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Maximum RPMs

VB242

I.M. Weasel
Joined
Sep 21, 2011
Location
Driving the No Malarkey Bus
Soooooooo, I have an autocross event at the same big venue as last month and with my 4.10 rear and T5 2nd gear I'm running out of RPMs. Using an online calculator I came up with a max safe RPM of the stock 6250, however I've been running it up to 7000 soft limit and 7250 hard limit. Even if it's not pulling hard I need those extra 10ths. I have B23 with RSI H beam rods and B23ET stock Mahle pistons which I believe are forged with the stock pin and of course the stock forged flat plane crank. Can I get another 100-200 rpm without detaching a piston from the rod? This is the venue:

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Why would 7250 be a problem with a 80mm stroke engine? I run mine to 7500 regularly with no issues. Hell, one of Culberro's rally cars hung out at 8000 for minutes on end. Piston speed is way too low to be a problem.

For added reference, a Honda K24 can and does see 8000 RPM no problem with a damn near 100 mm stroke.

Rotating mass should not be an issue either because a) your rotating mass isn't that heavy and b) see paragraph above.
 
If your valve springs can handle it, I don’t see why you couldn’t push it past 7500 and upwards of 8k.
 
If your valve springs can handle it, I don?t see why you couldn?t push it past 7500 and upwards of 8k.

The valve springs are from RSI as well, I do remember some chatter about bug pack something something back in the day. But I thought that was seat pressure issue being too high. I was more concerned about too much mass starting and stopping.
 
The valve springs are from RSI as well, I do remember some chatter about bug pack something something back in the day. But I thought that was seat pressure issue being too high. I was more concerned about too much mass starting and stopping.

I was floating the valves in my RSI stage 2 head hitting a 7k rpm limiter. Actual spring pressures when measured with my install height and cam were barely above stock. I'd check everything they did.
 
I was floating the valves in my RSI stage 2 head hitting a 7k rpm limiter. Actual spring pressures when measured with my install height and cam were barely above stock. I'd check everything they did.

The head was done by a local guy, he said they were definitely an upgrade over the stock springs. The springs have been in a couple heads but probably have less than 10k miles on therm.
 
The head was done by a local guy, he said they were definitely an upgrade over the stock springs. The springs have been in a couple heads but probably have less than 10k miles on therm.

stock size valves? What's your seat pressure and pressure over the nose? What lift on the cam?

Probing because I'd agree with Culbertson, don't worry about the bottom end but think about the head.
 
stock size valves? What's your seat pressure and pressure over the nose? What lift on the cam?

Probing because I'd agree with Culbertson, don't worry about the bottom end but think about the head.

No these are the oversized valves from the group buy. My guy did not measure seat pressure afaik. I'm running what I think is an IPD turbo cam. I got it from Fidel/ Lawrence Knox with part of the rear slot broken off. I had a machine shop cut off the broken part and make a washer for the end of it since I didn't need the slot. Lift according to the chart is 11.95mm
 
The valve springs are from RSI as well, I do remember some chatter about bug pack something something back in the day. But I thought that was seat pressure issue being too high. I was more concerned about too much mass starting and stopping.

Some of the RSI heads had the seat pad in the head cut down 1mm or so.
The KL Racing single springs measure out identical to the VW aircooled springs (bug pack, EMPI, CB Performance).
These usually install at about 100-120lbs on the seat if using a stock head (uncut spring seat areas).

With an IPD Turbo cam, good stock springs should be fine to about 7200-7400 rpm. You should be more than fine at higher revs if you have stiffer springs.
 
Cool, thank you, I'll get to test it out 11/8. I'll set hard limit to 7600 and the soft to 7500. I'll also have to shift some stuff around and set the TS maps up for 7500.
 
Just curious, have you tried third? It seems like you have the power, but it sounds like lots of wheel spin. Maybe third once you get going will help you keep the power on the ground. Second sounds fast, but third might actually be a faster lap time.
 
Just curious, have you tried third? It seems like you have the power, but it sounds like lots of wheel spin. Maybe third once you get going will help you keep the power on the ground. Second sounds fast, but third might actually be a faster lap time.

I did flip to third on one run in the long section but I didn't leave it there, maybe I'll give it a whirl next time.
 
the limiter on the gold car is around 8400, hasn't been a problem yet and I don't forsee any issues with it. Stock F pistons, hbeam rods.
 
As most have mentioned, your bottom end, if balanced and all happy, should be fine to 8k+. If you had a B230 bottom end and a stock harmonic balancer on the front of it, you are risking things by going over 7000-7500rpm. Especially not recommended if it's old and cracking! You don't have that, running a B23 though, so you should be fine.

