Hot Rod Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
97 Posts
Discussion Starter #1
jus wondering exactly what part(s) of an engine determines how high it can rev. I gave someone some info on my motor and they said it would red line at 5500. So i am wondering if there is a way to get it higher. Remember this is my "first" V8, i was all high revin' DOHC engines so far in life.
 

·
Registered
Joined
·
178 Posts
slow'n'steady said:
jus wondering exactly what part(s) of an engine determines how high it can rev. I gave someone some info on my motor and they said it would red line at 5500. So i am wondering if there is a way to get it higher. Remember this is my "first" V8, i was all high revin' DOHC engines so far in life.
the mass of the rotating assembly, and your valve springs have a limit before they float the valves,etc.
 

·
Registered
Joined
·
97 Posts
Discussion Starter #4 (Edited)
OK, am i wrong or are there a bunch of 6500+ rpm V8s?

my rotating assy: 383 forged crank, aluminum rods, forged pistons.
I am going to be running some heavier springs also.
intake is a Weiand Team G, Demon 850 BT carb, dont have the heads picked out yet...

also 302/Z28: your '34 is lookin pretty damn nice!
 

·
Registered
Joined
·
77 Posts
Yep more than 5500 in that package

:) Seems to me ya gotta lot more than 5500 rpm in that package with any kinda decent cam and spring setup. just my .02
 

·
Registered
Joined
·
119 Posts
best bet is mechanical roller man,
with excellent springs and heads, big racing cam, extreme well made rotating assembly,
you could get close to 8000-9000 rpm; nascar motor rev all through the day at those rpms
the old 302s could rev to 8000 rpm
 

·
Registered
Joined
·
420 Posts
slow'n'steady said:
jus wondering exactly what part(s) of an engine determines how high it can rev. I gave someone some info on my motor and they said it would red line at 5500. So i am wondering if there is a way to get it higher. Remember this is my "first" V8, i was all high revin' DOHC engines so far in life.

main limiting factor is the thickness of your wallet
 

·
Member - AMC/Rambler "guru"
Joined
·
1,772 Posts
MOST stock rotating assemblies (crank, rods, pistons) will handle up to 7K rpm FOR SHORT PERIODS. I wouldn't want to run most (there are a few exceptions) at 7K for more than 10-15 seconds.

As pointed out, the valve train will usually float (up-down motion overcomes the ability of the springs to keep the valves closed when they should be -- the valves are pushed open but can't close fast enough to keep in contact with the rocker arm, thus they "float" in the air between contacts) if it's all stock. Stronger springs will help, but there are other factors to consider then (spring bind, camshaft wear, etc.). Most stock valve trains will start to float in the 5-6K rpm range.

Size of intake and/or carb limits. Those will only allow so much air/fuel to be sucked in. Once the max is reached, you ain't gonna turn any faster! Same can be said for the exhaust -- a small exhaust system will only allow so much to be pushed out regardless of intake/carb size. Once you reach the limit...

Cam makes a big difference, as well as valve sizes. Same as above.

The really big point is what onovakind67 said though -- rpm kills engines. You will get better longevity and reliability by producing more power at low rpm than high. Low rpm power is generally torque, not big hp numbers. A low rpm torquey engine with the right gearing can stomp a high revving, big hp number engined car. Of course if the revver is set up right too it could be the winner, but not necessarily. Two different animals! The big thing is the revver will be rebuilding every season at least, the lower rpm engine might run three seasons before needed refreshing. All depends on how each is built, but a revver in general will not last as long nor have the reliability of a lower rpm engine.

Creating power is mainly a matter of getting lots of fuel/air mixture into the engine so it can be burned. A small engine can burn as much fuel/air as a large one, and therefore produce as much power. Because of the small size (displacement) the little guy has to turn like crazy in order to move as much mixture. That's why those DOHC engines you're used to have to turn so many rpm. They have a lot of size to make up for! But they won't last as long being turned up high all the time, though there are some design considerations to make up for some of the wear. OHC is one of them. Less valve train weight, and direct acting on the valves. I believe OHC is harder to float because there is less play -- only space is between two parts, cam and valve (on some designs -- others have a follower, similar to a rocker arm). You have both ends of the rocker and both ends of the lifter on a push-rod engine.
 

·
Registered
Joined
·
994 Posts
One way to impress the folks who are impressed by RPM is to use an x-pipe and a 6-cylinder tach. While your big V-8 is only turning 6000 rpm, it will sound like it's running 8,000 and the tach will verify that. Make sure you have the red-line plainly visible at 8200 or so.
 

·
Lost in the 60's
Joined
·
15,259 Posts
RPM's cost money..........How many do you want to turn, Lmao :D
 

·
Some Punk Kid
Joined
·
786 Posts
Destroke it. Make that 5.7l SBC a 3.0l (<-- dont think that would work, has anyone ever tried that low of a destroke or is not even possible with geometry of block.)and turn 15k and then have to change valvetrain every 10 thousand miles or less.
Might as well keep it low and slow otherwise more money more problems.
 

·
Registered
Joined
·
97 Posts
Discussion Starter #16 (Edited)
the cam is actually a 224/224 114LSA
Also i am OK with having a lower revving engine, but 5500? i would atleast like 6K before i have to worry about red lining.
was planning to use aluminum rods, Better off going with a set of H-beams?

and while on the rod subject... how do i know what size rods i should use? 5.7" 6.0"...?
 

·
Save a horse, Ride a Cowboy.
Joined
·
5,122 Posts
Valve train.

It is not so much how high will it rev in a pull, but how long it will survive when you miss a shift or overrev it in error. People thing about floating valves not closing and limiting the ultimate rpm, a worse problem is the valves and pistons touching.... then ya got a mess.

I have also seen flat tappet hydraulic lifters cracked in two by overrevving.

If the engine revs high enough, sometimes it makes a funny noise. Usually suddenly, unexpectedly, and spectacularly. :thumbup:

Rule of thumb. 6,000+ rpm takes money to be safe, not to mention the repeated and expensive valve train replacement every few thousand miles. If you neglect that as routine maintenance, broken springs can wipe out pistons.

Rod length is pretty irrelavent in the real world. But long rods flop back and forth less so there is less stress at higher rpms.
 

·
Bottle Fed
Joined
·
472 Posts
BME says that aluminum rods are OK for a street engine but in most cases drag racers will swap rods in between 200 and 400 passes.
Since you live in Iowa..... Number 5 on their maintenace list would apply to you.

(1) Do not hot torque bolts on BME rods. If you do so, as the rod cools; the bolt will lose some of its preload. If you over torque the bolt you may permanently damage it.
(2) Under no circumstances should you re-serrate the mating surfaces. If bearing housing distortion should occur, return the rods to BME for resizing.
(3) If the intended application is endurance racing, we strongly recommend that oil temperature be maintained between 200-220°F.
(4) Repairs to connecting rods should be performed by BME.
(5) If the engine is to be stored for any period of time (over winter, etc.) it is recommended to remove the rods, clean thoroughly in solvent, oil all parts and store with the bolts at least one turn loose.
 
1 - 18 of 18 Posts
Top