redwingvette

The book says the L-48 redline at 5300rpm. What is the limitation. Is the limit on HP and Torque or is because of internal parts used from the factory?

theanswriz42

I think it's about 5800, err at least my car has done that before :)

Chris O'

My stock (was) '77 L48 was flat out pushing 4900rpm. A few mods and 5500 every time.

:cheers:

dman535

From Car Craft Tech Talk:

Q: How do you tell if you have overrevved an engine ?
A: Its contents will loosely fit in a five gallon bucket.

There really is no reason to rev a stock L-48 over 5500 rpm, you are out of the powerband and its not set up for high revs.

Chris O'

:lol: :lol: :lol:

jdunne

Abone stock L48 only makes more noise above 5000rpm.....how long it will continue to make that extra noise is a moot point.......max torque is about 3K and max power low 4K........I am sure that there are folks about to tell me that THEIR L48 revs cleanly to 7000 rpm,spins the wheels in every gear and peaks at 120mph.......I've never driven one of those,but quite a few L48's and i cant get them to do that........john :chevy

Shark Racer

Not so sure about an L-48 not doing 120... I've taken my LM-1 up to 115 a number of times... with about 500 rpm left to go in 3rd(1:!). Of course, the LM-1 is slightly newer than the L-48, but cam specs are the same and compression is real close.
Not sure how much better the heads are.
Also, road tests put the stock 78 L-48 4-speed topping out at 126 or so.
-Steve

jdunne

Steve,my point was an L48 is 20 years old(give or take a few).i was ignoring the issue of gearing.....just trying to make the point flippantly that it is not a high revving high HP engine.....it always was a torquey engine at relatively low rpm...john :chevy

jerryp58

I'm not an engine expert by any means, but I think what you were looking for was a "physical" RPM limitation to an L48 (maybe the same applies to all internal combustion engines), YES?

I think one answer to your question would be "valve float". At a higher RPM, the valve springs can no longer properly control the opening & closing of the valves. That can result in at best a loss of power and at worst physical damage to the internals as the valves and the pistons hit each other. Engines designed to rev higher have stronger springs. You could put stronger springs in your L48 if you wanted to, but there's probably a trade-off there too like reduced cam or lifter life, maybe :confused:

I think I got that right. Anyway, I'm sure there are other physical limitations that others could point out.

Ganey

He is not talking stock L-48, note the mild cam- much better than stock L-48.

The exp. engine designer sets the rev. limit. In this case GM/Chevy. You can expect the rev. limit to be conservative. While it can be cammed to turn much higher, this would not be safe. Really needs rebuild, balance, & blueprint to increase rev. limit. Assembly.

So how much higher you can turn it & how many times depends. How lucky you feel? The GM/Chevy rev. limit has not been increased.

Ganey

PS Cam w/ anti pump up lifters will allow 6000 easily on stock L-48. Not rec.!

TedH

When I've dyno'd my rebuilt L48 at 5250rpm, it was just making max horse power; that's with the following performance adders: Energizer cam, Performer intake, hypereutectic pistons, Accel distributor, recurve, duals on exhaust manifolds, dynomax super turbo mufflers, K&N filter, stamped steel 1.5 ratio rocker arms.

190.5 rear wheel horse power on an engine originally rated at 190 flywheel hp.

I agree the base L48 is out of breath at 4000rpm but oh do they respond to power adders!

With the new DART IE heads, headers, rebuilt carb, and better dual exhaust system, I'm going to see how she does up to 5500rpm. Am hopeful to see rwhp in the neighborhood of 275-290... :smash: :smash: :smash:

gerry72

There are various definitions, some relevant, some not, for a redline. From an engineering perspective, there is only one definition...maximum safe engine speed. Meaning that you can operate the engine for an extended period at that speed and do no harm. This is a component limitation (pistons, rods, crank, block) meaning that the parts are not designed for stresses beyond the redline. They may fail, or the may not.

Most of the time though, unless you've improved the engine's breathing ability, you do little more than make noise once you get close to or exceed the redline since you're usually well out of the power band.

Fevre

If you can dyno it, that will tell you where your peak torq and horse are at. No sense in reving any higher then peak horse since no power will be gained. Now if you get crazy and ad a big cam, high rise single plan manifold and headers your car will probably make peak horse above the rpm's which would be safe for lower end in stock configuration. Personal I don't like to rev above 5000, my car is for fun cruising not and brief spurts of power not for me to learn how to diagnos and rebuild it everytime I rev it till it blows.

Fevre

BTW GO WINGS!

Metal Wulf

an L48 can do well over 120... I've had the spedo past the 140 mark and seemed like it could have gone higher. aside from a K&N filter my engine is stock. This was done when i still had 3.08 gears too.

Shark Racer

Agreed... just wanted to defend it in the case of the top speed. (Though it barely makes it to 120 ;) )
Even with the performer intake and slightly better exhaust, anything past 4400 or so RPM is just like beating a dead horse. I feel slightly more comfortable with the LM-1 as it has 4-bolt mains, but not much. My engine does have the same cam the L-48 did, if Ganey was referring to me.
As for the L-48 hitting 140, either the car was in a vacuum tube running with a bare minimum of tire and drivetrain friction, or the engine was definitely not stock. Far from it, as a matter of fact. That I can't believe... no offense...
-Steve

no_radio

Actually....if the engine has a few more RPMs left after peak HP you should rev it a bit past peak. This is so that when you shift to the next gear you are higher up in your power band and there's not as much delay. If you plot your best shift points in each gear (neglecting wheel spin) they will be some RPMs above peak in each gear.

Jeff

Fevre

Unless you powershift! :lol: That is something I will probably never do.

redwingvette

Tanks for the input. I have know idea as to how fast my car will go since I changed the rear end gears but I have had the rpm's up to 5500 when I power shift from 2nd to 3rd at 70mph. it felt like there was still some power left at that point. I need to put it on a dyno. I just put in an Hpipe yesterday and I haven't been able to run it down the track yet.