High compression with a turbo
Thread Starter
Joined: Nov 2008
Posts: 2,424
Likes: 229
From: A-Town, Ill side
High compression with a turbo Ok, so I have a question for you guys who have experience with turbos. An acquaintance says you can run a 10.1 compression motor on the street with pump gas with 7-10# of boost and have a better result than say a 9.1 motor with 12-15# of boost. He states it will get better mileage and have a better feel to it due to the compression. I am looking for guys who have run turbos, not just theory here.How many guys have at least a 10.1 motor with a turbo? BTW he's saying this about a stock LS6.
In order of power I would say its boost, then timing,then compression then afr. Just a rough guess.
I would think a person would be hardpressed to tell the difference in a car between 9 to 1 and 10 to 1 in everyday driving on boost or off. And higher compression can mean you have to run less boost and less timing so that can affect things too.
I would be very careful on stock motors. Sure see quite a few guys running them for pretty long periods of time at pretty high boost levels but also seen quite a few go kaboom pretty quick as well.
I went with a 9.5 in my car. Builder said if was going to run alc injection that would be a nice ratio. You could go a lot higher if you run e85 or lots of pure meth injection.
I was worried to go too low say to 8.5 to 1 figured that might make the car doggy off boost.
I would think a person would be hardpressed to tell the difference in a car between 9 to 1 and 10 to 1 in everyday driving on boost or off. And higher compression can mean you have to run less boost and less timing so that can affect things too.
I would be very careful on stock motors. Sure see quite a few guys running them for pretty long periods of time at pretty high boost levels but also seen quite a few go kaboom pretty quick as well.
I went with a 9.5 in my car. Builder said if was going to run alc injection that would be a nice ratio. You could go a lot higher if you run e85 or lots of pure meth injection.
I was worried to go too low say to 8.5 to 1 figured that might make the car doggy off boost.
On The Tree
Joined: Sep 2007
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Higher compression just makes it slightly harder to make power on low octane, but its probably a fraction of a percent.
The biggest issue with high compression is keeping compressor efficiency up. Most turbos are designed to be most efficient at 12-20psi. Flowing alot of air at low boost is a good way to make more heat than horsepower. But again at the end of the day its still only small percentages.
The biggest issue with high compression is keeping compressor efficiency up. Most turbos are designed to be most efficient at 12-20psi. Flowing alot of air at low boost is a good way to make more heat than horsepower. But again at the end of the day its still only small percentages.
Take a look at what we did with this APS Firehawk at 11.0/1 at the old shop. Bob
http://www.exoticperformanceplus.com...Car.php?car=39
http://www.exoticperformanceplus.com...Car.php?car=39
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TECH Enthusiast
Joined: Jan 2004
Posts: 608
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From: New Zealand
I have 10.2:1 and have run up to 18psi with meth,
Its just a matter of tuneing around the higher compression, should be a bit more lively off boost , but won't take as much timeing under boost as a lower compression engine.
Its just a matter of tuneing around the higher compression, should be a bit more lively off boost , but won't take as much timeing under boost as a lower compression engine.
TECH Addict
Joined: Aug 2004
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no it wont, but it will make the engine FEEL stronger down low. This will result in more power being made at any given RPM. THis in turn will reduce the lag felt while the turbos 'come onto boost'. also as the tubos atart to make boost then the engine will agian feel stronger than with lower comp.
Your right though in that the comp. ratio just means the engine is using the enrgy from burning the fuel better. there 'should' actually be less enrgy in the exhaust gas to drive the trubo(s) with a HC setup as the engine is harnessing more of the energy. However this will be pretty small.
This was always my interpratation of it anyway. lol
Chris.
By the way it might be worth noting that WRC cars (2.0ltr 4 cyclinder) often run 45psi of boost and run VERY HIGH comp ratios. they use mapped water injection into each cylinder, as well as vastly complex ECUS and EGT systems, to ensure they can run as much boost as poss on the fuel they have.
Your right though in that the comp. ratio just means the engine is using the enrgy from burning the fuel better. there 'should' actually be less enrgy in the exhaust gas to drive the trubo(s) with a HC setup as the engine is harnessing more of the energy. However this will be pretty small.
This was always my interpratation of it anyway. lol
Chris.
By the way it might be worth noting that WRC cars (2.0ltr 4 cyclinder) often run 45psi of boost and run VERY HIGH comp ratios. they use mapped water injection into each cylinder, as well as vastly complex ECUS and EGT systems, to ensure they can run as much boost as poss on the fuel they have.
Thread Starter
Joined: Nov 2008
Posts: 2,424
Likes: 229
From: A-Town, Ill side
Well if your running a stock piston I guess I just don't see it having a long life span, especially if you lean it out or worse, don't hear the knockin' at the door. I find it kind of ironic that in the FAQ's it basically says high compression and boost is not a good idea, and yet more than 50% of you that have chimed in have said it's not so bad. I think a lot of this IS opinion, and opinion is based on experience. I have not had good experiences with this combination in the past.
I had built a 10.1 2.3 and ran 20# boost, but it was a totally different animal than these LS engines. It was a fully forged lower end and it was run on race gas with a lock-wire setup and copper head gasket.
I appreciate the discussion and the experiences you guys have offered, keep them coming!
I had built a 10.1 2.3 and ran 20# boost, but it was a totally different animal than these LS engines. It was a fully forged lower end and it was run on race gas with a lock-wire setup and copper head gasket.
I appreciate the discussion and the experiences you guys have offered, keep them coming!
Most all these guys are running forged engines and then running e85 or meth.
Stock high compression and much boost is not a good idea. Seen lots of blown up stock engines and not that high boost levels. And these guys were not all stupid at tuning .
I think my 9.5 is pretty good compromise ratio. But do run alc injection we have no e85 option up here. I can run decent timing at lower boost like 8psi and still run like 18 degrees max with no alc on just pump 91.
And that is pretty much the point. You want to run high boost on pump..8.5 is nice. You want to run bit more 9.0 is pretty nice if you aren't going to run alc or e85. You want to run alc injection 9.5 is pretty nice and you want to run e85 or lots of pure meth than you can go higher to 10,10.5, 11 whatever.
I don't think my 9.5 car is doggy at all. No complaints.I have heard some say 8.5 gets doggy but others say can't even notice. It all might depend on cam,gearing, etc.But more compression does let you make more power at less boost.
Stock high compression and much boost is not a good idea. Seen lots of blown up stock engines and not that high boost levels. And these guys were not all stupid at tuning .
I think my 9.5 is pretty good compromise ratio. But do run alc injection we have no e85 option up here. I can run decent timing at lower boost like 8psi and still run like 18 degrees max with no alc on just pump 91.
And that is pretty much the point. You want to run high boost on pump..8.5 is nice. You want to run bit more 9.0 is pretty nice if you aren't going to run alc or e85. You want to run alc injection 9.5 is pretty nice and you want to run e85 or lots of pure meth than you can go higher to 10,10.5, 11 whatever.
I don't think my 9.5 car is doggy at all. No complaints.I have heard some say 8.5 gets doggy but others say can't even notice. It all might depend on cam,gearing, etc.But more compression does let you make more power at less boost.
