datsunlover Posted August 10, 2004 Share Posted August 10, 2004 Ok, I have to admit I'm not as well versed as I'd like to be in the Nissan Z motor.. and I searched, but anything I found.. well.. Im not sure what it really means.. Anyway, here's what Im thinking.. I have a 75 280z w/stock L28 (been rebuilt about 8-10 years ago) and Im running SU's and an open exhast (planing a 2.5" for the spring). I have come into a parts car with an L28; its a 81 280zx w/5 speed. Now, I want the 5 gear anyway.. but I'm wondering what would be the better motor performance wise? (I'm gona keep using the SU's whatever I do..) Or is there really much of a diffrence? From what I can tell, the ZX 2.8 has a slightly difrent head.. (apparently the exhast ports went to round instead of square?) but Im not sure what, if any, the diffrence would mean to me.. Really what I'm wondering is, would I be further ahead to just use my 75 2.8, or would there be any benefit to using the zx's 2.8? (either way, Im pulling the engine apart and doing a clean up/re+re as needed) Maybe make one good motor from the two? (I'd love to just do the 302 swap, but it doesnt look like it's gona happen this year.. Basicaly, I'm wanting a good reliable motor for street use.. but a few extra horses would be nice.. and Im trying to keep the budget in check too as I need to redo all the suspension as well this winter..) Soooo.... can anyone shed some light on this for me? Quote Link to comment Share on other sites More sharing options...
PUSHER Posted August 10, 2004 Share Posted August 10, 2004 Place the 75 280z head on the 280zx block. If you could read off the head stamp someone could probally find the compression that would make. Reason being is that the 280zx block has flat top pistons that allow for higher compression. And I believe the 75 280z head has a smaller dome making higher compression when matched with the 280zx block. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 10, 2004 Author Share Posted August 10, 2004 Thats what I was thinkng.. just don't know what combos work well, what swaps work, ect. I'll see tomorrow if I can get a number off my 75's head... So.. my 75 block has what.. dished/relieved pistons then? Im hoping to not get into too much head work as well.. maybe some new valves/seals/ect as needed.. just wanted a 'throw it together' and go kind of thing.. but I dont wana smash the pistons into the valves! Oh yah, the 280zx engine only has 160000 Kilometers on it (100miles right?), and it apears that the car was maintained well (at least mechanicaly) so Im assuming it has a good bottom end in it..well, probly better than the the engine in my 75.. 160+k MILES! Im gona to a compresion test n it tomorrow as well.. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted August 10, 2004 Share Posted August 10, 2004 Yup yup yup, 280Z N42 head on 280ZX NA F54 block => 9.8:1 CR, along with the 280ZX 5-spd and diff, SWEET setup! '75 has dished pistons. You won't have any piston/valve intereference problems unless you go with a pretty high-lift cam. Quote Link to comment Share on other sites More sharing options...
e_racer1999 Posted August 10, 2004 Share Posted August 10, 2004 also, i'd like to add that you are going to want to get your hands on the misc. parts you will need for the R200 conversion (i'm assuming that since you have 4sp you have an R180...?) but i'm sure you already know that, as far as the compression ratio part, dan got it on the $$ Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 10, 2004 Author Share Posted August 10, 2004 Yah well.. I have a 4 gear now.. but Im not sure if my 75 has the R200 to begin with. (??) Thing is, from what I can tell, the zx diff has better ratios anyway (3.9), so my 280 will get the 280zx rear diff and 5 speed as a package. (I have a whole parts car wohoo!!) As for the 75 head on the zx block.. I'll be ok with my stock 280z cam thats on it right now then? (assuming it's not too worn..if so, what are my options for replacement with this head/block setup?) I am thinking of doing a valve job and changing the timing chain/gears/ect anyway (its all apart why not right?) Just out of curiosity.. what would my comp ratio be right now? (bone stock 75 L28) Thanks for the help guys! Quote Link to comment Share on other sites More sharing options...
