L28 Head Gasket Thickness Installed

[NC280z]

Good afternoon everyone,

 

I rebuilt the L28 in my Z a few years back using a Clegg engine kit, and for the life of me I can't remember what brand head gasket comes with the kit. I'm attempting to determine my compression ratio, because I need to tune for e10 gas here in VA. Here's my thought, there's a small space at the rear of the head (near the brake booster area) where the gasket doesn't extend. If I grab a set of feeler gauges and see what fits between the head/block, this should give me my gasket's thickness, correct?

 

From what I've read in the "How to rebuild/modify" books, a Nissan-standard gasket should compress to around 1.2mm, whereas the Fel-Pro gaskets are 1mm. Earlier today I was able to get around 1.2 of feeler gauge in, so I'm guessing that the Clegg gaskets are close to OEM spec. This should put my flattop F54/F54 combo at 9.6:1. I have no idea of any other method to determine the gasket's thickness while installed. Any help will be appreciated!

[datzenmike]

A quick calculation shows the 1.2mm and the 1mm gasket difference is 1.1cc less of volume. If the stock L28 is 8.3, this 1.1cc less combustion chamber raises the compression to 8.435. I realize that your head may be shaved, different pistons.. any amount of things that will alter the compression but roughly about 1/10 of a compression point.

[datzenmike]

..and I missed the last sentence. What is an F54/F54? Also what is your combustion chamber size? A higher compression engine will increase the compression more for only 1 cc.

[CGraves]

Yeah your combustion is gonna be real dependent on what head you have. But didn't F54 blocks come with flattop pistons stock? Assuming your head is stock as well you should be at about 8.8:1 but I'm just going off memory cause math is scary.

[datzenmike]

Ah.. the block. Came with flattops or dished to lower compression if with turbo.

 

If you have L28 flattops and a P79/P90 head your compression would be 9.57. Assuming this was with a 1.2mm thick gasket a 1mm would bump it to only 9.75

[NC280z]

**CORRECTION***

 

Had a bit of a typo, I've got an stock '75 block and head, which is N42/N42 (squareport exhaust). I'm using flattop pistons, .020" over. I had a bit of a brainfart and put F54 rather incorrectly. The "Datsun compression calculator" online puts my compression with a non-Nissan gasket at 10.08:1, which I'm assuming is a bit much for 93 octane pump gas. I don't hear any knocking while driving around, and the plugs read a light brownish color, but I'm getting a bit of vibration at the 5-6000rpm region that I believe may be the onset of detonation. It doesn't bog, or seem to lack power (quite fast, actually!) but I'd rather err on the safe side, and assume that if I'm at a higher compression ratio that I'll need to consider fuel additives.

 

Sorry for the mistake, and thanks so much for the responses! Hope to hear more on how to check the gasket thickness.

[scooter]

Probibly .050

 

Is you dont have salt and pepper on your plugs (detonation) keep bangin!

 

That vibration could be anything

[CGraves]

Well you can still find the kit on Cleggs website so you could give them a call tomorrow and ask what gasket they use.

 

93 octane should be fine for 10:1 right? As for the vibration I don't know a lot about the L series but I know on RB motors the crank starts to get a vibration in it at a certain harmonic frequency so the L series might have something like that? Someone more experienced could chime in on that one.

[datzenmike]

**CORRECTION***

 

Had a bit of a typo, I've got an stock '75 block and head, which is N42/N42 (squareport exhaust). I'm using flattop pistons, .020" over. I had a bit of a brainfart and put F54 rather incorrectly. The "Datsun compression calculator" online puts my compression with a non-Nissan gasket at 10.08:1, which

 

I can only find two combustion sizes listed 42cc and 53.5cc neither work out to 10 compression and give 12 and 9.67. Do you have the combustion chamber size of your N42 head?

[CGraves]

@mike 

 

Could you post the numbers you used to come to that answer? I looked up the formula and did the math and I got 8.8

 

Edit. Nevermind I forgot he bored his block. I fixed the bore and got 9.678 so it checks out.

[datzenmike]

So I guess the combustion chambers are 53.5cc.

[scooter]

Well you can still find the kit on Cleggs website so you could give them a call tomorrow and ask what gasket they use.

 

93 octane should be fine for 10:1 right? As for the vibration I don't know a lot about the L series but I know on RB motors the crank starts to get a vibration in it at a certain harmonic frequency so the L series might have something like that? Someone more experienced could chime in on that one.

If its not balanced, could be it, i would put more money on the flywheel than the crank though. All inline 6 cranks can have potential resonance issues. If your wailing it around 6 grand all the time might not be a bad idea to buy a damper. If you want a nice one that works with stock pulleys, look at the bhj ones. Ati also makes one that fits an l series but then the pulley selection is up to you.

[NC280z]

Looking through some of my old receipts, I found that the Clegg kit came with ITM gaskets. I've also found varying accounts of the ITM head gasket thickness, anywhere from 1.2mm to 1.5mm! Either way, I should be in the mid-to-high 9's for compression. I'm still using the stock damper, so I will check the condition of it tonight.  Given that it's 41 years old, there's a good possibility that the elastomer is dried and worn. The machine shop I had bore the block also balanced the rotating assembly, so I'd believe it to be either in the flywheel or damper if the vibration is not ping-related. Thanks again for all the input guys!

[datzenmike]

The gasket will compress. Compressed the gasket is about 1.2mm. This is a small amount and not that important on a stock engine. It will either ping or it won't. So run better gas or turn the timing back till it stops.