Stock bottom end max RPM?

[mcglsr2]

Heyoooo! So I searched for the above, and after about 3 pages of not finding what I needed I gave up and created this thread. I'm sure it's been discussed before. If you don't feel like replying, a link to a post would be appreciated.

Alright, so I've got plans for my engine. Question: what's the bottom end on a stock 95 302 good for, RPM-wise? I've read a bunch of other posts on other forums, and they all mostly seem to say 5500: because there's a rev limiter, stops making power, blah blah. Every reason I've seen had to do more with the top end not producing power past 5500 (or really 5000 I guess) rather than a physical limitation on the bottom end.

So, assuming the top end can spin to infinity and can flow more air than there is atmosphere, what can the bottom end components (rods, crank, oil pump, etc.) capable of supporting with regard to RPM? My gut tells me that the stock bottom end is good to around 6500 to maybe 7000. Up towards 7000 and beyond is probably stressing the components too much. Thoughts? Thanks in advance!

 

[SLOW95GTS]

If your fuel injected, the fuel cuts out at 6250 rpm and if your were carbureted you can rev to 6500 and more but then you need hi-rev valvetrain.

 

[mcglsr2]

Thanks for the response. I am fuel injected, pretend that I raised the fuel cutout to 10,000 RPM Assuming that the valvetrain is not an issue and fuel cutout/rev limiter is not an issue, it sounds like you are saying 6500 RPM and above ain't no thang, correct?

 

[330CubeGt]

Heads and cams play a big role in RPM.I took my stock 4v to 7200. Same bottom end as a GT, but the heads allow you to make more power at a higher rpm. Make sence?

 

[SLOW95GTS]

A good set of heads with big ass ports, R-series intake and a Hi-Rev cam and valvetrain. You need Good internals and a dart short block too. Forged lightweight pistons, h beam rods and billet crank. should be good for 8,000 rpm

 

[330CubeGt]

If you stay N/A I think the stock Bottom end will handle high RPM's.Say 6500-6800 with the right cam and some AFR Heads...

 

[mcglsr2]

Heh, maybe I didn't ask the question well - I'm not asking what do I need to be able to spin to a higher RPM. I'm asking what will the stock bottom end support, assuming everything else allows it to spin freely. I specifically don't want a forged a crank or pistons or anything, talking about the stock bottom end.

The stock bottom end of a 95 (or equivalent year) 302, assuming the top end supports it, can safely be run at _______ RPM with no changes. Fill in the blank please

It looks like 330CubeGt is saying 7200 was fine on his stock bottom end...

 

[mcglsr2]

If you stay N/A I think the stock Bottom end will handle high RPM's.Say 6500-6800 with the right cam and some AFR Heads...

Ah, okay. That's what I was searching for, and 6500 - 6800 is Good News

 

[330CubeGt]

What are your goals for the car?

 

[mcglsr2]

Looking for around 260 whp. With my planned HCI and a very mild tune I'm probably looking at around 277 rwhp right now. I was looking to redline around 6200 to 6500, just wanted to make sure I wouldn't grenade the stock bottom end at those RPMs - I wouldn't think it would just wanted to make sure. The top end will be able to handle 6500 without much effort.

Specs of what I plan on running are in this post: #150.

 

[SLOW95GTS]

I think the stock bottom can handle 7200 Rpm also but I don't think you'll be able to do reach it if you put edelbrock heads on lol.

 

[330CubeGt]

You ment to say 360rwhp right lol.

That should be very possibly, and that won't bother the stock bottom end at all.

There are better intakes out there but the one you have should do the job!

 

[95opal]

Port that cobra lower and grab bigger heads those two pieces are gonna limit you power and rpm.

 

[mcglsr2]

I think the stock bottom can handle 7200 Rpm also but I don't think you'll be able to do reach it if you put edelbrock heads on lol.

I don't need to reach 7200, just around 6200 - 6500, which the heads will be good for

You ment to say 360rwhp right lol.

That should be very possibly, and that won't bother the stock bottom end at all.

There are better intakes out there but the one you have should do the job!

Nope, I meant 260 - not a typo. I'll be using the car in Time Trails, and will be limited to HP for my class. This is not a max RWHP effort, but rather a targeted RWHP effort, which is why I was going with the parts I had listed.

