318 Carb Size Question

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540slant6

540slant6

Mopar SB Ripper
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Gents

I have a stock bottom end 318 with stock cam. I have .040 decked 1.88 "J" heads with an Eddy four barrel performer manifold. I'm running Hooker headers and full dual exhaust with electric MP ignition kit. I currently have an Eddy 500 CFM carb. Seems to peter out around 5,000 RPM. I'm thinking it needs a bigger carb?



I found a deal on a 650 CFM but didn't know if that would be too big? The 650 has vacuum secondaries but wanted to get some opinions.

Thanks guys
 
500 cfm should be enough to go 6k rpm. Your stock cam duration and lift is more than likely maxed out by 5k.
 
You could put any carb you want on it and it will still "peter out above 5000 RPM". That's where the stock 318 cam peters out. I'd be surprised if you noticed any difference with the crab swap. If you were running a different cam, like an XE268, it would be a different story.
 
I ran that same CFM on a 318 years ago and it had less done to it than yours does - you'll probably get off the line quicker - more air, more fuel - it'll undoubtedly lead you to other needed upgrades too.. plus, you'll have it for that warmed up 340/360 you're planning.. :twisted:
 
Thanks guys, I have a 68 spec 340- 4 speed cam I'm going to swap shortly. Sounds like ito may help with the higher rpm.
 
My cousin has a 500 cfm 2bbl on a stock car that runs 7000 RPMs and pulls all the way, and 2bbl are rated different so a 500 cfm 2bbl equals a 350 cfm 4bbl.

I agree it's you cam just be careful cause of low CR with choice, you don't need to large, stock cam sucks so much any cam is a big step up.
 
A 318 will use about a good 600 cfm at 6000 rpm. 650 @ 6500 rpm in moderate useage.
IMO, I think your choking it out with the 500 cfm carb, which would be fine it were a Hwy. geared people moved car. You know, just a ride to get grocery goods, church on Sunday, a drive on the Hwy. to the ball game, etc......

Even with that mild cam, a 600 is the min. size carb I would use. And I'll consider the rest of the engine as a stock-ish like set up. Like small valves 360 heads and headers with a 3.55 or less ratio.

What's the plan &'set up?
 
im running a 670 holley avenger on my 318, 284/484 cam, its never felt too big. if i'm not paying attention shes at 7000 rpm. 650,670 should be fine
 
that 600 CFM holley would run good on a teener with a mild Cam. Been said before but, too much carb, you WILL lose low end throttle response.
 
I don't have any experience with the Holley carbs, I've only used eddy's so I'm not sure I could tune a Holley.

The plan is to install an SG rear I have with 3.90 gears and run hole shot hurst converter at 1,800 stall.
 
I'm surprised nobody has asked. What jets and rods are in it? What kind of tuning are you using, feeling it, AFR?
 
540slant6 said:
Gents

I have a stock bottom end 318 with stock cam. I have .040 decked 1.88 "J" heads with an Eddy four barrel performer manifold. I'm running Hooker headers and full dual exhaust with electric MP ignition kit. I currently have an Eddy 500 CFM carb. Seems to peter out around 5,000 RPM. I'm thinking it needs a bigger carb?



I found a deal on a 650 CFM but didn't know if that would be too big? The 650 has vacuum secondaries but wanted to get some opinions.

Thanks guys
Click to expand...

650 would be fine. It's petering out because of the stock cam.
 
I'm surprised nobody has mentioned how low the compression ratio will be on a stock 318 with Jheads!
 
It's runnin outta valve spring.
 
540slant6 said:
I don't have any experience with the Holley carbs, I've only used eddy's so I'm not sure I could tune a Holley.

The plan is to install an SG rear I have with 3.90 gears and run hole shot hurst converter at 1,800 stall.
Click to expand...
Stock 318 converter will flash to 2000.
 
U planning on new valve springs? I hope so. I had a 500 afb on a 1968 318 with a Streetmaster intake and it screamed, outdragged a 350 camaro. maybe yours is lean? for more I say a 625 avs off a 340 - 1968-70 - in nhra superstock they run 10's
 
Mines a 318LA with stock small valve j heads. 340 spec cam (not sure which one though it was free!), long tube headers 2 1/2 inch exhaust. torker 2 manifold eddy 600 carb.

Pulls to 6k. When I had just glasspacks off the headers to turndowns (purple hornie style) it pulled to 6200 but had a lot less low/mid range.

With low compression run a lot of timing, I am probably at 40-45 total timing on weak advance springs. runs very well for what it is and cost me barely anything to build.
 
Do I really need to change the valve springs with such a mild cam. Stock spec 340 4 speed cam is around .444 lift, I believe.
 
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