FVD chip raising my rev liimter to 7100

Vandit · 05-11-2011, 07:07 PM

I recently bought an FVD chip from a friend with a '93 C2. I installed the chip on my '91 C2. Since installation, i've noticed the rev limiter has been moved up to 7100ish. I've only taken it up there a couple of times to make sure I wasn't seeing things. I know this is not a good limiter to be running on an otherwise stock engine.

My friend who had it installed on his '93 C2 clearly recalls the limiter kicking in at 6800 like stock, however, on my car it is running up to 7100. Same chip, different cars, different limiters.

Is there anything that could explain this?

Tyson Schmidt · 05-12-2011, 02:13 PM

Your tach is optimistic, Pretty typical for them to read 100-300 rpm high.

RW964 · 05-20-2011, 02:06 PM

My two cents. I have been lurking on the forums and this subject has come up seems like most that are in the know say .. unless you have stronger springs and the lot do not take the revs to that limit period. The rod bolts are only made for a limit of 6800 and no more.
[I] a am not sure just what I have read not wanting a brother 964er to trash a engine.
Also you may want to dyno just to see how the hp curve is anyhow.
This is not what I was looking for but may help you out. Do not tell anyone I got this off the other forum

The standard 964 connecting rod is not the weak link in these engines and will support well over double the power of a standard 964 engine. The rod bolts are the weak link in the rod, however, they too are sufficient to 7200. You do not need carrillo or other aftermarket rods in this engine unless you are running beyond 7500 (assuming you've replaced the rod bolts with ARP or such). The issue is not with their strength, but the heavy weight of the stock connecting rod. For an engine running 7200, you need to have a minimum deck height clearance of .032" because as Geoff mentioned, the piston, wrist pin, rod assembly does stretch and you need to account for that. That is a function of piston speed and mass.

As Larry mentioned, the stock valve springs were designed for a maximum of 7000 with the mass of the valve and the acceleration rate of the camshaft ramps. Beyond that they will float over the nose, or worse bounce off the seat and contact the piston near 7 degrees BTDC due to overlap.

Vandit · 05-21-2011, 05:21 AM

Thank you for the feedback everyone. I was finally able to get in touch w/ FVD and they confirmed their chip does increase the rev limit by 300RPM.

I am going to keep running the chip for the time being, but will definitely stay away from the rev limiter.

trak ratt · 05-23-2011, 11:05 AM

Quote:

Originally Posted by RW964

My two cents.... As Larry mentioned, the stock valve springs were designed for a maximum of 7000 with the mass of the valve and the acceleration rate of the camshaft ramps. Beyond that they will float over the nose, or worse bounce off the seat and contact the piston near 7 degrees BTDC due to overlap.

Agree, plus as the miles rack up the springs loose some strength too. I recently broke a rocker on our new to us 140K+ track 964. Didn't really think much about the raised rev limit until the rocker let go... overall prolly the least expensive outcome. Will be very careful about the rev limiter until I can get the chip redone. We did a 3 day DE (2 drivers) at MO last month with no issues and really didn't miss the extra RPMs