383 dyno results

[c1500sbc]

Freshly built 385. Promaxx maxx 200 cc heads, scorpion 1.5 roller rockers, flat top pistons, static compression 10.68:1, crower roller cam 236/240 at .050 with .555 lift and intake closing point at 44 degrees. Weiand street warrior dual plane with 1” carb spacer, link bar lifters, Edelbrock 750, MSD 6AL with blaster coil and a non vacuum advance distributor (gunna order one with vacuum advance), 1 5/8 long tube headers and a dual exhaust. 3.73 posi rear end through a 5 speed nv3500.

I was hoping for a little more. It's weird to me to be making so much more torque than hp with the 200cc heads. I'm really thinking some Chad Speier heads in a little higher (220 ish) cfm would really make it wake up. I was hoping for something in the 350-375 for hp. I'm sure the tune could use a little help also.

What do yall think of the results?

[F-BIRD'88]

You may want to ask what the dyno correction factor was..
eg: corrected for weather or raw uncorrected.
look up and note the local weather conditions during the testing.
The drivetrain can eat up a lot of power. Everything driven off the engine consumes some power.
(friction, mass inertia)

You have a baseline now.

[F-BIRD'88]

To find more "as installed" net power start at the air cleaner and carb. Might want to look to see if that 750 eddy carb hs the restricted orrifice secondary booster clusters.
TUNER can advise on how to correct this..
Some air cleaners really suck. You'd be surprised.

[F-BIRD'88]

The more agressive the truck tires are the more power they will absorb against the dyno rollers.

[c1500sbc]

I need to just find a good carb tuner. The couple dyno guys in town are computer tuners only. AFR’s on the AFR gauge look decent, but I pulled one of the plugs when I got home and man does it look rich! It smells that way too, but I figured with no cats it was going to be a little stinky. Now I’m thinking there may be much more tweaking on the tune then I thought. Check out this plug! There’s probably 3k miles at the most on them.

28” tire so it’s relatively small.

[c1500sbc]

Same plug different picture.

[F-BIRD'88]

Plug looks pretty carbon fouled..
Can effect power for sure..
Lack of vacuum advance.. Low speed/idle carb setup..
On my old 750 I leaned out the primary "cruise" part if the primary metering rods. If the pcv is deleted the carb idle circuit will shift rich.

Can be an ignition fault too.
Be sure the engine is grounded to the firewall.

[rustbucket79]

I was about to type out a book, but let’s be honest, you’re just beginning your disease.

Invest in a quality in car AFR (wide band) and most of your tuning questions will be answered in real time.

You own a highly tuneable carb (assuming it isn’t pooched) and you can easily figure out what you need to do. If you’re seeing high 12’s on the dyno during the power pull that’s perfect, all you need to address is step up springs and the main metering rods, specifically altering the cruise step size to achieve high 13’s to high 14’s on cruise, whichever the engine responds to without bucking or feeling soggy. Set mixture screws equally to highest vacuum.

I find it very common for dual plane engine combos to have higher torque than horsepower.

[F-BIRD'88]

Make sure none of yhe air bleeds in the carb are gumed up.
Blow out with compressed air.. Wouldn't be the first time.

[c1500sbc]

I was about to type out a book, but let’s be honest, you’re just beginning your disease.

Invest in a quality in car AFR (wide band) and most of your tuning questions will be answered in real time.

You own a highly tuneable carb (assuming it isn’t pooched) and you can easily figure out what you need to do. If you’re seeing high 12’s on the dyno during the power pull that’s perfect, all you need to address is step up springs and the main metering rods, specifically altering the cruise step size to achieve high 13’s to high 14’s on cruise, whichever the engine responds to without bucking or feeling soggy. Set mixture screws equally to highest vacuum.

I find it very common for dual plane engine combos to have higher torque than horsepower.

You’ve just about described the tune in it already. I have a pretty good in cab AFR gauge. Upper rpm range at WOt is in the 12’s, 15’s at cruise and idle adjusted to highest vacuum.

With that being said, even if it’s an ignition issue, why are the plugs so fouled after such a short amount of time but the AFR gauge says the fuel mixture is on the good side?

[rustbucket79]

High overlap shows up as a lean condition on an AFR at idle. It also causes exhaust pollution in the chamber on the power stroke at every point until the engine gets “on the cam” and becomes efficient. More duration, more RPM before this happens. Vacuum advance helps to light off the polluted mixture in the less efficient “cruise” range.

You’re driving a std transmission, that means many more “pump shots”during a drive since you’re off and on the throttle with every shift.

A hotter heat range spark plug might be in order as well.

Dyno sheets aside, is it fun to drive?

[c1500sbc]

High overlap shows up as a lean condition on an AFR at idle. It also causes exhaust pollution in the chamber on the power stroke at every point until the engine gets “on the cam” and becomes efficient. More duration, more RPM before this happens. Vacuum advance helps to light off the polluted mixture in the less efficient “cruise” range.

You’re driving a std transmission, that means many more “pump shots”during a drive since you’re off and on the throttle with every shift.

A hotter heat range spark plug might be in order as well.

Dyno sheets aside, is it fun to drive?

That makes sense, I need to to just go ahead and order that distributor with a vacuum advance and stop talking about it. Is there a target idle AFR you would shoot for? Any suggestions on spark plugs?

Tons of fun to drive! Started off with a 4.3, built a small flat tappet Vortec 5.7 that put down 220 or so, sold it and bought a 355 short block and put some aluminum heads that made 275 and now the 383 putting down 320’s. Every 50hp to the wheels and it feels like a different truck!

[F-BIRD'88]

If memory serves, I believe on my Eddy 750 (1407) I changed the primary metering rod from 71x47 to 75x47
stock default .113/.107 p/s jets. The primary cruise seemed a bit rich... It was not a difficult carb at all.

[F-BIRD'88]

All those seem modest for chassis dyno power from those engines.

[mag2555]

Truck tires due to there size have a lot more mass then car tires, and since they are still part of the overall rotating mass factor they eat up a bunch of power that could be had otherwise!