[71 T/A]

I have a 72 Formula with 400 stroked to 455 with ported 7k3 heads (264/209 @.600), Stump Puller cam, reworked stock intake per Ruggles, B&M Nitrous 2400 Holeshot 10" converter and 3.42 gears.

How much performance loss on this strictly street car if I swap to 2.73 gears?

[1969GTO]

just hanging out,listing in.

[MescaBug]

Originally Posted by 1969GTO

just hanging out,listing in.

Tag. Same here.

[Navy Horn 16]

I went from 2:41 to 3:42. I wish that I had gone to 3:08. I have plenty of torque to get off the line, but red-line is red-line. I'd sure like to be several hundred RPMs lower on the highway and gain some top end.

[1976T/A]

Originally Posted by 71 T/A

I have a 72 Formula with 400 stroked to 455 with ported 7k3 heads (264/209 @.600), Stump Puller cam, reworked stock intake per Ruggles, B&M Nitrous 2400 Holeshot 10" converter and 3.42 gears.

How much performance loss on this strictly street car if I swap to 2.73 gears?

This might help you get an idea on the impact to HP:

http://www.wallaceracing.com/reargear.htm

[mrrat1]

lots..........

[71 T/A]

This is with 245-60-15 tires that are around 26 inches tall.

[HoneyHush]

Probably a half a second or better in the quarter.

[Tom Vaught]

Would be slower out of the hole for sure (even with a good converter) BUT NOTHING IS AS MUCH FUN AS ROLLING ALONG WITH THE BUSES AND TRUCKS AT 60 MPH WHEN EVERYONE ELSE IS DOING 80MPH. Get my drift?

Tom V.

[pontibeast]

Originally Posted by Tom Vaught

Would be slower out of the hole for sure (even with a good converter) BUT NOTHING IS AS MUCH FUN AS ROLLING ALONG WITH THE BUSES AND TRUCKS AT 60 MPH WHEN EVERYONE ELSE IS DOING 80MPH. Get my drift?

Tom V.

I have to agree with you on that. I currently have 3.55 and with my low profile 17" tires I pull 3000 rpm at 60 and it gets old sometimes. I don't take it anywhere the speed limit is over 60 because I don't want to be "that" guy holding up the flow of traffic. I am most likely going to wait until next year because I'm saving up to build my 428 and I'd rather get that done before worrying about taking it out on the highway and I will probably go down to 3.08 at least depending on the torque of the new motor.

[1967Tempest]

What would a carrier and gear set cost VS an overdrive trans? I really dont know. But Im in favor of keeping the rear and getting OD.

If the rear swap is close to 1500-2500$, I would look at a Gear Vendors OD.

Thats my $0.02

http://gearvendors.com/hrgm3s.html

[Tim Corcoran]

The problem is the cam. Put in a cam with less duration and you will end up with a better street combo and it will pull those tall gears and I doubt you will loose no more than a couple .10's.

[Region Warrior]

Regardless of type of build, the rpm needs to be in the engines power band at cruising speed for overall performance.
Just have to determine what that speed is during most of your driving conditions.
I've had 3.08 to 3.73 in few different combos. Never paid much attention to high rpm.
Have to sets of wheel/tires, and use smaller size for the track or round town. The largest diameter tire that would fit gets used for road trips.

[Blued and Painted]

2.73 at hi rpm's would be great if all roads were straight. But there are curves in many roads.

-Short Story-
Once had a 455 in a lemans with a tall gear. Wife had and emergency on vacation in Savanna Ga and had to see HER doctor. Made it to Atlanta in 2.5 Hours. Normal 4 hour drive. Only car that passed me was a Mar-cey-des-benz.

But that was the only time i really needed the tall gear.

[Grand73Am]

Originally Posted by 1967Tempest

What would a carrier and gear set cost VS an overdrive trans? I really dont know. But Im in favor of keeping the rear and getting OD.

If the rear swap is close to 1500-2500$, I would look at a Gear Vendors OD.

Thats my $0.02

http://gearvendors.com/hrgm3s.html

He doesn't have to do a carrier swap going to 2.73's. He has a 8.5" rearend in his 72 Formula, and 2.73's use a 3 series carrier in the 8.5's. Since he already has a 3 series carrier, it's just a ring gear and pinion swap in this case.

[Goatracer1]

Another problem no one has mentioned is your converter. With 2.73 gears at most speeds under a load your converter is going to be slipping and generating heat. Not good for your engine or trans. I have the same problem when I shift into overdrive but I have a lockup converter to overcome it.

[Half-Inch Stud]

Street/Strip advice

455 into 2.73:1 is a fun combo.

455 into a 3.54:1 is not as fun. See Sig. So I'm fixing the combo by going with 4L80 OD.

I think PMD had it nice with 3.08:1, possibly 2.73:1 if the cam is matched for it.

I propose a Street/Strip goal of 11's on Pump Gas with 3.08:1 or taller. THAT would be Street/Strip.

[ta man]

I went from 3.42 to 3.08 with a 28 tall tire..I lost very little if any qtr mile time.From a 3.42 to a 2.73 with a 26 tall tire and the "Stump Puller" cam it should work well.A 3.08 may be better,also as others have mentioned the convertor will have to stay tight at lower rpms with the different gearing.

[b-man]

That's a pretty decent drop in gearing going from 3.42 to 2.73.

With a well-tuned setup I'd say you might only lose 3 tenths in the 1/4 mile, maybe up to a half second.

You'll gain highway driving pleasure big-time, which is why I assume you're thinking about swapping to the taller gears.

[Navy Horn 16]

Changing gears is $500 or less. An OD transmission that is worth a crap, $2000 installed, minimum.