Heavy car carb advice wanted

[ewo357]

Your low end torque "feel" is going to be less carb than rear gear, tire height, first gear ratio, exhaust diameter size, and flywheel weight, none of which we know.

Rear gear is yet to be determined (3.70ish maybe?) 28 inch tall tires. 3.27 first gear ratio. 2.5 inch exhaust. and 29 lbs flywheel.
Does that help for a carb recommendation?

[cjshaker]

+4 (or is it 5, or 6?) on the 750. Any smaller and you're killing power with no advantage.

I don't know about the QFT's, never ran one, but on EVERY new or used Holley carb I use or mess with, I check the flatness of the main body. They are almost always warped, even from the factory, and it will give you problems sooner or later. True it up with a file and it'll give you much better service. Sometimes they're so bad I've had to use 40 or 60 grit sandpaper over a file, then finish it off with just the file to get rid of the sandpaper scratches. It seems ridiculous to have to do this stuff on a new part, and it is, but it can save you some headaches and chasing your tail trying to find a problem.

[ewo357]

+4 (or is it 5, or 6?)

What are you asking here...?

[cjshaker]

+4 (or is it 5, or 6?)

What are you asking here...?

I was just agreeing with the comments made above about the 750 being a good choice. I just lost track of how many people I was agreeing with.

[ewo357]

Oh I gotcha.

[My427stang]

Do you already have the TKO?  The 3.70 is darn close if you already have it, I wouldn't come off that gear ratio with a TKO or TKO-500 in my experience with a bunch of TKO installs.  If you haven't bought it yet, a TKO-600 with a 4.11 gear and .64 would be a little stronger and work slightly better IMHO.

1st gear X 3.70 in the TKO is 12.099:1 (absolutely as deep as I'd go, but good) but puts 5th at 2.51:1, about as tall as I would go. 

With the TKO 600 and a 4.11 you get 11.79:1 in 1st and 5th at 2.63:1.  Not a huge difference, but if you haven't bought it yet,  it buys you about 3% in 1st and  5% in 5th in the right direction, but it is also stronger and I like the gear spacing better.

Some guys like the TKO-600RR, I generally do not use it, but in this case I absolutely would not use it because the .82, your build will have enough torque that you will end up wanting more OD and if you gear it for the OD, you'll lose the 1st gear benefit

Again, if you own it already, the 3.70 is the gear for you

[e philpott]

for street I like Vacuum secondary's best for most applications .... and like mentioned earlier I think the early GM 3310's are the best if you can find one , I've had 7 of them and they all have adjustable idle air bleed near the air horn , truly a beautiful working carb that will work on anything from a 289 with Carol Shelby factory 1x4 cross ram intake to a 468 BBC jet boat with victor intake ... truly a great carb

[Lenz]

May as well toss in late, the 3310 gets my vote for street use, after initial setup on my 445 I haven't had to touch it.  Expert sources (such as Barry in his book) will tell you that a bigger carb can be tuned down, but you can't make a small carb run bigger.  If I was thinking about placing heavier demands on the engine I'd go bigger, but for my purposes the 750 is just fine.

[FElony]

1st gear X 3.70 in the TKO is 12.099:1 (absolutely as deep as I'd go, but good) but puts 5th at 2.51:1, about as tall as I would go. 

Again, if you own it already, the 3.70 is the gear for you

A minor point here. For comparison of SLR's, I always factor in tire diameter. Personally, I use a 26-inch baseline, as that is about what most of the OEM tire sizes average out to. In this case, a 12.09 SLR adjusts to 11.22. That makes things apples-to-apples, essentially what an RPM calculator does.

[My427stang]

Good technique

My recommendation was based on experience with a 28 inch tall tire, however, I do like that idea.  All the ODs I have put in are 28 inch tall tires or occasionally bigger, so I tend to just reference my unadjusted numbers

In this case, an tire-adjusted SLR of 11.22 would be comparable to a stock wide ratio tranny with a 4.03 gear and stock tires, or a close ratio with 4.86s and stock tires.  The close ratio comparison is ridiculous and shows why those trannies were silly in a drag car, but your technique does really help when compared to a wide ratio

I will say, adjusting the compound OD ratio is equally important, because you can see how some tire size can get the ratio real tall on the other end.  In my case, my 489 far preferred highway cruising with a 4.10, 28 inch tall tires and a .64 over the same setup with 3.70s. 

[FElony]

I will say, adjusting the compound OD ratio is equally important, because you can see how some tire size can get the ratio real tall on the other end.  In my case, my 489 far preferred highway cruising with a 4.10, 28 inch tall tires and a .64 over the same setup with 3.70s.

Absolutely. I think many people get fixated on Overdrive RPM's without realizing how inefficient a carbureted engine becomes under 2000, worse yet with a bigger cam. I think the 2.75-ish OEM gearing on factory cruisers remains ideal even today. I think the recommendation for a 4.11 for this wagon is good for cruising under 100 mph. Makes first real deep, but it will tow strong, show off well from a standstill, and help offset that middle-weight flywheel.

As for carburetion, for a weekender at some cruise-ins or something, I suggest dual 600's. Doubles up the wow factor from a wagon with a stick. Still need to work the R head exhausts.

[drdano]

750 Quadrajet.   

[turbohunter]

I suggest dual 600's.

Still LOL ing. I approve of wretched excess.

[Joe-JDC]

Holley 80529-1 750 cfm vacuum secondaries, down-leg boosters work extremely well on just about anything you want to put it on.  Summit HLY-0-80529-1 $639.95.  Joe-JDC

[ewo357]

I do have the TKO already but I will be starting out with the stock 3.00 rear gear and some old 24 inch tires until I decide what kind of RPMs it feels good at on the highway. Then I will fill up the rear wheel wells, break out the calculator and decide on a rear gear.

Joe-JDC  What makes the 0-80529-1 cost so much more than the 3310 that others are recommending?