I used to run 2.7x gears behind a Caddy 500 and powerglide, and I was still pretty traction limited. First gear final ratio was something like 4.00:1. In the 1/4 mile, it would shift out of first about 2/3rds down the track.

That caddy ran out of breath at 4300 and peaked torque super low, so it was a great combo.

 

That sounded like such a cool car man. With that engine, it probably didn’t need gears.

 

My Opel GT had 2.73 rear. However it only weighed in at 2112# with a built Buick V6 and a 5-speed.

I would ditch the TH350 for a 700R4

 

My car has a mild SBC, GM iron headed 350 with a Comp 282s cam 236@050
When I got it it had 2.56 rear gears and it just ran like crap around 30mph. It was just over idle and all chuggy. While the Rs were nice and easy at 55 it was pretty poor manners below 40mph
I went to a 3.42 and a new carrier

 

I'm using 3.08 with my mild 350 and TH350 auto trans. Rear tires are 26.5 " diameter. Great overall, and perfect for highway cruising. 2,350 RPM @ 60 MPH. But with an open diff traction off the line is minimal. I need to "roll into" the throttle to avoid excessive wheelspin.

 

This junk started life as a 6-banger low option car and is running the stock 2.73 gear with a truetrac and moser 30 splines. I ran it with a TH350 for a few years and then a 700r4 which as a daily driver kicked serious ass. The low, low first gear works well with the steep ratio and the overdrive makes it the fastest thing on the highway - we die like men!

Since the engine rebuild with roller cam and other mods, I blew up the 700r4, put back the TH350 and it blew up pretty damn quick. Car is on the lift as we speak.

Traction is just not there in first with the street tires no matter which trans... From what I understand, the steep ratio puts a lot of stress on the trans so it's not an optimal setup. Still, I asked my guy to build a 500HP nitrous ready 350 and it lasted a few thousand miles before boom - not right. The 700r4 was a better match because of the first gear ratio. I'm going to rebuild it and put it back in next. I think it was killed by a mud-dobber that got in the cooler line while doing maintenance - a true florida thing. So whatever, I have a pro-street plus kit from pro-stock automatics and 4l79.com front drum that should handle the pressure. If I decide to change the gear set it will be a 3.42 which will be optimal with the overdrive though I'll loose my 200mph capability - lol

Back to your question, the TH350 should live with the steeper gears. Just add a cooler if not already, watch the temps and be sure its a good build with the extra clutch, dual feed mod and a steel front drum. I didn't spring for that last bit and I'm guessing that's what broke - my other trans guy (same shop) says that's the one thing people cheap out on and it's the only weak link at this HP level. He put one in my mud truck and it's been through a lot of real high rpm smashing up **** without any issue.

Now, If you're happy with everything but the carb, that can most likely be fixed. Going to a 3.08 will put more stress on the trans so make that the last choice ... I'll check out your other thread later on and see if I can add something.

 

Thank man! That’s a great point! Also, I love that car. Them mid to late 70’s novas are the best. Remind me of the 1970’s. And guess what? Mine is a 4 door also. I really like the 4 doors. Nothing fancy here. Just a fun car to screw around with as cheap as possible. Thanks for the info. I may just stick with the 3.73’s, upgrade the radiator to a nice long core two core set up, and keep on tuning the carb. The side pipes are beyond awesome.

 

Cool! I think you'll be happy with the right radiator and tune. Not sure which one is your carb post so send a link

My 78 is a labor of love... and just my way of expressing myself artistically. I grew up when these cars were new so they are very close to my heart. I started turning wrenches on them when I was 14 helping out the big kids in the neighborhood...

