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Building an l28, need modification advice


Evanso

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Hi 

 

I am restoring a 280z and I am at the point where I need to decide what to do with the engine. I have a stock l28(N42 block, N42Head). The engine is out of the car, I have taken the head off and I am going to rebuild the whole thing. 

 

Scenario 

The car is going to be my daily driver for the next few years then after that I plan on it becoming a track car. Therefore it needs to be comfortable to drive but I also want to set myself up nicely to turn it into a track car in the future. I want it to be naturally aspirated and run of pump fuel. I plan on running triple Weber 45's and I have a ZStory race header already. 

 

Current Plan (Please let me know any of these are a bad idea)

 

  • I am going to clean up the block and give it a light hone. 
  • Get the crank balanced
  • Get the head ported and polished.
  • Skim 30 thou of the head to bring CR to low 9's, I don't want to add cam tower shims. (Is this worth doing or am I better of not skimming the head? What power increase would I get?)
  • Replace all the bearings, rings and valve stem seals.

 

 

Question

As the engine is apart, what other modifications/upgrades to the block and head would you recommend for my scenario? Potentially looking into a cam. I would prefer to do them now to the engine so I don't have to take it apart again when I turn it into a tack car.

 

 

 

 

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Hi 

 

Thank you for the advice. I already have the how to rebuild your Nissan engine book. I have now just ordered the how to modify your Nissan engine book.

 

clarkspeed is it worth the extra cost of getting flap top pistons over skimming the head to rais the CR? I am in the UK new pistons would be £300 from zcardepot where as skimming would be £50. Plus I am going to be running the stock cam so with flat top pistons the CR will to high?

 

 

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If you have the room I would get a second block and use it for your future track motor build while using the one you currently have in the car. A good tune-up and a few inexpensive mods should give you enough to both enjoy the car and add other non-engine mods to the car as you want. A second engine would  extend the life of the track motor depending how much you get into the build (mild, mid and full race}.  The closer ot gets to a track only build the shorter the life cycle (rockers, springs, bearings)

Edited by gnosez
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  • 4 months later...

Hi Everyone 

 

Only just managed to continue work on my engine and I thought I would give you all an update. I got the books you recommended and they have been very helpful.  

 

I have taken the head and block to a machine and they said the block needs to be bored at least 20 thou. So I was planning on putting in +40 thou flat top pistons to increase the compression ratio. I was then told that the head needed to be skimmed 20 thou for it to be flat.

 

Now I am worried that with head being skimmed if I were to use flat top pistons the compression ratio would be to high and I could risk detonation. I will be using a OEM head gasket and stock camshaft. 

 

Do you think I could get away with flat top pistons or should I get dished to not risk detonation? I would be buying ITM pistons. The online z-engine calculator gives a compression of 10.6:1 for flat top and dished gives 8.85:1 accounting for the skimmed head. In the future I do plan on putting in a longer duration cam but I want to be able to use pump gas as this my daily driver. 

 

Thanks for all the advice and help. 

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Rule of thumb is 10:1 for an L-series on pump gas. You can try 10.6 but its a risk. I see you are in the UK, and all my experience is from US 91 octane. If your fuel out there is higher equivalent octane or uses more than 10% ethanol, you should do your own research for equivalency. 

 

Detonation is not an all-day thing when you are borderline. It will show up on hot days, high load, with ignition timing advance, etc. If this is a daily driver, I would go dish pistons for a near 9:1. As a matter of fact, I would not change the cam either. You could look for a factory "C" grind. 

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Thank you for the advice AydinZ71.

 

I think I will go for dished pistons then as don't want to have pay higher prices for higher octane fuel as this will be daily driver. 

 

In the future when I change the car to a full race set up I will rebuild the engine then and change to forged DSI pistons. 

 

 

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52 minutes ago, Evanso said:

Thank you for the advice AydinZ71.

 

I think I will go for dished pistons then as don't want to have pay higher prices for higher octane fuel as this will be daily driver. 

 

In the future when I change the car to a full race set up I will rebuild the engine then and change to forged DSI pistons. 

 

 

 

Sounds good!

 

Just a word of advice, being in the process of restoring and upgrading a race car myself. Keep your car as a daily driver, and buy a separate 240z as a race car that may not be titled, have missing parts, no interior, etc. You will be tearing the car apart and spend months performing structural improvements, seat mounts, etc. Best to do this on as cheap and incomplete a chassis as possible. Almost nothing on the suspension will be left untouched, so anything on the car today that is "upgraded" or in good shape will likely be replaced with something that is adjustable and specific to your racing class. Just make sure the chassis is straight, and be ready to perform rust replacement of new metal as you reinforce. 

 

-Aydin 

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  • 6 months later...

My 2 cents from when I installed a l28 (IIRC F54 block, P90 head from a ZX). If funds aren’t an issue now just make the engine track ready now with the compression ignition and triple carbs. Get the adjustable cam gear and tensioner mentioned (I wish I had when I rebuilt) and spend the money to go to an EDIS electronic distributor-less ignition system (the distributors for these engines just really start to have issues now after 40-50 years). Better fuel delivery and ignition timing will make detonation control a breeze even on those higher compression numbers and you should be able to safely push the 10-10.5:1 compression so you don’t have to tear the engine apart again later to get that comp where you want for the track.

 

If funds are a limiting factor, which is kinda my problem at the moment, then what you mentioned in your plan seems like the way to go and just upgrade as you can. It will be a longer process and you’ll certainly want access to another daily anytime you have to put the new parts on.

Edited by Sanchez
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