Port that cobra lower and grab bigger heads those two pieces are gonna limit you power and rpm.

See above

Thanks for the input all, most helpful

 

[mcglsr2]

And to speculate - because I like discussions - how does the head limit the RPM? Rather, I think it's the valve springs/cam lift, and valvetrain weight (lifters, rods) that affect the amount of RPMs that can be turned. Heads just flow air. Now, the head might be maxed out with airflow, such that turning more RPMs will not increase power. Excluding insane head designs, how can they limit RPM?

Edit: did some quick reading. There are two main limitations to RPM: 1) physical capability based on the acceleration of the pistons/con rods and 2) valve float. As long as the tensile strength of the rods are not exceeded by piston acceleration, the physical limitation is not the limiting factor. In an OHV configuration, the limitation is valve float, which is the followers (or lifters if you like that word better) inability to stick with the cam profile, usually due to the springs inability to return the valve. To reduce this, one uses light(er) weight valvetrain components and stiffer springs. Stiffer springs work only up to a point, however, before the seat pressure and open pressure gets too high and damages the head. My understanding is that with the proper components, the RPM where the springs just can't cope is up near 7500 or so.

 

[95opal]

You can rpm to the moon but if theres no power there whats the sense. JFYI high rpms is a contributing factor in engine failure. Your combo will more than likely be done by 6k so there is no need to even worry about it. When you get serious about making power to 7k plus then youll have to worry and fork out the dough for the big boy parts.

 

[rw95gt]

The best way to keep the bottom end alive would be to keep it off the Rev limiter and don't push it over and over or for long periods of time. Short burst for 15 seconds or so keeping it off the Rev limiter a stock short block would survive a long time at a 6500rpm shift point. Just don't abuse it. Also there is absolutely no need in turning a engine past its power band. Shift at its peak power level.

Why do you want to turn your stock short block up to 6500? A 302 will make 275rwhp easy at 5k to 5.5k and live for a very long time.

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

 

[Saint]

The best way to keep the bottom end alive would be to keep it off the Rev limiter and don't push it over and over or for long periods of time. Short burst for 15 seconds or so keeping it off the Rev limiter a stock short block would survive a long time at a 6500rpm shift point. Just don't abuse it. Also there is absolutely no need in turning a engine past its power band. Shift at its peak power level.

Why do you want to turn your stock short block up to 6500? A 302 will make 275rwhp easy at 5k to 5.5k and live for a very long time.

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

+1

 

[mcglsr2]

The car will be used on road courses. So I'll be running it up to about 6000 to 6200 quite a bit. And probably for longer than 15 seconds. I don't need it to stay at 6500, I just want to know that if I need to stay in a gear longer because the situation on the road course requires it, I can run it out to 6500 or so if I have to. I don't plan on regularly shifting at 6500.

I was about to answer the question of "what's wrong with making power up 5000-5500 RPM" with....and then I realized I don't know. I think where I was going with it is here - of the components I looked at, the combination that made the best average power ad torque and still kept it in the ball park of my target rwhp have a range of 2000 to 6200 (specifically the cam). I don't necessarily want it to be a torque monster down low, and I care a little more about hp than torque, but I think the main reason is "because." Which is a shitty reason. Upon retrospect, I think the reason is more because the components I chose made power in that range, as opposed to idle to 5000 (I don't really care about performance at idle, I will never be at idle on the track - assuming all goes well ). And I don't know what else, my gut just says "run it up to 6K." <shrug>

 

[shoua50]

OK so no one actually answered you question. You can rev the bottom end as high as u want. The limiting factor is your valvetrain AND horsepower. Most aftermarket heads come with springs that can handle 6500 rpm safely. 260hp at lets say 7500 rpm should b fine cause you're not taxing the bottom end that much with only that much power. Switch to a solid roller cam with matching springs for what ever rpm u desire. Assuming that u have a road course tranny with 5 gears where there is no overdrive, u will need to keep the revs up for better lap times and performance. Hard part with road racing is that constantly downshifting the tranny causing the motor b used as a braking method will contribute to damaging you motor even if the revs are safe. So there u have it, valvetrain will determine max engine rpm but keep in mind that HORSEPOWER will determine BOTTOM end rpm.