Comparison I'd love to see: close ratio versus standard box on lap time.

So as I be been going round and round in my brain about my car needing a close ratio box (well at least one that doesn't break) for my little Datsun it started to occur to me that it may not make much of a difference.

The car makes power between 4500 & 8200 but is happiest between 5000 & 7800. Makes around 105whp. I've been using Nissan close ratio 4 speed gear sets but not up to the larger 1500cc engine (stock is 1171) I've since gone to larger stock 5 speed box that is ok except 2nd -3rd 3000 rpm drop. I only use 2nd in one spot on track. Everywhere else is 3rd or 4th. Being an idiot amateur racer I obsess about how golden life would be with a zooty gearbox. Meanwhile I have spare ring and pinion that will gear the car down that will allow the use of 3-5.

I have seen a comparison done with stock and close ratio on a Caterham 7 and the close ratio box netted .3 faster for a lap. That was with a stock engine, I'd love to see a back to back with for a car with a modified engine.

that is one you may need to do yourself, a close ratio box will give the 2-3 that you may need. 1st gear will wind up to a higher Speed so 2-3 don't have the spread you have now,and in a 5 speed some 4th are closer to 5th some are closer to 3rd with 5th being OD,and 4th is just 1to1.

A shorter finral drive might be an easier route than custom ratios, depending on your desired top speed.

3k drop between 2-3 is like a cliff...ugh

I don't have an answer, but I do have a question...has any racer, anywhere, anytime been satisfied with his available gear ratios?

Sometimes, less shifting is less time. It is really situational though. Obviously you have to have the right gear for each corner per track.

A peaky race engine would benefit from close ratios. A stock engine with a broad torque curve are not so choosy

A nice benefit to a close gearset is if you break the trans, you can skip gears without too much difficulties.

https://www.youtube.com/embed/D4ipMAU7orA

Streetwiseguy wrote: I don't have an answer, but I do have a question...has any racer, anywhere, anytime been satisfied with his available gear ratios?

I imagine anyone with a Jerico or similar is pretty happy (or at least should be) seeing as you can get basically any ratio set you want. You can even get OD gears for the 3rd position and build a really wide ratio box.

I have a semi valid comparison between the 4 speed ultra close and the stock 5 speed. The only issue is with one turn where 2nd gear needs to be used. Without going into the blow by blow it's a classic case of going down to 2nd then right back to 3rd or the car being a little lazy if you stay in 3rd.

Interestingly enough regardless of which gear I chose the spot where I upshift to 4th is pretty much the same (too close to say). Additionally the RPMs I'm pulling in 4th when I arrive at the turn in point for the next corner is also nearly identical between the close ratio 4 speed and the wide ratio 5 speed. It's honestly within 100 RPMs.

Here is the rub; yes the close ratio box likely results in a lower lap time, in my case it might even be 3/4 to a full second. The way my races have been going I finish between 4-6th overall. The cars behind me are easily 2 seconds a lap slower and pretty much the same goes for the cars in front.

The question for club racers is always where to spend the money? Close ratio boxes are not cheap, anywhere from $1500 to $3000 and more if you want dog ring box.

While driving around the gearbox may be annoying and my initial reaction is to throw money at the issue, it may well be a bad investment. For 3K I could buy trick dampers or put the cash in the motor.

Again I would love too see a test with stock versus close ratio back to back as I suspect the difference isn't what I and many other club racers think it is.

Tom

In reply to Tom1200:

On the bright side, if you put another three grand in the motor, you'll probably be more likely to need the close ratio box.

A Winters final drive with hot swappable gears might be a decent measure so atleast you can set up the best compromise for the track you are racing on if better ratios are not available for your transmission.

THey are modular so you can get them used cheap from dirt track guys and remove the axle tubes (especially ones bent in a wreck!). They sell adapter side plates made to run Porsche IRS axles. I had elaborate plans to do this to the E30 up until the part where I realized it really needed 120 more HP and 1000RPMs to fix it.

Datsun 1200?

If you're not running out of RPMs on top, then a shorter final drive that keeps you from ever going to 2nd is probably the cheapest remedy.

Or stay off the brakes and use that momentum to keep you out of 2nd if possible... That's the free option.

In reply to Huckleberry:

The quick-change sucks up a bit more power, though. Lots more rotational inertia.

snailmont5oh wrote: In reply to Huckleberry: The quick-change sucks up a bit more power, though. Lots more rotational inertia.

I think it's the greater number of gears in a quick-change diff (it has the two quick change gears in the rear plus the ring and pinion, vs. just the ring and pinion) that makes the difference in power loss rather than the rotational inertia.

