Baseline jet size

[Dusty Dude]

Hi All,

Just purchased a Proform 1050 cfm carb for my 496" (383 stroker) and I am curious if anyone has this carb on a similar engine as described below and if so where have you ended up with your jet sizes?
This engine is in my '69 Coronet resto-mod street cruiser. I doubt seriously it will ever see a race track.

The carb was shipped with 87.5 primary and 91 secondary and a 4.5 PV in primary, none in secondary.

440 Source stroker kit
10.5 comp
Stealth CNC ported heads
Mopar M1 intake
Howards roller 565/565, 241/247 @ .050, 110 LSA
HS 1.5 rockers
MSD ignition
Hooker long tubes (1-3/4")
3,000 stall converter
3:55 gear

If this was a pair of 1050 Dominators on a 468" BBC I could tell you just what you need to be in the ballpark but I don't have much experience with the single carb setups.
I know how to tune it, I am just asking if it's close in its as-shipped state.

Thanks for your input.
Mike

 

[JackpotJim]

Just my 2 cents but 87's in the primary's seem a little big for street car, I'd stick 72 or 74's in the front and 84 or 86's in the back. The way the carb was shipped is more of a extreme street strip setup. Obviously reading the plugs or air-fuel meter will get you dialed in.

 

[PRHeads]

What size are the HS air bleeds?
Does it have downleg or annular boosters?

I’d suspect it’ll be happier on the street with less primary jet, provided the air bleeds aren’t too big.

I’d also lean towards a higher rating PV to go along with the smaller jets.

 

[Dusty Dude]

What size are the HS air bleeds?
Does it have downleg or annular boosters?

I’d suspect it’ll be happier on the street with less primary jet, provided the air bleeds aren’t too big.

I’d also lean towards a higher rating PV to go along with the smaller jets.

Air bleeds are 31's and are changeable, boosters are down-leg.
Agree on PV.

PVCR jets are also changeable. I haven't measured them yet so not sure what they have in there.

Thanks
Mike

 

[PRHeads]

Most of the common 4150 “1050’s” have a 1.59” venturi.
If that’s what you have, with downleg boosters they generally use pretty big jets, but admittedly I’ve never run one on a combo as mild as yours.
I’d leave the secondaries alone for starters, and would try 84-85’s in the front with a 6.5pv.

Ultimately you may end up wanting to install an O2 gauge in the car to see what’s really going on.
It might be challenging to find the balance between the correct a/f ratios for part throttle cruise and wot.

 

[BobH]

I've got a very similar engine combination with a Holley 950hp. Currently running #67 primary jets, # 78 secondary. Idle air bleeds #82, high speed #28. Primary power valve is a 10.5, secondary 6.5. I've got an AFR gauge on it and with this setup it is a little rich at cruise, I'll probably go down to a #66 primary, but this motor does not like to be even slightly lean. If it's at 14-14.5 afr at cruise light acceleration has a lean surge. Accelerate hard enough to open the power valve and it's good. If I put a billet metering block on the primary and played around enough with emulsion tube jets that surge could probably be tuned out of it. Make sure to get your timing curve right before you try to do the carb. David Vizards "How to Super Tune and Modify Holley Carburetors' is well worth the money for tuning information. Hope this helps.

 

[BSB67]

I don’t think a Holley 950 will have much in common with a 1050 for jets size.

 

[cj's mopar]

I have a 493 solid roller 250 256 with 630 lift .
Sr Indy.heads
M1
850 demon with anular boosters.
MSD
Running 84 jet primary 8.5 power valve to open quickly.
94 jet in back.
Idle AFR is 13.0
Full throttle AFR is 12.8.
I would try 82 and 92 in your carb
With a 59 idle air bleed.
A 28 idle jet. Starting point.

 

[91r/t]

Couple of my buddies that build engines always said you usually wanna see 6-8 jet size differences between primary and secondary sizing as a good baseline for a street motor. Obviously if you are shooting for huge power at the track this may change, but a good place to start.

 

[BSB67]

Couple of my buddies that build engines always said you usually wanna see 6-8 jet size differences between primary and secondary sizing as a good baseline for a street motor. Obviously if you are shooting for huge power at the track this may change, but a good place to start.

Without any qualifications, that’s horrible advice

 

[91r/t]

Without any qualifications, that’s horrible advice

It's always got me atleast somewhat close on my mild street engines anyway. Alot of combos on here jet wise end up being in a similar ballpark. I am not saying its an end all be all but seems to be alot end up in that range.

 

[PRHeads]

The closest I could come to giving any type of “broad range” starting point for carb jetting advice would be…….. and even this needs a qualifier stipulating that the carb in question is appropriate for the application………. Start with the factory jetting, and adjust from there.

 

[91r/t]

The closest I could come to giving any type of “broad range” starting point for carb jetting advice would be…….. and even this needs a qualifier stipulating that the carb in question is appropriate for the application………. Start with the factory jetting, and adjust from there.

I guess I’ve gotten lucky and used the correct sized carb for my application like you said. I usually over analyze and pick brains like crazy though and have reasonably common combos so that’s probably why I’ve made out pretty good. Plenty of more qualified members on here to comment other than me.