|
Backdraft build - Diff question
Hi guys
My backdraft cobra build is underway and playing around with some diff ratios. Any advise out there?? Specs: Engine = Roush 427R Engine rated = 550hp, but dyna shows 500hp @ 6000rpm Gearbox = Tremec TKO600 Gear Ratio: 1st = 2.87; 2nd = 1.89; 3rd = 1.28; 4th = 1; 5th = 0.64 Tyres = 315x18x35 I am going for the progressive slip diff (just to avoid some of that 360deg recoveries). Have been looking at the 3.9 / 4.11 ratio but not sure what will kill me first: the noise or the power. |
Henkdt,
I would talk to Jay or Brian at Vintage but I am running the Coyote with a TKO 600 and 3.91 ratio. I am pretty sure my previous BDR which had a 427R and TKO 600 was running a 3.63 ratio. |
thanks - how did she perform? power and fuel wise.
|
It was a great combo. Loads of power and acceleration. Mpg was around 12 which was about what I expected.
I am no expert but I would have thought that the 427R with a 3.9 or a 4.1 diff maybe too much, particularly with all the torque that engine kicks out. The coyote is a lower torque, higher revving unit and the 3.9 suits it perfectly. Andig |
I was just working on a friends Shelby aluminum block 427 this morning for his Kirkham and we had this same conversation. With the .64 OD I would go with 3.50, but with the .82 OD 3.43. With the 3.9/4.11 gears first gear will be useless and and you are just going to spin the tires way to easy. So I vote for the 3.50s.
|
Plugging values into this tool and then building a spreadsheet (optional) will provide insights.
Second Strike Gearing Calculator How you intend to use the car makes all the difference. |
With the 427 I would do the 3.46 unless you just like spinning tires in 1-3, and in that case, go with the 4.11.
If I had the Coyote I'd do the 3.91 or 4.11. I have the 3.15 rear and spin too much in 1 and 2 during normal driving with an engine similar to the Roush 427R, but when the tires are heated up I start thinking that the 3.46 would be nice. |
My BDR has the same TKO-600. My rear came from BDR as a 3:46 open diff. I switched it out to a 3:73 with 40% lock up. It is way better.
Because the 1st gear is tall at 2.87, you can run alot more gear in the rear without winding 1st gear out at a low mph. I find the real problem is the .64 OD. The jump from 4th to 5th is just way to great. I really wish I had the .82 OD. I never noticed a difference in gas milage between the 3:46 and 3:73. |
Gentlemen - this has been awsome feedback. And you have confirmed my worries.
Chilibit - great calculator. The 3.4 to 3.7 range seem to be the sweetspot. Now I can worry about the colour - CHEERS!! |
Why do u want the .64 over the .82? U will eventually want a LSD diff. ;)
Since u are going with a big V8. I would humbly suggest U go with a 3.46 and .82 OD (75MPH around 2750RPM). if U want a little more performance go with the 3.64 and stay with the .82 OD. (70MPH around 2750RPM). |
3.46 is what I have. Unless you have drag radials, the lower gears are useless.
|
I have drag radials and the 3:46 and it is still useless...I cant imagine a shorter rear end in the car provided we are talking 500hp plus. I was discussing a shorter gear with Brent due to the new engine we are building to help with "lugging" but ill just stay in 2nd through the neighborhood:D
|
Sorry "useless" referring to RPatton3's post about the lower gears...
|
I'm with those guys, 3.46 here, running street legal road race slicks and the lower gears of my TKO600RR are useless at anything above half throttle.
|
Just my point of view:
I have a 508 hp 408 stroker in a coupe with a TKO 600 with .82 5th gear and I have a 3.50 : 1 detroit locker. I will be replacing my gears with 3.73 : 1 for a little better overall performance. The current setup will spin the tires quiet well but coming out of a corner the increase in torque will help in the overall performance. I took the coupe to the track and found although the 3.50 gears work well a better combo would be going with 3:73 package. Granted, the 3:50 gears will yield better gas mileage but the 3:73 gears will improve track times. You can still cruise the freeways in 5th gear under 3000 RPM at 70+ mph. My redline is above 7000 RPM if I ever need those RPM's. |
Quote:
|
| All times are GMT -7. The time now is 01:04 PM. |
Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2026, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
The representations expressed are the representations and opinions of the clubcobra.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Shelby American, any other replica manufacturer, Ford Motor Company. This website has been planned and developed by clubcobra.com and its forum members and should not be construed as being endorsed by Ford Motor Company, or Shelby American or any other manufacturer unless expressly noted by that entity. "Cobra" and the Cobra logo are registered trademarks for Ford Motor Co., Inc. clubcobra.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting clubcobra.com. For full policy documentation refer to the following link: