Rearend Gear ratio and trap speed

[turboman38]

I have been reading and responding to some posts about tire sizes and you guys have me a little spooked. I have 3.73s in the rear. Car had them when I bought it. Alot of you are saying you like the 275-60-15s to run on the strip because of the trap speed.

First question is why do we worry about trap speed? I thought the name of the game was E.T.??? If you were running for points in NHRA and got a bonus for top MPH in your class then I could see being worried. Maybe I'm not understanding the importance of trap speed.

Second question: With the 3.73 that I have and a 26 inch tall tire am I going to be over revving the motor on the top end? This is where I'm spooked. I know a couple of local guys with stock blocks tha rev as high as 5300 r's when racing because of the way they have the chip setup. Will I be over that with 3.73s to the point of hurting the motor?

 

[REDS HOT AIR]

depends on how much power your making..

you want your gearing so you just get to top side of your power range in 3rd gear going thru the traps.

a bone stock GN should run out of breath with 3:73's and 26" tires

as far as et and mph.. which do you do driving on the street??

et is how hard you launch the car...dont think you launch it like that leaving a stop light...other than from a dead launch what you feel is power and power = mph thru the traps

mph is a measure of hp et is a measure of how much of it you can put to the ground from a dead stop

 

[Lee Thompson]

gear

Well stated, Red. Did you ever think about going into politics?

 

[turboman38]

Thanks Red.

My car is not stock. Have a TE60,50 lb injectors,206/206 cam and a bran new bottom end (new crank,rods and pistons) with the two center caps being steel. Will eventually get the heads done and a stock location intercooler (V4 hopefully).

Running a stock modified convertor with the stall supposedly being around 2900. I know that's slowing me down but with the 60, it pulls like a bear thru the mid and upper rpm range.

Hoping to get into the high 11s with my current combo. Low 11s with the heads done and a V4.

 

[UNGN]

Originally posted by turboman38
First question is why do we worry about trap speed? I thought the name of the game was E.T.??? If you were running for points in NHRA and got a bonus for top MPH in your class then I could see being worried. Maybe I'm not understanding the importance of trap speed.

Second question: With the 3.73 that I have and a 26 inch tall tire am I going to be over revving the motor on the top end? This is where I'm spooked. I know a couple of local guys with stock blocks tha rev as high as 5300 r's when racing because of the way they have the chip setup. Will I be over that with 3.73s to the point of hurting the motor?

You worry about MPH because it REAL hard to hit 11's if your car is artificially limited to 110 mph, 300 feet before the finish line. The sensation is like throwing out an anchor vs. accellerating through the traps (with proper gearing)

Reving to 5300-5400 won't hurt the motor, but stock heads don't allow much HP to be made at that RPM. Your cam will help, but even so, I'm guessing you'll be disappointed with the ET and MPH your combo will do vs. other people with similar mods (and 28" tires and 3.42 gears)

 

[Nashty]

With a 28" tire and 3.73's, you're pretty close to the stock set-up. (~1-2 mph) I like the bigger tires for a longer contact patch.

I do have to shift into 4th gear to keep off the rev limiter (6000 - Speed Pro controlled).

FWIW, I run 131 with them (3.73 & 28 X 10.5) and feel that I could pick up a mph or two with the 3.42's.

BTW, if you switch to a 3.42 get a late model GM truck ring and pinion. They are a 8.625" vs. a 8.5" set and are a direct bolt in swap (both are interchangeable). I have a set of these gears from my truck if you are interested (8.625").

My opinion is they're probably NOT hurting you now, especially if your 60' sucks. I WOULD recommend them if you're running the 1/8th mile track.