Help "tune" my supercharged 360 1972 Dart, please!!

[daniel_depetro]

We got the Dart running pretty good, but it still has a pretty good hesitation/bog when the throttle is pressed down fast (or on a quick/hard launch). Then the car comes to life and pulls like a freight train.
The car is very basic and just put together for pennies so it is making do without anything fancy.
The engine is a stock 1974 360 4-bbl. out of a 53,000 Dodge Truck.
The Supercharger is a B&M 144 (B&M says it maybe a 162?) which was just gone through including new nylon strips in the rotors for tigheter clearencing/better performance.
The intake manifold is a Holley 'Street Dominator' aluminum single 4-bbl. unit with the carb flange shave level/square so the blower sits on it nice/flat.
The car has standard Hooker 'Competition' headers that dump into dual 3" exhaust with Flowmaster 3" mufflers. The exhaust stops at the rear axle.
It also has an Accel 'Super Coil'and the plug gap is at .040".
Thre Carburetor is a Holley 'Street Aveneger' 770 cfm vac. secondary unit with electronic choke. The primary jets are 75 and the secondary jets are 79. The accel pump is a small one (30cc?).
The timing was set around 8 degrees initial (idle) and around 30 degrees coming in around 3,000 RPMs. The ditributor on has one spring in it (light factory spring).
The car has a .429"(I)/.444"(E) with a blower friendly 114 centerline camshaft/lifters/springs, with a double row true roller timing set.
Transmission is a stock 727 and the rear is an 8-3/4" sure-grip with 3.91:1 gears. The chassis is all stock with Yukon big bolt pattern axles, and 1973+ A-body front disc brakes.
The car uses an aluminum radiator as well an external transmission fluid cooler.

We ran the car last year with a 670 cfm vac secondary Street Avenger carb and I had the 770 sitting on a 440 in my garage still in the plastic so I wanted to try it on the Dart because surely the 670 was too small. The car had the same bog with the 670 cfm carb.

The car definitely runs better with the larger carb, however I hate that stumble it has.

When I had the 670 cfm carb a couple people said I should add bigger squirters.
I knew I was going to swap the carb and I did but was shocked when I found out this 770 has smaller squirters (.025") then even the previous 670 (.035"), according to Holley.

Trying to get the car set-up right as we are going to bring it to the strip on Sept. 25th for the first time. Not too mention it would be nice to have it ready to just pull out next spring and have it "ready to go".
The car just runs on street tires, however I have a set of slicks I'll be trying out at the track this time.

Any ideas what would get that nasty hesitation out of there and any other tips?!?

 

[yellowdartdave]

Sounds like you need a bigger accel pump shot.

 

[ramcharger]

Bigger squirters and maybe a 50cc pump like yellowdart says would be a good first step.

What do your plugs look like? 74's are what I run in high altitude hear on my mild 360. I would up those jets two sizes at a time while keeping the stagger the same. Also, I really think you should be running a double pumper on a blower.

I have a zero experience with SC cars but I think dedicated SC carbs have a different vaccum reference for the power valve too. Let me check on this...

I might carefully up the intial timing while keeping the total where it's at for now too. Detonation on SC car is deadly to pistons.

 

[ramcharger]

Hey, I just checked on this.....

A blower engine on the street should be running a manifold referenced PV style carb. Reason being is that the PV is referencing the vacuum between the carb and blower which is always high and the PV won't open as it should. They detail the mod to do this by yourself too.

Here's an excellent Q&A on Holley's website:
http://www.holley.com/TechService/FAQ.asp?category=Blower

They also say that initial timing should be around 12-20 BTDC inital, but no more than 32 total and all in by 2800 rpm.

 

[Babyblue66]

Also with the strong vacuum signal the secondary spring may be a little week, causing the rate of opening too fast.

I hope you hook up that kick down, or its bye bye tranny clutches.

 

[Mad Dart]

The Initial timing at 8* seems very low to me. I would try increasing the initial timing to 14-16* and 32* all in at 3000 and also check your fuel pressure at BOOST.

 

[nemesis]

Out of curiousity,what fuel pump are you also running???