PUSHER Posted August 10, 2004 Share Posted August 10, 2004 Your stock 75 motor has a 8.3:1 comp ratio. Dan Baldwin, are you sure that is what the comp ratio will be raised to? Thought it was in the 10s:1, dont know for sure, just asking. Thought there was some stock head/block combo that raised compression to above 10. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 11, 2004 Author Share Posted August 11, 2004 Well, I just got back from the shop and doing a compresion test on the 280zx motor. Got 150 - 155psi across the board.. a little lower than I would like, but at least they're all the same! So ah.. with my 75 head(N42 right?) on the zx F54 block.. and running 2.5 exhast, zx dizzy and SU's.. any guess on potential power I can make? Assuming the head work is decent and the stock cam is useable... Quote Link to comment Share on other sites More sharing options...
Guest eric-z Posted August 11, 2004 Share Posted August 11, 2004 maybe with a 1mm head gasket if you could get 10:1 Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 11, 2004 Author Share Posted August 11, 2004 What's the stock head gasket thickness? Not really a big deal though.. I'll be uping the cr either way by swaping this head on that engine block.. I dont think I'd notice much difference between 9.8 and 10 anyway... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 12, 2004 Share Posted August 12, 2004 Stock is close to 1.25mm. Not going to make a really noticeable difference and if anything the higher comp would make you that much more likely to ping. Ask Bastaad what to expect hp wise. I want to say he made 170whp with basically the same setup, but that's all from memory. I thought there was a rule, like 15hp per point of comression. If ON3GO made 145 stock, and you've basically raised the compression 1.5 points, you should make ~165 or so. Cam, porting, etc will add to that. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 12, 2004 Author Share Posted August 12, 2004 Thats kinda what I was thinking.. Im looking into (If the money holds out!) getting some bored out/rebuilt Ztherapy carbs, a decent cam, and straight 2.5 exhast (cherry bomb/glass pack in the trans tunel; I like the sound and it cheep!) .. shooting for about 200 horse in the end. Of course all the suspension and brakes (300zx/toy 4X4 swap) have to get done this winter too (my bank acount is screaming at me already ). For starters, I'll rip the driveline out of the ZX and go over the whole block and re+re as needed (new oil pump/timing kit/ect) and get the head done profesionally... Guess I should start ordering some gasket kits and get pricing on cams.. On a side note, a friend of mine suggested I simply do the motor 'junk yard' style. Pull my head, drop it on the ZX block (new head gasket) and drop it in with the 5 gear.. I must admit I am thinking about it.. I guess I could rip out the engine(s) in a weekend, get it together and running in another week or so and see if it works.. but I'm wary about 'trusting' the parts car tranny/clutch/block internals/ect to actually holding up to something like this with no prep work done.. and I figure I'll put the car away for the winter in a few months anyway... I dono.. I think about this stuff too much.. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted August 12, 2004 Share Posted August 12, 2004 PUSHER, An E31 head on a flat top L28 would make 10.2:1, that's probably what you were thinking of. Probably stock or Felpro gasket would be fine, and a lot cheaper than an HKS metal one. For hp estimation, I've heard/read that a straight ratio of compression ratios will give an estimation, albeit an optimistic one. I figure, all else being equal, and within the CR range that works for available fuel, you should be able to get at least half that gain. 10/8.5 = 1.18, figger that means at least a 9% gain in torque EVERYWHERE in the rev range. Woohoo! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 12, 2004 Share Posted August 12, 2004 Forget the cherry bomb. Most of them are HORRIBLE for flow. Really horrible. If you look inside them the pipe that goes through doesn't just have holes drilled in it. Sometimes it's more like a cheese grater, where the ends of each hole is bent into the stream of the exhaust flow. Even though this doesn't look like a big restriction and you can see right through the thing, it is a very big restriction. You want CHEAP and decent quality? Last Dynomax SuperTurbo I bought was $29.49 from http://www.jcwhitney.com. It's a GOOD muffler with minimal backpressure, and cheap. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 13, 2004 Author Share Posted August 13, 2004 Hmm.. maybe I'll try my hand at building a 'cherry bomb' style mufler.. My boss just did this for his sons motor bike (83 yamabog 400) and it seams to work pretty good! Just took a pipe with the same id/od as the stock pipe out of the engine, drilled a BUNCH of holes in it, and welded a cap on the end. Welded that to the stock pipe, then slid on a pipe (over top) with a bigger id/od (about 1/4" bigger I think..) and welded it to the stock pipe just in front of the smaller pipe with the holes.. Meh.. it'd be something to do/build in itself.... but I'll look into Dynamax anyway I think. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.