Discussion Starter · #1 ·
I have a Pontiac 455 bore 0.30 over.. It has 11.5 to 1 compression with comp 270 cam with Edelbrock intake idle to 5500 what carb would you put on it...
A big carb will increase compression.NXS said:A big carb will also help bleed off some of that compression on the street.
Less restriction = more cylinder fill. Imagine a 1 barrel carb. It would take for ever to fill the cylinders, where as a Dominator would fill them immediately.NXS said:Well I could be wrong, but it seems like the static compression would be lowered. The velocity will be lower and incomplete cylinder filling will occur. It will also run richer helping cool the cylinder. Maybe "bleeding off" is the wrong choice of words.
That is a big misconception. You will always need to jet a carb that is too big UP. A carb that is too big will have less intake velocity passing through it. That will make the signal lower. Less signal will draw less fuel. That is why bigger carbs come with relatively larger jetting.Tmod said:Well the cutting of the vacumm in half for the power valve is a baseline guess. That will get you in the ball park and maybe right where you want to be. You will have to try it out.
I don't know much about the street avenger as I have never owned one.
I have had a Edelbrock carb and they usually run lean out of the box. BTW the edelbrock 1406 is a 600 CFM carb.
What is your cam duration @ .050?
A big carb will usually run leaner as the area in the venturi is larger and therefore has less of a signal at the boosters.
Now if you run a annular booster then you may have to jet it down a bit as it may be on the rich side.
You can throw that formula out the door.Max Keith said:I would go with a carb between 700 and 750 CFM. Thats what my magic formula calls for.
displacement times desired rpm divided by 3456. Figuring with 5500 RPM, you need 725 CFM.
Either one, a 700 or a 750 would carry you well past 6000 rpm as well.
Isn't that what I said?lluciano77
That is a big misconception. You will always need to jet a carb that is too big UP. A carb that is too big will have less intake velocity passing through it. That will make the signal lower. Less signal will draw less fuel. That is why bigger carbs come with relatively larger jetting.
If it runs leaner you would have to jet it up wouldn't you?A big carb will usually run leaner as the area in the venturi is larger and therefore has less of a signal at the boosters.
Most carbs should actually be jetted pretty darn close to start with, and even if you get a used carb, you should always use stock as a baseline. And, stock for stock, the larger carb will have larger jets, so that's not an issue.lluciano77 [/i][b] We are talking about an 11.5:1 455.[/b][/QUOTE] And that brings me to the next point... does anyone else think this is WAY too much compression for this combo? It's basically a very mild engine - Edelbrock Performer intake (assuming said:Isn't that what I said?
If it runs leaner you would have to jet it up wouldn't you?