Do you guys think I can safely turn 7000 rpms with stock 4 bolt main caps and a stock crank on a 1 piece roller block 350 bored .030"? My pistons are very close in weight to stock and my rods are significantly lighter (I will have it balanced). Compression will be around 10.2-10.3:1. Other option will be less cam, spin around 6500 rpm and occasionally hit it with a 100 shot at the track. (I have so many parts laying around and I refuse to sell anything)

 

ive been running my 7 year old 350 build to 7,200 rpm regularly. its a stock crank, cut undersize, 4-bolt, with flat-tops.
IMO, smallblocks like high RPM's. alot of it's in the tune.
you'll probably get 20 different opinions if 20 different people respond.

 

Id prefer more stroke and less rpm.

Good valvetrain will be mandatory. Short bursts to 7k probably would last a while. I wouldnt want to hold it there.

 

Id prefer a forged crank but make sure you have good rods/rod bolts, and if you need new pistons i would have made the swap to a long rod 6" setup for the rpms to take some stress off the rods and crank but it should work. Guys have taken stock cranks pretty far. Block will be fine. Splayed caps would be safer but i turned 6800-7k on my 4 bolt factory block. Had a good rotator tho but nothing special on bottom end. Try main studs instead of bolts for more clamping force. All goes along way in keeping motor safer and gaining life on the parts

Then again what you building? 7k rpm and 1000 hp turbo monster is a whole new ballgame compared to a na 500 hp setup lol

 

Guys have used stock 5.7 rods with good rod bolts and made them live at 7k for decades. Not sure Id do that with a cast crank though and expect it to hold too long. Some get away with it some dont. Ditton on studs

 

Maybe I'll spin it a little lower to like 6,500... the rods aren't the greatest anyway (5140 SIR eagle rods).

 

True dat...

Other guys have lovingly worked over the best rods they could get their hands on, and the first pass, turned them to shrapnel.

It's all a matter of probabilities. Especially with used parts.

How lucky do you feel?

Personally I wouldn't (don't, actually) make a habit of turning a stock crank much past 6k. Once or twice, by accident, maybe; as a deliberately established matter of policy, no.

 

Now you guys have me nervous I have to find something to build using the eagle rods/speed pro pistons, stock crank 4 bolt block, victor jr and trick flow 195 heads. Thinking about a 286hr cam (230/230 .560"/.560") then again don't a lot of gen 2 lt1 guys spin way past 6 grand with the stock crank?

 

Sure, of course they do.

Question you SHOULD BE asking is, how many times?

That cam won't turn that many revs and still produce meaningful power, anyway; that's not what it's made for.

 

On a decent headed 350 most all 230 deg cams will turn over 6k. Especially if you are considering a single plane. That cam is the magnum series correct? Old lobes but still pretty powerful. I believe its similar to the intake lobe on the cc306 which in LT1's turns over 6500. I was spec'd the high lift version 286/230 lobe in my 383 and it held power to over 6600 rpm.

For reference i tuned a afr190 headed L98 with stealth ram. Had a 280xfi cam. It didnt have the springs that the cam really needed (i didnt do the valvetrain) so it floated at 5700, but before we knew that we shifted it at 6200-6400 alot! Car ran great on stock crank. How long will it live? Who knows. Cant never tell but i wouldnt be too nervous. Alot of block failures come from main webbing pulling out and not main caps or cranks. This question was asked on a engine builder site and most agree stock cranks can turn some rpm, and that 4 bolt mains usually hold more than the block webbing allows. So if anything fails the entire bottom half should drop out with all caps still bolted up lol

Its a risk but low 6000's rpm with light pistons wont stress it as much

 

Orr89, interesting information. It is the old magnum style cam. I would think a cam like that would hold power to 6,500 rpms. Are you guys telling me it probably wouldnt rev that high anyway with the proper springs? Please don't tell me I've been over revving a 224/230 350 by spinning it to 6100 rpms with vortec heads too :s
I was always under the impression when cam companies rated the rpm range it was done with a low flowing head and that a descent aftermarket head would benefit from higher revs with the proper springs.

 

No i am saying it should rev to 6500 or near that with 195cc heads. May start to fall off soon after with single pattern and tight lsa. It could peak 6200-6400 i think but power after will suffer more than a 6-10 deg split grind or a wider lsa cam

The 280xfi cam would have peaked closer to 6400 if you extend the slope of the dyno graph before floating. It was moving up pretty quickly. Most 280xfi cam guys here operate in the 6-6.5k rpm range depending on heads intake and cubes.

And the 224 cam with vortecs would be good to 6k. Better heads you can pull higher. Better the heads the less cam you need to peak at the same rpm, generally. Restricted heads need more cam to make power

I would run the combo as is with the rods and piston upgrades. Just my two cents

 

Thanks again for the input. I was questioning myself and the few things I have first hand learned after reading Sofa's reply. I'm going to assume he read 7,000 RPM and the magnum 230/230 cam. My other choice was going to be the 236/242 duration xtreme energy cam (for closer to 7,000 RPM).

Guess it's all good to go then. Thanks again everybody.

 

I doubt ANY HR cam will produce meaningful power to 7000 RPM, or anywhere close.

Put it on the dyno after you build it. I bet peak HP (which is as high as you derive any benefit from turning it) won't be ANYWHERE NEAR that. Meaning, if you spin it past its peak HP, the car will go slower; same as any other car or crank or cam or RPM. No sense kidding yourself about it, numbers don't lie.

