1st/2nd gear ratio question?

Hi,

I have a Swift DB4 with a carbed Toyota and Staffs 5-speed. I am selecting gear ratios for my next event and was wondering if anyone had any advice or comments regarding the maximum ratio spread between 1st and 2nd gears. In other words, what is the minimum acceptable engine rpm after the 1st to 2nd gear upshift? Note that I have the dual Weber carb setup and my engine is therefore not quite as responsive as the FI engines at lower rpms. Thanks, Rick.

You can't answer this without knowing the shift point. How much do you want to rev the engine in 1st?

Using 10,200 with carbs, we sometimes run a 12:31 first and a 15:30 second. That works fine.

Thanks, Paul. I probably did not phrase the question very well. I am essentially seeking input on the lowest acceptable rpm in 2nd gear after the 1st/2nd up-shift. For example, I know that the engine will not "pull" well from 5000 rpm. But what about 6000? At this point I am going to try and be closer to 7000 rpm after the shift.

My normal planned shift point is 9600 rpm, but in this case I could use a higher number (closer to 10,000) for the 1st/2nd upshift as it will only occur once at the race start. After the start I will be in second gear or higher for the remainder of the race.

Rick

Prioritize like this:
If you are using second gear on the race track select the proper gear for that/those turns.
Then pick a first gear that will result in an acceptable drop from 1st to second, which can actually vary depending on the actual second gear you have, the shorter the gear the faster it will accelerate through/from a "bog" situation. I ran a lot of that generation engine, keep it above 5500 min., 6000 would be better. Now, further tuning may be had by making sure that the pace car speed matches a good acceration point for your engine. At the next race ask the pace car driver what speed you will be expecting at the drop of the green (usually 45 or so), then consult your gear chart/program to see where that is. On an out lap, after the tires have some temp, practice running at that pace speed and hit the throttle; a bog or wheelspin will show you that you are on one side or the other of optimum. Also, run up through secod and third, to get a feel of shift points/ timing, usually on the start your eyes are not on the tach.
Tony Ave

Hi Tony,

Thanks so much for your comments. The method you describe is exactly how I arrived at my question about minimum rpm's for a carbed Toyota. I have already determined that if possible I would like to use a relatively tall second gear (around 1.67 or so) at my next event. The problem is that my inventory of Staffs 1st gears is VERY limited, and the tallest 1st gear I have will still result in a very large rpm drop after the 1st/2nd upshift. Essentially I am trying to determine if I can get by with my current 1st gears, or if I need to shell out $400 for another 1st gear set, such as a 14/32 or similar. I will only be using 1st gear at the start, so I don't want to buy a brand new gear set unless it's really necessary (I would rather spend that money on other things......like tires!)

Rick

Rick,

With carbs I think you'll find that a 1.67 second is too tall for any track other than an oval. Looking back at the old records I have 1.85 was the tallest 2nd we ever used on a road course and that was Mid Ohio which has no slow corners. I think you would find that anything taller that 1,85 will require that you keep the rpm over 7,000 if you want to use full throttle. With that gear if you get down below 7,000 and you go full open on the carbs there is a good chance the motor will stumble pretty bad. Depending on the track you might get away with it under perfect conditions but otherwise you'll be frustrated in traffic and it will force you to step down to first frequently.
What track are you planning to run?
Steve O'Hara

Thanks, Steve. I have sent you an e-mail.

Rick

Rick,

The first issue you have to consider is your comfort level with 1 - 2 shifts. Many (if not the vast majority) of atlantic drivers opt to use first gear in the pits only and never select it on track. There have been some very fast drivers who opt for this technique just as there have been very fast drivers who use all 5 gears. Obviously it depends on the track. Most of the starts I've ever experienced in atlantic have placed me well into the second gear rev range obviating the need for starting in first gear. Your choice of a second gear ration (as has been pointed out) is a bit high IMO and will necessitate using first gear often at most tracks. You seem to balk at the prospect of buying new ratios due to their cost. I would posit that the learning curve of shifting in to first during a race might well mean replacing your first gear more often than you would like.

My suggestion is to gear for the slowest part on the track at an appropriate rev range for your second gear and adjust the remaining ratios to your particular engine power/torque curves and use first gear in the pits only. There may be some tracks that require the usage of first gear (Mt Tremblant, Memphis) but most will not. I still believe the ability to seamlessly use first gear in a race is a critical one - just not needed at all tracks.

You can add to the "needs first gear" list Pocono, Summit Point, and NHIS.

Thanks to you all for your comments. They are very helpful. I wasn't going to bore you with the details, but here goes.......

