HadesOmega Posted November 2, 2005 Share Posted November 2, 2005 Ok well here's the deal, I blew my head gasket and took the head off and sent it to the machine shop. He said it was pretty warped, I was surprised I didn't think it would be that bad having been through a water pump and boosted it with the blown gasket. heck it might've been warped when I got the engine. anyway he said it would have to be resurfaced top and bottom, he said it might raise compression by half a point also. He would also have to shim the top but he said that would fix the problem with the cam gear alignment being too low. would it be a good idea to get the work done or just find another head? The compression for the L28ET is pretty low already right like 7.5:1 so it'd make it like a 8:1 or something. Was the L28ET made to run on low octane or high? I put 91 in mine and I don't plan on running some crazy high boost. something around 10 and 14 at most. oh and this is on a 82' L28ET if that helps any. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 2, 2005 Share Posted November 2, 2005 I don't know any exact numbers, but I'm sure milling your head won't increase your compression ratio THAT much. It is 7.3:1 stock, so you got a fair bit of breathing room. Most people would welcome the increased CR. I wouldn't advise using low octane fuel on a L28et unless you have your boost turned lower than stock or have some other method of controlling detonation like a intercooler or water injection. Quote Link to comment Share on other sites More sharing options...
HadesOmega Posted November 2, 2005 Author Share Posted November 2, 2005 cool sounds good to me, hopefully I won't encounter any timing problems. That is some rediculously low compression it is a really old engine but I was running 10.5:1 on my eclipse at 10 psi and it held up fine, I guess thats new combustion chamber technology for ya. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 2, 2005 Share Posted November 2, 2005 Yes combustion chamber design is a big part of it. The eclipse also no doubt had a intercooler, and good ecu tuning. Quote Link to comment Share on other sites More sharing options...
Pyro Posted November 2, 2005 Share Posted November 2, 2005 I believe you can raise compression or raise boost but not both at the same time without an aftermarket efi system with ignition timing control. 7 to 8 psi (stock boost) will run ok with 8:1 cr but will be tricky to run 12 or 14. Quote Link to comment Share on other sites More sharing options...
pjo046 Posted November 7, 2005 Share Posted November 7, 2005 I am going with a 8.5:1 compression on my engine. And I will shoot for at least 14 psi of boost, likely more. But then I'll use a standalone engine-management system, a good intercooler, and forged pistons. Quote Link to comment Share on other sites More sharing options...
Thumper Posted November 7, 2005 Share Posted November 7, 2005 The stock compression ratio is 7.38:1. By putting either a felpro or 1mm headgasket on there you are raising the compression to 7.52:1 If the head is shaved .010" the compression ratio will be 7.67:1. If .020" then 7.82:1 So every .010" shaved it will raise compression roughly 0.15:1 Unless your head is major fubared he should only need to shave .010-.015" Non-turbo 280zx motors that have had a turbo put on, can handle 13-14psi and their compression ratio is 8.52:1 Good luck Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 7, 2005 Share Posted November 7, 2005 I put an N42 head on my turbo bottom end for a 8.3:1CR. I'd never build another 7.38:1 CR engine again unless it was an all out, peaky power, drag car. Quote Link to comment Share on other sites More sharing options...
DAT240Z Posted November 7, 2005 Share Posted November 7, 2005 Drax240z Did you just bolt the N-42 to your turob block or is there more to it than that. if you can yuo tell us what was done as I to have a 240zt and looking to up my comperssion. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 7, 2005 Share Posted November 7, 2005 Basically that is all there is to it. I did put the turbo cam in the N42 head however. Quote Link to comment Share on other sites More sharing options...
DAT240Z Posted November 7, 2005 Share Posted November 7, 2005 Drax240z, I have another question, did the N42 head come with a cam oiler, if so are you running it? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 8, 2005 Share Posted November 8, 2005 No and No. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 8, 2005 Share Posted November 8, 2005 "Cam oiler only came on 240z's, N42 is from a 280z." Better qualify that statement to "US or North American Specification Vehicles" I have an N42 headed L28 from a Nissan Cedric that has the cam oiler spraybar. The JDM L26 we installed in my buddie's Fairlady also had the E88 and a cam oiler bar. When it threw a rod, we snagged a 75 Cedric L28, and it tooo had the spraybar. My understanding is the drilled cams came in 77-78 vehicles. This seemed to jibe with non-US market junkyarding as well. Quote Link to comment Share on other sites More sharing options...
Thumper Posted November 8, 2005 Share Posted November 8, 2005 I too have seen a n42 with a cam oiler. Not sure about n47's though. Although I thought they didn't go internal intill 79' but not sure about that. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted November 12, 2005 Share Posted November 12, 2005 This thread is great!! I was just wondering how to increase the compression ratio on my 82 turbo Z motor, the low compression ratio is killing me on short autocross tracks. So by changing out the P90 head for a N42 head Drax240z increase CR. However the P90 head was for the turbo motor so what is the trade off between the P90 and the N42? Also will any other head work if I can not find an N42. Thanks HB280ZT Quote Link to comment Share on other sites More sharing options...
GrayZee Posted November 12, 2005 Share Posted November 12, 2005 or put flattop L28 pistons in your L28et Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted November 12, 2005 Share Posted November 12, 2005 Here is some more info i got online So how does a lower static compression benefit a forced induction engine? Let's look at an example. Compare these two situations: 1) On a stock 5.0 with ~9:1 static compression it is found that a non intercooled supercharger can run a maximum of 9psi of boost without detonation. The effective compression is ~14.5:1 and 320 peak rwhp is produced. 2) Same engine/supercharger combination but with low compression 8:1 pistons installed. It is found that a maximum of 13 psi can be run without detonation. Effective compression is again ~14.5:1 but significantly more air is allowed to enter the combustion chamber. Peak rwhp is now 380. In both cases the same octane fuel is used. Here is the entire article, it is a good read http://www.tazzo.com/turbo/technical.html Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted November 12, 2005 Share Posted November 12, 2005 The best tool that I have found so far for looking at what a setup would give you is this one from Atlantic Z: http://www.atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html Now if it could only tell you what will happen if you have to surface your head or deck, that would be really cool!! HB280ZT Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 12, 2005 Share Posted November 12, 2005 Remember that if you are racing, especially in autocross situations, peak horsepower doesn't mean squat. A broad torque curve and good throttle response will make much more difference, which I have found myself with my compression increase. A dyno number is just a number... it is of little importance on the autocross track. I'd choose a higher than stock compression ratio and the potential for less boost anyday over a stock CR and more boost on the track. HB280ZT make sure you use a lightened flywheel as well, another huge difference and well worth the money. I had my stock one lightened to 17.75lbs, not too extreme, but it was a huge improvement over stock as well, and still lets me launch the car easily. Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted November 12, 2005 Share Posted November 12, 2005 That is my thought exactly. My car just does not get out of the turns very good because of the low CR. My friend is running a stock 77 280Z and in a short technical course he beats me evry time. But when the course gets longer and I can get into boost I beat him every time. So that is why I am interested in increasing the CR by about 1 point. As for the flywheel already did that and it helped some, along with a better clutch. Now the magic question is which head is better the N42 or the N47?? Also what should I have done to it other then check for straight, valve job and have my turbo cam installed? Thanks for the help. Also looking at installing the intercooler that I have and a MegaSquirt ver3, a P82 intake manifold, pallnet fuel rail with 460cc injectors and a 60mm TB this winter, along with new frame rails from bad dog products. So I have a bit of work before next season of autocross starts in April. Wish me luck!! HB280ZT Quote Link to comment Share on other sites More sharing options...
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