I was woundering what would be the max rpms for a 355, a 383 , a 377 (400sbc block and a 350 crank), and a 406? if they had the following parts,
solid roller lifters,
roller cam .600 lift 250 dur.,
roller rockers,
tripple valve springs,
and a good set of heads...
Thanks

hey popeye ive never taken my 383 or any other smallblock above 6500rpms and never blown one either!!! if u go higher beef that crank and jurnouls!!! i dont now if 6500 is max for smallblocks but wouldn`t risk any higher myself!!! c u later

I think a lot of guys will tell you that the top RPM is determined more by how you build the bottom end than the bore and stroke.

Cast cranks are good to about 6000RPM regardless of horsepower if the engine is carefully balanced IMO. Steel cranks are necessary above 6000 R's IMO and exotic alloy steel cranks with nitride treated journals are kinda the top of the line for all out race.

If all things are equal (crank type, balance, rod type, etc.) I think the shorter the stroke, the higher the RPM she will take.

Soooo, I think that a 355 and a 377 (same stroke) would rev the best, then the 383 and the 406 (same stroke).

Of course longer connecting rods in any of these motors will help them hold up better at higher revs too. Not to mentioned forged connecting rods, main bearing studs, connecting rod bolts, yada yada yada . . .

It will rev right up until it blows http://www.camaros.net/forum/biggrin.gif. Seriously though, just like the others said, it depends on the bottom end. Forged crank, longer and/or lighter rods, lighter pistons, etc. will allow higher rpm. A shorter stroke will as well by reducing peak piston speed.

Once the bottom-end is strong enough, you need to look at the heads, large cube small-blocks place a very large flow demand on a head that has limited space for modifications. Even if a 406 can rev safely to 8000 rpm, you'd need some very good flowing heads to support the airflow.

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The limit of a motor speed is not based on RPM..But instead is based on piston speed, ie... piston velocity..
As the stroke is decreased ..you are able to achieve higher RPM for the same limit of piston speed.. This is why a destroked motors make more HP...
CHEERS
Chris

I wouldnt' say that a destroked motor will have more HP. I could agree that there is more HP per cubic inch potential, but whether it really does or doesn't depends on a lot of variables.

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[This message has been edited by Grape Ape (edited 05-07-2001).]

Hi...
Maybe I should explain a bit more...
Yes..your right ..there are too many variables..but I was generalizing...
Using VERY basic general equations.. I will spare you the derivations for now....
HP= (RPM * torque)/(5252)....
Now ..you can't have it all...you can play with the RPM and the torque curve..but this is controlled by the application at hand..
With SBC and BBC in "street" applications the high RPM is simply not practable or safe.
So your are limited to TORQUE..so you use as much CID and or as much stroke as you can.. and you choose a cam and heads that can do the best torque for the limited street bandwith...( 2000 to 5500) reasonbly speaking... and since 99% of street SBC's use the same parts vendors..edelbrock,comp-cams,AFR..ect..there are just a dime a dozen and no one has got one up on the other..just a few http://www.camaros.net/forum/smile.gif
Now you can get more HP if you move the RPM up in the HP equation since this has a steeper slope than the torque that can be made...Peak torque will roughly be the same..but will move up the band and follow the higher RPM provided things are designed correctly...
Bottom line: Get the RPM up there and screaming...and you will get the BIG HP numbers...
The motor is limited in RPM by it's piston speed which is limited by stroke and bottom end strength...
Piston speed is ratted in feet per minute.. FPM..
Stroke is in inches...
Piston Speed=(stroke*RPM)/6 ... in FPM..
The standard limitations of a "plain-jane" stock bottom-end with cast crank, ect.. would be about 3500 FPM..
With heavy duty 4-bolt cap bottom end, forged crank..ect..figure on 4000 FPM.
ALL-OUT serious racing motors that are just for short runs can tolerate up to 6000 FPM..
If your bottom end is limited to 4000 FPM and you wanted to get the most HP ( point A to point B very fast)...then destroking the crank will allow the higher RPM's to be obtainable without putting a window in the block and still maintaining the 4000 FPM limit... The climb to high RPM's with it's limited torque will still turn way higher HP figures than anything from the streetable RPM range... But getting SBC's to 10,000 to 12,000 RPM for drag racing requires $$$$$$$$$$$.
So the average Joe racer is usually limited to the 6000 to 7500 rpm range...which requires more thinking to get the system to gell... the one who can optimize the peak torque at the highest place in the RPM bandwidth wins...
This is why some like the 327..since the RPM can go a bit higher than 350 while still retaining similair torque.. http://www.camaros.net/forum/smile.gif
CHEERS
Chris



