Where do I start with tuning this Holley?

68stang351 · Aug 11, 2010

I'm about to stick a Holley on my 68, and I just wanted to see if anyone with a similar combo could steer me in the right direction on a good combo of power valves, jets, needle and seats, accel pump cam and diaphragm. I have the large trick kit that comes with all the extra tuning stuff. I understand that this carb may be a bit big, but it was free. I've got it all cleaned up ready to re-assemble.

Someone gave me a Holley 3310-1, it's a 780 vacuum secondary. I'm just wondering what stuff to put in it as a good starting point to tune from. I was told for power valves, that I should check my vacuum, then divide by 2 and use those valves. It also currently has 72 and 76 jets. What about the other stuff?

Here's the setup:

68 Coupe
69 351w
Trickflow TW 170 heads
Comp XE284 cam--- Lift .541/544 | Dur @ .050 -240/246 | Adv Dur 284/296
T5 and 3.50 gears.

Any input would be appreciated.

woodsnake · Aug 11, 2010

My free advice is to take it apart and inspect it, then install it. To tune it, you need a vacuum guage and a good timing light. I'd leave the jets and stuff alone until after you get a trial adjustment to see how it performs. I don't really think it is too big for your application.

D.Hearne · Aug 12, 2010

woodsnake said:
My free advice is to take it apart and inspect it, then install it. To tune it, you need a vacuum guage and a good timing light. I'd leave the jets and stuff alone until after you get a trial adjustment to see how it performs. I don't really think it is too big for your application.

Ditto. You might want to install a lighter secondary spring and a 50cc accellerator pump (depending on what intake you're running)

68stang351 · Aug 12, 2010

woodsnake said:
My free advice is to take it apart and inspect it, then install it. To tune it, you need a vacuum guage and a good timing light. I'd leave the jets and stuff alone until after you get a trial adjustment to see how it performs. I don't really think it is too big for your application.

D.Hearne said:
Ditto. You might want to install a lighter secondary spring and a 50cc accellerator pump (depending on what intake you're running)

Doh! I knew I forgot something! For now it's a Performer RPM intake.

It's already been disassembled and cleaned.

Thanks for the advice!

68stang351 · Aug 14, 2010

I put everything back together and I must say it's like a totally different car! I ended up leaving the jets alone, leaving the accelerator pump cam alone (it's a brownish orange type color) and put in 3.5 power valves. My vacuum was bouncing between 5-9 and the 3.5 was the closest thing I had to half of that.

I think there may still be a few issues to work out but overall it's a huge difference over the 600 edelbrock that was on there.

68stang351 · Aug 14, 2010

Ok, now my main issue I'm having is when I give it throttle at under 1500 rpms under load, like taking off or shifting during normal driving, it will stumble a bit until after 1500 and then it's fine.

Do I need a bigger accelerator pump diaphragm? I have a huge one in the kit but I need a deeper cover to install it. If that will fix the off idle bog then I'll buy one. Other than that it's great. I think I will also take the advice of a lighter secondary spring too.

D.Hearne · Aug 14, 2010

Just me, but I think your choice of the 3.5 powervalve wasnt a good one. Most come with a 6.5 and I've never seen the need to use anything different.

brianj5600 · Aug 14, 2010

What is your initial timing? Total?

68stang351 · Aug 14, 2010

brianj5600 said:
What is your initial timing? Total?

17 initial, seemed like a little much but it's happy there and 36 total.

PoppyMod · Aug 15, 2010

68stang351 said:
I'm about to stick a Holley on my 68, and I just wanted to see if anyone with a similar combo could steer me in the right direction on a good combo of power valves, jets, needle and seats, accel pump cam and diaphragm. I have the large trick kit that comes with all the extra tuning stuff. I understand that this carb may be a bit big, but it was free. I've got it all cleaned up ready to re-assemble.

Someone gave me a Holley 3310-1, it's a 780 vacuum secondary. I'm just wondering what stuff to put in it as a good starting point to tune from. I was told for power valves, that I should check my vacuum, then divide by 2 and use those valves. It also currently has 72 and 76 jets. What about the other stuff?

