L28 Safe Rpm Range

[Chickenman]

It's been a long time since I've run an L6 engine, but I used to race L24's many, many years ago. Right now the car pulls really hard to 6,500. What is the safe engine Redline on an L28 with a stock bottom end?

 

I've have a freshly rebuilt L28 engine with a 280 duration .460 lift cam. New Nissan factory valve springs ( 13203-F2000 Outers and matching Nissan inners ), Doug Thorley headers, 2.5" custom exhaust. Factory balance job. Stock rods. Stock Flat tops.

 

I will be autocrossing this car a bit next year and maybe running some Track days. I used to run my L24's to 7,000... but on the L28,  I'm thinking of using a 6,500 RPM max shift point with Rev Limiter ( Crane Hi-6S ) set to 6,700 rpm. Shouldn't be any reason to go above this should there?.

 

Car will likely have a Mega Squirt 2 or 3 system by next year.

 

 

 

 

[Diseazd]

I think you are dead on with those numbers......my L28's make max h.p. at 5400 rpm anyway. 6500 for the L28.....7000 for the shorter stroke L24.

[John Coffey]

The issues isn't the bottom end, the issue is the valve springs.  Anything over 7,000 rpm on the stock valve springs is risky, especially if there's a bunch of hours on them.  6,500 on the stock valve springs is fine.  What happens during autocrosses and on a race track is that you have to stretch the rpms past what's ideal to keep from doing an up and down shift in quick succession.  So, you may want to keep a hard redline at 6,500 but you can gain a .5 second by running to 6.800 rpm before a specific corner.

[Chickenman]

The issues isn't the bottom end, the issue is the valve springs.  Anything over 7,000 rpm on the stock valve springs is risky, especially if there's a bunch of hours on them.  6,500 on the stock valve springs is fine.  What happens during autocrosses and on a race track is that you have to stretch the rpms past what's ideal to keep from doing an up and down shift in quick succession.  So, you may want to keep a hard redline at 6,500 but you can gain a .5 second by running to 6.800 rpm before a specific corner.

Thanks John. That's pretty much what I figured, which is why I'm imposing the 6,500 rpm shift point. I'll set the rev limiter to 6,700 which gives me a bit of room if I have to stretch things.

 

We did re-use the old 9mm Rod Bolts and Nuts. So that does concern me a bit. And we did not balance the assembly. Normally the factory balance is pretty good and if memory serves me correct, you can re-use the Rod Bolts once on a non-race engine. 8 mm bolts would scare me re-using them. 9 mm not so much. Am I correct on this?

 

This engine is pretty much just a nice stock rebuild, with the exception of an HP  Cam. Valve train is all new ( Springs, valves, valve guides etc ) with a fresh 3 angle valve job.  I figure there's no point in twisting the bejeezuz out of it. The original engine builder is a great guy... but a bit of a story teller. Last thing he told me after the engine break in was that the engine should be good to 7,400 !!  Yeah right   I just smiled and drove away slowly...

 

Richard

[conedodger]

Spend some time on a Dyno too. I completely agree with Jon but if you want to know what is safe that's one thing, beyond a certain point, the engine doesn't make any more power, just noise.

[John Coffey]

I've run an essentially stock L24 to 7,300 rpm every lap at Cal Speedway when drafting another car.  Had to do it to stay in the race.  The engine was a bit soft after that event.  Swapping in new valve springs brought the engine back to life.

[Chickenman]

As mentioned, the Valve springs are new OEM Nissan 13203-F2000 outers and 13204-23000 inners. The 13203-F2000's are a superceded part number from the 13203-E4100.

 

Does anyone know if the F2000's have more spring pressure than the E4100's ?