 

[daniel_depetro]

My dad is a transmission tech by trade so he knows how to adjust the kickdown and it is hooked up. This photo was taken while getting the car to fire with the new larger 770 cfm carb.
It runs great now and thanks for the link(s) and help. This will all help us get it dialed in. Looks like lots of tuning (carb & timing) coming our way.

The fuel pump is just a stock replacement from Advance Auto Parts.

 

[daniel_depetro]

My buddy never drove a "muscle car" before so we went for a ride and I let him drive it back to the shop.
While out we went to the local certified scale and weighed it.
The car is 3,240 lbs. The fuel gauge doesn't work so I wasn't sure how much was in there but it should have been around 1/2 tank.
Obviously that's with the supercharger and the car is fully dressed (full interior even though most of it is in pieces and is lying in the rear seat & all options still functioning). This car is also lugging around some extra weight from using power steering, power disk front brakes (with stock cast iron master cylinder), steel wheels, factory large/heavy starter, and such...

 

[daniel_depetro]

The next day we removed the original bench seat and put a bucket seat in its place. We just customized a set of early 90's Eagle Premier bucket seat tracks and they fit pretty well. They are very comfortable, but don't look right in the car (fabric covered). Not too mention they sit a tad high for my liking. I prefer to sit very low in a vehicle.



We also got the driveshaft loop welded up and installed, so now we can run slicks whenever we choose to.

The water pump just started leaking so we ordered a new one and it'll be here tomorrow. Also we just noticed that the passenger side steering arm just wore a hole into the header primary tube. :thumdown
Nothing a little weld wont fix but damn it these motor mounts are brand new. Todays rubber just doesn't have the durometer that they need to. Like everything else, they just don't make them like they use to. Probably have to go with a urethane mounts to keep everything put (and maybe a torque strap of some type?).

 

[daniel_depetro]

The following day we welded up the header primary tube with the hole in it and shimmed the engine about 1/4-inch (higher) for more clearence.
We also got the new water pump installed and changed the oil. My dad robbed the Sun 'Super Tach II' out of the 1964 Ford F-100 and hooked it up so he had some type of reference.
I also mounted/balanced the slicks on the rear rallye wheels for the car and that pretty much left it as completed as it was getting.
Unfortunately we didn't have time to finish up the slap stick so there would be no shifting into the gears. Simply put the car in 'D' and let the transmission pick when to shift.
The good news is that the trip went without anything grenading itself.
The car launched straight and drove smoothly down the track like a Sunday cruise.
The bad news is we only got 2 passes and then the event got rained out.
That's too bad because there was only about 50 cars down there and we could have easily got 10+ runs in that night. We got there at 5:00pm and a few people already had 5 runs in by 7:00pm when it was cancelled!

The first run seemed to go pretty good, however the serpentine belt was off the pullies by a tooth (or was it two?). We left the timing at 8 degrees initial so we could slowly crank it up on each pass.
It didn't run very fast, however your first outing with a street car on a new set-up surely isn't going to be impressive anyways. It ran a 14.0288 @ 98.11 mph. Not Earth shattering by any means, but considering the car was shifting ~4,600 RPMs, the carburetor is not dailed in (and wrong altogether), the stock transmission has a low stall speed and no shift kit, that's not so bad either.
My dad said it was extremely strong through the middle of the track, but felt like it nosed over on the big end?!?
Heh. We'll get it there.

I decided to put the shorter 'race' belt on (takes about 20 seconds to swap belts on this system we have) which just bypasses the power steering pulley. The only thing the serp. belt goes around then is the supercharger, crank, and tensioner. This gives the belt more bite and would help eliminate any slippage (though I doubt there ever was any). We also bumped the timing up a few degrees.
On the second run the water pump belt came off and the blower belt broke. It wrapped itself tightly around the harmonic balancer and made scary noises. It sounded like the bottom end was knocking.
We quickly tossed the 'street' belt back on and got back in the staging lanes. When we got up to the front of the line, down came the rain.



Sitting in the staging lanes before the first run:

Launch on the first heads up run against Brad LePine:

Pulling up to stage for their second match up: