Jetting down 450 Holleys - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

SIC-23T · 04-18-2005, 05:19

hello there. I have 2 450 holleys and they are running very rich. could i jet them down to 350 specs. will this improve them or will i have to buy the 350 carbs. my egine is a 351C stock.

Mike Gayner · 04-18-2005, 12:25

Two 450s is far too much for a stock 351 to begin with. It is possible to jet them down, but you can't really jet a carb to a different CFM "spec" because the carb will always be 450 CFM, not 350. I would recommend getting some time on a dyno with an exhaust gas analyser up its date, it's the most efficient way of jetting a carb.

crochunter · 04-19-2005, 00:30

Two carbies on a stock 351 is way too much.

grey_esp · 04-19-2005, 01:56

Is it just me or does this sound alot like MR ts question with the tunnel ram?

Mr FORD · 04-19-2005, 06:06

lf you change Holley jets more than 3 to 4 sizes either way from standard you have the wrong carby(s) for the job on a street car , they are set up from the factory for fuel ecomomy / performance / streetability in hundreds of different sizes/models for this reason .

tufLTD · 04-19-2005, 08:21

Quote:

Originally Posted by SIC-23T

hello there. I have 2 450 holleys and they are running very rich. could i jet them down to 350 specs. will this improve them or will i have to buy the 350 carbs. my egine is a 351C stock.

G'day. I'm new to the list but have a bit of experience with carby's. If it's a stock 351, throw the twins over your left shoulder & fit a 750cfm 4-barrel Holley with vac secondaries. Even on a stock 4-barrel manifold this will work well. It may require minor changes to the main jets or power valve. It will give you good torque & good top end and fuel economy should be about the same as a standard carby but heaps better than twins!
Mal.

grey_esp · 04-19-2005, 17:55

you could always throw that stock 351 over your shoulder and fit something a little bit lumpy under there.

Mike Gayner · 04-19-2005, 23:26

I can see why he would want to keep the twin carbies, they look bloody awesome! Maybe it's time for a massive cam and stroker kit, that would justify the two carbs :D

longroof351 · 04-20-2005, 08:32

Quote:

Originally Posted by SIC-23T

hello there. I have 2 450 holleys and they are running very rich. could i jet them down to 350 specs. will this improve them or will i have to buy the 350 carbs. my egine is a 351C stock.

I run twin 450s on a clevo so it can be done. Are your 450s the 450 econo carby (piece of shit) or the list# 9776 450 which holley produce as a street tunnel ram carb. If it is the later i have found i had to do a metering block conversion on rear of both carbs to get them to give good mixtures (i had to richen mine up tho).

When are they rich? at idle, cruise or wot. It could be a number of things so before i suggest anymore can you give me more info.

John
ps. i do not have a stock motor but we can get them to work.

SIC-23T · 04-22-2005, 04:22

Quote:

Originally Posted by longroof351

I run twin 450s on a clevo so it can be done. Are your 450s the 450 econo carby (piece of shit) or the list# 9776 450 which holley produce as a street tunnel ram carb. If it is the later i have found i had to do a metering block conversion on rear of both carbs to get them to give good mixtures (i had to richen mine up tho).

When are they rich? at idle, cruise or wot. It could be a number of things so before i suggest anymore can you give me more info.

John
ps. i do not have a stock motor but we can get them to work.

thanks for replying. they are the 9776 models. i had the timing at 3 degres and they weren't rich but i have it at 12 now and they are very rich. this is only at idle though.