Holley Question

[70c10stepside]

I am wondering rather not a 750 vacuum secondary will be to big for my motor. The 600 we had on it is just to small, and for the price there is no in between. I am on a strict high school budget.
Motor specs
355, cam is 508 lift 313 duration. Heads are 327 double hump heads 64cc. Flat top pistons, Should be close to 9:5 compression.. Supposed to have a close to stock crank and rods. It is bore .30 over. Edelbrock Torker II intake. Arp rockers, its a Hydralic setup. The motor will ping like crazy with a 600, if it isnt getting premium fuel. I''ve had the motor rev to a little over 6k, with out a sweat. We are running a turbo 400 with 4.11 rear gears. It has black jack heads, straight back to flowmasters. What i believe to be a classic 40 series.

Sounds ok? The 600 is going back tomorrow, and a 750 will probably go in its place...



How it sits.

[Marv D]

Just because the 600 may be calibrated too lean,, I wouldn't condem it until it's tuned correctly. For a 355 to bneed 750cfm your going to have to be spinning it north of 6800rpm. That 600 will hopefully bring back some of the torque you loose to that Torquer II intake below 4000rpm.

just my 2¢

[70c10stepside]

We tuned the 600 the best we could, just couldn't get it working. Messaged Holley, they said it was way to small for the application.

[Captainfab]

What is your initial timing set at? What is the total? do you have the vacuum advance connected to ported vacuum or manifold vacuum?

That 600 should be just fine on that 355. What all have you done to it in trying to tune it to your engine?

[70c10stepside]

Because I talk to some of them more and they respond quicker lol Big deal about it?
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[bk2life]

the 750 would be great depending on your driving style..... which is??

for a normal grocery getter and occasional light to light fun, the 600 might be really good for you, but sounds to me youve never had it "tuned" correctly.

get your self an A/F gauge and see where your stioch is.

your in HS got to be plenty of awesome tools in your shop class. hook it up and get it all tuned.. dont forget timing!!

[70c10stepside]

My high school shop class is my shop outside lol Homeschooled... But, my dads a mechanic along with my grandfather. As for timing we played around with it a lot, it just never would work right.. It would only ping in a dig, with regular pump gas. Now that we tried premium, it wouldnt ping unless heavy load and it would sound like its starving for gas.. It wasn't as bad. And the use of the truck is a toy really lol Its not a daily driver. It gets driven only a few times a week. And its never more then a 20 mile round trip. And normally only on back roads. The big reason we are upgrading is the loss of hp its loosing. In another thread I made, a lot of people told me We were loosing a lot of power and the 600 was to small. And yeah..... hm.

[Blue Rat]

I would try the 750 VAC. an see how it does with your setup. Sounds like it would work to me.

[70c10stepside]

It'll be here tomorrow
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[Marv D]

Well you may get drivability from a properly workling carb but consider this... to properly size a carb you take the cubic inches (355) times the MAXIMUM RPM you are going to be driving at (lets say you stab this thing and bring it up to 5500 rpm

355x6000 = 2130000
That number divided by 3456 tells you the cfm required ,, = 616cfm. Your 600 Holley was near PERFECT to 6000rpm.

Work the formula backwards and you are going to have to spin that little 355 to 7300rpm to need a 750cfm carb

Here,,, Holleys own page has some good information you should read.

I believe the Captian had you headed down the right path. You have compression and a igintion tunning issue not a carb issue if the 600 was properly jetted for the elevation you live and drive. If the bolck is a standard 0.025" deck you have 9.6:1 compression. Todays crap fuels will have a hard time supporting that in an iron headed motor. And if the block has been decked, or Zero decked, you could have as much as 10.36:1. NO WAY are you going to run 10.3 with iron heads and anything less than 91 octane,, even then you better not be very agressive with the advance curve. But,, you can lead a horse to water......

[Marv D]

ooops, here's the Holley link mentioned above.

http://www.holley.com/TechService/FA...ory=Carburetor

[GASoline71]

The 355 in my truck has a blueprinted 3310 with a metering blcok in the back and a 4 corner idle circuit. High flow power valve, and air bleed work... that little engine goes north of 6,800 RPM's a lot!

If I wan't spinning it so high... I would definately run an 1850 on it.

I have a buddy that has a very snotty 355 in his 1972 Monte. It has a reworked 1850 on it, and that car flat out rips!

Gary

[WadmalawJoe]

Hey 70C10,
You have that 750 on yet? What's up?

[70c10stepside]

Holley had to send us a replacement fuel inlet were the hose connects with the front bowl, it was damaged. The part got here today, so it'll be going on tomorrow. Ill let you guys no
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[70c10stepside]

We got it on. Fixed the pinging and what not. Revs so quick and smooth. No bog, or anything. We also had to use a one inch spacer. Which, wasn't in the plan, but had to so we could clear the heater hose.

[WadmalawJoe]

Outstanding!
I have always had better performance using those spacers.
I have been thinking of getting one to put under my 600 just to see. I plan on putting a 750 on my engine soon.

[70c10stepside]

Sweet, we got this spacer from AutoZone for only 20 bucks. Its aluminum and seems pretty strong. This 750 didn't give any problems. It was pretty much already set up.
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[Blue Rat]

That's good news to hear. Sounds like a fun ride.