2.7RS rev limit? Options

[john77]

I competed in my second auto x yesterday and after being on the limit of second gear a few times I want to install a rev limiter.

Does anyone know what I can safely push a 2.7RS spec engine to?

My car has an MSD 6AL ignition that takes plug in modules in 100 rpm increments - so 6900, 7000, 7100 etc.

Thanks
John

[colingreene]

depends on who built it and what springs and valve train stuff is in it.
whats it set at now?

[Qarl]

What cam profile is in it?

[SLITS]

If it has RS pistons, valve springs, etc ..... 7000.

Stock is 6300.

Mine has RS pistons / heads and I hold at 6300 with a "Bump Rotor".

[GeorgeRud]

Mine seems to maximize it's horsepower at about 6000 rpm (RS pistons and cylinders with a S cam), so I don't take it much beyond 6300.

[john77]

Thanks guys, these are all good questions that I have no idea of the answers to (IMG:style_emoticons/default/smile.gif)

I've left a message with the shop that built the car, hopefully they can tell me. All I know right now is that it's 'RS spec' built on a 74 case.

[john77]

depends on who built it and what springs and valve train stuff is in it.
whats it set at now?

There's no module plugged in the MSD right now, so I'm assuming it has no rev limit set up. Or if it does, it's set higher than anyone has said here, because it didn't kick in yesterday...

[sixnotfour]

S was 7300

buy one here;
http://www.ebay.com/itm/BRAND-NEW-ORIGINAL...M-/281137777465

[0396]

S was 7300

buy one here;
http://www.ebay.com/itm/BRAND-NEW-ORIGINAL...M-/281137777465

Yes, S was a 7300 limit.

[john77]

S was 7300

buy one here;
http://www.ebay.com/itm/BRAND-NEW-ORIGINAL...M-/281137777465

So that's what that is? I actually have one somewhere.

Builder surprisingly called me back and said full RS internals, so good to 7300. Which is good as some of the numbers earlier worried me after I hit 7100 yesterday (IMG:style_emoticons/default/smile.gif). I'll probably get a 7100 to be safe®.

[Downunderman]

With an RS twin plug motor with good valve gear; viz titanium retainers, Vmax springs good for 8k, 10.3:1 compression, albeit relatively small ports but smoothed out, gave about 190 rwhp at 6,300 with GE 80 cams, but safe to 7,300 on upshifts all day long. Its giving it a buzz on a downshift that you have to worry about, which is why i have a downshift light set to come on under 5k.

It pulls strongly from 4k and anything over 7k is wasted. I set the orange shift light at 6,900 and the red one at 7,100 and the limiter at 7,300.

Cheers,

[Downunderman]

One further thing to note. A lot of engine builders set up the valve springs to the factory heights without checking the seat pressure and open pressure, with dire results. My experience had been that with that a good set of factory springs and an S cam it will not rev to where it is supposed to without increasing both seat and open pressure to avoid valves bouncing.

Cheers,

[john77]

With an RS twin plug motor with good valve gear; viz titanium retainers, Vmax springs good for 8k, 10.3:1 compression, albeit relatively small ports but smoothed out, gave about 190 rwhp at 6,300 with GE 80 cams, but safe to 7,300 on upshifts all day long. Its giving it a buzz on a downshift that you have to worry about, which is why i have a downshift light set to come on under 5k.

It pulls strongly from 4k and anything over 7k is wasted. I set the orange shift light at 6,900 and the red one at 7,100 and the limiter at 7,300.

Cheers,

Thanks. I'm new to auto x, can you explain the danger with downshifting? And come to think of it a down shift light? I'm assuming that's an aftermarket piece of equipment?

[john77]

One further thing to note. A lot of engine builders set up the valve springs to the factory heights without checking the seat pressure and open pressure, with dire results. My experience had been that with that a good set of factory springs and an S cam it will not rev to where it is supposed to without increasing both seat and open pressure to avoid valves bouncing.

Cheers,

I'm hoping it was built right, it was built by a shop with a very good rep for racing engines in SF. I'll ask the guy when he gets back to me with the build details.

[brant]

Thanks. I'm new to auto x, can you explain the danger with downshifting? And come to think of it a down shift light? I'm assuming that's an aftermarket piece of equipment?

over reving the motor occurs during shifting
in 2 ways:

1) a missed shift. intending to go up but accidently going down. results will usually break non forged rocker arms or the shaft they ride on if its caught before the clutch is fully out. If worse, it bends the valves when they hit the piston face.

2) often people down shift and have the motor doing brake work. Sometime without even realizing it. A shift light or tell tale tach, will point this out and can be used as a training tool.

[john77]

Thanks. I'm new to auto x, can you explain the danger with downshifting? And come to think of it a down shift light? I'm assuming that's an aftermarket piece of equipment?

over reving the motor occurs during shifting
in 2 ways:

1) a missed shift. intending to go up but accidently going down. results will usually break non forged rocker arms or the shaft they ride on if its caught before the clutch is fully out. If worse, it bends the valves when they hit the piston face.

2) often people down shift and have the motor doing brake work. Sometime without even realizing it. A shift light or tell tale tach, will point this out and can be used as a training tool.

Thanks Brant. A shift light sounds like something that would definitely be of use to me.