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Hi List,

I've been hearing so much conflicting info about E31 heads on L28s. I have an E31 with big valves and a choice of L28 blocks (dished and flattop pistons). The head has been cut something on the order of 0.020". Even with a 2mm gasket, the compression ratio seems high for the crummy gas we get around here. Especially if I have to bore the block (which is certainly possible).

On the other hand, I don't mind the CR I get with the dished pistons (.5 mm overbore) and a 1 mm gasket, especially if I have to cut another few more thou off the head to clean it up, but I've heard a few horror stories about the "fundamental incompatibility" of the closed chamber E31 head with dished pistons.

This is intended to be a street engine with a mild cam, SUs and a stock exhaust manifold.

Any recommendations? Anybody ever tried the E31 with dished pistons?

Advice appreciated,

Pat
 

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It's not really a horror story...but all the benefits of the combustion chamber shape are lost if you use dished pistons. That just means that you will not be able to run as high a compression ratio with it as you could on flat tops. It won't run any better than an e-88 with the same CR, and it will ping just as easily.
 

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I've got a '71 240Z with a dished piston L28 block, E31 big-valve head (slightly shaved, not sure how much), Shadbolt (now Colt) M445 cam, round-top SUs with SM needles, stock manifold, ZX electronic distributor, stock tranny, 4.11 diff, and 2 1/2 inch exhaust.

The engine feels very strong and has run flawlessly for about 1000 miles (as long as I've had it) on 92 octane, and another 5000 miles before me with the previous owner who autocrossed his car with this engine very successfully (usually set fastest overall time).

Based on how much quicker my 240Z is than my SE-R Spec V, I'd estimate a 1/4 mile trap speed of about 95mph, which means about 165 rwhp, or close to 200 at the crank. The car also has a stripped interior and no bumpers.

The engine pulls decently from 2000 rpm, nicely from 3000 rpm, and really comes alive from 4000-6000 rpm. Idle at 900 rpm is just a bit lumpy, and fuel economy sucks :)

So I'm very happy with my engine, but your mileage may vary. Good luck!
 

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JimCanuck, I don't have the cam specs at the moment, but I do know that it's high-lift short-duration.

My car was built by a great little local shop (on Vancouver Island) and they've told me that this cam has worked really well for them on a bunch of cars - it's a custom grind and was manufactured in Vancouver by Shadbolt, which at some point morphed in to Colt cams - not sure of the details.

On top of the good power, the engine sounds fantastic, with a metallic throaty snarl at high revs.

I'll try to get the specs this week and report back.
 

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L28 flattop, Triple Webers, E31 head with 280Z valves. Isky Stage III cam (290 adv dur 490 lift) Headers, 4.11s, etc.

Pings and diesels a little on 93 octane. Requires a little boost in octane (1 gal Cam II per 15 gals), but it sho' do run good. Eats Mustangs for breakfast....
 
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