The track in question is quite fast. First gear will definitely not be required, except possibly at the start. If I wish to utilize second gear at all at this track, it must be rather tall. I have data from a pro shop that used to run DB4's there and they were using a 1.77 second and a shift point north of 10000 rpm. This equates to a top speed in second gear of around 100 mph. For me to acheive a similar top speed using a 9600 rpm shift point a second geat ratio of around 1.68 is required. I have tested at this track already with the wrong gears in the car (too short), and based on this experience I am confident that a 1.68 second would work well for my car if using a 9600 rpm max. If I wanted to shift a 10200 I could obviously utilize shorter gears.

The only problem is that if I use a 1.68 second I then have a huge ratio gap between it and my 2.58 first. This ratio gap is the reason for my original question -- what is the minimum acceptable rpm after the 1st/2nd upshift? The general consensus seems to be somewhere in the 6000 to 7000 rpm range, depending on whom you ask. At this point I have at least four options:

1. A 1.68 second and purchase a new or used 2.40 or 2.28 first gear set - problem solved.
2. A 1.68 second with my exisiting 2.58 first gear - low rpm after 1st/2nd upshift.
3. Forget all about second gear and just gear the car so that only 3rd thru 5th are used.
4. Some other option that I haven't even considered yet........

Charlie, I am not particularly comfortable using first gear, and I plan to avoid it when possible, although I did utilize first in my 5 speed Webster box for years without any major problems. Obviously there are tracks at which first gear will be required. As for speeds at the race start, with a 1.68 second I think that it is quite possible that the start would be too slow for second gear, thus making first gear necessary at least once during the race.

Again, thank you all for your input.

Rick,

IMO 100 mph in 2nd gear is overkill (especially for an atlantic) and limits you in your choice of gearing - as you are finding out. In looking at the gear charts for my RT-4 and Shadow my top speeds in 2nd (Glen, Tremblant, Elkhart) are 75 and 93 respectively. I use 10,000 for the Shadow shift point and 9000 for the RT-4. (recommended by Cosworth for 1st and 2nd gear shifts, BTW, and applicable to the 4AG as well.)

In re-reading your post I need to ask: are you trying to avoid using 2nd gear altogether (only 3-5) or trying to use the ratios you have without purchasing others?

I have never had to use 1st gear for a start, no matter how slow. My suggestion is to consider something around a 14/33, 14/32, or 15/33 for 2nd and work from there. With that ratio your 1st gear will be moot as it will ONLY be used to get the car moving so what you have works fine. Are you using a gearing program?

Be careful relying on "pro" data as they usually do not care about engine life or care and feeding of the car. And I find us mere mortals do not necessarily reach the same speeds at the same points on the track that they do. Nor is it guaranteed that they actually ran the gears that the data shows. I would contact someone in your area with a like car and sit down over a couple of beers and compare notes. Much more accurate and applicable: again, IMO.

Also, be careful in buying used gears. IMO you should ask for a magnaflux inspection with the proof that the gears are in good shape. Using used gears can easily be an example of false economy as a broken gear can ruin more than just a session. Ask Stan and Rennie Clayton about that.

Charlie,

Good points about used gears and the use of pro team data. I would definitely magnaflux any used gears that I obtained. However, if I absolutely refused to utilize used gears I would have to discard every gear set that came with the car.....and I don't plan to do that anytime soon :D !

To answer your question -- I would definitely like to use second gear if possible, and I do not want to purchase an additional first gear set UNLESS it is necessary to do so. If it turns out that I need to purchase another gear set....so be it.

I have already tried a 14/27 (1.93) second gear at this track and it was WAY too short, not even close to being useable. If I were to utilize any of the second gear ratios that you have recommended then I would be effectively limiting myself to the use of only gears 3 thru 5 at this track. I could always choose to do this, of course, and in this scenario you are correct in that I would definitely be able to start the race in second gear, and my first gear ratio selection would be irrelevant.

Here's the bottom line. If I wish to use second gear in the slowest corners of this track, then the second gear ratio will need to be in the 1.68 to 1.78 range. Anything shorter means that I will have to gear the car so that only gears 3 thru 5 are used. If I utilize a 1.68 second then the engine rpm at 60 mph will be approximately 6000 rpm, which obviously means that it is entirely possible that first gear may be necessary for the race start (however uncommon that may be). In this case the 12/31 (2.58) first that I have is shorter than optimal, but who knows, it may work out OK. A 2.28 first gear would be perfect....but is it really necessary? And should I buy a brand new 2.28 first gear without knowing for sure? Probably impossible to say until I try it out on the track, in my car, with me driving. Which is part of what makes racing interesting, right?

Oh well, I think we have beat this one to death. Thanks again for your input and assistance. Cheers,

Rick

Rick,

I have to ask: what car, what track and what final drive ratio are you using? Also, what are you using as an optimal rpm drop between gears? Do you have the dyno sheet to determine these drops?

Hi Charlie,

Check your PM's. Thanks, Rick.