What rear gear?

[wireweld]

So there has been some talk about these heads. These are the First ones I have used. The reason was to get as much air flow and port volume for what we wanted to do. The goal was to make as much power as early as possible. I think we got what we wanted, but without a back to back test its hard to tell if these heads were worth it or not.

Anyhow, here is the combo
360 stroked and poked to 416
Flat top pistons 10.8 to 1
BM heads
MRL/BAM offset roller lifters
RPM dual plane intake
FiTech EFI
MRL solid roller cam 281/285 duration(seat to seat) .620 lift
Milodon gear drive
Well, you get the idea. Torque is what we wanted. Did we get some? Ummm........... Yeah we did.

525tq at 3100rpm, yes 3100rpm. Damn. Peaked with 582tq at 4350rpm. Still making 550tq at 5500rpm.
It also made 584HP at 5800rpm. Fuel pressure was dropping as I had the pump hooked up wrong, didnt figure it out until later. Might make closer to 600hp with the right fuel pressure.

All this on pump gas, and a nice idle. It pulled 14in vacuum at 950rpm idle. 1.40 hp per ci, not to bad for a Pump gas street engine.

View attachment 1715028325

View attachment 1715028326

View attachment 1715028358

View attachment 1715028359

What rear gear would you use for a street performance car with an 8 3/4, 200r4, and 29 inch tires? I have 4.10, 3.55 and 3.91. 72 Dart.

 

[273]

How deep is 1st gear ?

If it's got something like 2.50:1 than 4.10
But if to deep probably 3.55 or 3.91

 

[wireweld]

How deep is 1st gear ?

If it's got something like 2.50:1 than 4.10
But if to deep probably 3.55 or 3.91

2.74

 

[69_340_GTS]

With that size tire the 3.91 ought to be about right.

 

[AJ/FormS]

4.10s

The ratios are 2.74-1.57-1.00-.67od

65mph will be 2070 with zero-slip, that's pretty low for a performance engine.
The starter gear will be 11.23 which is equivalent to 9.30 corrected to a 24" tire. I run a corrected 9.75 and it's perfect.
Kicking down into first at 32mph will be 4400@5% slip, and that is a rocket
Hitting 60 at the top of second will be 4700, a little low but 5.38s were not on the option list.
106mph will be 5300. This for 350 hp. A little low but 4.56s were not on the list
111mph will be 5550. This for 400 hp. A little low but 4.30s were not on the list
116mph will be 5800. This for 450 hp, just about perfect for a streeter and 4.10s
Second gear is good to about 81mph,a little low, but 4.56s were not on the list.

EDIT
I missed that you were pushing 600 hp
assuming;72Dart@3600 raceweight, street suspension, 5% TC slip.
With 600hp, your qtr is looking like 3600/600= 6.0WP, and that's looking like 128 mph
4.10 is the gear to start with; 124 will be close to 6200, and 128 will be about 6400.The 3.91s would bring those rpms down to 96.36% or approximately to 128=6100
If your raceweight is less than 3600, you'll go faster.
At 3400 the WP is 3400/600=5.67 and that is closer to 131mph. Now the 3.91s will get you about 131@6250
But 3.91s are a crummy gear for the street cuz you can't get 60 mph with them at the top of first but will have to shift at about 47 mph. Oh never mind, you have somewhere way over 550 ftlbs, it will be spinning all the way anyhow.
Cruizing with 3.91s will get you 65@1974 or so in overdrive,which with that cam is probably a little low; the intake will be full of a crap mixture, and the mpgs will probably suck. 75 will be better@ about 2280,and 85 just right at 2580
So I'm changing my vote to 3.91s,lol
And on the street,she'll probably be a lil more controllable with a spread bore, small-primary carb.
Ok with EFI, throttle body injection, you'll probably be running a single-plane. So rev it up in neutral, until the vacuum peaks, then slowly drop it down until the vacuum begins to fall again;then check your tach. That is your target minimum cruise rpm for best fuel economy, where reversion in the intake is at the smallest amount. With port sequential EFI, you could run less with properly timed injection.
With my combo (230*.050) this is 2200, and so I'm geared for 65=2240

 

[RustyRatRod]

4.10 all the way.

 

[wireweld]

4.10s

The ratios are 2.74-1.57-1.00-.67od

65mph will be 2070 with zero-slip, that's pretty low for a performance engine.
The starter gear will be 11.23 which is equivalent to 9.30 corrected to a 24" tire. I run a corrected 9.75 and it's perfect.
Kicking down into first at 32mph will be 4400@5% slip, and that is a rocket
Hitting 60 at the top of second will be 4700, a little low but 5.38s were not on the option list.
106mph will be 5300. This for 350 hp. A little low but 4.56s were not on the list
111mph will be 5550. This for 400 hp. A little low but 4.30s were not on the list
116mph will be 5800. This for 450 hp, just about perfect for a streeter
Second gear is good to about 81mph,a little low, but 4.56s were not on the list.
72Dart@3600 raceweight, street suspension, 5% TC slip.

I looked and found a set of 4.56. I'm not against buying a gear set if that is what I need to do.

 

[273]

If your gonna race at the track and want every last drop. Probably take some trial and error. Since you own these gears you can play around.

If it's just street fun and want stop light to stop light action. Basically the 1st and some of second gear you can go deep as you want.

Either way I'd start with the 4.10 and go from there. Probably all that you need.

 

[AJ/FormS]

Post 5 edited

 

[71DodgeDemon340]

If it was a 4 speed id say a 3:55 or 3:73 but with the automatic id consider at highest gear a 3:73 but deff would lean towards the 4:10. Then again the 3:55 would be fine too

 

[wireweld]

I forgot to say I'm using the Fitech Efi.

 

[AJ/FormS]

k then 3.91s hands down the winner

Post5 edited

 

[wireweld]

k then 3.91s hands down the winner

Post5 edited

Thank you for your input. I will give the 3.91's a spin.