The_Jeremiah

hey everyone, on my 69 350 block, im going to put an edelbrock performer rpm. i have had lots of people tell me that a 750 cfm carb will work out great with an olds engine that has a hotter cam with headers and the rpm intake, thats mine lol. but what i was wondering, is what carb would work out best, i was wanting to put a holley with mechanical choke, and secondarys, easiest to put in. so for this engine, which is better vaccum secondarys, or mechanical.

captjim

Vacuum secondaries are almost always a better choice on a driver. I have a 670 Street Avenger on my 9 to 1 355 with a 210/216 cam, works great.

Oldsguy

Quadrajet.

The_Jeremiah

ah yes, im a big fan of the quadrajet, my main concern here, is money. if you can show me one that is in good working order for cheap, let me know. lol

Oldsguy

Cheap is relative. Danny Sarvis rebuilds Quadrajets for less than the price of a new Edelbrock and he doesn't require a core. Not cheap, but a fair price.

GoldOlds

I'm considering the same carb for my 350 Olds, which I plan to buy a Comp hyd. flat tappet cam for with .485/.490 lift and 224/230 .050" duration. My final compression would be about 9.3 to 9.5:1. Would the same carb work, or would I need more cfm?
Thanks!

- GoldOlds

captjim

I would go with the 770. Mine is pretty mild, 9 to 1, 210/216 cam, and I am at 68/73 on the jets, which is 3 and 5 sizes over what it came with. Also needed to go to a 50cc pump. Read this if you care to,
http://www.oldspower.com/vb/showthread.php?t=34984

Not trying to bash or start an argument, but some have found that certain cam grinds work better in our Oldsmobiles. The Comp cams have low lift relative to duration, Engle, Crane, Lunati, Bullet, etc are the opposite, lots of lift. I also think that is too much cam for a 9.5 to 1 350. Just my opinion. Something like this http://www.holley.com/60801.asp might work better.

kevinkpk

Quadrajet is fine carb! I'd also add have the jets and ports matched. A good carb man that does performance would have done that, little more bucks, but anything less is a waste.

Olds64

A 750 cfm carburetor for a street engine seems about right. I read an article on carburetion in the November issue of Popular Hot Rodding last year. They gave the following formula to determine cfm size of your carb:

cfm = CID x RPM x CF / 2 x 1,728

With CF being a correction factor given in a chart they provided in their article.

Looking at the article I imagine the CF for an engine with stock heads and a cam with 215 degrees of duration would be about 1.005. Of course, I never heard if this article was very acurate, but it is worth plugging the numbers in to see what you would come up with. I kept the magazine because I thought it was an informative article.

88 coupe

In some Olds applications, that would be a good thing.

EDIT: But the topic is carbs.

Norm

88 coupe

Should not happen with an “out of the box” Holley, on a 350 Olds. Good indication that there is a problem with the carb, if not the engine.

Interesting, that no one at OP picked up on it. There are several on ROP who would have, had you posted it there.


From: http://www.oldspower.com/vb/showthread.php?t=34984

You were asked for the rest of the numbers. Without them, any discussion is pointless.

How could a carb change be the cause?

Vacuum advance, or lack of it, will not affect your ¼ mile times. The exception would be, if you staged at “idle” and “floored it” at the “go”.

Based on what evidence?

Norm

captjim

Yeah, there is a problem with the engine. I have an 8.9 to 1 355 with a 3.42 gear in a 4000 lb wagon that runs 13.9 shifting at 4600. I am not going to get into it with you here, Norm. For those that don't know, Norm was tossed off of Oldspower for being argumentative and confrontational, taking things out of context, etc. So, he has a little problem with me. I am not going to get into an argument and muck up this nice site. Whoever wants to can read it and decide for themselves. I will state for certain that the carb caused the poor brake pedal. Holley carb on, great pedal, Q-jet on, crappy pedal, Holley back on, great brakes.

