So I have a 77 ta. 400 4spd.
I have headers, comp cam 262 or something along those lines. Edelbrock performer rpm intake. And a Edelbrock 650 off road carb. I was wondering what people are running for jets and rods
I wondered that same question about Q-jets back in the 70's, except there was no Internet then. So I bought what Pontiac books there were (H-O Racing, etc) and saw a few pages here and there in various articles where the Q-Jet set up was actually given. I tried to copy that set up on my then '74 400 Firebird and I was disappointed. The engine ran "just OK" and I soon realized that I was going about it all wrong. When I finally learned that the jets (metering rods included) controlled the fuel volume going into the engine, and that the vacuum "signal" that the carb was working with was what was siphoning fuel from the carb bowl. The more vacuum, the more fuel was pulled into the incoming air stream. I realized that the manifold vacuum my engine was making under certain conditions was not very likely to be the same as another engine when you consider all the variables that effect the manifold vacuum at any time. Cam design, compression ratio, engine size, ignition timing, to name a few all effect the vacuum "signal' a carb sees, and the stronger the vacuum, the richer the mixture, given the same jet/metering rod combination. I finally visited an old time carb shop where the guy said I can have as many jets and metering rods I want from a pile he had collected for years for $10. I then would start to change one thing at a time, and see if it made any difference. If it did not make a difference I would go the opposite way and so on. In other words, I had to do real world trial and error to find the answer, otherwise you should leave the carb the way it came out of the box and just do the normal external adjustments. I actually think a 650 is a bit on the small side for a 400 with headers that sits in front of a 4 speed ..... being that the factory Q-jet by '77 was 800 CFM. If not, at least it was a 750 CFM. I would not spend much time tuning a 650 CFM carb on a 400 4 speed car, I'd get a Q-jet and tune it, or if you like Holley's, get a vacuum secondary spreadbore carb in the 800 CFM range and mess with it.
Well, when I read this, I has similar thoughts. But, the question of which carb to run was not ask. So, I didn't respond.
BUT, since someone else mentioned it 1st, I'll agree with him. :yes
There have been LOTS of posts, on several Pontiac sites, about the shortcomings of Edelbrock carbs. The only one I'd run is an Edel-Q-jet.
Everybody knows, by now, that I always recommend a Q-jet. But, I know some prefer the Holley type carbs. And, there have been millions of 'em used successfully, over the years. So, for those who prefer the Holley type carbs, I also recommend a vac secondary model. Since you have a Performer intake, you can use either a square or spreadbore.
There is a guy who posts over on the GTO forum who did some testing with a Q-jet and several other carbs. For his 400, his conclusion was that the Quick Fuel SS-680-VS, was the best choice. These vac sec SS series carbs come in several sizes. But they are not cheap. :no
A 455 bracket Ventura I bought, came with a square bore Holley vac sec carb(choke tower was removed, so I don't know the part # or cfm), on a Torker 2 intake. It ran good and worked perfectly, either from an idle or a 2000rpm powerbrake launch. So, a Holley will work, too. And, a good used 750 vac Holley is a lot cheaper than a new Quick Fuel. :smile22:
Edelbrock carbs get a bad rap in many forums, but they are pretty good carbs if tuned correctly.
The issue with them is, you can tune them for the street, and they are pretty good, but not the best at the track. Tune them for the track and pretty good there, but not the best on the street.
One thing you can do is call Edelbrock. They have a great support staff. They can take your engine configuration and give you what will work best for the way you plan to use the car. It might not be a perfect setup, but they will get you close.