Rev Limiter - Fuel or Spark??

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What is the best way cutting fuel or or a spark based rev limiter?
 
Thanx Craig, my stock ECM is still controlling the fuel pump and it cutsoff at 5500 I think. I'll rewire my relay to be controlled by the SpeedPro unit. Right now I have a MSD 6BTM but it has no rev limiter built in. Any suggestions on a good upgrade, I still need the in car ajustable retard (wife drives my truck alot, I love her but I like my engine to).
 
Bryan, you are correct in that the FAST system uses a fuel shutoff for rev limiting. It works well as a "last-ditch" effort to keep the engine from over-revving, but there's nothing quite like a good ol' ignition rev limiter. The MSD soft touch limiter built into most of their ignition systems is a good one, and anyone who makes an ignition system also offers some type of rev control. I would definitely set things up so that the ignition limiter is the first line of defense.

If your MSD box doesn't have the rev limiter built into it, you probably should check with MSD on how to upgrade. The separate rev limiter module they make is not compatible with their capacitive discharge ignition systems.

Craig
 
Originally posted by Craig Smith
Bryan, you are correct in that the FAST system uses a fuel shutoff for rev limiting. It works well as a "last-ditch" effort to keep the engine from over-revving, but there's nothing quite like a good ol' ignition rev limiter. The MSD soft touch limiter built into most of their ignition systems is a good one, and anyone who makes an ignition system also offers some type of rev control. I would definitely set things up so that the ignition limiter is the first line of defense.

If your MSD box doesn't have the rev limiter built into it, you probably should check with MSD on how to upgrade. The separate rev limiter module they make is not compatible with their capacitive discharge ignition systems.

Craig

I'd rather turn the fuel off.
When you use an ignition cut you wind up will excess fuel everywhere, and then a spark to light it.
I've seen mufflers blown off cars running ignition cuts.
With an ignition cut you might have alot of EGT and instantly spool the turbo, fuel cut will drop EGT and give a chance for driver activity for correcting things.
YMMV
 
Originally posted by bruce


I'd rather turn the fuel off.
When you use an ignition cut you wind up will excess fuel everywhere, and then a spark to light it.
I've seen mufflers blown off cars running ignition cuts.
With an ignition cut you might have alot of EGT and instantly spool the turbo, fuel cut will drop EGT and give a chance for driver activity for correcting things.
YMMV

uuummm isn't fuel more important at high rpm with boost or juice than ignition? I'd rather blow my lil $30 muffler off than blow my fairly more expensive engine ;)
 
Originally posted by Bobo


uuummm isn't fuel more important at high rpm with boost or juice than ignition? I'd rather blow my lil $30 muffler off than blow my fairly more expensive engine ;)

Turning the fuel off is fine, running lean is entirely different.

In an exterme event think of hydralicing a cylinder.

Like I said, I'll stick with turning the fuel off.

Also, in my opinion it's a million times easier on the engine if you drop cylinders as a function of prime numbers. ie (on a v8) you start by dropping ever 7th cylinder firing, if that doesn't work then ever 5th, then every 3. I did my own system that way and it was tons better then the stutter boxes.
 
I can vouch for the FAST rev limiter working well without blowing the exh off :-) I went wot against a C5 vette on the highway, nitrous on and 28 psi boost. Grabbed 2nd on the column PRNDL instead of 3rd and all it did was... rev limit (thank goodness :-)

TurboTR
 
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