C2- 340hp

[Michael S.]

I recently purchased a '63 SWC with a 340hp close ratio T-10 and 3.08 rear. The car bogs coming away from a stop unless I slip the clutch excessively or try to punch the throttle thru it. Car has had a tune up by a Vette specialist who said the problem is a bad combo of the tranny and rear. A few others I have spoken with agree that this is a common problem. I live in a rural and hilly area and the car will see limited highway driving. It has been suggested a switch to a 3.55 or 3.70 rear will cure the problem. Do any of the experts on the board agree ? If so, which rear ? I am concerned that a 3.70 may leave me looking for a higher gear to drop the revs while cruising around.

Thanks

[Norris W.]

Re: C2- 340hp

Mike, let me take a shot at beatin' around the bush on your question by using several different cars. First, my '63 340 horse car has a 3.36, but I've never driven it. I've got a '69 Camaro with an LS7 (the 454 one) with a 3.73 that I drive around to cruises. One of my '67 435's has a 3.55/M21, and finally, my '69 L88 which came from the factory M22/4.11 was coverted to 3.08 by the original owner who fancied himself a top end street racer. (although nobody around here remembers ever seeing any such contest involving the car) I left it in when the car was done in the '80's

The L88 is hard to get going without slipping the clutch as you mentioned. The LS7 Camaro is a joy to run around town to the local cruises with, but I feel like I'm screamin' it at highway speeds and usually trailer it to anything that's more than 25 or 30 miles from home. All around I like the 3.55 in the '67 better than the others, but think the 3.36 would be an excellent choice also.

Two of my cars have 4.56's............ I guess there ain't any sense in talkin' about them.

[Duke W.]

Re: C2- 340hp

My SWC is the same combination that I special ordered. It's not for the faint of heart, and my car spent the first five years of its life in Seattle, which is known for its hills.

It's not drag racer, but I never got beat by anything on a freeway as long as I had open road in front of me.

The OE '63 340 HP engine has a poor spark advance map setup. First, the 15" vacuum advance control (201-15) is not well suited to the idle vacuum of the Duntov cam. Replace it with a 8" NAPA VC1810 or equivalent, and search the archives if you want to understand the full story.

Second, the OE centrifugal curve is "lazy". Lighter springs to bring the centrifugal in as quickly as possible - to the limit of detonation - will improve low end torque significantly. The combination of the two above changes will considerably improve low end tractibility.

Of course, since you just bought the car you need to collect all the service and assembly documentation and map out the spark advance since you likely have no idea what's been done to the car over the last 44 years. This should be your first task before you lay a hand on the car.

Beyond this it's a matter of style. Once you have made the spark advance map changes, set the idle speed at about 900. On a level road, launch by just letting out the clutch a little to get the car moving, but don't use throttle. Then give the throttle a little blip and let out the clutch. It's kind of like launching a race car, and you have to accept a little bog if you want to avoid excessive clutch slippage.

Try to avoid stopping on steep hills if at all possible.

The 3.08 axle yields relaxed highway cruising, 150+ MPH top speed and 20+ MPG on highway cruises.

The 3.70 axle was standard, and there was a good reason. The 3.08 axle is not for everyone, but I still like it.

Duke

[Joe L.]

Re: C2- 340hp

Mike-----

I think your drivetrain combination is exactly the cause of the problem you describe. I've often wondered why Chevrolet ever offered the 3.08:1 rear gear with a SHP small block engine with close ratio 4 speed. However, they only did it for 4 model years. It might be fine for certain racing applications, but it's a VERY poor choice for street operation. I would say that a 3.55:1 would be about the lowest numerical ratio I'd use for the application if you want good streetability.

[Clem Z.]

Re: C2- 340hp

easier change is a wide ratio 4 speed would give you about the same 1st gear overall as the 3.55 with the close ratio and you would still have your 3.08 highway gear

[Tom S.]

Re: C2- 340hp

If it were me I would go with the 3.55 in a hilly area and not to much highway driving. I changed the 4.11 out in my 69 and put in 3.36 and it was great on the road, and a little high from a stop. But I also had the M-21 transmission which is high in 1st gear.I bought a good unit for $300.00 core and all and saved the 4.11. Good luck Tom

[Joel T.]

Re: C2- 340hp

Mike,

I have basically the same setup as yours except for the rear which is a 3.70. Even with that set up, I still need to slip the clutch a bit, probably due to the factors which some of the guys mentioned. I'm running an aftermarket solid cam with about 500 miles on a total powertrain rebuild.

