Hey everybody first post here. I've had 240sx's, a maxima, a frontier, all modified, im no Nissan amateur, found this site, and will hopefully find some answers!

Alright, im looking to do a drift car (shop car)...350-450 daily driven horsepower (reliable), I'd like to do an L28et in it. I've noticed that different L28's come with different head items:
the older models had adjustable rockers, and square exhaust ports, the more recent ones had hydraullic rockers and round exhaust ports.
Wondering which head has a better valvetrain for my power range. I've heard that the valvetrain is the weak link on these overall fairly strong engines...Do the L24's or L26's have stronger head internals? stronger springs or anything? Any useful information is appreciated.

 

I believe only the '83's had hydraulic rockers, though I've heard they weren't great anyways.

 

The turbo L28 came out only in 1981-83 in the 280ZX model. The older 240Z and 260Z heads are not generally used on a turbo engine. Smaller valve ports in some, higher compression.

The two heads used on the turbo engines were P90 and P90a. P90 is 1981-82 with manual rockers. 1983 P90a had hydralic rockers. The hydralics work good but there are no replacements made anymore. Both styles of heads have square exhaust ports. The best head to use for the turbo setup is the P90 turbo head. Don't bother swapping heads around. Keep the lower end with the dished pistons. You will definatly want the lower compression that it offers for the boost levels you'll need to get over 350 horsepower. About 350+ is where you'll probably want forged pistons.

 

My buddy here in AZ runs 22PSI all stock motor excluding, valvesprings and SDS standalone, water injection, and 1 additional 550cc injectors {the other 6 injectors are also 550} and puts down 517WHP.. in the last year the only prob he had was he blew the head gasket {stock}.. I am shooting for 450WHP myself which is almost a given.. Also Welcome to the board...

 

If you upgrade to forged pistons and a better fuel management system I'd say stick with the compression ratio from the NA motors. The 81+ had the same block as the turbo and damn near the same head with only the exhaust ports being different. The stock compression ratio in the turbo motors is only like 7.4:1. Which is actually really low, even for a turbo motor. Some turbo motors now run close to and even up to 9:1 compression ratios which is higher than the NA. I'm planning on running a forced induction setup on an NA F54 block with no worries of wether the C/R is going to be too high. I'm gonna see how long it'll last on the cast pistons then tear it down and rebuild it with forged ones. I'd prefer to stay with cast if they can handle the pressure though. I'm going to go with the P90 head though as it just flat-out out-flows any other Z head.

 

Oh and is that a Yashio Factory Silvia in your Avatar Rubber Burner? I saw the pink and it made me think of them.

 

On the subject of compression ratio, I is there a chart somewhere to see what the CR is on my 81 NA?

 

i believe all NA 280zx's were 8.8:1...I'd like to run NA pistons, 550cc's, Z31 (88-89) turbo ecu/maf/o2 etc... with the P90 head...stronger valvesprings, and possibly a cam, i am currently undecided on the turbo though...how does that sound? people disagree with the 8.8:1cr? well the 4g63 in the evo's come with 8.8:1 and 19psi STOCK...i think it should hold on moderate (10-15psi) boost. What is the stock boost level on the L28et? No thats not the factory car...its a car locally that was in a magazine.

 

I dont think that the Z31 MAF will support your hp goal of around 450, maybe in the 350 range. And how do you plan to run those larger injectors? You could reprogram the Z31 ECU.

If you really want that kind of power you will be better in the long run to just go stand alone now, there is unlimited potential. There are plenty to choose from SDS, HALTECH, ect. And if you want cheap Mega Squirt can be built for under $500.

As for the turbo I would go with a Hybrid t3/t04e turbo. I my self do not have one so I can't tell you exactly what to get but if talk to the place you are buying it from they will set you with what is best for your set up.I would try going to http://www.speedshopthagard.com/

 

Newer DOHC engines have better quench designs in the head, superior computers and ignition setups. That's why they can run higher compression. We're talking about a fuel injection system designed in 1974. The basic L-series deisgn was designed in 1967, and the 'new' P90 head designed in 1980 for the 81 turbo.

The late Z31 turbo ECU will make some adjustments for larger injectors. That's the beauty of that ECU swap. Looks like you know more about your buildup than I had thought. I'm glad you did your research.

The turbo sounds good, but I've joined in discussions about the compression ratio and more experienced builders all agree that you will blow something on the L28 with higher compression. Run 8-9psi on the 8.8:1 engine for safety. It is just so much more prone to detonation. higher compression, less boost is not good. Lower compression, more boost will still get you where you want to be horsepower wise.

 

The top rings on the N/A pistons dont like boost too much!!