[This message has been edited by cerrem (edited 05-07-2001).]

Balance,Balance,Balance. The more vibration you can eliminate the faster you can turn also

To say you are limited to torque rather than hp for street motor is a contradiction. HP and torue are directly related. HP is a measurement of torque over time. Time is in minutes, or rotations per minute I shoud say. If you have 300 hp at 6000 rpm in one car and 300 hp at 7500 rpm in another, they will have the same power. Gear them both to get the same rear wheel speed, and they will both have the same rear wheel torque (assuming parasetic power losses are the same). It does not matter what rpm you make the hp, as long as you make it. I'll agree that racers rev them high to get more hp, through pressure wave and inertia tuning. I have beaten a lot of high rpm drag cars, with my 6000 rpm redline nitrous motor, beacsue I made more hp than them. I didn't need rpm to do it either. You need more than rpm to make hp, like I said, there are too many variables to say.

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I just got thinking about this and I think some confusion might be with cubic inches. If you have two engines of the same size, one with a larger bore and shorter stroke, the shorter stroke engine will have more power potential. Other than more complicated variables like less valve shrouding and higher rpm potential. A larger bore short stroke has more leverage on the crank that a small bore with a longer stroke. This is true of engines of equal size, as the cubic inches go up, so does power potential.



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I lost everyone on this, my fault, i want to build another motor for my new project, a ROAD RACING TRUCK, yes you heard rite! Im building another mazda truck for road racing, i.e. bigger brakes, 18" rims racing suspension, i want to be new and since everyone started building trucks for drag racing (just like i did)lol, i wanted to be the only person in my town & mabey state http://www.camaros.net/forum/biggrin.gif to have a road racing truck.....
it will need to see 170-180mph to keep up with all the new mustangs, yes i said the forbiden word (mustangs are faster at road racing) :Screams with Crys:Noooooo the painnn!!!! Any how my test motor a stock 305 (only motor i had on hand) brings the truck up too 120mph till it starts its valve floating crap! Hears the deal i do not want to change the rear end gears cus it will hert my cornering speeds.... but i do want to have around 450-550+HP & i need to get the motor to turn 8,000-9,000rpm to go the speed i want to go!!! Now out of those motors
witch can turn 8,000+???


-------------------------
Warning: No people were killed or hert while doing 120mph on the freeway http://www.camaros.net/forum/eek.gif

P.S. this will be raced on a real track when its done.... http://www.camaros.net/forum/rolleyes.gif
Really.......
How come u dont belive me http://www.camaros.net/forum/biggrin.gif
J/Klol

Here is the best answer I got when I posed this question recently in the Engine & drivetrain section:

b-boy
Tech Team
Posts: 85
From: fayetteville, arkansas usa
Registered: Oct 2000
posted 02-07-2001 07:02 PM
--------------------------------------------------------------------------------
What you are searching for is very easy: It's called MAXIMUM AVERAGE PISTON SPEED. For using stock smallblock chevy parts you should keep your maximum average piston speed at 4000 feet per minute (FPM). The formula for doing this is simple: (CRANK STROKE x RPM)/6. That will give you your maximum average piston speed. Then to determine the ENGINE RPM at a maximum average piston speed of 4000 FPM is: 24,000/ STROKE. So the maximum RELIABLE rpm for a 383 with stock parts is 6382 rpm. For a 350 it's 6897 rpm. For a 327 it's 7385 rpm. For a 302 it's 8000 rpm. A 283 is also 8000 rpm. Look at these numbers and think. You will see they are very close to what everyone for years have turned these engines with no problems. Hope this answers your question.