 

Cool! I think you'll be happy with the right radiator and tune. Not sure which one is your carb post so send a link

My 78 is a labor of love... and just my way of expressing myself artistically. I grew up when these cars were new so they are very close to my heart. I started turning wrenches on them when I was 14 helping out the big kids in the neighborhood...

man I love these novas. I like when they look like a regular used car but modified. Not in great shape either. Same here. Labor of love…

 

By the time I was done at AG, I would say 75% of my new construction trans' were 2.98 1st gear custom units.
These were usually paired with 3.08-3.36 axles in GM midsize cars, corvettes and F-bodys. Im talking Thousands of them built in 15yrs. Its a very good system on the street and I had some BBC chevelle guys running in the 11s pretty routinely. I also did some for LSR guys and the Dana 300 T-case conversion in some Jeeps and LandCruisers

The gimmick for a 3spd auto is really, truly get a custom built converter to work with your motor and the rear gear; AND make sure your tires aren't too tall for the 3.08s. I'd really want them below 28" H. You get up around 28" and 9-10" wide, you're better off with 3.23 or 3.31s. Better take off and the cruise with the tall tire will be the same as the 3.08s approx.

If the GearVendors was an option, its actually pretty darn good, just dont tow with it; or go up a long grade, in OD.

 

great info. I am thinking 3.31’s too. Thank you for sharing your experiences.

 

Very nice 72 PRNDL!

 

I had 2 1969 Camaro's. One was a 327 with a 3:08 and the other was a 396 with 4:11. Both the same color and the same wheels. I would race you on the street with the 396 and then say let's go to the highway. I had put a 283 crank in the 327 because I turned a rod bearing, possibly from to many rpm HAHA. In order to make power because there was so little compression I had to put 55 degrees of timing in it. I locked it there. I was running the Z/28 off road cam with the cross ram manifold. I modified the carbs with 660 base plates which I also modified the linkage to run on primary's up to 3500 then it was wide open throttle. A 4 x 4 TH400 with a torque converter from a Vega and a full manual valve body with the line pressure turned up to 300 lbs. I would start in high gear at 50 mph and yank it back into 1st gear, tach would fly to about 8000 which I then shifted to 2nd, the car would jump ahead when I did that. The most fun street car ever. I ran both cars with only straight pipes that dumped in front of the rear end. Those were fun day for sure. You could not get away with that today. If you drove that engine at 60 mph on the highway it got 25 miles per gallon running 116 octane fuel.

 

This is probably a silly question, but is the rear end limited slip or open carrier?

I'm in the camp of keeping the 3.73 and working on the cooling system. You're making good power with the engine combination and I wouldn't be afraid of a higher cruise RPM. The 496 in my G body sees 3000-3500 at cruise and I've never worried about it or had any problems. I usually don't go too much over an hour either way as the noise level starts to wear on me a bit.

 

Good point.

I’m running a Trutrac limited slip.

 

You need larger air bleeds on the primaries
Temp creep, I assume you are running a thermostat and you have 5ested it on the stove with a thermometer.
Your rich mixture and how much quench clearance? could be causing detonation. You said timing most would run with race gas.

Talker gears might increase wheel spin. Put new springs on @ 225lb and drag shocks on the front. That's way less $$$ than a gear change and addresses the traction issue. 60 year old springs don't have any spring left in them, hence, the wrap up and tire hazing

 

Air bleeds: Low speed:
That was my first instinct, but this 3310-2 has .078 factory IAB’s. My transition is clean and tapers off nice and lean under 2500 rpm. I find the air bleeds only help with the end of the circuit.

Air bleeds: High speed:
They are the factory .025. My last two carbs were a 750 AED double pumper and a Holley Street HP 750 vacuum secondary. Those has adjustable bleeds. I found the same thing to be true. Bigger high speed bleeds meant the main circuit would lean out as I gave it more gas at moderate acceleration. Then I needed a higher PV and bigger PVCR’s. On those carbs, I had to drop the MAB’s to .025 to get a decent flat fuel curve. Jetting seemed to only affect the entire curve. The emulsion on the AED were 5. Too many. I had a lean main circuit onset. Opposite of this. I’m thinking of drilling out the top emulsion on a spare 3310-2 metering block from .028 to .030 and going from there.

Thermostat: I tested the two I have. Plus it’s stays at 190-195 all the time other than sustained 3000 rpm highway use.

