ok i'm not sure if this has been said, but i'm too tired to read it all now. Im just taking a break from nascar o5 on x-box. (stupid roomate walked in front of TV durring qualifying, now i'm starting 32nd in a short race )
its also 11:45pm

this may sound a bit counter intuitive but it is easier to launch on a steeper gear than a shallow one.

for example, T-56 on 3.23 vs 4.11
at a 2200mph roll out
you are making you tires go 0-20mph instantly (off the line once the clutch is engaged) vs 0-15 instantly. obviously the clutch slips a bit but you get the idea.


if you try to launch at a high rpm with shallow gears 1 of 2 things will happen.

1. tires will spin because they cant go 0-45mph instantly.
2. engine will bogg to half the rpm and you will launch way below your powerband, slowly get into your powerband (due to being outside it) and fight the tall gear to do so.

now you sound like you have enough to roast them at any rpm in 1st, but i hope you see what i'm saying.

Its why people do high stalls AND high gears


Also FYI;
the saleen s7 road car orignally had a taller 1st gear ratio which was cut down to a steeper one due to the fact that drivers/owners complained about the jerky launches. with a mclaud (spelling anyone?) clutch as grippy as that, a tire that GRABS HARD and a motor that WONT bog down - it was a problem because they "idled" at 11mph!


edit: all the above also implies that your foot isn't an on off switch!
using shallow gears to launch easier is traction control for dummies

 

Jim.... money always calls money

I'm glad you finally put it together.. it simply looks great and awesome...
I would have thought you would have gone with the c5 rear.... but still... nice nice setup man

we have more or less the same gears as i have a 94+ with 4.10 and a strange diff.

 

Thanks!

The C5 has an 8.25" ring gear vs. the Ford's 8.8", and the differential case would have presented some mounting issues that the Ford case didn't, but I did consider it. Basically, we mounted the diff in much the same way that Factory Five Racing does in their Cobra replicas. Why reinvent the wheel? Oops, never mind...

The inner CV joints on the '03+ Cobra axles are also identical in construction to the RX-7's, which made making a hybrid axle as easy as possible. I cut the tripod end off a Cobra axle, milled out the center (I bought a milling machine a year or so ago) so that the RX-7 axle center shaft would fit into it, and drilled and tapped 3 holes to use bolts to hold it in place for mock-up on the car. I used the "Frankenaxle" to determine the length I needed for the new center shafts, then welded it in place. The result looked like this. Some people actually thought I was going to use that axle on my car.

 

With all the knowledge on this board I'm almost in shock that no one has posted some very basic track tuning tips

If it was me....... I'd gear for a conservative rpm passing through the traps at what speed you expect. Period.

To get traction, you need to retard the lower rpm's timing until it hooks up.

 

There is no modifier vs speed or gear to the timing tables...

 

I don't believe "Jimlab" is all that interested in drag racing.... hence his basis for gear selection might not be based on trap speeds.

 

Ya well that makes it even harder. I'd try and find some road race guys and get their opinions. That's a whole other ball park where I've never played ball.

If you're a street racer, then the drag race tuning stuff is still the same only tune it for a rolling punch on the street.

Got traction control? Why do you think it's illegal in Pro Stock?? Get the drift?

Trust me, if too much power was my problem, I'd re-educate the right foot first and if that didn't work...... go to intended use tires and suspension tuning way before I'd get hung up on real high gearing.

I mean...... why did you do the engine?? To give um hell right! Then do it!

With the money you got tied up and the rpm capability, I'd try 3.90 gears, tires, suspension, timing and if it still doesn't work..... then bump down the gearing. Them gears ain't all that expensive compared to what you got in that engine and you can easily pull 3.42's but I wouldn't, if I didn't have too..

Have fun and good luck. Just wish I had your problem to worry about. But then again, I've got a pretty educated right foot who just loves being challenged.

Kinda like the way "give um hell" rolls off my lips. Ya, I like that idea. Give um hell guy!

 

jim, it sounds as you have built quite a monster, could you please post some pics if you don't mind

 

I based my decision primarily on 40-140 acceleration simulations. Trap speed was secondary, but the car should trap in the high 130s anyway.

RaceLogic with launch control.

As I said, I have a 3.55:1 ring and pinion. With my M29 T56, my gearing is comparable to a standard T56 with 4.10s, except for 4th. I've got plenty of gear for a 2,750 lb. car. If it's too much, I'll drop down to a 3.27:1 or lower. 3.73s, 3.90s, or 4.10s would be way too much gear.

2.97:1 x 3.55:1 = 10.54:1
2.07:1 x 3.55:1 = 7.35:1
1.43:1 x 3.55:1 = 5.08:1
1.00:1 x 3.55:1 = 3.55:1
0.80:1 x 3.55:1 = 2.84:1
0.62:1 x 3.55:1 = 2.20:1

2.66:1 x 4.10:1 = 10.90:1
1.78:1 x 4.10:1 = 7.30:1
1.30:1 x 4.10:1 = 5:33:1
1.00:1 x 4.10:1 = 4.10:1
0.74:1 x 4.10:1 = 3.03:1
0.50:1 x 4.10:1 = 2.05:1

 

It's still very much in progress, but this should give you a general idea...

http://home.gci.net/~jimlab/images/E...d/PA030002.JPG
http://home.gci.net/~jimlab/images/Misc/P8080013.jpg

 

Wow, that motor is a thing of beauty!! That is gonna hall **** when you get it done!

 

That is NICE, bro.

Mike

 

Jim
how long have you been working on this project? how close are you to putting it on the road?

 

Nice to see you're still around Jim

The differential mount/rear subframe looks freakin sweet. Tough as nails too I'm sure! The T2R is a great diff too. It is THE one to have if you want to put power down in turns.

Keep up the great work, once its finished there will be nothing else like it on the streets

 

Consecutively or chronologically?

I pulled the engine subframe to start the V8 swap in October of 1999. However, the car has been sitting for most of the intervening time, since I've had other cars (1994 Supra turbo, 2002 Z06) that I've been "distracted by" since. I do a little here and a little there when I feel like it, which really isn't very often. Some times weeks and months go by without even touching it.

A lot of my lack of interest is due to the crap I've had to put up with during the project. I had one a**hole set me back a couple years while I waited on conversion pieces (subframe, trans brace, etc.) that never really materialized, and another a**hole who set me back a year or more on my engine, stole a bunch of parts and $$$ from me, and basically got away with it. It's a long story.

Not that far where parts are concerned, but probably another year where interest and free time are concerned. I really don't care any more, but it's sort of a point of pride to eventually finish it.