Guest Anonymous Posted June 9, 2001 Share Posted June 9, 2001 Ok fellas....got a 76 280Z Need bout 165-170 H.P. at the flywheel. what kinda mods should i run for it? Right now, bone stock, down to the nice rusty exhaust. Don't really want to do anything major, will be removing the head in a few weeks to get a valve job. Should i get it shaved a bit? How much? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted June 9, 2001 Share Posted June 9, 2001 First off, its nice to see someone with a realistic power goal from their L28. 170hp at the flywheel shouldn't be too hard or too expensive. Were it me, this is probably the route I'd go: -Stage 1 or 2 cam (motorsports auto ones) -Header -2.25" mandrel bent, or 2.5" press bent exhaust -K&N filter That is probably enough to make you meet your power goals. I would be somewhat tempted to find a flattop piston block to put with your N42 head however. That would bump your compression up a bit, and give you that much more power. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted June 9, 2001 Share Posted June 9, 2001 But changing the pistons means rebuilding the motor in essence, don't you think? I'm not saying it's wrong, I'm just saying I'm not so sure that's what he has in mind. Richard, you are an L6 kinda guy, would you or would you not recommend shaving the head just a wee bit to raise the compression ratio? David Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted June 9, 2001 Share Posted June 9, 2001 shaving heads on l28 means shimming the cam towers -not good.the later 280zx motors had flat top pistons.if i hadf a fleet of different z cars i would have a car with a high compression efi l28 motor - with sds and big throttle body and big cam-a revver Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 9, 2001 Share Posted June 9, 2001 Racnoth, The previous suggestions are "realistic". I'm not an Inliner expert so I can only go with what the books say about the engine. The books say you already have that "165Hp"...the only problem w/that is the books go on to say the 165HP doesnt come into play until @ 6000rpms. With that in mind & the fact that Mfg's usually like to s-t-r-e-t-c-h the hp/torque readings...I couldnt honestly tell you if those are true numbers. So you need your Peak HP to come into play a little sooner. Also the factory books list the I6 as having a miniscule 8.3:1 Comp.Ratio. As you stated in an earlier post-you want a 1/4mile ET = 15.9/86mph & need the 165HP-yet you need it to come into play @ 4235rpms. This means to me, IMHO, that what you need is a higher comp.ratio & a better breathing engine-which means upgrading your intake/exhaust as well. Make this a slow methodical transition-dont rush into anything. First and easiest to change would be a better breathing intake & exhaust. Look to the aftermarket premium headers & premium intake (K&N for the intake-as mentioned earlier by Richard). Once you've opened that restriction-then you can concentrate on the cylinder heads/pistons and deckign the block if that comes into play. Remember-you already have the 165hp-you just need it an lower RPM; so a mild performance cam is also in the picture; but do the exhaust & intake first; what good is all the performance add on's to your engine if the intake/exhaust are the primary restrictions? Before your engine can perform-it has to breath..then after it's capable of breathing it can become a performance engine. Take the suggestions you have thus far & find a local engine builder that specializes in performance building Datsun L6's; go talk to the local Nissan Dealers-they always have a few shops they sublet to when a customer wants performance. Take our suggestions & offer them to that shop & weigh their answers w/what you already know! Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Drax240z Posted June 10, 2001 Share Posted June 10, 2001 Well Davy, I'm no expert on the L series really. But I wouldn't do more than a .010"-.015" surface plane without thinking about tower shims. Most of the time when you hear about guys shimming their towers, they are going with a .080" plane, and longer valves with it. At this point I think your timing chain would be pretty sloppy without shims. As kevin was pointing at, more torque is probably going to help you more than peak power. Upping the compression ratio is a good way to make more torque. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 10, 2001 Share Posted June 10, 2001 thanks a bunch! Now, just gotta make all this work with the local emission laws.... Quote Link to comment Share on other sites More sharing options...
Guest MM_280Z Posted June 10, 2001 Share Posted June 10, 2001 I am in almost the same position as Rancoth. I have a stock 75 280. From what I gather the hot ticket is a P90 head shaved 0.080" to raise compression to 10:1. Am I hearing now that this is not so good? Why is shimming the cams bad? Supposedly the L6 responds "very well" to this compression mod and a quality valve job (aside: what is the difference between a 3 and 5-way valve job?) What compression do you get just putting flat pistons (can one do dome pistons too?) on this motor, unshaven. What about a lighter flywheel? How much would it help? What kind of HP would end up at the wheels with 170 up front? I can say from personal experience that torque is lacking at 2-3000 RPMs with stock exhaust. Anyone have direct experience if replacing exhaust remedies this? Also, wouldn't a hot cam push the HP to higher RPMs, not lower? Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 11, 2001 Share Posted June 11, 2001 RACNOTH/RACNOTH/RACNOTH!!! I hate to admit it but I made a mistake in your HP needs; the formula was for RWHP-so that required 165HP at an .85% Volumetric Efficiency is actually a 195 FWHP!!! Sorry for the confusion...I hate it when I do that...there are just so many numbers to crunch sometimes I forget which ones I'm crunching at times. Again; your required hp is 195 FWHP which is the same thing as 165 RWHP if your engine is running w/an 85% Volumetric Efficiency! Hope I didnt cause too much confusion. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 11, 2001 Share Posted June 11, 2001 The three and five way valve job just refers to the number of angles that are cut into each valve seat, three angle, uses a very flat angle, the next cut is the angle of the seat itself and then a steeper angle is cut which would be below the seating area of the valve. The reason for it is to smooth out the flow into and out of the chambers. Five way would be the same except five stones would be used for cutting. While I've no hard evidence nor a flowbench to prove it, on the butt dyno, I doubt you'd see much difference on a three way valve job compared to a five way.. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted June 11, 2001 Share Posted June 11, 2001 I'd get a flat-top piston (ZX) bottom end. Kind of a big job, but the NISMO catalog recommends against shaving the head to get increased compression. Going from the dished pistons to flat-tops with an N42 head takes you from 8.3:1 to 9.8:1 compression. 93 octane required. You will feel the difference. If you do go the head-shaving route, you wouldn't have to shave the N42 nearly as much as a p90 to get a decent compression ratio. Quote Link to comment Share on other sites More sharing options...
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