9:1 compression + high boost

D

Doward

Banned
Jan 11, 2006
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Everything with a turbo is trade off - that's why the very first question I ask, when someone's asking 'What do you think of this turbo?' is

"What are your goals?"

Be sure not to go too big ;)
 
M

MRSUPRA

New Member
Apr 11, 2005
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Please do not try to make 600-650rwhp on pump gas, especially with a stock ECU. On race gas with the 71, not a problem..even with the 9.1 compression.
 
Q

quake

toyota tech
Apr 13, 2005
619
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16
r.i.
MRSUPRA said:
Please do not try to make 600-650rwhp on pump gas, especially with a stock ECU. On race gas with the 71, not a problem..even with the 9.1 compression.
Click to expand...
those numbers are resurved for the c16
 
gilberjj

gilberjj

Friend of Fast
Apr 14, 2006
661
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Tacoma, WA
Doward said:
I love you guys. :D

You've got a lot more factors at play, than just the psi you are seeing on your gauge.

Everything else equal, 10psi from a T66 is going to create more power than 10psi on a CT26, because the 10psi from the T66 is more efficiently compressed. When you compress air, you heat it up. The efficiency of your turbo is a measure of how much more it heats it up than necessary. A CT26 is NOT efficient over about 13psi. It heats up the air to insane temps.

The T66, on the other hand is barely working to compress the air @ 13psi - so your temps are not increasing much over what the Ideal Gas Laws state it should.

Hot air = less dense. Cold air = more dense. The denser the air, the more power you make per volume of air. That's why we run intercoolers, as well.

Now that's just turbo sizing!

Suppose we now take two cars - one a T66 on a log manifold, stock everything else, and run 10psi.

Car #2 has one of Ron's FFIM and tubular header, as well as a set of those 272 cams. Still 10psi.

Car #2 is going to make a little more power than car #1. Possibly in the order of 20-30rwhp, but I would not expect much, at this low volume of airflow.

Now take both cars, and run 20psi. Car #2 is now going to make a LOT more power than Car #1 - why? Airflow. Car #1 is making 20psi, but the air is having to fight its way into the engine, and back out.

Car #2, on the other hand, is having no such problems - the air is easily entering the engine, flowing through it, and leaving the engine. That also means that T66 is being much more efficiently utilized ;)

To specifically answer your questions -

#1) Yes, the T66 is flowing more MASS of air, due to higher density (colder air charge)
#2) The compressor sizing is actually a slightly different part of this equation, due to what I wrote up above - You've got to take into account how dense your air is, and then how well it will flow through the engine. 2 seperate things, working together for more power :)
#3) The turbine wheel is the exhaust wheel - don't get that confused with the compressor wheel ;) A larger exhaust wheel allows more air to exit the engine, easier.

Turbine sizing is ALWAYS a trade off between maximizing power, and minimizing lag.
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thanks for your help, and yes i knew that the turbine wheels is the exhaust wheel.
 
B

bigboost7m

New Member
Apr 20, 2005
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I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.
 
D

Doward

Banned
Jan 11, 2006
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bigboost7m - only if you are detonating like crazy - that's not a matter of compression, that's a matter of tuning.

I have personally run 16psi from a T61 on 9.6:1 compression aluminum headed GM 3100 V6, with ZERO detonation (on pump gas)
 
bountykilla0118

bountykilla0118

In Pursuit of 500rwhp
Jul 16, 2005
1,088
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39
Atlanta GA
bigboost7m said:
I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.
Click to expand...
:nono: So in other words someone else told you all that bla bla bla ...... That motor you are referring to was detonating. Granted higher compression increasing your chance of detonation. But like Doward has said if tune it right you can pretty much run anything you want. Not to stray to far from the topic but this kinda reminds me of all the negative talk about the factory head gasket..... I had my block and head machined and a year and 7 months ago and i have been running 14-15psi since and she is holding up just fine mind you i drive really hard most of the time. I also have a pretty good tune of 291rwhp and 336lbs of tq with A/F ratio of 11.5 using SAFC II, with my factory 440 injectors, pump, AFM and a holy accordian hose.

It has been, still is , and will be all about the tune
 
suprarich

suprarich

Guest
Nov 9, 2005
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ohio
bigboost7m said:
I wouldnt even think about going past 8.5:1. The turbo is already forcing air into the cylinder, you dont need that extra pressure (high compression). Yeah, your motor may live, but its getting beat to hell on the inside, bearings especialy, if you do a couple full dyno pulls after that build with that compression, and you pull those upper rod bearings out (considering you have all your clearences correct) you might as well junk them because that babbit material will get worn of so quickly its not even funny. If you do go through with this build at that compression, i reccomend doing some dyno or street pulls, drain the oil while its hot and cut the oil filter open, then you'll see the bearing material that im talking about. That was a half a-sleep explanation, but for further info contact Bill Miller Engineering at 775-887-1299, and they will be glad to guide you in the right direction.
Click to expand...

Crap! I guess I need to return the custom 10.5:1 7m cp pistons I ordered...
 
F

foreverpsycotic

Back in the game!
Jul 16, 2006
3,171
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ATL
i would not concider 9:1 high compression, its all in the tune and fuel (notice i didnt say gasoline) that you are running. i know of someone with a MONSTER turbo AND high compression (over 11:1), but they are on standalone with a sick tune running strait meth
 
H

Halsupramk3

Member
Apr 4, 2005
444
0
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Mississippi
remember 9.5:1 is very different from 9.0:1. doesnt sound like a much but it is inapplication. so comparing CR of 10:1 to 9:1 is quite a different engine. as long as your octane can be compressed in that 9:1 cylinder without igniting you can run it. watch that timing.

to help keep detonation or autoignition away on my 9:1 cr i had the tops of the pistons coated and also the chambers. also the exhaust ports. that way i will keep heat out of the engine to help keep detonation away. at least thats my theory.

unfortunately i have not gotten boost control to work yet so i have not gone over 12psi on my engine yet. sp61gt. only been on pump gas 93 so far. of course i dont buy off brand cheap gas.
 
I

IJ.

Grumpy Old Man
Mar 30, 2005
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I come from a land down under
It makes for a very responsive snappy motor but leaves NO ROOM for error 1 tank of crap gas WILL ruin your day if you don't have a strategy in place to deal with detonation.

Just not worth the risk for me.
 
Kai

Kai

That Limey Bastard
Staff member
May 18, 2006
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rationalrecipes.blogspot.com
With a turbo build, i know you can use high compression ratio's, but....i'd rather stick to the safe side and not go over 8.8:1....unless your tune is perfect and you know the fuel going in the other end is also perfect, you could end up with a very expensive rebuild...
 
M

MRSUPRA

New Member
Apr 11, 2005
838
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Maryland
I have owned a 1st gen eclipse turbo which comes with a 7.8:1 compression and a 2nd gen eclipse turbo with a 8.5:1 compression. The off boost response is clearly better in the 2nd gen eclipse due to the higher compression. (Of course it has smaller intake ports for higher velocity air intake to also help low RPM drovability)

I purposly bumped up my compression to about 9.0:1 in my new 7M for improved response and drivability at low RPM. The pig can use it too.
 
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