Q:What's your Tyre size + gearinfo + Engine power?

[Piglet]

Hi!
I'm about to order a gearbox for my Cobra project. But since I have a 2.7:1 rear gear ratio, I'm curious about what gearbox I should go with (the engine I'm puting in is a CSB LT1 with ~280hp for starters, aiming at 380-420hp when my economy allows it). I'm choosing between the Tremec boxes (TKO500,600,600RR). Now, I've made an Excel sheet that lets me calculate the speed with different gears + tyre sizes, so I'd like to put in your's to see what your ride looks like, and compare it with my engine setup to see what gearbox I should go with (yeah you get the picture)... Also, if you could add some thoughts on how your car performs on different gears thats highly apprechiated aswell (e.g : "1st is far to short, I have to change gears far to soon" or "5th is only usable at high speeds, over 70mph, I have to shift down to 4th for something to happend when I push the accelerator")...

Kind regards, Hans B

[nbracken]

Hans, there is a spread sheet already on the site that does waht you are seeking to do re gear ratios etc.
Re your questions, I have a CSB ZZ4 (355 US hp) with 2.88 diff and Tremec TR3550 combination. It gives good combination of performance and economy. I get great accelleration and can lope along all day on teh autobahn at 80 mph with 2000 rpm in 5th. However if I were to ever get the opportunity I would change the diff to a 3.07 or maybe 3.31 if I could get one with Powerlock. INHO I think 3.54 would be too short.

HTH

[MetaJacko]

Hi,

2.7 is unusual. I would think you would end up with 1st being way too tall if
you put a TKO500,600 on it although it may work better with a TR3550 since first is
a lot lower on that as far as I know. Ether way, 5th wouldn't be much use with that size diff.
I don't think I would want to use a 2.7 on my FE and I have quite a lot of tourque!
Are you stuck with the 2.7? What axle is that in fact?

Paul

[Piglet]

Hi Paul!

Yeah, I guess the 2.7:1 is abit unusual (and low) but I'm kind of stuck with it (unless I pay some money to get a gearshift done). It's a Dana 36 (Corvette C4) rear thats going into my cobra... Btw, I thought the TR3550 and the TKO500 had the same ratio in the gears (3.27 1.98 1.34 1.0 0.6, while the TKO600 has a 2.87 on first and the TKO600RR also has a 0.84 in fifth gear (at least acording to : http://www.5speedtransmission.com/tr-3550.html + http://www.5speedtransmission.com/3550_tko.html)... Here's a rundown of rpm vs speed with my 2.7:1 reargear, the different boxes and with 255/45-16" wheels (each column is speed at the given RPM on gear 1,2,3,4,5) =>

TKO500
RPM
1000 008 014 020 027 040
1500 013 021 031 041 061
2000 017 028 041 055 081
2500 021 035 051 069 101
3000 025 042 061 082 121
3500 029 048 072 096 141
4000 034 055 082 110 161
4500 038 062 092 123 182
5000 042 069 102 137 202
5500 046 076 113 151 222
6000 050 083 123 165 242

TKO600
RPM
1000 010 015 021 027 043
1500 014 022 032 041 064
2000 019 029 043 055 086
2500 024 036 054 069 107
3000 029 044 064 082 129
3500 033 051 075 096 150
4000 038 058 086 110 171
4500 043 065 096 123 193
5000 048 073 107 137 214
5500 053 080 118 151 236
6000 057 087 129 165 257


TKO600RR
RPM
1000 010 015 021 027 033
1500 014 022 032 041 050
2000 019 029 043 055 067
2500 024 036 054 069 084
3000 029 044 064 082 100
3500 033 051 075 096 117
4000 038 058 086 110 134
4500 043 065 096 123 151
5000 048 073 107 137 167
5500 053 080 118 151 184
6000 057 087 129 165 201

Sorry it's kinda big, but I wanted to show you what it would look like...
Regards, Hans B

[MetaJacko]

Hi,

I was sure the only differece between a 500 and 600 is the HP they are supposed to handle
(or maybe tourque) IE 500 and 600 respectively.

Anyway, with my setup, CR toploader 3.31 and 275/60R15 my specs at 1000rpm are:
1st 11
2nd 15
3rd 20
4th 25

1st is quite high on a CR toploader (2.32)
Remember that my FE has a lot of low tourque!

What tyre size are you using?

Paul

[MetaJacko]

Hi again,

I just looked at TCC and you right about the ratios. I guess your tyres are about 255/40R17?
I would have thought for your engine the 500 would work OK at that.
If you can get a TKOII then you would have a 0.82 5th and that would be more useable.

Paul

[Piglet]

Hi Paul!
Thanks alot for your input!

I have not decided on tyres yet, but I expect it to be 16" (with 17" the rims look to large, but I've noticed thats its a huge problem to find 15" wheels, and I'll guess that soon it'll be the same with 16").

You've hit the nail on what I'm worried about. It's to end up with a sluggish 5th gear. Now the TKO600 has a 0.82 5th gear, that gives me something like 67mph at 2000rpm. Thats very close to our upper speedlimit on the highways in Sweden (69mph). The question is:
will 2000rpm use much more fuel than 1600rpm? running at 70mph? I mean if Nigel is able to run 80mp at 2000rpm...
The more I look at it I think I should get the TKO600, for it's longer 1st gear (10mph =>50mph), and simply use the 5th gear as a highway gear (keep the fuel consumption down).

Do you guys think thats plain stupid? And that the car will be dead in the water because of that long 1st gear?

[mylesdw]

The car is comparatively light, so the long first gear should be no problem unless you are keen to go drag racing. Looks to me like the TKO600RR is just about your only choice with that rear ratio. For the rest the 5th gear will be almost useless. Remember if you are intending to change cams etc in the future the power band will tend to move up the rev range so the point at which it will run well in 5th would be even further above the speed limit.

[Piglet]

Myles, your right. My goal is to do some headwork + camswap and that it will move the powerband up the rpm range (the machine shop claims that it will "pull" from 2000rpm)... I guess I can live with 2000rpm'ish going at 70mp , it's mainly for cruising, and ocasional redlight driving, and some plain crazy acceleration driving... (no track use intentions).

I estimate the car weight to be around 1100-1200kg (~2500lbs)...

[MetaJacko]

Hi Piglet,

Is the TKOII not available?
If you want 'plain crazy acceleration driving..' the 600 first may still be a bit high with your
dif for your engine. the TKOII has a low first like the 500 but also has a lower 5th like the
600RR (TKOII ratios 3.27,1.98,1.34,1.00,0.82) and it can handle 475lb tourque which should be fine for what you are looking for. I'm sure some people here are using TKOIIs

'"pull" from 2000rpm' is about right for a typical fast street cam,
mine works from 2000 to 6000 so while I'm running I would want to stay in that range.
Not such a problem for me since I don't have a 5th. In fact my crusing rpm is 3000 at 76mph

Paul