Thread: Dumb questions...

Tweet

I'm new to the forums and new to the more technical aspects of car repair/upgrade. So please forgive me for my ignorance and if these questions have been asked on these boards before.

Okay, number one: my engine (see more info about it below) has an Edelbrock performer series intake manifold on it. On it resides a carb that does not fit the intake proberly nor is it set up properly. I have decided to replace it with an Edelbrock performer series carb. I have'nt ordered the new carb yet, because I'm not sure whether I need a a spread-bore or a square-bore carb. I have'nt removed the old carb yet, so my question is when I remove the carb, how do I know which bore type it is? What's the difference between square & spread bore?

Also, the engine in my Jag is supposedly from a '74 Chevy pickup. I wanna know though how do I tell if it's a big block or small block, what's the difference between big and small block?

Thanks in advance guys.

The only dumb question is the one you don't ask. Greetings. When you remove the carburetor, look at the mounting on the manifold. If it is square with four holes the same size, then it is a square bore. If the two rear holes are way bigger than the front ones, then it is a spread bore.

If the engine in your Jag is a 350, then it is a small block. You can tell by looking at the valve covers. A small block valve cover is held on at four mounting points--two on each side. Big blocks have more.

Greetings! And thanks alot. I thought your answer to the carb question was how it worked, but I wanted to be sure before I drop 300-400 bucks on a carb.

Another question on big/small block. Does engine size have anything to do with it? Meaning is there such a thing as a big block 350?

No. 350's are in the small block family. You can bore and stroke them to a much bigger size, but they are still referred to as a small block. It is designated that way because of external physical size, not internal cubic inches.

Don

Originally Posted by Itoldyouso

No. 350's are in the small block family. You can bore and stroke them to a much bigger size, but they are still referred to as a small block. It is designated that way because of external physical size, not internal cubic inches.

Don

Ah! Thank you!


That answers a very old question for me.

Some of the guys like Denny on here are very good at finding drawings and things like that. Maybe one of them will post some showing the difference between a small and big block for you and others who may need this info.


Don

The performer has accomidations for both Spread bore carbs, and Square bore ( holley ). You can mount either one. What do you currently have on there?

It's a quadrajet that does'nt fit right. It leaks around the bottom.

See, the guy that had the car before me was trying to do everything on the cheap and apparently had no clue what he was doing.

Makes me wonder. The performer should bolt up a Qjet just fine. The performer RPM on the other hand will not.

Hmm I'll do some more looking and take some pics. Maybe it just has a bad gasket on it. I'm going to replace it anyway I think, because the current one has setup issues, as well as the the fact that it's old and needs cleaning, etc.

Its probably just a bad gasket..............a Quadrajet is a direct bolt on a Performer manifold.

For anyone still folowing this thread, I went ahead and took some pictures of the carb/engine on my car, in case that helps things at all.
The images are at this link. WARNING! The images are 1600x1200 res and as such are quite large.


Also, for the new carb I'm thinking of going with an Edelbrock Performer Series 750 cfm carb. Jeg's has a factory remanufactured one for $209. Seems like a good deal to me. Any thoughts guys?

Yep, a picture is worth a 1000 words...........

What you have is a small block Chevy, non Vortec, prior to 1987 (I think 87 is the start of Vortec. The carb is a Rochester Quadrajet.

No, the 750 is way too big for a 350 Chevy (assuming this engine is a 350 and not a 305) You want no more than a 600 CFM or you will be overcarbed.

Evidently your intake is set up for spreadbore and squarebore (from what others have said, but to be sure pull the carb and look at the base pattern).


Don

Okay, thanks. And quick question, what do you mean by 'overcarbed' what happens then? Also I would guess that what I was told about the engine is atleast possible if not indeed correct. Also, what size/type of carb would folks recommend for a 350?

The deal is that I bought the car from a small dealership, and everything I know about the car comes from the guy that worked at the dealership and most of what's been done to the car so far was done by the guy that had it before the dealer. So, most of what I know about it is second hand.

Thanks for the help guys. All the answers in this thread have saved me many hours of trial and error and research. Thanks!

Edit; Just wanted to correct my semi drunken grammar/spelling. Haha.

Overcarbed is just what the name implies.........the carb has too much airflow and fuel being metered into the engine for it to all burn/be used. As an extreme example, if you put a four barrel carb on your lawn mower it would be overcarbed. The engine can only use so much, and will run very rich and badly if overcarbed.

Ideal for your engine is about 600 cfms. There is some mathmatical formula that I think Richard (techinspector1) has posted, but I forget what that is exactly. I just know the typical small block runs well on about 600 cfms.

Just for sake of asking, why do you want to lose the Rochester that is on there. Although they generally don't have the performance image of Holleys or Edelbrocks, they are actually very good carbs for a street engine. Mercruiser and all the other boat engine manufacturers have used this carb for years and years, and the nice thing about them is that they are very economical to operate due to the small primaries. You could have it rebuilt and probably be fine. The Jag isn't a drag car, so for smooth street performance the Rochester would not be a bad choice IMO.

Just a thought.

Don