 

Oh yeah s/c. I plan on changing those . I'm just talking stock C/R. And I'm definitely going Stand Alone and distributorless ignition to handle the boost and compression. The quench of the P79/P90 is actually pretty good with the heart shaped chambers. Before that though it was pretty poor with round chambers. And I'm running cast pistons (not stock) and stock rods and crank. I'm also going to be utilizing the highly touted windshield fluid injection that s/c's always raving about combined with an intercooler will allow me plenty of boost at 8.8:1 on 91 without detonation with a programmable ecu and ignition. I'm talking the works here (hey it's gotta be, it's the company car ).

And you don't see too many pink cars. You also don't see too many silvia conversions. So to see a pink Silvia conversion just screamed Yashio to me. Guess not though.

Z31=not worth it with everything you're planning rubber. More like an upgrade for the stock turbo 280zx. Not really good for high performance.

 

Oh alright, i wasn't sure about the maximum output for the Z31 setup. Megasquirt i've heard are fairly easy and cheap. Probably go that route. I'd be running 93+ octane if i raised the compression to 8.8:1...i'd probably just get some 8:1 forged pistons (ross/JE/etc...), Still low enough to prevent most detonation, run mid-grade (89*) gas, and high enough for decent power during lag. I'm also thinking about piggybacking a knock sensor that will cut the timing back a few degrees. What kind of timing advance do the L28et's come with? vacuum, electronic? This is going to be a daily driven shop car, and compete occasionally as well...just trying to keep it going once its together. Does anybody here have similar power on thier L28? just wondering what setup you have...maybe you can convince me to run a different fuel management system etc...

 

As far as the stand alone goes MS is probably the best value from what I have read. And if you go to www.hybridz.org there is an entire section for MegaSquirt for our cars! mobythevan on hybridz even made an install guide specific to the l28et. I would check that website out also, there are some guys running that much power over there. Another site to check out is JeffP's website
http://www.angelfire.com/extreme/280zxt/
Also check out
http://www.atlanticz.ca/zclub/techtips/turbo/index.html

 

thanks for those sites KTM, I just started on Hybridz.org the other day, theres a good bit of information on a lot of different subjects there.
I've heard that on the NA L28's, the cam was more radical than the turbo camshaft...anybody know specifics on the lift and duration of both??? it would be much appreciated.

 

N42, P79 & P90(a) head casting numbers are the ones to use. Any of these four can make the power you're looking for.

For a turbo application, the P90 is ideal. The P90a uses hydraulic rockers and was to quiet the valvetrain not improve strength or performance. These rockers are no longer available which is why the P90 is preferred.

The valvetrain is not the weak link in these cars, it's the FI intake manifold, the transmission and the axels. The rest of the system is about as bullet proof as it can get.

 

Really the axles?? You think I will be good 450WHP on stock axles with heavey huty U-Joints{N/A}??

 

Right now im trying to figure out, if the 4.56's in my frontier rear end will fit in a z32 diff, otherwise i'll just get an R200 LSD diff. As for the tranny, not sure if im gonna do a Z33 6-spd, z32 5spd (kinda bulky) or possibly an R33 GTS-T tranny, with a custom driveshaft. the 300z axles should hold up to around 600 fairly well.
And what vehicles came with the N42 and P79?

 

I've seen some good U-Joint axels take serious power and I've seen the 3 bearing CV axels snap on what should have been low power. So, in my opinion, all our axels are suspect including the CV's.

The 4 bearing CV's on the Z31 are the only one's I'd consider 'safe'.

Don't get me wrong, I'm using the 3 bearing CV's on my 280ZXT and I have 2 spare sets ready to go in if these fail. Right now, my weakest link is the original T5 tranny. But I will eventually convert to Z31 CV's, but that'll happen after I get my T5 re-built with a GForce gearset.

 

Z Car Cylinder Head Casting Timeline:

 

Thanks a lot LWW, helps when im going to be searching for parts.

 

OK, a few more questions... E88 heads came with the larger (44mm instead of 41mm) valves correct? Can you put those valves in the N42 and P90 head (of course having a machine shops help)? And what are the main differences between the N42 and the P90 heads? I got some bad info from someone that the "n42 was an intake manifold"...but i thought it was a head casting number!? Tell me if any of what i think or say is wrong please!

 

hmm, how about a carb setup with turbo. I've seen people do it on their 510s, I wonder why it isn't common to do that on an L6

 

That would take more time in design. most of these cars have dual, and tripple carbs. you would have to make a complete chamber to conseal the carbs so that there is equal preasure all around them. other wise you blow seals crush floats, and spit gas all over and no more vroom vroom.

 

Mmmm ... boost boxes.

A neighbor of mine has a Ford T-bucket roadster under pressure - he's got Offenhauser heads, built bottom-end, and 4[!] Weber DCOE carbs mounted inside a sealed box, which is fed about 10 pounds by a Paxton Novi1000 centrifugal supercharger. Only fuel management mods are a rising-rate fuel pressure regulator. Now that, is simple.