Power mods for the I-5

[f5fstop]

Ah, but GM got the 20+ HP from boring the engine out to a 3700. The engine is capable of obtaining quite a bit more HP with a turbo or SC, but unless GM offers it, it would void the powertrain warranty.
Later engines, or those with the new cylinder head, should be able to take the extra HP, as long as you keep it low, around 270. This is not from any GM official information, but from what I know someone did with this engine.

[HummBebe]

The best and only way to improve the acceleration and mpg is to hook the H3 to the back of an H2, put the H3 in nuetral, and relax. It works great.

Been there, done that, got the t-shirt

[HummBebe]

So if that is all they did, was bore, we will now have 10.5:1, 11:1??

Will they now have to step up in octane rating, or will the computer take care of it?

[marin8703]

Thanks for the replies everyone!

[f5fstop]

Originally Posted by HummBebe

So if that is all they did, was bore, we will now have 10.5:1, 11:1??

Will they now have to step up in octane rating, or will the computer take care of it?

Compression ratio is 10.3:1. so it went up .3 (current has a 10:1). You will not have to burn premium fuel, the computer is programmed to compensate.

[Michael1]

The limiting variable for drivetrain life is torque, not horsepower. Keeping that in mind, the torque drops off from the peak about 20%, so that is your opportunity. You can forget about all those air filters, and exhaust systems. You won't get 20% with those. I'd suggest you look into what people do who race this engine. The first place I would look for more power would be porting the heads, and putting in bigger valves. Then I would be looking at the intake manifold. I would shorten the runners for tuning at a higher RPM, and port it for better airflow. The other place would be the exhaust manifold, and replacing it with tubular headers. This is a touchy area though, because there is a close couple catalytic converter.

Michael

[ChevyHighPerformance]

Originally Posted by Michael1

You can forget about all those air filters, and exhaust systems. You won't get 20% with those.

Michael

I bet you can get to 265 BHP with the correct air box/intake, exhaust, and tuning.

[PARAGON]

Originally Posted by Michael1

The limiting variable for drivetrain life is torque, not horsepower.

Actually, that's not really true. Since HP is the measure of torque over time, HP is just as limiting a factor as torque.

You can't have HP without torque.

Now suggesting one to copy what race engine builders do, is not a very good idea either. They get to tear their engines down after relatively few miles and are pushing the engine to the limits during most of it's running life.

You simply are not going to be able to do much with this engine to justify a tear down, port, polish and rebuild just to gain a few HP on the high end.

265 hp not likely with aftermarket stuff (excluding turbo, s/c). GM did it the right way to the I5 in 2007, and the power increase is modest.

All Hummers (H1, H2, H3) are slow street machines as usual, because their strength is offroad ability.

S.

[HummBebe]

Very few people would actually "race" with an inline 5.

Rod Hall, maybe.

If you have the shop, tools, talent, ability and machinery to do something you all are desribing, why not just put a 350 in it??

It makes just as much sense

Want in one hand, crap in the other, see which one fills up faster

Leave the I-5 alone. It is what it is.

Different vehicles for different purposes for sure, many of us have fast sports cars in the garage for fast road work.

S.

[ChevyHighPerformance]

Originally Posted by Steve - SanJose

265 hp not likely with aftermarket stuff (excluding turbo, s/c).

S.

I've already seen the before and after dyno plots.

[PARAGON]

Originally Posted by Steve - SanJose

265 hp not likely with aftermarket stuff (excluding turbo, s/c).

S.

So now it's:

Originally Posted by ChevyHighPerformance

I've already seen the before and after dyno plots.

after previously saying a few minutes earlier:

Originally Posted by ChevyHighPerformance

I bet you can get to 265 BHP with the correct air box/intake, exhaust, and tuning.

[PARAGON]

[ChevyHighPerformance]

Originally Posted by PARAGON

So now it's:


after previously saying a few minutes earlier:

Nothing like a sure bet.

. Someday I'll get to drive one too.

S.

[PARAGON]

Originally Posted by ChevyHighPerformance

Nothing like a sure bet.

RIIIIGGGHHT!

[ChevyHighPerformance]

Just as an example, here is someone else's dyno plot from another website for an H3 with an airbox, exhaust, and tuning. This after these mods the BHP is about 253 hp. From what I was told, this is without port matching of the CAI, stock throttle body, no thermal shields, and no cold air ducting. Also, this might have been with the stock resonator.

[PARAGON]

Originally Posted by ChevyHighPerformance

Just as an example, here is someone else's dyno plot from another website for an H3 with an airbox, exhaust, and tuning. This after these mods the BHP is about 253 hp. From what I was told, this is without port matching of the CAI, stock throttle body, no thermal shields, and no cold air ducting. Also, this might have been with the stock resonator.

so, the extra 100HP is arbitrary?

What I see is a 12-13 point increase in HP which is less than a 10% increase at the rear wheels even.

[HummBebe]

100 pts both HP and Torque, yes?

It reads 153 not 253? I'm confused