427/390 Auto with a 3.08 Final

[William C.]

Re: 427/390 Auto with a 3.08 Final

Start with the basics! Have you VERIFIED the distributor curve is correct to the factory map? Timing mark checked to ACTUAL TDC on the engine? Simple things, Many, are NOT when the car is new, let alone after 45 years...... I supported a drag racing habit for many years with my distributor machine back when these cars were new. A little tuning can go a LOOONG way for a lot less $$ than a gear change.

[Bob S.]

Re: 427/390 Auto with a 3.08 Final

Start with the basics! Have you VERIFIED the distributor curve is correct to the factory map? Timing mark checked to ACTUAL TDC on the engine? Simple things, Many, are NOT when the car is new, let alone after 45 years...... I supported a drag racing habit for many years with my distributor machine back when these cars were new. A little tuning can go a LOOONG way for a lot less $$ than a gear change.

Mechanic tells me the timing is "Dead On" as is the cam...Points look great. I guess I'll have him check the mapping...

[William C.]

Re: 427/390 Auto with a 3.08 Final

Does he own or have access to a distributor machine? Initial timing is easy, but doesn't tell you ANYTHING about the advance curve where the power is actually generated.

[Bob S.]

Re: 427/390 Auto with a 3.08 Final

Rear end work = $$$$
Engine tuning including carb and distributor = $ to $$

Any questions?

Oh, and if the carb and distributor aren't working well now, they won't work any better at the higher RPM's you'll turn with a 3.70 gear.
Make sense?

Patrick

Got it.....THANKS!!!

Bob
(9944)

[Gary R.]

Re: 427/390 Auto with a 3.08 Final

Hi Bob,
I recommend doing as the others said and get your engine in better tune. I wouldn't change the TC while still using 308's, only if you go to a 355 or 370/373 gear. As mentioned the cost to build a diff will be a lot more then a distributor curve & tune. There is a fellow named Lars on corvette action center who is an expert on tuning and timing, he wrote several papers on it and he offers them to fellow corvette owners, you may be better served to get them and do some of your own tuning. If you still don't like the feel off the line then going to a 370 gear and TC will improve it but you will lose highway cruising as RPM will be up about 400 rpm. The best of both worlds is an OD trans but I never felt the high cost of an OD trans for a car driven 1000 miles a year or less was worth it so I always kept the TH400 and Muncies.

[William C.]

Re: 427/390 Auto with a 3.08 Final

One other thing to check is the reference of the timing mark on the damper to TDC. Many a slipped damper has caused a "lazy" engine.

[Bob S.]

Re: 427/390 Auto with a 3.08 Final

Hi Bob,
I recommend doing as the others said and get your engine in better tune. I wouldn't change the TC while still using 308's, only if you go to a 355 or 370/373 gear. As mentioned the cost to build a diff will be a lot more then a distributor curve & tune. There is a fellow named Lars on corvette action center who is an expert on tuning and timing, he wrote several papers on it and he offers them to fellow corvette owners, you may be better served to get them and do some of your own tuning. If you still don't like the feel off the line then going to a 370 gear and TC will improve it but you will lose highway cruising as RPM will be up about 400 rpm. The best of both worlds is an OD trans but I never felt the high cost of an OD trans for a car driven 1000 miles a year or less was worth it so I always kept the TH400 and Muncies.

Thanks, Gary,



Appreciate the input. Guess I'm leaning more toward tuning as suggested

Bob
(9944)

[Bob S.]

Re: 427/390 Auto with a 3.08 Final

My 67 air 427/390 POWERGLIDE car had a 3:55 gear in it when we did a body off frame restoration in 1992. The tank sticker showed 3:08. I thought the 3:55 would be fun, so I left it. The car ran very strong and would burn the tires off. On the freeway however, it ran 3000RPM at 68 mph and I always wished ''would you please shift to high gear?''

Gas mileage was also 9-10 mpg. You could order 3:36, but nothing hiher numerically. Dukes answer covers it well. If you want to go racing, buy a race car.

I hear you, James....I know there would be a definite trade off...Not to mention mileage. Probably stay put and just move toward the tuning and mapping

Thanks,

Bob
(9944)

[Chris H.]

Re: 427/390 Auto with a 3.08 Final

Back in the day, I in my 65 396/425 coupe with a 3.70, and another fellow with a 67 427/390 vert with a 3.08, were caravaning at a high rate of speed on Interstate 89 in Vermont. Pushing triple digits and watching my temperature gage rise, I was helpless as he motored off into the distance...

[Bob S.]

Re: 427/390 Auto with a 3.08 Final

Back in the day, I in my 65 396/425 coupe with a 3.70, and another fellow with a 67 427/390 vert with a 3.08, were caravaning at a high rate of speed on Interstate 89 in Vermont. Pushing triple digits and watching my temperature gage rise, I was helpless as he motored off into the distance...

LOL!!! OK, OK....I get your point!!!

I'm moving toward mapping and all, and leaving the 3.08's in!!!

Appreciate the reply,

Bob