Regardless, a stock crank won't hold up to that kind of RPM very many times or for very long. It would be metallic suicide to deliberately design an engine to actually be USEFUL at that RM, yet have only that fragile of a crank.

4-bolt mains have nothing at all to do with it, one way or the other. Not a factor in the slightest.

 

Making sure you use good hardware (arp bolts, or studs preferably), assembling it correctly and carefully with the right clearances and following torquing procedure from the manufacturer will give you the best chances of making it spin that high with no problems. Like sofa said, it's about probabilites. Unfortunatley there's always a chance that you get the negative outcome, the only way to lessen that chance is to remove all things that increase your chance of getting that negative outcome.

Bottom line is, do everything possible to put this together correctly and take the human factor (you assembling it) out of the equation. Now all that's against you are the parts themselves.

Putting everything beside except the rotating assembly, I think you can get it spinning up to 7000 without problems, just watch how long you keep it there.

 

Sofa are you telling me that right at peak power is the optimal spot to shift? Don't see many car companies setting shift points right at peak power but generally 400-600 rpm after. I'd find it hard to believe they'd do something like that to yield a slower vehicle and put more stress on everything.


Motor is going behind a trans brake/manual shifted
TH400 and will very rarely see anything above 5500 rpms.

 

Go take a car... ANY car... find the peak HP RPM, and then take it to the track and experiment with shift points vs the RPM curve. Come back and tell us what you find out.

It's simple physics, that you'll no doubt recall from your high school classes. HP = the time rate of applying energy to the car. Energy is a function of mass times velocity. Which means, the most energy gets transferred to the car, at the peak HP RPM; and the downward curve on the high side, is MUCH steeper than the upward curve on the lower side.

Then not a lot of sense in worrying about what it'll do at 7000, eh? Build it to make the most power where it will actually be running. Which, if it makes max power at 5500, then that's right about where it'll need to be shifted; and a stock crank will be fine at that RPM, as far as that goes.

 

i ran my HOT cammed/vortec headed 87 2 bolt 350 with the stock crank, PM rods, and lightweight forged TRW pistons up to 7400 on a regular basis- it's fun shifting the 4 speed out of first gear and going straight to 4th at 65mph... i had the rotating assembly balanced when i put it together... i upgraded to ARP main studs at the recommendation of my machinist- he said the 2 bolt blocks were good to 8000 rpm and 500hp set up like that in his circle track motors, with the stock 4 bolt blocks being not quite as strong.

 

I understand where you are coming from with the shifting at peak power but doesn't a transmission gear ratio come into consideration. Best way I can explain what I am asking is with this example. Lets say you want to time your 0-60 but at WOT your car is shifting at 5600 rpms. Your car only hits 56 mph in 2nd and would require you shifting into 3rd to reach 60 mph. Would it be faster to shift back down to a lower rpm where you build more power with a numerically lower gear ratio?

 

IF you can have infinite gears like a continuously variable transmission, you would want to stay at peak hp for fastest times down the track. But since we dont, we have to compromise.

This is where shift rpm comes into play. What you want to have happen is the motor needs to operate in an RPM band that produces highest average power across the pull. Shift at one rpm, the next gear will obviously cause engine rpms to fall back down and then start to rise again. Where that falls on the torque curve and starts to pull again is where you need to experiment to find optimal shift rpm.

If you shift at peak hp, the rpms may fall into a spot in the torque curve thats low, and thus low hp is produced, and acceleration is reduced. Shifting beyond peak hp where your hp curve starts to fall will slow you down up top in that gear, but falling back down to the next gear's rpm may produce a more HP spot and pick acceleration back up again, offsetting the effects of over revving.

Ideally you do not want to have the motor fall off in power after PEAK hp rpm in a drag race motor. You want hp to hang on past peak rpm. To do this you need more cam duration and usually its on exhaust side...generally. Proper induction and exhaust design will also help you here but its not uncommon to see drag cams with a good deal of duration on the exhaust side and thus very broad hp curves. Some race motors that turn 8K rpms may peak at 6800-7000 rpms but hold onto that peak until 7800-8000 rpms. Some only fall off 10 hp by then.

My experiences have shown you can make power to 7K rpm with a HR. It takes the right components and a good intake/heads/exhaust combo, but not saying that magnum 230 deg cam will in a 350 motor. Not enough duration/lift and not enough head for that. Just saying it may peak in the 6200-6500 rpm range and you may find optimal shift alittle higher. It may not be. Really have to experiment. I found my 383 to like 6600-6800 shifts. Didnt change much ET between there and it only peaked at 6250 and held flat to 6500-6600. If you wanted a cam that peaks in the 6000-6200 range and held power to 6500+, get a custom grind. Open up that exhaust side duration.

If you are not taking it to 6000+ often, why not just cam it alittle smaller and build more lower rpm power? Ease your worries on stock crank?

 

Thanks very much for the explanation. I am kind of set on what I want and since the car probably won't see more than 1,000 miles a year and hit up the track a handful of times I don't see any point in building something that I could easily daily drive.

 

The whole point of a race cam vs a street cam is to raise the hp level RPM wise and to raise the torque curve to RPM wise overcome the shifting to a higher gear.It should be a smoother transition.Also the four bolt blocks have some history of OEM blocks cracking the outside bolt holes.Best bet is to splay the mains with aftermarket main caps and line hone.