Here's the setup:

68 Coupe
69 351w
Trickflow TW 170 heads
Comp XE284 cam--- Lift .541/544 | Dur @ .050 -240/246 | Adv Dur 284/296
T5 and 3.50 gears.

Any input would be appreciated.

I will offer, first install a couple (or one) O2 bungs. Either buy, or borrow a wide-band AFR, or visit your local go fast shop with a chassis dyno. This will save you so much time and effort. Every engine has too many different characteristics, even running the same go fast goodies.
Good Luck!

doogie67 · Aug 15, 2010

The problem you now have could be a few different things. Get a wide band and read,read and read about how to tune a Holley with a wide band. Quickfuel's techline is also a great resource. I am tuning a 393 stroked 351W with a big cam and 5 inches of vacuum in gear so I have a 2.5 power valve because a 6.5 would be dumping fuel at idle in gear. There is a lot more involved than just a few adjustments. You need to understand how a carb works in order to make the correct adjustments. I will not tell you what to do because without a wideband you cant tell if its a lean or a rich stumble.

68stang351 · Aug 15, 2010

PoppyMod said:
I will offer, first install a couple (or one) O2 bungs. Either buy, or borrow a wide-band AFR
Good Luck!

doogie67 said:
Get a wide band and read,read and read about how to tune a Holley with a wide band. I will not tell you what to do because without a wideband you cant tell if its a lean or a rich stumble.

A buddy of mine has been wanting a wideband for tuning also, we had talked about splitting the cost, we may end up doing that.

brianj5600 · Aug 15, 2010

If you get a wideband, don't get too hung up on the numbers. Different combos need different A/F ratios for max power. Mine was on the rich side for best performance. Also not all dynos can load a motor enough to get a proper tune. If you try the 50cc pump you will need a yellow or brown cam to get enough lift to take advantage of the larger pump. Here is a chart for 30cc cams. http://www.carbdford.com/tech/Holley20PumCams.gif Make sure there is no slack at idle and maybe try one that the lift is steeper early in the throttle. It sounds like you are talking about a hesitaion on light accel? Or is it wot at 1500rpm.

68stang351 · Aug 15, 2010

brianj5600 said:
It sounds like you are talking about a hesitaion on light accel? Or is it wot at 1500rpm.

Yep, light acceleration. I've only been WOT from 3k-6500, and it runs good there, but stumbles on light acceleration and steady cruise around and below 1500.

Actually, I think that either today or tomorrow after work I'll make a vid where you can see the tach and hear the car so you can really see what it's doing. It has a brown pump cam in the #1 position, and a 25 pump nozzle. It shoots strong streams immediately upon throttle.

It kind of slightly surges at cruise also.

brianj5600 · Aug 15, 2010

Does it shoot fuel as soon as the throttle is moved?

68stang351 · Aug 15, 2010

brianj5600 said:
Does it shoot fuel as soon as the throttle is moved?

68stang351 said:
It has a brown pump cam in the #1 position, and a 25 pump nozzle. It shoots strong streams immediately upon throttle.

Yep, at the slightest touch.

brianj5600 · Aug 15, 2010

WOW that is tiny. In that case I think you need a bigger squirter.
here is a good read. Carburetor Tuning the Scientific Way

68stang351 · Aug 15, 2010

brianj5600 said:
WOW that is tiny. In that case I think you need a bigger squirter.
here is a good read. Carburetor Tuning the Scientific Way

Thanks for the great link! It's bookmarked now.

68stang351 · Aug 15, 2010

Found some great vids on youtube also. After watching this, YouTube - Mr. CarbTune's Garage - Accelerator Pump Tuning I think I might try a 35 nozzle.

68stang351 · Aug 20, 2010

Well I ended up putting a 32 nozzle on it and it still does it. Maybe I need the 50cc pump kit or my problem is somewhere else.

I made a vid of what it's doing, I think I'll try to upload it tomorrow.

Where do I start with tuning this Holley?

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