Your main concern is valve float. If it is indeed an IPD Turbo cam, they are pretty mild and I'd default to saying you're going to be ok. Pay attention to that, though, as if you do get float, it's obviously very hard on things and worst case you can drop a valve if the keepers get loose.
For added reference, a Honda K24 can and does see 8000 RPM no problem with a damn near 100 mm stroke.
With a much smaller and lighter piston, too.

I was floating the valves in my RSI stage 2 head hitting a 7k rpm limiter. Actual spring pressures when measured with my install height and cam were barely above stock. I'd check everything they did.
What camshaft? And on my RSI head, I also recently had the valve spring seat pressures measured as barely above stock with my "7500rpm valve spring kit" from RSI, too. Not cool when I am about to slap in a much larger than stock type camshaft.
 
What camshaft? And on my RSI head, I also recently had the valve spring seat pressures measured as barely above stock with my "7500rpm valve spring kit" from RSI, too. Not cool when I am about to slap in a much larger than stock type camshaft.

Their stage 3 cam.. 12.4mm lift or something like that? I'd like to try something different but don't really have any complaints with the cam.

My head has the spring seats machined ~.060". The taller bug pack springs they used were supposed to compensate for that but it turned out to not be the case. Like you, barely over stock pressures and poorly matched for the install height; then add in 48/40mm valves and high rpm and yeah... Shim under bucket setup and the valves were floating bad enough that I dislodged a lash cap under the bucket and it jammed the valve open.
 
Their stage 3 cam.. 12.4mm lift or something like that? I'd like to try something different but don't really have any complaints with the cam.

My head has the spring seats machined ~.060". The taller bug pack springs they used were supposed to compensate for that but it turned out to not be the case. Like you, barely over stock pressures and poorly matched for the install height; then add in 48/40mm valves and high rpm and yeah...

Most high performance springs will loose a significant amount of spring force after a while, especially if using am aggressive cam and lots of RPM. They're usually a consumable with race engines. They either get timed out, or replaced when the installed force drops below a certain value.

The dual VW spring setup (KL racing, empi, bugpack, CB) has pretty high initial installed force when used on an 8v, but drops down to a much nicer level after a while.

What camshaft? And on my RSI head, I also recently had the valve spring seat pressures measured as barely above stock with my "7500rpm valve spring kit" from RSI, too. Not cool when I am about to slap in a much larger than stock type camshaft.

It's not just about installed force with springs, but their rate as well. Even with clapped out VW springs, you're probably near double the spring force over stock springs at full lift :rofl:
 
Their stage 3 cam.. 12.4mm lift or something like that? I'd like to try something different but don't really have any complaints with the cam.

My head has the spring seats machined ~.060". The taller bug pack springs they used were supposed to compensate for that but it turned out to not be the case. Like you, barely over stock pressures and poorly matched for the install height; then add in 48/40mm valves and high rpm and yeah... Shim under bucket setup and the valves were floating bad enough that I dislodged a lash cap under the bucket and it jammed the valve open.
Ouch! Could've been much worse it sounds like.

It's not just about installed force with springs, but their rate as well. Even with clapped out VW springs, you're probably near double the spring force over stock springs at full lift :rofl:
Yes, but when they're advertised as being one thing and actually are another, that's not cool. I haven't found the paperwork yet that says what I was told they were, but I can locate it or an email with the info I think. We didn't have any issues with the ENEM K13 camshaft and the larger valves when we ran it in the General Leif last year revving to 7k rpm though and I don't think the seat pressures have changed since you worked on it last.
 
Ouch! Could've been much worse it sounds like.

Yes, but when they're advertised as being one thing and actually are another, that's not cool. I haven't found the paperwork yet that says what I was told they were, but I can locate it or an email with the info I think. We didn't have any issues with the ENEM K13 camshaft and the larger valves when we ran it in the General Leif last year revving to 7k rpm though and I don't think the seat pressures have changed since you worked on it last.

Were the springs brand new when they were measured as being " barely above stock"? Was this on the head that had the valves sunk super far into it? I can't honestly remember :oops:

What I'm was trying to say earlier is that ANY spring will soften up and be significantly lower than it's advertised rate/spec after a few cycles (more like 1 million cycles)
 
Were the springs brand new when they were measured as being " barely above stock"? Was this on the head that had the valves sunk super far into it? I can't honestly remember :oops:

What I'm was trying to say earlier is that ANY spring will soften up and be significantly lower than it's advertised rate/spec after a few cycles (more like 1 million cycles)
This was on my big valve, RSI 530 head that you had to open up the valve seats/throats on because they couldn't be bothered to make it work properly with big valves. Or whatever. :roll:
 
This was on my big valve, RSI 530 head that you had to open up the valve seats/throats on because they couldn't be bothered to make it work properly with big valves. Or whatever. :roll:

Ahh, that head had a few... issues.
 
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