Quench: 4 inch bore but .030 over. Weisco 10cc dish pistons. Zero deck pistons not in the hole. AFR 195 heads with 65cc chambers and MLS gasket I think .040 thick.

new rear factory lead springs but with slapper bars.

timing is 36 all in at 3000, 14 degrees vacuum. Seems reasonable.this thing wants a lot of timing at idle.

 

I missed your quench, found it

 

Spark plugs?, cruise speed, Temp creep, neutral shut off motor and pull a plug and read it?

You didnt answer Quench clearence.

 

Too much timing. Reduce to 32*. 36 might be too much and this might smooth everything.
Roll start racing is very popular on Saturday night anyway and easier on the car.

 

Spark plugs test during idle and low speed cruise a bit dark.

Spark plugs at highway cruise dark.

wot test shows tan.

 

For the highest rpm and vacuum at idle, I have to be at about 13.1 AFR. it likes a lot of idle timing. 32 degrees

Comp cams XR282HR 230/236@50 110 LSA 550 lift with 1.6 rockers.

I’m thinking the cooling is this factory single core radiator. It’s new. The core is about an inch think or more.

I’m going to play with that upper emulsion regarding the mixture. I just have to find the time.

I was thinking the 3.08 gears would ease up on the rpm’s on the highway. I do like the feel of my 3.73 a lot though. Hate to lose that.

 

I’m thinking the cooling is this factory single core radiator. It’s new. The core is about an inch think or more.

That's it. The general rule is overheat at idle and ok at cruise is not enough fan. Ok at idle and overheat at cruise is not enough radiator. Obviously there are a number of caveats there (airflow getting around the radiator, missing or improper fan shroud, weak electric fan blocking airflow through the radiator and so on). I'm thinking none of those apply here and as you suggested, a radiator upgrade makes good sense.

 

Awesome. I will try a reduced timing

 

Copy that brother. New radiator coming up.

 

What do you guys think about plugging the lower primary emulsion holes? Then I can jet down and keep that fuel curve flat.

 

I can say I've never seen any factory tune , nor a custom carb builder tune, that has the bottom emulsions plugged.
My thoughts are it just won't work; it will badly influence system timing in the hand-off from transition to main circuit in the fuel curve.
Emulsion and air bleeds have as much to do with circuit timing as they do with just rich/lean changes.....both get changed when you alter one of them.

 

Copy that.

 

What are your thoughts on the AVS2 800 for my set up? Do they really kill top end compared to a Holley?

 

At this point, I know 3 people with them.
My father has an 800avs2 on his mild 383
My ex has one on her 73 Charger SE 440
Another Mopar guy (Dave) has one on HIS 73 Charger with a 340 transplant (I don't think its the 800cfm variant.
Dad's was a factory refurbished unit, he accidentally ordered the manual choke one and when he finally opened the box, figured he could just adapt an elec choke or buy a kit. Nope, theres some hole in the body casting that has to be drilled. If I had a bridgeport, no sweat.
Ran fine, minimal adjustment needed. The next season he tore into it a little bit and I think he changed the step up springs and metering rods. Its VERY crisp and part throttle driveability are both very similar to my EFI motor. Is he giving up power up top? Maybe? But he never takes it over 5k so whats it matter. Cold start is easy, no famous edelbrock dead-spot, good economy

Christines 440? The Install was very easy, its a stock smogger 440 from an RV. Ran like a singer sewing machine. I put it on over Christmas vacation so I never got to drive it due to winter, But it was legions better than the hopelessly fubar Edelbrock Performer it replaced. That had a cracked casting.

Daves SB Charger? He dove into it head first and really micromanaged it. That thing RPMs like a chainsaw, and still sips gasoline

TLDR If you need every horsetorque available, probably stick with the Holley gang. Theres more tuning info and probably more tuneability and a larger community of situational experts.
But if you want an efficient and easily managed carb? Theres nothing inherently wrong with it

 

I personally hate the AVS2 compared to a Holley

Near 0 support from Edelbrock, a while bunch of support from Holley


However YMMV