Kevin.pk Posted May 23, 2007 Share Posted May 23, 2007 I have a p90 head that has apparently been shaved .080 based on the number of cam shims that it has. i figure that puts me around a compression ratio of 8.5:1 with stock turbo pistons (i think, correct me if I'm wrong). i have no intercooler and stock eccs... i plan on running stock boost at least until an intercooler is in the picture.... Would it be safe to run this head with N/A dished pistons and block? The reason I ask is cause I'm having trouble finding a turbo block locally and I can pick up a n/a dished piston block fairly easily. i did search but most people with the increased compression ratio on a turbo motor had either an intercooler or an aftermarket efi or both. Thanks in advance, Kevin Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted May 23, 2007 Share Posted May 23, 2007 I'd say wait until you have an intercooler and build a motor properly. 8.5:1 *may* work at stock boost but you better plan on an intercooler... Quote Link to comment Share on other sites More sharing options...
David K Posted May 23, 2007 Share Posted May 23, 2007 I had a plan to build an 8:1 turbo motor using the same setup you are considering. Discussing it with several experts didnt present any problems with the setup. I believe a lot of turbo cars from the manufacturer use 8:1 engines. Some of the later Mistubishi Evos are using 8.8:1 engines with 19 pounds of boost, so i wouldnt see any problem with an 8.5:1 engine getting 6-7 psi. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted May 24, 2007 Share Posted May 24, 2007 It might just be a typo but just FYI they probably shaved .080" or 80 thousandths of an inch off of your head. .8" is 8 tenths of an inch and that's a lot. Quote Link to comment Share on other sites More sharing options...
Kevin.pk Posted May 24, 2007 Author Share Posted May 24, 2007 oops ... yeah meant .080 my bad.... thanks for catching it. ill change it. so far it seems iffy at best to run it with this head.... keep any comments/ suggestions coming Kevin Quote Link to comment Share on other sites More sharing options...
NCchris Posted May 24, 2007 Share Posted May 24, 2007 I had a plan to build an 8:1 turbo motor using the same setup you are considering. Discussing it with several experts didnt present any problems with the setup. I believe a lot of turbo cars from the manufacturer use 8:1 engines. Some of the later Mistubishi Evos are using 8.8:1 engines with 19 pounds of boost, so i wouldnt see any problem with an 8.5:1 engine getting 6-7 psi. My build plans are similar, stock non shaved P90 w/flattops and holset. Remember that the evo's and other modern turbo motors have 4 valves, cross flow with some form of pent roof combustion chamber. This setup is more resistant to detnation (spelling) than our older design. What I'm trying to say is that just because they can do it at 9:1 doesn't mean we can. chris Quote Link to comment Share on other sites More sharing options...
David K Posted May 24, 2007 Share Posted May 24, 2007 My build plans are similar, stock non shaved P90 w/flattops and holset. Remember that the evo's and other modern turbo motors have 4 valves, cross flow with some form of pent roof combustion chamber. This setup is more resistant to detnation (spelling) than our older design. What I'm trying to say is that just because they can do it at 9:1 doesn't mean we can.chris If you know who bigjim is (you probably dont), he put a turbo on an n/a and boosted up to 10psi and had no problems. Im sure others have done the same and they will reply soon. Quote Link to comment Share on other sites More sharing options...
ckelly78z Posted May 24, 2007 Share Posted May 24, 2007 I beleive that P-90 head has been used on a N/A car running the N/A flat top pistons. This mod of shaving the head .080", shimming the cam towers and spring bases .080", and then using the longer N-47 valves gives someone 10.0-1 compression ratio while keeping the timing chain tension, and valve geometry correct. It is usually done on a P-79 head for availabilty purposes but could certainly be done on a P-90 with the same results. Needless to say, using this kind of compression ratio with a turbo is not optimal. Quote Link to comment Share on other sites More sharing options...
David K Posted May 24, 2007 Share Posted May 24, 2007 Needless to say, using this kind of compression ratio with a turbo is not optimal. No, thats not true or you arent addressing the question he asked. I have a p90 head that has apparently been shaved .080 based on the number of cam shims that it has. i figure that puts me around a compression ratio of 8.5:1 with stock turbo pistons (i think, correct me if I'm wrong). i have no intercooler and stock eccs... i plan on running stock boost at least until an intercooler is in the picture.... Would it be safe to run this head with N/A dished pistons and block? YES. The compression ratio is FINE. The only thing holding him back is the design of the piston, the N/A pistons may be weaker where the rings sit. Other than that, the setup is fine for 6-7 psi which is STOCK. Do you guys even read these posts before you reply? lol. Quote Link to comment Share on other sites More sharing options...
Kevin.pk Posted May 24, 2007 Author Share Posted May 24, 2007 i know the engine was used with a turbo previously... i don't know how successfully though... it originally came with a rayjay turbo attached to one of the u shaped pipes coming off an n/a manifold from a BAE turbo set up. . and i realize the p90 shaved .080 is normally used with a n/a set up... i got the head with a turbo short block that ended up needing rebuilt.... one of the rod caps came loose or something and the motor cracked off a piston skirt on the crank... spun the bearing... etc.... i figure it wouldn't be too risky to run the shaved p90 with n42 block since there are folks who have run the n42/n42 combo with out much trouble at stock boost level.... and the compression ratio for a n42/n42 is something like 8.3:1... thats only .2 :1 less than my estimated 8.5:1 i just figured i'd see if anyone else had run this specific set up successfully with out intercooler/aftermarket efi Kevin Quote Link to comment Share on other sites More sharing options...
aarang Posted May 24, 2007 Share Posted May 24, 2007 I think you will be fine with stock boost and no I/C as long as you set your initial timing lower than stock and bump up the fuel pressure. Also, running 100 octane wouldn't hurt either. I had a setup that was F54 flat top/ P90 with N/A 'A' cam, stock ECCS, stock turbo, no I/C , etc .. Ran great. The low end torque of that motor would DESTROY the tires!! Quote Link to comment Share on other sites More sharing options...
Guest 280ZForce Posted May 25, 2007 Share Posted May 25, 2007 you guys, my car when I first bought it was running on a stock n/a engine L6 (flat top pistons and crane cam) that had around a 9.5:1 compression ratio according to the engine calculator and it had a t4 turbo setup on it running on 7-10 psi w/ 91 octane and it was a daily driver for 20 years before the head needed to be rebuilt, so then I just went another route. I seriously just recommend an ic and you will be fine. Quote Link to comment Share on other sites More sharing options...
Kevin.pk Posted June 2, 2007 Author Share Posted June 2, 2007 ok, one last idea... if i use a 2mm head gasket would it be completely safe to run the p90 that is .080 shaved with dished pistons... im not sure how low the compression would be but i think it would be more suitable and allow me not to have to put in an intercooler Kevin Quote Link to comment Share on other sites More sharing options...
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