Tremec TKX Gear Ratio

[mbisett]

I am not a gear head and need some advice on the new Tremec TKX transmission gear ratio's.

There are 5 different gear configurations on the TKX. I am purchasing a Blue Print Ford 302 (300hp) and TKX transmission package.

The gear configuration's I am considering are the TCET18084 - 1st gear 2.87; 2nd 1.89; 3rd 1.28; 4th 1.00; 5th 0.81 or the TCET177765 that has all the same gear ratios except 5th @ 0.68.

I plan to run a 3.55 rear end so my (dumb) question is which 5th gear ratio would provide me the best (lowest) cruising rpm's at 80 mph?

[Jeff Kleiner]

My (dumb) question is which 5th gear ratio would provide me the best (lowest) cruising rpm's at 80 mph?

.68

Jeff

[GoDadGo]

I am not a gear head and need some advice on the new Tremec TKX transmission gear ratio's.

My (dumb) question is which 5th gear ratio would provide me the best (lowest) cruising rpm's at 80 mph?

Most folks run a 315/35-17 a or 275/40-17 rear tire with 3.55 R/E gears and both tires are 25.7" tall.

At 2,500 RPM with 3.55 R/E Gears with a 25.7" tall tire and the .68 OD will equate to 79.2 MPH.
At 2,500 RPM with 3.55 R/E Gears with a 25.7" tall tire and the .81 OD will equate to 66.5 MPH.

Just understand that there will be a big drop in RPMs between 4th and 5th if you go with the .68 OD.

[Jim1855]

The .68 fifth is a cruising gear. Lower RPM, generally less fuel. Great for 80 mph.

Don't worry about the RPM drop, you'll have all of your fun in the first 4 gears.

If GoDadGo would be so kind as to show the two OD RPMs at 80mph it would help to understand the differences and potential benefits.

BTW, I had 3.27s with the .64 OD. 80 mph was about 2,200. This build will use 3.31 gears with the same engine/trans/tire combo.

Jim

[Jeff Kleiner]

Assuming 3.55 rear end ratio and typical 315/35-17 rear tire:

80 MPH in 1:1 fourth gear=3,720 RPM
80 MPH in .81:1 fifth gear=3,020 RPM
80 MPH in .68:1 fifth gear=2,530 RPM

Jeff

[mbisett]

Thanks Jeff, that is what I thought.

[hineas]

I went through this with my build and ended up with the 0.64 on the TKO-600. Not much different than the 0.68. My reasoning was to have a good cruising gear at 80 mph since that is the speed limit in my area. I spoke to many who have it and they said it made cruising more pleasant. I am still building so I don't have any real world experience, though.

Here are their responses to my queries on the subject. https://thefactoryfiveforum.com/showthread.php?37665-Mk4-Complete-Kit-Purchased-yesterday!&p=431935&viewfull=1#post431935

[toadster]

came here for this exact info/question - looks like the TKX only has the .68 where the TKO-600 had .64 - not a huge difference - but major difference from the .81(X) or .82(600)

[Kmcallahan]

I am not a gear head and need some advice on the new Tremec TKX transmission gear ratio's.

There are 5 different gear configurations on the TKX. I am purchasing a Blue Print Ford 302 (300hp) and TKX transmission package.

The gear configuration's I am considering are the TCET18084 - 1st gear 2.87; 2nd 1.89; 3rd 1.28; 4th 1.00; 5th 0.81 or the TCET177765 that has all the same gear ratios except 5th @ 0.68.

I plan to run a 3.55 rear end so my (dumb) question is which 5th gear ratio would provide me the best (lowest) cruising rpm's at 80 mph?

I am waiting for my drive train now. I went with the TCET17765 for the overdrive gear ratio. I used theatre mechanism gear ratio calculator also to help me decide tire size along with imput from the forum.