Short Stroke L28

[chris b]

I am interested in finding out about experiences with short stroke L28s.

I have just had an L28 built with a 2.4 crankshaft. The motor has been bored out to the first size overbore and flattops fitted. The block has been decked to bring the compression to 10.5 to 1. Everything has been balanced and blueprinted. The flywheel has has as much material as possible removed.

I think it is about 2750cc.

The head is an E88 with a lot of porting etc. A MSA stage 4 cam kit has been fitted.

The engine has triple 40 DCOEs, headers and 3 inch exhaust and I have a 4.1 diff.

My previous motor was similar but with maximum size pistons and completely worn out. I decided to stay with the specification because of the interesting crank with the 8 bolt flywheel (see picture).

I am hoping for a very revy motor for trackday fun but at this stage a little nervous if it will workout.

[Bart Hoedemaker]

Higher rpm needs bigger carbs, for more power in the upper rpm range.

[d240zx2]

You should have a quickly revving motor, but I would be cautious above 7500 with the short-throw crank....you'll likely run out of gas much beyond that, anyway. :dead:

Frank

[240znz]

Wouldn't you be better off with 44mm or 45mm carbs for that sized engine if you want to pull high revs?

[chris b]

Thanks for the feedback on the carbs. I suspect that the 40s will run out of gas. I will know more in the next few weeks after the motor has a few more hours on it and I can try reving it.

I am curious about the potential crank problems. Does anyone know anything about the after market crank that I have (see picture in the original post) is it also susceptible to failure?

Cheers Chris.

[bkelly]

This is what I've been thinking of building. I'm not too big on low RPM's with lots of torque, I love a screaming engine at high RPM's. What rods are you using with this build? A few weeks ago I bought Bob Leitzinger's cylinder head that was used on his 280ZX race car. It's a HEAVILY modified E31. I've been looking into building an engine to match it. I'm not sure if I'd use it in my 70 project or save it for future use. It's a back burner project as all my efforts are going into finishing up the car. I'd still like to know what else to buy so I can snag it if the part pops up.

[chris b]

I am not sure about the rods, I know that they had, had a fair bit of maching done on them. Will check with my engine builder next time I see him and let you know. Also hope to get it on the dyno in the near future.

[29pgc10]

It is nissan competition crank, or similar. I used to have flywheel for one long ago. m

[bradyzq]

Thanks for the feedback on the carbs. I suspect that the 40s will run out of gas. I will know more in the next few weeks after the motor has a few more hours on it and I can try reving it.

Cheers Chris.

Theoretical question here about Webers:

Since 40's, 42's, 45's, etc., all use the same jets, shouldn't you have the same capacity to draw fuel with all DCOE's? With the smaller venturis of the 40's, and therefore higher air speed, you're certainly getting a strong enough "signal" with which to draw the fuel.

So, it appears that you might actually run out of AIR, not fuel.

Which means that, instead of leaning out at the top end, you may actually go too rich.

All this to say that with an upper limit of 36 main venturis (biggest available on 40DCOE I think), you may be ok.

Any holes in this logic?

Cheers,

[bradyzq]

BTW, how high do you intend to rev?

I think your cam's power band should start tapering around 7000RPM or so.

[29pgc10]

Those are from:

DATSUN 240Z

SPORTS OPTION PARTS

MODEL: HS30 SERIES

ref no: RB-300

Date: Dec 15 1974

... I like the idea short stroke motor ...

[bradyzq]

Still on the carburation of your de-stroked L28, I still think you'll be pretty close with the 40's.

Here's why:

The stock Weber kit for 240Z came with 40DCOE18's with 28 main chokes. If someone can find their Pat Braden book on Weber carbs (which I can't at the moment), it'll be listed at the back with all the kits.

And it's the chokes that really determine how much air can flow. And air flow is proportional to cross-sectional area, soooo

28's for a stock 240 means 29's for a stock 260.

You can go all the way to 36's on 40DCOE's.

That would represent a 54% increase in airflow over 29's, which would be the "stock" starting point.

So, if your engine is making more than 54% more power than a "stock" 260, then you'll have to look at 45's.