Gear ratio suggestions

[boyd36]

Hello , my very first post ever on any type of forum . 65 New Yorker 2 door . Pulled original 413 and built a 440 based stroker , took a long time to build as I did in steps as I could afford . Just got motor in for a dyno run , 640 lb ft at 3900 rpm 560 hp at 5200 . My question is for anyone that has a big torque engine , what gear ratio do you run ? I will be changing out the open 2:72 for a locker but would like to get the ratio rite , thinking 3:23 or 3:55, this is not a race car , just a fun cruiser . Just wondering besides my cruise rpm is there a better or worse ratio for a bigger torque engine like this , any opinions will be appreciated .

 

[twostick]

I vote for the 3.23 depending on what idle speed the cam requires to be happy.

Kevin

 

[Polara_500]

That sounds like a monster engine. If you'll spend any time on highways at 70+ I'd go with 3.23, if pure in town with short highway trips 3.55's would be a lot more fun.

 

[polara71]

323 unless you're doing an overdrive then 355s

 

[67Monaco]

Depends. How high is the stall on your convertor? You're going to want your cruise rpm above your stall speed. Or you're going to want to add extra cooling for the added heat from slippage.

 

[boyd36]

I have the breakaway tci torque that says 1100 rpm over stock , with that amount of torque I am guessing should stall around 2500 to 2800 rpm . Thanks for confirmation on the ratios I was thinking . I guess my other question is how big of a tire can I run on my car , has anyone tried to get as big as they could safely fit in there car .

 

[boyd36]

I won’t know my true idle speed until I get motor in car , dyno guy had idle set at 1200 to prevent stalling when pulling back off of pull . But on first start up it sounded very smooth with the carb pre set out of the box . I am probably jumping way ahead on the ratio install , a lot of work to do yet with electrical and motor install , just wanted to start talking with other c body people for advice on things .

 

[polara71]

Why This ?


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[FURYGT]

I put a 520" stroker in one of my '68 Sport Furys that is used as a street and drag car. I have 3.73 gears and I think that they are the perfect compromise for me as I don't plan on driving the car anyplace that is more than an hour away. At 60 MPH my recall is that I am turning almost 3,000 RPM's. If I were to use the car just for the street I would probably go with 3.55 gears if I did not plan on any long distance driving and would go with 3.23 gears if I was going to drive long distances, assuming that you are not putting in an overdrive unit. BTW, my engine idles very smooth at 600 RPM's but I don't have a radical cam in it as the engine and the car were built to drag race in a stock appearing, stock tire racing class and the rules don't allow you to have a very "lumpy" idle.

 

[polara71]

Once upon a time I had those 373s in a 69 Sport Fury. It was my daily driver . I loved them as they pulled the Hell out of the car but at 4 miles to the gallon . 11 to 1 compression, 292 duration on the cam with a 510 lift, it pulled and pulled and pulled .

 

[CBODY67]

You are probably correct in waiting until the engine is in the car to do the idle speed tuning. With a 3.23 and a tire diameter similar to the stock 8.55x14 size, that would probably be about 24.5mph/1000rpm in high gear. 3000rpm cruise would be about 75mph, so that would probably be in the meat of the torque curve of your motor, when cylinder pressure is good for decent fuel economy and response.

In the '78 Chyrsler service manual, it lists the stall speeds for the stock 400s and 440s used that year. Many of the HO motors spec'd 25-2800rpm stall speeds.

"Stall speed" is measured at WOT with the brakes locked. You CAN d. rive a looser torque converter with a lower-number axle ratio and everything "lives" just fine. BUT you have to use a steady throttle foot. Not only will an unsteady throttle foot (varying engine rpms at cruise) result in engine rpm changes with little vehicle speed change, but that also eats into the cruise fuel economy. It can build a little more heat, too, but the big contributor to trans fluid heat is deceleration, not acceleration. In "decel", the fluid runs into itself and that builds heat in the converter.

A 3.55 gear will make the car feel more responsive, but will have higher cruise rpms and such.

You probably WILL need some rear suspension upgrades to get the power to the ground effectively! "More spring" and possibly some type of traction bar?

Just some thoughts,
CBODY67

 

[twostick]

My 493 idled at 1100 and made torque right off idle. So much so that if the 1100 idle didn't pound the driveline so hard when you went from P to R or D, I would have left the stock converter in it.

I put in a 2800 Turbo Action converter in it and that solved the harsh engagement but the 248@.050 cam didn't care for the cruise RPM with the 2.76 gear and neither did the converter. It was good enough for a very traction limited 13.92 @ 101 tho.

3.23's made everything happy again. Never did get it to the track again.

Kevin

 

[boyd36]

Thanks so much for responses to everyone , some great info in there to chew on . Yes will defiantly need some new springs and a taller snubber , was hoping not to use traction bars , but if needed I guess gotta use . The lowest rpm on dyno pull was 2650 and is making 540 torque , I know now that I went a little to crazy on this build and may regret a bit for driveabillity , should have went with a .230 or .236 duration cam . Went with a .248 hyd. Roller on 114 Lsa , regrets or not can’t wait to put it down for first time , thanks all .

 

[Turboomni]

Just got motor in for a dyno run , 640 lb ft at 3900 rpm 560 hp at 5200 . My question is for anyone that has a big torque engine , what gear ratio do you run ?

So interesting to me. If he ran 3.23 ratio with 640 of torque at 3900 rpms would it just blow away the tires with little feel when they break loose as compared to say a 3.73 or what ever. In other words less predictable to the driver's feel on the go pedal?

 

[boyd36]

Thanks turbo , that’s kinda what I was thinking about , hoping to learn from others expierence in this matter , I think it will be hard to drive at times and any advantage will be beneficial for me , I have never had a car with this amount of power and want to have it drive with as good of street manners possible considering .

 

[twostick]

That 114 LSA will help a lot with the low rpm manners especially if you are planning on EFI.

Mine is 248 on 108 LSA. The EFI was not happy with all that overlap below 2000 RPM.

Kevin

 

[300rag]

BTW, where in Alberta are you, and who did your 440?

 

[boyd36]

I am in cold lake , all machining and balancing was done by fast engines in Edmonton, I assembled engine . Is a 69 gtx engine , 10.8 comp ..65 over diamond pistons with a 13 cc dish ,4.25 scat crank and 6.8 rods , ed rpm heads and intake and carb 750 . Crane roller , comp rockers . I like the smaller size carbs for response but will probably switch up to a 850 mighty demon ? I am getting the dual afr gauge set up and will see how well I can get this 750 to work first though .if by some reason I came into extra money I would go with efi , the 114 lsa works well efi .

 

[Turboomni]

Sounds like a very stout setup. I really like the idea of 2 wide band sensors one for each bank. You will never be trying to see in the dark what the ratio is and keep the engine in the safe zone..