So guys, high compression ratio with moderate to high boost. Say 10:1 with like 15-18psi. Or 8.9:1 with 25+psi. Same turbo for both setups. Which would be better? Plus say e85 is the fuel for both setups. this is all just hypothetical of course. Just want your input.

On e85 I would do 10:1 with 25psi. hell if the turbo would do it if try 35psi lol.







"A car just isn't a car without a little blood, sweat, and beers." -- Shadowfire

Turbo's max is 25 I guess, I'm just trying to get ideas for when it comes time to build the engine. I know the Honda guys take a stock k20a which is 11:1 cr and throw 10psi on it (idk what cfm tho) and make like 300whp. I wondered why we couldn't do the same. I wonder why the gm build book recommends lower compression. Unless they aren't taking into account the fuel being used

You'll have better out of boost power with the 10:1. I am putting 10:1 in my S/C build and am going to run ~25psi on them. Well whatever psi my 2.6" pulley on my TVS will make.

That's the other thing is that I didn't want a sluggish out of boost car, cause 90% of the time I'm out of boost. I guess I'm just confused as to why anyone would lower their CR if the results are better with higher compression. Would you only need to do it for a huge turbo with a lot of boost?

Tuning is a bit easier with the lower C/R and you can get away with lower quality fuels. Higher C/R requires better tuning and fuels.

That is something I have pondered but am unable to test. Yes low compression decreases out of boost performance, but when are you ever out of boost and care about performance. I suppose in a turbo situation it would make more of an impact because of spool time, but that is something that can be played with too. With the roots blower, I'm boosting early so what does it matter to me if I am 10:1 or 9:1. I don't know enough about them, but centrifugal superchargers might be an option for turbo boost levels with earlier usefulness since you can change pulley sizes. I have contemplated dropping compression when I go for my hybrid build. More blower vs turbo fodder.

I guess it probably mostly comes down to the fuel, when you think about it. Most people want to run pump gas. High CR and big boost would make that difficult. But for people who run meth with pump gas it's probably not a problem. Thats nearest I can figure lowering it other than making tuning harder.

e85 is pump fuel lol




"A car just isn't a car without a little blood, sweat, and beers." -- Shadowfire

High compression and lots of boost. People shouldn't be scared.



FU Tuning

Quote:

High compression and lots of boost. People shouldn't be scared.

Word.

Crank it up till it just won't go no more. Then get a bigger turbo.










"A car just isn't a car without a little blood, sweat, and beers." -- Shadowfire

I can't tell if this is sarcasm...

Not really.

I ran ~35psi through a gt35 on an ln2 with a shaved head, I don't know what the compression would be but I never gave it a second thought.

It never knocked on e85. Ever. 26* total timing at wot.




"A car just isn't a car without a little blood, sweat, and beers." -- Shadowfire

Addicted to meth wrote:High compression and lots of boost. People shouldn't be scared.

This.

When I swapped from L61 to LK9 the loss in compression and displacement was noticeable in the mid range by butt dyno and at peak hp on a dynojet.



"In Oldskool we trust"

Would the motor have to be re sleeved to accommodate the high cylinder pressures it will see by going high compression, high boost?

The L61 block is good till ~500hp. Once you reach that number you should look into sleeveing it.

Matt Linke wrote:

Quote:

High compression and lots of boost. People shouldn't be scared.

Word.

Crank it up till it just won't go no more. Then get a bigger turbo.

Word!!


I'm not joking .

My dream motor is like a 12:1 compression with lots of boost.



FU Tuning

So say I change the fuel to be 91-93 oct. Would you guys still say the same thing it would you say go lower compression?

No matter what you will have to run 93.

Tinkles(KGM) wrote:No matter what you will have to run 93.

Boom!!



FU Tuning

If I'm understanding addicted' post right then that's what I thought.

Ill run e85 till they stop making it. Which they wont.

93 is the new 87




"A car just isn't a car without a little blood, sweat, and beers." -- Shadowfire

Matt Linke wrote:Ill run e85 till they stop making it. Which they wont.

93 is the new 87

If you have E85 available, and having the tuning for it great.

In my area we do not have it readily available.





FU Tuning

I would say E85 is the new race fuel.



FU Tuning

All the skittles here run corn. Smells good going to car meets. I just want to research now so I only build This engine once.