Guest Magic Posted September 8, 2004 Share Posted September 8, 2004 Hi Guys Out here in Australia we didnt get the P90 turbo in the L28. But I have managed to source one and am looking to hook it up to the following setup in my L28. Intercooled T3/TO4E turbo 370cc injectors Fully programable Engine Management Stock turbo inlet / exhaust manifolds port matched & ceramic coated. 57mm throttle body My question is, what is your experiance / recomendation with engine compression ratios for the P90 head? Im rebuilding the motor so changing the compression ratio is an option. At the moment im thinking of aiming for a target of 14psi (250-300rwhp?) & I want to get the engine compression ratio as high as possible to keep things efficient and punchy low down for a street application. Your thoughts and experiances would be really appreciated in helping me decide what I will do. Thanks in advance. Magic Quote Link to comment Share on other sites More sharing options...
fl327 Posted September 9, 2004 Share Posted September 9, 2004 stock turbo motor here is 7.4-1, kinda low but it works great. 8-1 would be about as high as I would be willing to go here in CA-home of the bad gas. Quote Link to comment Share on other sites More sharing options...
Guest Magic Posted September 9, 2004 Share Posted September 9, 2004 Thanks for that. Out here we can get either 96 or the premium 98 Octane fuel. What do you run on in CA? Quote Link to comment Share on other sites More sharing options...
DAT240Z Posted September 9, 2004 Share Posted September 9, 2004 I have heard to rase the comperssion on the turbo engine you can shave the head, is this true if so how much would you have shave to get 8-5-1 comperssion? would you have to shimed the cam, if so what size shim would I need. Quote Link to comment Share on other sites More sharing options...
Guest Magic Posted September 9, 2004 Share Posted September 9, 2004 You can change the compression by shaving the head, enlarging the bore & pistons, changing the brand/thickness of your headgasket and also by changing the "height" or contruction (dished or flat) of the piston to some degree. If you shave the head you will need shims to compensate the amount you have shaved off. Most engine builders can work out what is required to change the CR if you know what the standard engine dimentions and compression ratio is. Back to the original post, Anyone else out there raised the compression of their P90 and gone into 14psi+ boost territory? Quote Link to comment Share on other sites More sharing options...
Clifton Posted September 10, 2004 Share Posted September 10, 2004 I've run an L26 flat top with N42 head, L28 with N42, and L28 with P90, all turbo'd. What little I lost in off boost torque didn't matter with the P90 as I could make more on boost power . You could use a 1mm MHG HG, stock is 1.2/ .050" and take just enough off to clean the head and get it straight. I wouldn't run anything but the factory dished turbo pistons or forged, All N/A pistons are weaker. 14 psi / 8.0:1 will make less HP than 17 psi / 7.4:1 but both have the same compression ration under boost. If you cut the head and don't use shims it retards the timing, just gives a little more top end. I have never shimmed the cam towers and have cut .120" off of an E88 on an N/A motor. Here's a couple of links http://not2fast.wryday.com/turbo/compression/compression.shtml http://www.turbofast.com.au/javacalc.html Quote Link to comment Share on other sites More sharing options...
Sean73 Posted September 10, 2004 Share Posted September 10, 2004 I'm running P79 flattops with a P90 head and it works fine, with a static CR of 8.8:1. I'm running about 10 psi w/ an NPR IC in the AZ heat, and it doesn't seem to mind with the Z31 ECCS. I like having the extra bottom end for street driving. Of course, I can't run as much boost as a 7.4:1 CR motor, but right now, my boost limit is dictated by the ECU/injector limitations, and not by the CR. The only difference I can see between a dished turbo piston, and a flattop P79 piston is the dish. The rings and ring lands are the same size. It's the pre-81 NA pistons that are the weaker ones. Since you do have access to high octane fuel, and you're using programmable EFI, I think it's safe to bump up the static CR, especially since your HP goals are modest. Sean 73 240Z, L28ET, T3/T04E, NPR IC, Z31 ECCS Quote Link to comment Share on other sites More sharing options...
auxilary Posted September 10, 2004 Share Posted September 10, 2004 Thanks for that.Out here we can get either 96 or the premium 98 Octane fuel. What do you run on in CA? don't laugh, but courtesy of our incompetent air resource board, we get maximum of 91 octane. used to be 92 Quote Link to comment Share on other sites More sharing options...
Guest Magic Posted September 21, 2004 Share Posted September 21, 2004 Ok cool. I feel a lot happier with upping the compression now. I took my motor out yesterday and have started to strip it down. Will keep you updated, any one elses experiance with raising the CR is appreciated Quote Link to comment Share on other sites More sharing options...
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