Hi all, I have NOS Holley 4160 650 Spreadbore I picked up from Allstate Carb on Long Island.
I am installing on my stock 73 BB spreadbore manifold. Original Quad long gone before me.
My question is whether anyone has any experience with the gasket set up. I would like to use a std 1/4in thick gasket but since the Holley has bigger primaries than the Quad which style gasket makes sense. Holley spread 4 hole, Quad spread four hole or full open.
My concern is while both are spreadbore the holley primaries may force the air fuel charge down on the smaller manifold opening and cause a disturbance as it hits the manifold.
Anyone with personal experience? Thanks all.
Much appreciated.

 

I can’t offer anything regarding your spacer questions but I can tell you that I really liked the spreadbore Holley that I used on my last 69 350/350hp. The “rebuilt” quadrajet that came with the car when I got it was a real mess. I happened to have a spreadbore Holley available so I bolted it on. The out of the box calibration was pretty close to correct. I simply reinstalled the dropbase air breather and enjoyed many hours of trouble free cruising.

 

Do you happen to recall which gasket style you may have used? Holley base match, intake(Quad) match or open? I’m thinking in the end probably doesn’t matter as no matter which is used there will always be a fuel flow interference fit given the differing size primary and secondary openings. I have never seen an adapter for spreadbore to spreadbore variants as with squarebore to spread.
Thanks.

 

3998912 is the OE part number for a 1973 QuadraJet. Use it. You'll be fine.
https://quadrajetparts.com/quadrajet...12-p-2444.html

 

Use the open one unless you need to tame a big cam down. I have tried both. Depends on what manifold you are running. If it's got a full height divider you could use the 4 hole to tamp down the cross-talk from the 2 sides due to overlap. Helped me with 1700 RPM cruise problem in OD with my bigger cammed stroker. Makes it more "streetable" in my experience. Hurts power at the top end though.

 

Many thanks. Ok I going to use the open, again it’s a stock set up but while the one “Drifting” identified as the oem quad gasket regretfully it is only an 1/8th in thick and the Holley 4160 throttle arm huts the factory intake mounting boss which is why I mentioned originally needing a 1/4 in gasket. Since the throttle arm has no room for grinding down I am still on the hunt. 1/4 and 1/2 in. quad open gaskets don’t seem to be out there, at least so far. Summit
does have a 1in spacer and gasket set up for the spread but will be a very slight rub fit on the hood using my stock air cleaner.

 

Bought mine from quadrajetpower. Ebay and his own web site. He has both types.

 

uh. late model cars have a @1/2 inch phenolic spacer?
it is open and if the holley primaries were/are bigger diameter I would grind clearance in the spacer/gasket.

 

Holley spread bores are direct replacement for Quadrajets. Exactly what list number carburetor do you have? Look at the front of the choke airhorn

 

Allstate carburetor should be able to help you . They are really good people in spite of being in new yawk 🙄

 

If you believe the opennings are smaller, put it on the carb and open primary and secondary blades all the way and make sure they will not have an interference issue. If not buy the correct holley gaskets and get a quarter inch thick phenolic spacers and put gaskets on both sides to close any of the stock ports on the intake manifold. I used a Holley spread ore on my 430hp 327 with a RPM intake with a L88 hood. It performed awesome and gave me 16 mpg

 

I've used that carburetor on many factory q jet intakes and they bolt right on..

 

I'll try again, what is the list number of the carburetor found on the front of the choke airhorn?

 

Thanks all for the comments and feedback. I am believing I may have an acceptable solution as Corvette Central had a 1/4 in thick open spreadbore gasket that I ordered even though the Qjet part number often comes up as being only an 1/8 inch.
Will see.
All Holley spreadbores are considered "direct replacements for Qjets but in a generic manner as they will fit on top of Gm Ford and Chrysler SB intakes all of which are slightly different in primary and secondary size venturis. The reason for my original inquiry was to see if anyone had ever tried experimenting with the various 4 hole, and open gaskets for Holley and Qjet to determine the best running characteristics rather than re inventing that wheel myself. The fact is Holley SB's have different size venturis than a stock chevy SB intake. Everything will fit and play but interference can happen on 4 hole gaskets in one direction unless modified or spaced whereas the open will not. In some instances 4 hole and open perform at slightly different levels. Also as I had originally mentioned that while for the stock application it may not be even noticebale Holley SB will try and push the air/fuel mix down the smaller primary opening on the stock Qjet intake and there will be some albeit maybe minor disrutption as it bounces past the intake primary opening wall. Certainly not an optimal charge disbursement but again I relaize unless in a hi perf app maybe not ever noticeable. Just trying to see if anyone else had ever done the trial and error since the Holley SB was a popular replacement for many C3 Qjets.

Again many thanks for all the suggestions and guidance and in the end I was steered in hopefully ok solution since presently I have been using the Qjet 4 hole with the primaries cut to match the bigger Holley and while working have long felt maybe others have tried and done all this before.

I will report back once received and done.