AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,861
- Reaction score
- 12,209
As for safety; IDK, but
here is a formula for maximum piston-speed; click on this
https://en.wikipedia.org/wiki/Mean_piston_speed
as for fun; this I do know;
I've been taching my Eddie-headed-360LA (factory reciprocating parts) up to 7000/7200, since 1999. That's over 100,000 miles ago. Some say that's over 1500 rpm past the power peak. Maybe so, but um, so what; my 367 is a streeter. I'm not looking for ET.
In my combo, 7000 at the top of Second gear is 82 mph; and it's often/usually still spinning the tires. I like the jump on the shifts (A833), and I love the sound of the screaming 360, out the dual 3 inch cannons.
Plus here's the deal; when the tires start to grab, and the rpm plateaus or starts to fall, the power is INCREASING towards the power-peak, not falling into oblivion.
And besides all that,
um, when the guy behind me, (now well-intimidated by those 3" cannons screaming "loser" at him) can't hear his own sweet engine; and so he shifts early, his hood drops, and it's all over for his combo. OK; I made this last part up, I never race on the street. At least not against another car ..... Cuz honestly; with 3.55s she's a two-gear car, hitting 60=5100 in Second gear..... or would be if the tires ever caught up. Oh wait, that's right in the thick part of the power peak ............
At the bottom of this post is a power-curve for a 5.2M
with a stock cam. The 5.9Ms have a similar cam; so the power numbers will be a tad higher, but the shape and placement will be similar, if a tad higher.
The thing I'd like to point out is this;
Using this curve, typically, one might shift this at 4800.
With a TF automatic the splits are .59 and .69. So ;
on the 1-2 shift, the Rs will fall to about 4800 x .59 =2830, and
on the 2-3 shift the Rs will fall to ~3310.. Forget Second gear because that is pushing over 90mph with 3.23s..
Notice the outgoing power is ~225@4800, while the incoming power is ~155@2800, for a simple average of
190hp.
The thing is, you can increase your AVERAGE power by shifting later at the top. Say you held it in first to 6300 and say the power there had fallen to 200. And so the incoming power would now be at
.59 x 6300=3720 and the power there is say 210 ........ for a simple average of
205hp. That's 15hp! which is the equivalent of about one cam-size right there, if shifting conventionally ......... In fact, the power@6300 could fall to;
(190 x2) less 210= 170@6300, and you'd still make the simple average of 190hp .......jus saying .....
Second gear is a different story.
So in other words; put some decent heads on your combo, that won't choke the cam, and with adequate valvesprings, and adequate exhaust sizing; then just let her buck. And don't let someone talk you into installing a big ol' cam into your engine until you have tried this. There is, IMO, far too much talk of big cams on this Forum. The typical street-geared combo does not need, nor want, those.
