boosted 427 lsx compression ratio build

[on3wego]

Originally Posted by SuperchargedStealth

Standard turbo setups. and centri blowers, will typically have lag up to about 2500, so from idle and up, it'll feel like stock.There are turbos that keep from getting lag, but they are more pricey. So the only blowers that will give you that instant response is a Maggie, Whipple, Edelbrock....anything top mouted. Streetability, is all depend on your right foot.

Im actually decent while daily driving. I just drive.. I do get into it while racing tho. But it's basically on weekends.

[on3wego]

Originally Posted by sprayedv

10:2 comp running 28lbs on twins 6766s on e85 or c16.

What's ur setup and power and tq? If u don't mind giving the basics... that sounds really good on e85.. sounds like the exact setup I want..

How's ur boost while street driving.. When's boost start coming on.. how Instant is it?

[jrpxxii]

Im running 9:8:1 and pushing 34psi and turning it up from here. Im running a Procharger F3R-136 on straight race gas

[Unreal]

Originally Posted by SuperchargedStealth

Standard turbo setups. and centri blowers, will typically have lag up to about 2500, so from idle and up, it'll feel like stock.There are turbos that keep from getting lag, but they are more pricey. So the only blowers that will give you that instant response is a Maggie, Whipple, Edelbrock....anything top mouted. Streetability, is all depend on your right foot.

That is WAY WAY WAY WAY too generalized. Twin 56 in a .63 housing on a 427 with 10.5:1 compression will come on basically at idle. Same turbos, same cost, swap them in a 1.0 housing, on a 9:1 motor will come on 1500+rpm later. Compression, engine size, exhaust, cam, etc all have major effects on when a turbo comes on.

I've driven and messed with cars from 8:1 to 11.5: with boost. I would never do another street car below 10:1.

[on3wego]

Originally Posted by Unreal

That is WAY WAY WAY WAY too generalized. Twin 56 in a .63 housing on a 427 with 10.5:1 compression will come on basically at idle. Same turbos, same cost, swap them in a 1.0 housing, on a 9:1 motor will come on 1500+rpm later. Compression, engine size, exhaust, cam, etc all have major effects on when a turbo comes on.

I've driven and messed with cars from 8:1 to 11.5: with boost. I would never do another street car below 10:1.

This is the kinda input I'v been looking for here and jrp.. What power r u at?

Unreal.. why wouldn't u do anything below 10.1?

[Unreal]

Because turbos will spool slower, feel lazy down low, hurt gas mileage. Modern head/plug/chamber/piston/ecus allow good boost and compression. Yes you may have to turn the timing down, but as long as you aren't running single digit or negative timing to run the boost you want, I would keep the compression. Then on high octane or e85 you get even more out of it.

Either way the octane you have will only support a certain cylinder pressure. If you make 1000rwhp on 10.5:1 and 15psi or 9:1 and 20psi does it matter? The high comp build will drive much better, spool faster, and either way you are octane limited so I rather not have a lazy car off boost.

[bct10985]

That explanation was so good it was almost unreal

[on3wego]

Originally Posted by Unreal

Because turbos will spool slower, feel lazy down low, hurt gas mileage. Modern head/plug/chamber/piston/ecus allow good boost and compression. Yes you may have to turn the timing down, but as long as you aren't running single digit or negative timing to run the boost you want, I would keep the compression. Then on high octane or e85 you get even more out of it.

Either way the octane you have will only support a certain cylinder pressure. If you make 1000rwhp on 10.5:1 and 15psi or 9:1 and 20psi does it matter? The high comp build will drive much better, spool faster, and either way you are octane limited so I rather not have a lazy car off boost.

I agree. Just trying talk my builder into more compression. What your describing is exactly what I want

[H-E]

Originally Posted by on3wego

I agree. Just trying talk my builder into more compression. What your describing is exactly what I want

With e 85 you can easily go a point higher

[Unreal]

If it is e85 hell I would almost just do 11:1. Look at the c7 vettes, they are doing 11.5:1 and 15+psi without issues. They are direct injection, but just goes to show what can be done.

I think a street car the sweet spot is 10-10.4:1 for a boosted motor. I'm at 9.8:1 on my blower setup and wish I went higher.

[stevieturbo]

Originally Posted by on3wego

Is there that much difference in low vs high compression on boost applications? ?

Not really, no. Lower will give you a much wider safety margin, especially if using pump fuel.

But really depends what sort of power and boost you intend to use, and the quality of fuel available to you.

But certainly gone are the days were you'd be aiming for 8:1 or anything silly like that almost regardless of what fuel you're using

[on3wego]

Going to be using e85.. and or ignite. Or both..

Always going to use the best fuel.. I will always do what's right and want my car to run its best and IL keep it that way. Once I do a rythem.. IL stay with it.

[BullF-16]

Originally Posted by stevieturbo

Not really, no. Lower will give you a much wider safety margin, especially if using pump fuel.

But really depends what sort of power and boost you intend to use, and the quality of fuel available to you.

But certainly gone are the days were you'd be aiming for 8:1 or anything silly like that almost regardless of what fuel you're using

I went mid range with -23cc pistons. My calcs put me at about 9.5 :1 Can anyone verify that. 4.125 bore with .055 head gaskets 70cc chambers. I figured it was close.

I wanted some safety built in for a bad tank of 93. NO E85 here but do blend in torco and dual meth. I notice no lag at all. As a matter of fact i now just keep my CO2 bottle turned off and am at about 6 psi on the gate springs. I thought the gate springs were 4.35 psi but on my boost leash and boost gauge i see between 6-7 psi and this seems more than enough for fun on the street.

I often wondered it i should have gone with -20cc or a little less for 10:1.

Now i dont wonder anymore based on the performance i am getting.

My tune at 25psi only went to 12.5 deg timing. so fairly conservative.

[sprayedv]

I've always said if you're going to spend huge amount of money building something why not just be safe... but that's me. As unreal has stated, 10-10.4 is pretty much perfect for high boost street cars.