E31 w/ L28 block

[red_dog007]

What is your guys take on this?

I might have the chance to pick up an 82' L28 engine for $300. Think that is a good price? I am going to be finding out more information sometime soon. Already emailed the guy.

Just would like to see what is your guys take on an E31/L28 set up. It seems like the compression is way up there near 11:1 with a little searching.

If I get this, is it really going to turn it into more of a unstreetable car or what?

Would this be a better option then getting a Stage III cam on my L24? Would save me a few pennies.

Though how would a cam do on an L28?

The Z I am wanting to get to the point were it is my daily car, and I want it to be powerful with an L engine N/A, but not too annoying to drive as a daily car. That high compression kind of scares me a little. Already with my current setup, it can/will already diesel a good bit with a little advance in the timing. If I went L28, having that high compression, would I need to add a octane booster each fill up to prevent it dieseling on me?

What is your guys take on this and what might be the best route to go with my E31.

L24 with Stage III?

or

L28?

[mark belrose]

Where are you coming up with these compression numbers? Unless you had an L28 setup with positive deck height pistons, you shouldn't be getting anything near 11:1 (my quick search shows 10.2:1 with flat top pistons). Using earlier L28 blocks with dished pistons further reduced that compression ratio. Also, make sure to enter into your cost equation the installation of larger valves into your E31. Othewise there wouldn't be much point in even considering that head/block combo.

Mark

[Carl Beck]

L28 – Flat Top Pistons (79-83) & E31 Head

Swept Volume of Cylinder = 458.9

Combustion Chamber volume = 42.4

Gasket Thickness = 7.7

Deck Height = -3.69

505.31/458.9 = 11.1 C/R with a positve deck height

509.0/458.9 = 11.09 C/R with 0 deck height

Now mill the head to flaten it, reducing cc to aprox 38cc, then unshroud the valves to put it back at 41cc - or add an over-bore and you’ll push it even higher...

With the crummy pump gasoline we have in most parts of the country today - I wouldn’t want a street engine with much over 9.5:1 C/R... Run higher C/R and you have to retard the timing -and that kills the engine response/power anyway....

FWIW,

Carl B.

[Oiluj]

Listen to Carl...

9.5:1 compression is what I specified for my engine because of the quality of gas these days... Higher than 10:1 means you have to start putting in octane boost additives in each tank of gas and that gets expensive!

[red_dog007]

Mark, I got my numbers from "The Datsun Z Garage."

It is a good point about the gas. Will have to consider that. We have 93 octane here, but even then sometimes my Z would diesel.

Will have to think this one over.

What kind of compression could I expect with a Stage II or III cam on the L24 with increased valve size?

How would that compare to the L28?

How about performance wise? Would it be just a little power difference, or could you notice it.

I could always put in a fuel cut off switch if I half too, so dieseling would be too much of a problem to fix.

Which would be more streetable? Give me plenty of power and performance when I want it, but also give me a nice time around town. Having a rough idle is fine, but being crazy would be a bit much.

[mark belrose]

L28 – Flat Top Pistons (79-83) & E31 Head

Swept Volume of Cylinder = 458.9

Combustion Chamber volume = 42.4

Gasket Thickness = 7.7

Deck Height = -3.69

505.31/458.9 = 11.1 C/R with a positve deck height

509.0/458.9 = 11.09 C/R with 0 deck height

FWIW,

Carl B.

OK, I'm still not sold on the calculated compression Carl stated above. Please see the attached image and verify if I'm way off regarding input into the calculation program. I guess-timated a deck height of -0.3mm which I believe should not be too far off for stock flattop pistons and used a gasket thickness of 1mm to come up with the 10.2:1. Here's the link since as it's not very clear on the image: [email=http://www.csgnetwork.com/compcalc.html]http://www.csgnetwork.com/compcalc.html

Mark

[ktm]

I am calculating 10.2 as well from http://www.ozdat.com/ozdatonline/enginedesign/

Stock gasket thickness is 1.2 mm.

[Carl Beck]

Hi Mark:

Most of the guys seemed to agree that the L28 head gasket was 88mm - you have 86. I also get 1.27mm for the compressed height of the gasket .05 inch or 1.27mm. You are using 1mm

Also you have a piston deck clearance .3mm - ie. below the deck - - all my notes say it should be .-0.741 above the deck. I was using -0.3 by mistake as that is for a 0.5mm overbore.

FWIW,

Carl B.

[Carl Beck]

Bo - what specific numbers are you putting into that calculator?

thanks,

Carl B.

[ktm]

Carl, they have pull down menus that you select and it inputs the correct data.

Block: L28

Crank: L28

Head: E31

Rods: L28

Pistons: L28 Late (this will be flat tops)

Cam: L28

Gasket Height: 1.2 mm - stock gasket height

[e_racer1999]

also, remember if you play with the e31 you have smaller valves. sure you can modify the head to fit the larger valves, but i would just run with an N42 and expect a 10:1 CR. you can run crummy gas without much fear. that's what i'm doing at least...

[Carl Beck]

OK, I'm still not sold on the calculated compression Carl stated above.

Hi Mark:

Yes- and it's a good thing too. I totally screwed up the calculations - I must have been falling asleep or having as Senior Moment..

Had time to go back through this - to see why such difference.... between my calculation and the Web Based Speadsheets...

Holding the Deck Height at "0"... as there seems to be some disagreement to the actual data being gathered.... I should have written:

L28 - Flat Top Pistons (79-83) & E31 Head

Swept Volume of Cylinder = 458.9cc

Combustion Chamber volume = 42.4cc

Gasket Volume = 7.7cc

Deck Height = 0

558.9 + 42.4 + 7.7 = 509

and

42.4 + 7.7 = 50.1

so 509 divided by 50.1 = 10.16

Thanks for catching that... Mark/Bo...

FWIW,

Carl B.