 or turbo 400.


I have 93cc 265 cfm d-ports - good for either combo.
I would use twins just because of appearance.

[ponjohn]

Originally Posted by charlie66

I know the whole theory about the 4 cylinder . I agree with you 100%. But i still think 100 - 125 hp per cylinder with a turbo is safe to have . especially being a street driven car... Im building a 400 4 bolt main 9.5 to 1 steel headed motor with twin 6870's . So ill be finding out how right or wrong im am. I believe ill be fine....

What cam?

[Tom Vaught]

ONLY a few years, at 14 psi of boost and a cast Eagle crank. The engine owes you nothing.
You sure put that "it will blow up tomorrow after you use those non racing parts" bs to rest with your engine. Plus you are about 800 lbs heavier vs the expert with the supercharger. Nice work.

Tom V.

[charlie66]

Originally Posted by ponjohn

What cam?

Im workinng on that with Tim at Bullet cams..

Will be on a 114 around 580 lift and 230-240 duration..

Nothing in stone right now though...

[Boostedbird]

Originally Posted by Tom Vaught

ONLY a few years, at 14 psi of boost and a cast Eagle crank. The engine owes you nothing.
You sure put that "it will blow up tomorrow after you use those non racing parts" bs to rest with your engine. Plus you are about 800 lbs heavier vs the expert with the supercharger. Nice work.

Tom V.

Thankyou! No, that old engine has treated me well! I'm planning to go the track in two weeks. If I do I'll post in here.

[ponjohn]

With a 30" tall rear tire - what do you think would be ideal 3.73 or 3.50 gear?

[charlie66]

I run a 3.50 with my 4cyl. It works good...

[Tom Vaught]

3.5 gear has worked well (with a bunch of turbo cars) as the Engines make so much torque at fairly low engine rpm. Higher load on the engine and the turbos work that much better.

Tom V.

Ignore the idiot in the Race Forum Charlie.

[Boostedbird]

I have a 3.25 gear with 28" tires. The next set of tires I buy will be 30". There is so much torque available that there is no need for any higher. Plus, all that boosted Pontiac torque likes to loosen converters up so you'll have to watch the rpm on the big end if you want to keep the rpms under control.

[Boostedbird]

Originally Posted by Tom Vaught

3.5 gear has worked well (with a bunch of turbo cars) as the Engines make so much torque at fairly low engine rpm. Higher load on the engine and the turbos work that much better.

Tom V.

Ignore the idiot in the Race Forum Charlie.

You beat me to it. Lol

[ponjohn]

Originally Posted by Boostedbird

I have a 3.25 gear with 28" tires. The next set of tires I buy will be 30". There is so much torque available that there is no need for any higher. Plus, all that boosted Pontiac torque likes to loosen converters up so you'll have to watch the rpm on the big end if you want to keep the rpms under control.

In either combo N/A or turbos I am running a 4l80E with lockup.

[GTOGEORGE]

Originally Posted by Tom Vaught

3.5 gear has worked well (with a bunch of turbo cars) as the Engines make so much torque at fairly low engine rpm. Higher load on the engine and the turbos work that much better.

Tom V.

Ignore the idiot in the Race Forum Charlie.

Don’t start name calling! I haven’t called anyone names just stating my opinion!


GTO George

[charlie66]

Originally Posted by Tom Vaught

3.5 gear has worked well (with a bunch of turbo cars) as the Engines make so much torque at fairly low engine rpm. Higher load on the engine and the turbos work that much better.

Tom V.

Ignore the idiot in the Race Forum Charlie.

Yes i remember you telling me that .Thats why i tried the gear change from 3.90's . It was a good choice ....

[Tom Vaught]

Everyone has an OPINION.
All I will say on that deal.

Tom V.

[Tom Vaught]

Here are a few facts:
1) Supercharged engines use a belt system to drive them or they are driven by a drive mechanism off the crankshaft. They take horsepower away from the crankshaft power to drive the supercharger. So the bigger the load from the supercharger the more power you need to make from the engine to reach a given power level.

2) Turbocharged engines use some of the energy the engine produces to drive the Turbocharger Turbine. Rough rul of thumb: 1/3 of the engines heat pushes down on the piston, 1/3 of the engines heat is transferred thru the cooling system to protect the engine from engine damage. 1/3 of the engines heat goes out the exhaust and is lost forever with a supercharged engine. 1/3 of the engines heat goes out the exhaust and is USED BY THE TURBINE to drive the compressor wheel on a turbocharged engine.
Turbo engines like load so a turbocharged engine will make more power the higher load it sees and it will drive a larger turbocharger unit and make more overall hp.

Supercharged engines hate load so a supercharged engine will make less power as the parasitic loss, (LOAD) gets higher and higher.
Bigger engines offset some of that higher load and so the engine makes more overall power.
A High HP supercharged engine might take 1.5 HP for every 10 hp it makes. 1000 hp at the crank needs 1150 hp from the combustion process. Turbocharged engine uses energy normally wasted out the exhaust pipe to do work. More load, more work, more exhaust, more power to drive the turbo, more power.
Very simple really.

A 281 cid engine with Turbos has run 5.7s in the quarter mile. A 670 cid turbo engine might run 6.00s because the same sized turbos are not seeing the same load as the 281 cid Turbo engine.

So the comment made in a forum that a given racer needs a Larger Engine is inaccurate.
One of the racers actually went the other direction and went to a smaller engine with turbos as it is easier to make more power and the traction capability on the street is more predictable.

So not surprising in the turbo forum that members changed their gear ratios to a smaller number and the engines made more actual power.
Higher Load, more efficient HP from the turbos.

Simple really if you actually understand how turbos work vs superchargers.

Tom V.

Keep after it Charlie.