I will say that as far as drive-ability goes, the combo as installed is fun. With the lower rear, I manage to spend most of my time in 4th and still have nice acceleration. As far as gas mileage and top end speed go, I really do not care all that much.. this is a Sunday afternoon car. I will say however that I have been impressed with the highway performance as well. This thing will pass and climb hills with most anything on the road. I've had the car up to about 90 on the interstate, which is fast enough for me, and she had plenty to go. It is kinda neat to see the looks you get when this red antique blows by folks on the road!

While it may be a more costly road, if it were my nickel, I would re-do the rear. Depending upon the condition of the drivetrain, you might justify the change as part of a rebuild... I think you will be well satisfied with the result.

Good luck,

Joel

[Peter M.]

Re: C2- 340hp

Mike,

71 LT-1,M21,411 factory ratio - pretty good around town or winding roads up to around 50-55. Highway driving a drag but you say limited so depends on whether you can live with the infrequent highway bouts. You also don't mention whether you just want a more liveable getaway from a stop only or whether you also like to lay your foot into it from time to time. If the latter, suspect a 4:11 will please you more than 3:55 or 3:70 though the experts on here know best. And, of course, you would have the hwy issue. So, when all said and done, middle ground already suggested is probably best. But me, if I didn't mind changing factory ratio and you clearly indicate you are willing to do, would go with the 456's to really get up and go, live with the hwy drag since hardly ever done, and enjoy the newfound feel of power by 'exercising' that 340hp! As Duke pointed out though, your top end would be gone, but again, you don't hit the hwy so... Of course, Clem's idea works just as well for middle ground too.

[Joe C.]

Re: C2- 340hp

Mike,

I agree that the W/R gearbox will be your best bet. Are you obsessed with originality? If not, then the ultimate solution would be the TKO-500 from Tremec.

Joe




http://www.5speedtransmissions.com/5sp_comparison.

[Verle R.]

Re: C2- 340hp

I agree with Clem, switch to a wide ratio 4 speed. I have that combination, 3.08 with wide ratio. You can live with first gear start up and you have a good highway gear. Make the changes Duke suggests for the distributor and things will improve with the current combination.

Verle

[Jack H.]

Chiming in...

We had a customer with a '65, 365 HP SB, A/C, 3.08 rear end and close ratio tranny. He too complained of '*******' out off the line and looked for a 'fix'. After looking at the alternatives and costing them, he bought a second Muncie with wide vs. close ratio first gear and kept the original in his garage for 'posterity'.

That provided the benefits of making the initial rolling start less aggressive on the power train AND maintained his highway crusing fuel economy vs. changing out the rear end. But, the 'drawback' to this approach is once you're out of 1st gear, revs won't climb any faster than they do with your current close ratio gear box...

However, after the tranny 'transplant', the owner was pleased as punch with the car's overall performance profile. He wasn't trying to build a drag strip competition winner, just make a nice weekend warrior ride....

[Jim T.]

Re: C2- 340hp

My 68 327/350 M21/3:08 requires just a little clutch slipping at the first stop sign leaving my driveway because of the incline. Years ago considered purchasing a used M20 to save on clutch wear. After the clutch was replaced in 73 (pressure place side of clutch disk really worn) the wife quit using the 68 as her main driving car. So did not pursue getting a M20, I continued to use the technique Duke mentioned to get the 68 going and still have the first replaced clutch in the car. My 64 327/300 air conditioned convertible had the wide ratio tranmission and a 3:08. No problems on take offs even with the air on. It would really wind out in fist gear. With Duke's recommendations on tuning your 327/340 hope you find it easier to take off. I don't know if your tune up by a Vette specialist included inspection and cleaning of the centrifical advance, but you can do it easily. Remove the rotor and completely remove the springs and weights and clean the pivit points and mounting holes in the weights. I use just a very little of lubrication on mine at the mounting pivits and on the underside where the weights slide. Use lubricant that was purchased for rubbing block on points. It is a Blue Streak product in a tube, don't know if it available now, mine was purchased in 1969.

[Duke W.]

Re: Chiming in...

The 30-30 cam is going to be a lot worse than the Duntov with tall gearing because the 30-30 has marketly less low end torque due to the greater overlap and later closing inlet valve. The Duntov actually makes pretty decent low end torque on a 327, especially with an aggressive spark advance map.

A good wide ratio transmission would be the current Richmond Super T-10 wide ratio - 2.64, 1.75, 1.34, 1.00:1. This gearing set up puts the big gap between first and second rather than third and fourth as on the vintage T-10s and Muncies, so the engine won't fall on it's face ever time you shift to fourth - even in normal driving.

Duke

[Norris W.]

Re: Chiming in...

Let's not forget that a transmission change on a '63 will require a bell housing change also UNLESS it's replaced with another '63 transmission.

[Donald L.]

Re: Chiming in...

To convert from close ratio to wide ratio trans ones needs only to change the input gear and the cluster gear.Also this is good time to check the condition of the engagement gears and synchros.