570 Street Avenger Update

[Bucky]

Ok, so a little back ground on the issue, had a TA-470, everytime you hammer the Accelerator it would stumble. Once it got off idle, it would run pretty good. Called Holley and they said it was too small!
So Holley switched it out for a Street Avenger 570. Had to re-route all the fuel lines due to the duel feed of the SA! During the test drive, it was doing the same thing!
So back to square one!
Crate 302, GT-40P Heads
Edelbrock Preformer RPM Air Gap Intake
All New MSD 8.5 Plug Wires
BCB Headers
MSD Pro Billet Ready to Run Distributor(Currently Have the 2 Heavy Silver Springs installed. Seemd to run the best after idle!)
Checked timing (Curently set to 14 Degrees Initial)
3.50 Gears, 32 Inch Tires(I know this is not good for the problem I have, but before I starting restoring it, it ran really strong wiht this combo)

So today I picked up a .40 Accelerator Pump Nozzle, installed it and I was actually able to turn the tires over! Still had a little stumble, but not bad!
After doing some reseach, I guess if you install this big of a discharge nozzle, you should change to a 50cc Accelerator Pump. I think my next move is to install the 50cc, what do you experts think?

Thanks for all your help! I'm almost there!!

 

[DonsBolt]

The 570 should be plenty of carb for your engine. I used to run a 570 street avenger with my 340 HP crate motor and never had a problem.

I think part of your off idle stumble might be due to the air gap intake. While a good intake for a high reving motor I don't think it is the right intake for a Bronco

You might want to try a performer 289 intake as it will give you better off idle performance

the air gaps are best suited for 1500 RPM's and up performance

 

[Bucky]

DonsBolt,
I agree with you on the intake! Got talked into that one by a friend who thougt I was building a 10 Second Mustang! I'm trying to make it work, but it may be the next componet to change if the 50CC Accelerator don't work!!

 

[oleguy74]

might want to check first.if it came with a 30cc acc pump you might have to get a 45$ kit to convert.50cc pumps are deeper and require a different housing.

 

[Bucky]

Hey Oleguy,
It has a 30cc on it now, and I should have a 50cc tomorrow! And your right about the $45!

Thanks Again!

 

[oleguy74]

keep us posted about the 570.you are most welcome.

 

[Wyldebill]

I had the same trouble when I put my 670 TA on my 302, and was convinced it was too large. Some one was on this board asking how to set his Bronco for altitude as he had just moved to Colorado. Someone on here, I think from Colo. Springs said that he used a formula to determine his timing. It was set at stock setting and add one degree for each thousand feet of altitude. I set my timing at 11 degrees, the stock 6 plus 5 because I live at 5200 feet. It changed every thing to my favor. After that I was able to fine tune my 670, before it would not respond to the tweeking I was doing the way it should have. I now am pleased with the way it is working. If you are having trouble getting responses from the tweeking you are doing on your 570, playing with the timing might help. By the way, my thanks to who ever the member was that gave that information.

 

[broncnaz]

There has to be some other issue here. But I do ask about "hammering the throttle"? being a heavy vehicle with a small engine and not the best gearing/tire combo it will tend to stumble as the engine just doesnt put out the torque to hammer the throttle. othewise I's suspect a Vaccum leak somewhere? The 50cc pump will only mask your issue and I dont believe that the manifold size is the problem I run a holley 600 cfm on a old Edlebrock trauntula single plane manifold and dont need the 50cc pump and my squirter is only a 28 I tried a 31 but is was a little to rich. But a smaller intake can help one of these days I'll be stepping down to a RPM type manifold. Maybe your going in the wrong direction with your squirters have observed the exhuast when you tap the throttle if its spouting black smoke then your to rich.
The avenger series carbs should have better metering than standard holleys meaning they should respond faster to changes in vacuum so I'm not convinced that the squirters are the problem. Again it could be basic jetting that is off a little.

 

[Bucky]

Thanks Broncnaz for the input! I've tried the other direction with the discharge nozzle! I orginally went the other way with the nozzles, The 570 came with a 31, I installed a 28 and it got worse! Installed a 35 and it was a better, still not black smoke! When I installed the 40 it was the best yet, which is what lead me to my conclusion.
As for timing, I've spent a whole day going from 6 degress to 16 degress with around 14 being the best!

Thanks Again! I'll keep you posted on the results!

 

[Bucky]

Well, I installed the 50cc accelerator pump last night and took it for a spin this morning! Much Better!!!! I think I have a little tweeking to do, but it is real close! I agree with Donsbolt about the intake, as soon as it reaches 1500 RPM it screams! I can at least now turn the tires over and it doens't seem to stumble, just a little week on power until 1500 RPM!!!!!
Thanks for all the help! Next move my be intake!!!!

 

[CDHUNTER]

Just something else you can tinker with easily is the pump cam. There are different cams with different lift rates and timings. However, the cam on your carb has a couple of positions. You can move the screw to another hole and "
advance" the curve. Potentially it could get you into the power earlier.

Here is some documentation about each color cams behavior.
URL="http://www.holley.com/BrowseCatalogs.asp?Catalog=Holley&Page=65"]http://www.holley.com/BrowseCatalogs.asp?Catalog=Holley&Page=65[/URL]

 

[Bucky]

Thanks CDHuner!
I didn't get a chance to play much this morning! It started raining, so hopefully I will get a chance this weekend! Might get some dyno time on Saturday so I can do some measuring!

 

[broncnaz]

When you change the intake you may have to retune the carb all over again, But hey at least you'll know the ins and outs. You may also want to play with your advance curve a little more before swapping intakes as you might be able to use a quicker curve that could be the cause of your feeling it open up at 1500 rpm.
I still think theres some other problem here as you shouldnt need a 50cc pump with that engine combo. My combo is more out of wack with big valved heads and a single plane intake 3.50 gears with 33in tires and it runs fine without the 50cc shot. I've never had a lot of luck changing the pump cams guess I always just needed a little more than the cam could give.

 

[Bucky]

Yeah,
I'm going to try and play some this weekend with the advance and Carb! It's driving me crazy that the RMP Airgap is rated between 1500-6500! I should have looked at that closer when I was building the motor! If I would have researched it more it would have a Performer 289 Intake!

 

[malcolmzilla]

Interesting that the stumble improved, with the larger pump shot, I have a similar stumble on my 470TA on a stock 302, Weiand Action+ ...

 

[Bucky]

Malcolmozilla,
It might we worth a shot to try a larger discharge nozzle! I had the same problem with a TA 470, but I never tired the 50cc on it! The first think I tried was the 40 discharged nozzle on the 570 and it has got me going in the right direction I think!
Good Luck

 

[broncnaz]

Yeah,
I'm going to try and play some this weekend with the advance and Carb! It's driving me crazy that the RMP Airgap is rated between 1500-6500! I should have looked at that closer when I was building the motor! If I would have researched it more it would have a Performer 289 Intake!

I really dont think the air gap is the problem as its just not that big. Vacuum signal should still be strong with a stock type cam. I remember seeing a dyno test between a performer and a RPM intake and the RPM actually made more lowend torque than the performer manifold. Talk about a wrong application My torker manifold is nothing but a big hole and with a 600 cfm holley I only had to step up from a 25 to a 28 squirter to cure the bog. The torquer manifolds were the hot item in the mid 70's this was really before 4x4 were being built and 33in tires were huge.
If you were closer I'd trade you a performer for your air gap. Darn the bad luck I'm always in the wrong place.