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#1
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How Much Performance Loss: 3.42 to 2.73 Gears?
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? |
#2
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just hanging out,listing in.
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color me gone |
#3
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#4
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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.
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#5
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Quote:
http://www.wallaceracing.com/reargear.htm |
#6
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lots..........
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#7
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This is with 245-60-15 tires that are around 26 inches tall.
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#8
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Probably a half a second or better in the quarter.
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#9
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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.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#10
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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.
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#11
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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
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1967 Pontiac Tempest 2dr HRDTP Coupe 468 C.I. 500 HP 5 speed = FUN!!! 1990 Chevy Suburban R2500 Daily Driver 1986 Volvo DL245 Wagon.. Project car!!! The Burb Files |
#12
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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.
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Tim Corcoran |
#13
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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.
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If you cant drive from gas pump to gas pump across the map, its not a street car. http://s207.photobucket.com/albums/b...hop/?start=100 Last edited by Region Warrior; 09-24-2015 at 06:29 PM. |
#14
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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.
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Bull Nose Formula-461, 6x-4, Q-jet, HEI, TH400, 8.5 3.08, superslowjunk Last edited by Blued and Painted; 09-24-2015 at 07:20 PM. |
#15
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Quote:
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Steve F. |
#16
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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.
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#17
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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.
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12.24/111.6MPH/1.76 60'/28"/3.54:1/SP-TH400/469 R96A/236-244-112LC/1050&TorkerI//3850Lbs//15MPG/89oct Sold 2003: 12.00/112MPH/1.61 60'/26"x3.31:1/10"/469 #48/245-255-110LSA/Q-Jet-Torker/3650Lbs//18MPG 94oct Sold 1994: 11.00/123MPH/1.50 60'/29.5"x4.10:1/10"/469 #48/245-255-110LSA/Dual600s-Wenzler/3250Lbs//94oct |
#18
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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.
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#19
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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.
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1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
#20
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Changing gears is $500 or less. An OD transmission that is worth a crap, $2000 installed, minimum.
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