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Old 10-11-2020, 10:26 PM   #1
VB242
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Default Maximum RPMs

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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Old 10-12-2020, 12:31 AM   #2
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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.
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Old 10-12-2020, 01:15 AM   #3
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If your valve springs can handle it, I don’t see why you couldn’t push it past 7500 and upwards of 8k.
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Old 10-12-2020, 03:20 AM   #4
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Originally Posted by culberro View Post
If your valve springs can handle it, I donít see why you couldnít 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.
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Old 10-12-2020, 08:24 AM   #5
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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.
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Old 10-12-2020, 09:14 AM   #6
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Originally Posted by Stiggy Pop View Post
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.
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Old 10-12-2020, 09:57 AM   #7
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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.
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Old 10-12-2020, 10:09 AM   #8
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Originally Posted by Stiggy Pop View Post
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
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Old 10-12-2020, 01:45 PM   #9
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Originally Posted by VB242 View Post
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.
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Old 10-12-2020, 02:34 PM   #10
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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.
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Old 10-12-2020, 06:58 PM   #11
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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.
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Old 10-12-2020, 07:09 PM   #12
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Originally Posted by rb92673 View Post
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.
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Old 10-13-2020, 10:59 AM   #13
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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.
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Old 10-14-2020, 02:07 PM   #14
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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.
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Originally Posted by Harlard View Post
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.

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Originally Posted by Stiggy Pop View Post
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.
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Old 10-16-2020, 12:09 PM   #15
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Originally Posted by klr142 View Post
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.
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Old 10-16-2020, 12:14 PM   #16
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Originally Posted by Stiggy Pop View Post
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.

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Originally Posted by klr142 View Post
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
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Old 10-16-2020, 12:59 PM   #17
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Originally Posted by Stiggy Pop View Post
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.

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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
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.
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Old 10-16-2020, 01:06 PM   #18
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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

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)
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Old 10-16-2020, 01:41 PM   #19
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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

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.
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Old 10-16-2020, 01:45 PM   #20
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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.
Ahh, that head had a few... issues.
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Old 10-16-2020, 03:01 PM   #21
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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.
It will probably pull harder in the higher gear. You have gone past your efficiency range at that high rpm.
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Old 10-17-2020, 12:24 PM   #22
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Drop the rear to 3.9
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Old 10-17-2020, 06:37 PM   #23
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Drop the rear to 3.9
Mike P offered me a set of 3.73 gears, not sure how much work it is to swap in an 8.8. Plus I've got about $60 worth of Ford friction modifier additive in there now. I know it's not going to pull hard past 7000 but at least it shouldn't be banging the limiter if I set it to 7500.
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Old 10-17-2020, 08:21 PM   #24
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It all depends on whether it’s worth shifting. That extra 200 RPM may be all you need. I run into a gearing issue with my GT every now and then where it would take more time to shift than it is worth.
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Old 10-17-2020, 11:38 PM   #25
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I have found that on a big sweeping course iíll shift to 3rd and keep smooth.
But if you need a bit more and want to stay in 2nd, hereís the idea i was going to throw at you: set up the new gearset with new pinion bearings. keep the 4.10 ring gear, and the 4.10 pinion with the bearings and crush sleeve.
Use synthetic gear lube, i usually donít need much if any modifier. Or use gear lube with modifier. Or strain your oil through a coffee filter. It takes a while but i donít stand there and watch it.
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