Olds64

That is odd that a carb could cause problems with your brakes. I suppose changin your carb affected your engine vacuum. I know I generally set my idle mixture screws to maximum vacuum or maximum idle.

88 coupe

Yeah, it is a possibility. Do you have another reason why you would need to use so much jet/pump shot?

And it needs larger than normal jets to accomplish it. Why?

Since the Q-jet mixtures were not changed in the same manner as the Holley, it could easily be 2 tenths slower. Not because it was inferior, but because it was jetted too lean for that application.

Here it is, again.

It was a question, not an attack.


RE: The original question:

At this power level, there should be no difference in ¼ mile times/speeds between a Q-Jet and an equal size Holley.

The clear advantage the Q-Jet has over the Holley, or AFB, is in its efficiency at under 2500 RPM cruising speeds. At WOT, you should not see any difference.

Norm

GoldOlds

Not to say that it's impossible for Comp to be wrong, but the same cam guide states that 9.0:1 compression is necessary for their .541/.544 lift, 240/246 @ .050 hyd flat tappet cam. If that REALLY is the case, 9.5:1 should be plenty of compression for the .485/.490, 224/230 @ .050 hyd flat tappet cam. Am I missing something? It's entirely possible that I am.

- GoldOlds

GoldOlds

Damn, whatever it is you're doing wrong, keep doing it!

- GoldOlds

Oldsguy

That is why I don't post much at ROP, those guys are serious go-fast addicts and I am out of their league. I would say the same as you Gold.......

captjim

The problem in a lot of those guides is that the some ones are used for all engines. A cam that is too big in a 350 might be just right for a 455. Maybe time to start a new thread, huh?

GoldOlds

As I've quite recently joined the Olds camp from the world of Chevy, I sometimes assume that if a cam fits in a small block that automatically means it WON'T fit in a big block. Oops. I've gotta get used to the fact that Chevy rules don't always apply to Olds. . .
And yes, the knowledge tossed about on ROP is sometimes WAY over my head. I honestly don't understand things like why or how lobe overlap is a good (or bad) thing, the difference between hyd./mechanical/solid/roller cams, etc. . . or why you need a certain gear ratio/compression ratio for a certain cam, etc. Lots still to learn!

- GoldOlds

captjim

In all honesty, I like ROP, but this site is much kinder and gentler, with a ton of smart fellas. Start a new thread, and ask about your cam choice, see what they have to say. Do a search, there is a ton of info out there. Also, just to confuse you more, a cam that works great in a 9.5 to 1 350 Chevy, won't work as well in a 350 Olds, and vice-versa.

The_Jeremiah

lol you guys are great. ok so my cam is 268 lift and a .455 duration for each valve. it was the best deal i could get. but i am wanting to drive this more than once a month lol. now before anyone gets into the brake subject, i have manual brakes lol. and being an original 69 block its got the number 5 heads, the performer rpm intake will go on, coupled with headers that run to a 3in. collector, and reduced to 2.5in exhaust all the way back. so back to the original question lol. i think i would rather go with a quadrajet, so will almost any one work, or do i need one from like 68-72 ? i dont mind buying one that was originally on a chevy, but will it work is the question ? im not familiar with the quadrajets, this is why im asking for your guys' help lol again. im sorry to say that i have only recently become interested in GM. so therefor no prior experience with Q-jets. thanks for the input

88 coupe

Any 350 B, O, P, or C, non computer, will work fine.

Norm

The_Jeremiah

good to know. thanks a lot. im glad i dont need to dish out like 300 for a fully refurbished q-jet off of a 69 442 or something. so anything that doesnt have all the plugins for the electronics is good. great thanks.

J-(Chicago)

Hey Norm....
What about swapping let's say....
an 87 monte ss Computer carb
onto an 87 442 vin 9..
?
Could you just reset the M/c solenoid and T.P.S. to the olds specs by adjusting the carb accordingly?

88 coupe

Two things:

Norm

J-(Chicago)

I understand.

Those carbs are not very fun to mess with, but your post sparked my curiousity on that subject.