I race a '69 Alfa Spider (a momentum car), and I went from stock to a custom (Schwitters) close ratio gear box a few years ago. I believe it saved me about a second or more per lap on a 2.25 mile track (Pacific Raceways International). The bigger difference came with a shorter rear differential. Going from 4.1:1 to 4.56:1 saved about two seconds per lap on the same track.

But the biggest difference was suspension related. Going from stock trunnion to a sliding block to better locate the rear end and lower the rear roll center. That (and slightly wider tires) saved me about 2 seconds. So over the last few years, I went from backmarker, up to midfield, and now top 5. Some of that is likely driver improvement as well.

GameboyRMH wrote:

snailmont5oh wrote: In reply to Huckleberry: The quick-change sucks up a bit more power, though. Lots more rotational inertia.

I think it's the greater number of gears in a quick-change diff (it has the two quick change gears in the rear plus the ring and pinion, vs. just the ring and pinion) that makes the difference in power loss rather than the rotational inertia.

Well, there's two sets of gears, but the ring and pinion are inline instead of hypoid. I'd give friction a wash.

@kb58 yes Datsun 1200, I'm a regular on 1200.com AKA Rallytwit.

@ Tyler H carry more momentum isn't going to happen, I'm skating the car through every corner, I'm pretty much known for maintianing a ton of corner speed. The lazy in third is even with eking out every last RPM with momentum.

@Nader your info is exactly the kind of thing I'm talking about; a ring and pinion is cheap relative to a gearbox. For many cars the suspension work is reasonable as well.

@ Snailmount5oh; There are a couple of things that can be done without killing the power band. I can up the compression from 11.5 to 12-1 with a head gasket change. While the head is off I could go to slightly larger valves. Also when I ported the head I was conservative with the valve guides, they could be shaped without giving up any reliability. Some of the Datsun guys cut the guides flush with the port roof but it does accelerate the wear. With the flat slide carbs I could build a ram air box for a bit more. All that would run about $500-$700 and net as much as 15hp. That would drop the likely lap times 2-3 seconds or more.

So few us get to do real back to backs; going from the A12 to A15 (20-25HP jump) was a big jump but I also went from a 4:11 to 4:38 R&P as well as installing a rear axle with 3" wider track and widened the front to match. Plus I stopped using take offs and went to new Hoosiers. All these things cut lap times by 12 seconds. The problem of course is I have no idea of how much time each individual change was worth

Again we club racers reflexive think we cannot live without $3000-$4500 gearbox. As more time passes I'm thinking it should be last item on our list of go fast parts. Of course I'm cleaning out my garage because I'm putting the money aside for, you guessed it, a proper gearbox.

BrokenYugo wrote:

Streetwiseguy wrote: I don't have an answer, but I do have a question...has any racer, anywhere, anytime been satisfied with his available gear ratios?

I imagine anyone with a Jerico or similar is pretty happy (or at least should be) seeing as you can get basically any ratio set you want. You can even get OD gears for the 3rd position and build a really wide ratio box.

No ones every really happy. I helped out a guy with some money test for a couple days. We swapped between four different Jerichos on a 5/8 mile oval. He was looking for an advantage that wasn't there but would accept it. The only time you're not in 4th is restarts but when given a chance people can overthink anything.

In reply to Wall-e:

My buddy's circle track car only had third, fourth, and reverse. First and second were gone.

On a stock MGA Twin Cam (a model that I race) the change to a CR box and a swap from a 4.3 to 4.55 diff ratio yielded an improved 0 - 100 time by 11 seconds and a 1 second 1/4 mile advantage despite initially slower acceleration off the line due to the long first gear ratio.

@wspon what gearbox was in it and what did you go to I.E. How do the ratios compare. I'm assuming this was a Quaife gear set. If my car improved 1 second over a 1/4 mile that would likely add up to 1-2 seconds per lap.

Tom

Stock MGA box:

1.000:1 1.374:1 2.214:1 3.636:1 4.755:1

MGA factory close ratio box:

1.000:1 1.267:1 1.619:1 2.448:1 3.201:1

Note: 4.3 diff = stock, used 4.55 with CR box. Ist gear non synchro so only used for starting.

The results are from an old Road and Track road test where they compared stock and CR fitted cars.

In the race car I run a 4.55 or 4.88 diff (but then it uses a 7800 rpm red line and I also have a 0.83 OD in it in conjunction with the CR box)

When I switched from a stock 4 speed to a close ratio 4 speed my lap time immediately went down 2-4 seconds depending on track. The car in question a BMW 2002 has a very wide gap between 2-3 and runs a 3.90 LSD diff. New ratios are 1.6/1.3./1.1 (2/3/4). Stock ratio was I think 3.0/2.0/1.3/1.0 if memory serves. I'd choose the right gearbox over 25 horsepower any day.