1/8 th mile racing. Suppose you have an engine that makes maximum HP at 7000 and continues to make about the same HP at 7100, 7200, 7300. Here’s the question. Would gearing the car to cross the 1/8 at 7300 be more consistent than gearing to cross at 7000 or same? What say you.

I think it depends on how good the car works because you are adding more SLR to the car, unless you do what I had considered doing. That is pulling gear out of the trans and adding to the rear. My car is only 2000lbs so I was looking at putting a 1.58 gear set in and adding rear gear to get the finish line rpm I wanted.

I think would be faster using all of you engine's power curve, just not sure whether it would add consistency. It would force a converter change also, if your converter is correct now.

I set my car up to be at about 6500 at the finish (estimated weight by hp) for which I needed a set of 5:23 gears. After I got my gears setup and was talking with a very experienced local who told me I would light 'em up at the start and it was more important to gear for a good launch.
Mechanical issues have prevented me from running so far, so I don't know if I'm good or not.

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Originally posted by markemark:
1/8 th mile racing. Suppose you have an engine that makes maximum HP at 7000 and continues to make about the same HP at 7100, 7200, 7300. Here’s the question. Would gearing the car to cross the 1/8 at 7300 be more consistent than gearing to cross at 7000 or same? What say you.

A typical SS car the engine peaks at 74-7500. They go through the lights at 8800... IMO a race car makes all the ET in the first 1/2 of the track. Gear is your best friend and ET maker.

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unless you do what I had considered doing. That is pulling gear out of the trans and adding to the rear. My car is only 2000lbs so I was looking at putting a 1.58 gear set in and adding rear gear to get the finish line rpm I wanted.

If you haven’t already, you might consider looking at the price of that planet. It’s extreme and carries extra clutches…… but I know little about transmissions.

I’m already at where you are considering on going being geared strictly 1/8 with a 1.56 planet and 5.14 diff presently.I have new 99 and 101.5 RO tires on the floor and a 5.00 gear set on the shelf. I'm trying to decide which way

quote:

Originally posted by markemark:

quote:

unless you do what I had considered doing. That is pulling gear out of the trans and adding to the rear. My car is only 2000lbs so I was looking at putting a 1.58 gear set in and adding rear gear to get the finish line rpm I wanted.

If you haven’t already, you might consider looking at the price of that planet. It’s extreme and carries extra clutches…… but I know little about transmissions.

I’m already at where you are considering on going being geared strictly 1/8 with a 1.56 planet and 5.14 diff presently.I have new 99 and 101.5 RO tires on the floor and a 5.00 gear set on the shelf. I'm trying to decide which way

Yes, I know the cost. I decided not to chase that set up but not because of the gear set price. Right now I go through at 6800 and if I wanted to optimize I needed to go through about 7500 and just decided in the end I'm just bracket racing. I don't need to chase every hundredth, plus I'm a pretty quick Footbrake car.

Another thought about gearing. The engine power curve is an important factor to consider. Many of our common bracket-race engines don't carry the power well beyond peak. If you gear to the point where the engine is nosing over, you have gone too far.

Kind of a parallel to Larry's comment above -

Most racers like to be the chasing car in bracket racing. Is quicker ET more important, or is higher finish line MPH more important?

Maybe consider whatever gearing maximizes MPH

My two cents:

Considering the cost of changing the gearing in either the differential or the transmission, (and it won't be cheap) first ask yourself if it's worth the expense. Either way it's expensive and the benefit is usually minimal unless you are considering running a specific class and can't cover the number. Shoe polish is cheaper.

This change also limits you to 1/8th mile tracks, and usually doesn't make the difference you had planned on finding. One last thing to consider is the change to your starting line ratio and how you intend on dealing with the potential new problem it will create, ie: traction.

Buy a blue bottle if "Faster" is really important, it's a ton cheaper and doesn't care if it's 1/8th or 1/4 mile, it'll be a lot faster everywhere.

Sorry for the intrusion, it was just my 2 cents:

Bob

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Originally posted by SlyFox:
Kind of a parallel to Larry's comment above -

Is quicker ET more important, or is higher finish line MPH more important?

Yes

The question was about consistency bracket racing strictly 1/8 mile. If I wanted faster I’d increase the size of the 388 I presently have.

I prefer slightly less SLR to aid when track conditions become poor even though it gives up some ET. Leaving wheels down is also more appealing to me.

A loose converter is more consistent than a tight one. So I’m wondering is running an engine at it’s peak hp longer (7000 -7300+) in the same distance (1/8) more consistent than achieving only the initial peak (7000).

Depends on how much your engine falls back on the shift. Most will fall 800 to 1,000. Based on your dyno sheet and if your fall back is 800 I would maybe try shifting at 7500 and fall back to the same horsepower I shifted at if the valve train is adequate for that rpm.

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Originally posted by old school:
Depends on how much your engine falls back on the shift. Most will fall 800 to 1,000. Based on your dyno sheet and if your fall back is 800 I would maybe try shifting at 7500 and fall back to the same horsepower I shifted at if the valve train is adequate for that rpm.

It always going to fall back to the stall RPM, changing the shift RPM doesn’t change the fallback RPM.

My opinions. 1. Shift several hundred RPM over peak Hp, that will drop it closer to peak after the shift. 2. Yes, you want consistency and once again my opinion is keep it in peak powerband as much as possible. 3. A loose converter is faster and more consistent because it helps keep you in that peak powerband.

The most consistent ET should be the fastest because that means you are in the power band longer.

Think of it like a ten speed bicycle, if you start off in too high of a gear it takes quite a ways to get bicycle really moving and accelerating. But if you start off in the lower gears and keep shifting at right time it is faster and easier on your legs. The longer you are out the power band / Gearing the more inconsistent it is going to be.

Too tight of converter will kill a lot of ET and consistency to for same reason, it lets it drop out of power band and lugs motor a little lower.

So to answer your question yes it should be faster and more consistent to gear it to come across at 7300 RPM. Your converter plays a large part in keeping it in that range to.

What does your convertor stall at now I'd be looking for 6200-6400 stall.

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What does your convertor stall at now

I decided to continue with the 5.14 gear and installed the 99” RO tires that are 1” narrower, 2# lighter than the 101.5 RO that I’ve run prior. Converter flashes 6375 – 6400 @ 0.50 after launch and crosses the finish line at 7275 on Saturday in 2400 DA. I plan to continue and review the results. If installing 5.00 gear I’d loose 225+/- rpm finish line and gain slightly more flash stall.

One other change I made this weekend along with rear tires is, I put one size taller front tires that I’ve been wanting to change and decided to try MT ET Street Front Radials that weigh 4# more than the bias in same size.