poundinpopeye,
For your wants, I would go another route. A small-block 400 block with a 3.25" stroke will make a 348 cubic inch engine. This will also let you run a longer rod than any of the above mentioned engines.

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[This message has been edited by Grape Ape (edited 05-08-2001).]

I agree with GrapeApe. The 400 block, 3.25'' stroke crank can fit a 6.25'' rod and will give you a good rod/stroke ratio for those high rpms. Also, with the super high rod stroke ratio and a good set quench height you can run 11:0 compression on 87 octane. Check this out...
http://www.airflowresearch.com/Articles/A3-P1.htm

Thanks for the help guys! http://www.camaros.net/forum/smile.gif
The 400 block and 327 crank i was going to do to my last motor but i wouldnt make anuff hp for drag but it looks like i mite use that combo for road racing, just another thing to think of......
Poundin Popeye

[QUOTE]Originally posted by Grape Ape:
[B]To say you are limited to torque rather than hp for street motor is a contradiction. HP and torue are directly related.

I totally agree with you...but thats not what I was implying...
I ment that you are limited to torque rather than high RPM's when achieving HP in a streetable application..
So, such things as superchargers, turbos, NOS, more stroke..more CID's is all productive towards gaining more HP when RPM is limited in street application..since this contributes towards Torque ...which directly leads to increase in HP..
As for balance...of course, thats a given http://www.camaros.net/forum/smile.gif
But cast cranks are limited to HP not RPM..
since as you approach the limit of 0 with stroke the forces approach 0 as well regardless of RPM...
Long rods are great for higher RPM applications but hinder lower RPM performance...
CHEERS
Chris

cerrem,
I think we agree on everything here, there was just some confusion as to the way we interpeted each other.

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To chime in on the rod lenght discussion, my vote is for the longest rod possible. I base this on what I have read on the subject as written by Smokey Yunick. Two main reasons are dwell time at TDC and the mechanical advantage of the longer rod. For backup see this article. http://www.carrun.com/teck8.html

No Offense to Yunick..I respect him for his years of dedication to the sport and I have read all his stuff when I waw a teen...
The problem is he's NOT a degreed engineer and his articles lack the physics and mathamatical derivations to really prove his point..Some or part of his theories don't always pan out..
Yea longer rods have some desirable benefits..but not because I read about it.. I did the proofs and the reserach over the years myself...Longer rods are only beneficial at higher RPM's and all this HP increase is only slight but still important in competition.. The lag time at lower RPM's is not desirable in street applications, since this lowers the pistons linear velocity to and from TDC/ (BDC)...
Also...side loading is not a big wear issue unless you driving your stroked hot-rod as a daily driver an hour or so to a from work..since most hot-rods/restored cars are driven on the weekends...and not for long term..the side load wearing would take a lifetime to show up to be significant..
Yunick was working with high RPM circle track racing motors, not weekend hot-rods...
CHEERS
Chris


[This message has been edited by cerrem (edited 05-10-2001).]

[This message has been edited by cerrem (edited 05-10-2001).]

[This message has been edited by cerrem (edited 05-10-2001).]

Hear me out this relates - My family runs pulling tractors. 4000+ rpm diesels! They ate up a bunch of motors before they started spending the money to balance and beef the bottom half. It works, the last two major breaks were a broken cam, and shredded turbo.
ps. - These thing have very long rods (4" stroke").

[This message has been edited by 1stgenZ (edited 05-11-2001).]