Gear ratios

Now i know that it depends on a bunch of stuff from engine hp and torque down to the size of the tires for the car but also on the track you are running. Manufacturers tend to gear 1st so you do not need to shift to 2nd to get good 0-60 times, so ratios just becomes a starting point.
Let's base this discussion on LS9/MH3, LS7/MM6, LS3/MZ6 and Ford 5.4/Ricardo.
The current ratios are as follows:
MM6 MZ6 MH3 Ricardo
1st 2.66 2.97 2.29 2.611
2nd 1.78 2.07 1.61 1.708
3rd 1.30 1.43 1.21 1.233
4th 1.00 1.00 1.00 0.943
5th 0.74 0.83 0.82 0.767
6th 0.50 0.57 0.68 0.625
Final drive 3.42 3.42 3.11 3.364

So for the SLC running let's say an NA engine 700hp/600 lb ft. I am looking at using a 5 speed for the street and a 6 speed dog box for the track. Opinions of ratios for both?

Thanks
Rob

sorry about the table formatting, could not get to to look nice

Rob.

what are you trying to discuss here....

Without knowing what size tyres and what RPM redline you have and what you are trying to achieve the info is a little useless really.

Whatever the stock 19" SLC tire size is. Redline is around 6700-7000, but shifting is going to happen way before that for the street and for the track, shifting will be at whatever the rpm that the max hp is at (usually a couple of 100rpms below redline).

My question to the people who have some experience with the LS engines and their opinions on ratios. Richard Oben on the other forum has a some opinions of the street ratios, so I was looking for the same here. I just listed the factory engine/trans for reference.

For the street the gearbox will be a 5 speed with synros and the ratios are TBD so looking for some opinions. For track days, (once I get a little serious on the track, but still not racing), I'll be able to swap the 5 speed for a 6 speed dog box, so looking for the opinions on this one too.

What I am trying to achieve/determine is ratios for a nice driving 5 speed street car and a nice geared 6 speed track day car.

Thanks
Rob

OK, here is just about the most generic answer EVER!

Street: a reasonably wide ratio spread with reasonable rpm drops 1-4, with a 5th gear overdrive of about .7 should be reasonable. Must also consider clutch type in making this driveable and yet still hold torque in 4th gear.

Race: you want a close ratio with rpm drops that keep you from dropping below max torque. So you'll need a dyno chart to see spread from max torque to max hp. Then figure rpm drop from shift point. You want this to be just about even for track use. Now unless your racing type has standing starts you want first to be almost as high as your combo can tolerate without burning up clutch. This will let your stack be closer and still give a good top end as you'll want the minimum overdrive in 6th as necessary as it weakens trans and builds heat. Remember that a short 1st gear is just about useless on most road course work. In race case you want the lightest clutch package that will hold torque as it makes life easier on shifts and helps free up revs. Now balancing this change over with ease and cost for street will be trick. Probably a multi disc at least 7.25 in diameter I would think.

As Fran alluded to, without more data and desires its really hard to help. If you simply answer drag racing or autocross, everything I said just about goes out the window.

Thanks for the info. Yes the plan all along was to dyno the engine for the hp/torque curve to determine optimal shift points and race gear ratios.

In the earlier stage of planning and did not think heavier about the clutch. I will have to compromise a little on the clutch as the clutch and diff will not be removed when swapping between the 5 speed and the 6 speed.

Thanks
Rob

Rob

Changing the gearbox from street to track. Interesting to say the least.

SLC is a sportscar. Almost noone is driving it like a cruiser on the street. An engine with that power and torque don´t need a street gearing ( besides you plan to attack the roush hour daily, but than i would go to an automatic 7 speed doubleclutch).
I drive my GT40 with a close ratio gearing regulary and love it also on regular streets. With the correct clutch setup it is also nice to drive in dense traffic ( still organice friction disc). My revlimit is set to 7200 ( although i could go up to 7800) and i´m using this on regular ( speak every drive ) base. 1st is geared up to 110 km/h. If i shift at 7100 RPM. RPM drops are
1800 1st to 2nd,
1700 2nd to 3rd;
1600 3rd to 4th;
1500 4th to 5th,
5th gear geared to 300 km/h at 7200RPM ( that´s all the overdrive you need)

no need for a 6th gear, but clearly no need to go to a full race box. According to what you wrote you will not fight for the last second and a dog box ( most if the times now sequentiell) will only improve shift times if you know how to handle it.

There are plenty of gear calcualtion tables available. Use one of them ( one on this forum is provided by myself).

TOM

MZ-6. Here's why.

I like the lower 1st for stop and go traffic, padocks, and on and off the trailer. About 2.0 2nds are just about right for the really slow corners (hairpins) on most tracks with that much torque. 1.4 3rds are a good medium speed corner (60-80 mph) gear. 1 to 1 4th would be my choice. And something around .8 for 5th will see about 2800 at 80mph and plus 145 at the rev limmit. The 6th is a good gas mileage freeway gear. All these with the 3.44 is
just about right.

On track you will be 3rd and 4th (50 mph - 140 mph) just about all the time.

Tom, I downloaded one of the ones on this forum about a year ago user name TIMTT and found yours. I have fooled around with some of them on the web too.

An automatic is the only way to go for a daily driver and that is always my comment to the young guys at work who drive stick as a daily driver. Not much rush hour stop and go traffic if I use the toll highway to drive to work.

A sequential box is available but I did not want one and the only reason I mention the dog box is that you can change gear sets in 15-min.

And thank Howard make sense.