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Discussion Starter #1
4:30 and 4:56 gear users..NEED HELP!

Well I've been doing all the calculations and right now I trap 5150-5200 rpm on a 26" tall tire so I figure the swap to 4:30's will put me up around 6100 and the 4:56's around 6400rpm. The rpm calculators on the sites don't really match up and confirm this they are off for my combo. I could go to a 28" tire with the 4:56's and keep the rpm around 6200 as well right? The car should trap atleast 117mph, best last year was 115.3mph

What is your basic combo, tire height, HP if you know it and what finish line rpm do you cross at? I am stuck and really don't know what gear to pick for my NA combo. My cam is made for 4:40-4:56 and is good till 6700..though my stock block may not be..lol

I am planning on staying NA for awhile until I can get a healthy turbo for my next motor which will be a 408 or 418, then I will have to swap the gears to a 3:55 or 3:27.

Thanks
 

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I just went through the same thing with my car. I'm running a little faster than you, but pulling more RPM. I shift at 6500-7000.

I have a 351W that has run a previous best of 11.9 @ 118 MPH on 25.7" tall nitto's. I was running a 3.70 gear (9" rear). I was going through the traps around 5400 and I wanted to be at 6500. The car bogged like hell with 10.5" x 26 " slicks and I could only get 1.8 60' times.

I swapped in a set of Richmond 4.33 gears and all I can say is WOW! :cool:

The car felt better driving on the street and kicked ass at the track. I've only run on an 1/8th mile track, but I had a 1.58 60' time at a poorly prepped track. I can't wait until I get to Houston Raceway Park! I was running 7.5's in the 1/8th at 92 MPH. I usually run a few tenths and a couple MPH faster at HRP.

You'll be better off staying conservative on gear selection. 4.56 is a lot of gear and if you start running higher trap speeds it may be too much.
 

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Rick,

I don't have 4.30's, but I can tell you that you are going to trap higher than 6100 rpms with the 4.30's at 117 mph. If I trap 112 mph or higher, my 5800 rpm shiftlite comes on with the 4.10's.

I'd go with the 4.30's for your set-up.

Later,
Kyle
'93 Cobra #1058
 

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The 4.56's will be too much unless you run the 28" tire. I was trapping 120mph last year with the 4.30 gears and crossing the line at 6400 rpm's. This was with at T-5 with 2.95 first and a 6600 rpm shift point.

I'm running 4.56 gears this year with a 26" tire and a 7000 rpm shift point and the shift light is on BEFORE the finish line.

Go with the 4.30's. They should be the best gear for your combo.
 

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Coiled:

I looked at your website and I am extremely impressed with your times and how simple your combo is. Is your modification list current on the site?

What were the mods for the [email protected] with a 1.59 60ft time that is listed on your site. Was this done with a factory-stock short block?

Have you ever dyno'd the car? What is your race weight?
 

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Discussion Starter #6
Thanks for all the replies guys..I figure the 4:30's would be the best choice if I stay with a 26" tall tire..but if I go to the 28" tire to decrease the side wall deflection on hard launches with the manual tranny and give me a wider foot print the 4:56's would be better.

Darrin- Have you ever run 28" tall tires for the reason I listed above?

Kyle- Any new track times with the new combo? I hope to have mine running by Memorial day, I just got all the wires and dash in, working on bending all new brake lines now..man what a lot of work.
 

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I would agree with Darin on this one. I ran a 4.30 last year with a 6,500 shift point and went through the traps at about 6,300 on a 26" tire. With my 4.56 I'm over 7,000 rpms at 120+. I have a FMS 4.30 for sale if your interested. Good luck.
 

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I just swapped from 4.30's to 4.56's last week. With the 4.30's, I was crossing through the traps right around 6600rpm at 120mph on a 26" slick when my peak power is around 6700rpm. Went up to the 4.56's and now I'm crossing at around 7200rpm at 120-121mph (no loss in mph). That's a much better finish line rpm for me. I had always been told to cross at 400-600 above your peak power point which now I am. Car responded to dropping from a best of 11.34 with the 4.30's to 11.09 with the 4.56's.
 

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Discussion Starter #9 (Edited)
Great Job Jeff! I see 10's right around the corner for you...Did you ever run the 4:30's with the manual or just the AOD?

Well according to my Speedbrain which I have had excellent results with it shows peak power around 6350rpm, which makes sense to me. Although last season I was going a tad lean up top due to lack of fuel, my 155lph pump just couldn't feed my 30# inj, so I have a 255lph HP pump now. The cam is good for 6700rpm, and I have the springs to take the rpm so that doesn't worry me, I just didn't want to take it passed 6400rpm if I don't have to to be safe. With nice cool air I shift it at 6600, launch at 6000rpm and hold on.

Can anyone confirm my reasoning to going to the 4:56's and 28" tire? I have always been told the 28" tire will give me less sidewall deflection and a wider footprint which will greatly help me off the line with my manual trans.
 

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Rick,

The 28" tire will help your 60ft's but if you can make it hook on the 26" tire then it should be faster with the 26's.

Jeff,

Damn! [email protected] Thats a killer MPH. IS this with you new carb motor?
 

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Carb motor? Where'd you ever hear a thing like that?

Actually, yes it is. The new motor is making some mondo power. I've only got about 10 passes on the combination so I'm still shaking it down. I want to be the first S/W car in the tens!!

I ran the 4.30's both T5 and AOD. My best in T5 form was [email protected] and with the AOD was [email protected] with basically the same engine combination (I was about 120# with the AOD though). I actually thought the 4.30 was a fantastic street/strip gear with the T5. I could cruise around town in 5th gear without the car chugging.
 

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Discussion Starter #12
Thanks for all the replies and help..looks like the 4:30's will be the best for my combo right now, can't wait to get the 33 spline Strange Light Weight Alum spool and axles installed, they should help my 60ft times on my 180,000 mile stock rear! Looking for 1.50 or quicker.

Those P/S and S/W cars are getting faster and faster, hats off to you guys for doing awesome times.
 
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