Edelbrock Carb on a 354 hemi...tuning questions

DanBabb · Aug 26, 2013

This is in my 52 Dodge 1/2 ton (link to build in my signature line).

I have an Edelbrock Thunder Series 650 carb on my 354 Hemi. Timing is at around 11.5 degrees btdc. Using the MSD ready to run distributor I got from Hot Heads. Compression ratio is about 8.5:1. Running a Sig Erson cam. Trans is a TH350 auto. Even if I manually shift it...feels the same way.

The truck starts up, idles and cruises fine. Doesn't smell rich or ping at all.

When I really step on the gas, the truck just doesn't have the get up & go that I think it should have. It will accelerate...but it's kind of a slower increase in speed than I think I should have.

It does this at any speed.

So if I'm at idle and give it a stomp on the pedal...it moves forward. Doesn't put you back in your seat at all.

Same thing if I put it in second while cruising at 35 and punch it. Just seems to be a little anemic in acceleration.

If anyone is running a carb like this on their Hemi...what jets and rods should I be using? I'll have to look at mine to see what's in there now.

Could my exhaust routing be stifling performance? Here's a picture of the exhaust routing now. I believe it's 2 1/2" pipe all the way around. The Driver side had to route around under the pan to the passenger side. The passenger exhaust T's in the pipe and then out to the back. There is a muffler after the merge too (probably 5-7 feet after the T)

Anyone have any thoughts? I don't expect this to haul-ass. It weighs around 3500lbs without me in it...but I do expect a bit more oomph.

hendo0601 · Aug 26, 2013

What have you got for rear gears? The exhaust doesnt really look like it is restrictive at all, so I would pretty much rule that out as a possibility. Where is the accelerator pump lever at? There are three settings on it....since it isnt bogging out I would assume that it isnt getting enough fuel. Try moving the accelerator pump rod into the hole which allows the longest movement i.e. biggest "shot" of fuel. Get yourself the tuning kit for this carb and I believe a T20 torx screwdriver to take the top plate off to access the floats, rods, and jets...and basically start to expirement! The kit comes with a little chart that at first looks confusing but after staring at it for a few minutes it starts to make sense. I had a Thunder series AVS 800 on a built chrysler 383...wayyyyy too much carb and I had to seriously lean it out in order for it to put me back in the seat, sounds like you have the opposite problem!

Jon

mustang6147 · Aug 26, 2013

If it was me, I would be lookin at other things, not only the carb...

I don't know what cam you have, you only posted the mfg name. You didn't mention if it was installed straight up or what...

The Cam and Tq converter need to match.... If your runnin a stock converter.... Big problem..... Gear ratio??? How heavy is the car? Tire height??? SO many qiestions...

But off the top, I would be runnin a Holley 850 Double pumper, jetted 84 to 86 sq and a plugged PV..... But many argue, I like a crack to the throttle, the PV lessons the punch. SO now let the critics tell me I am wrong...

hendo0601 · Aug 26, 2013

Nothing wrong with a double pumper, but 850 might be a bit much for a mildly built 354 hemi...I had an 850 Holley on a built 440 and it ran like a raped ape! I agree with you that the carb may not be the only culprit here. We need more info..

greybeard360 · Aug 26, 2013

You're wrong.

850 too much for that 354, I am assuming fairly mild cam and probably a stock or low stall convertor. Otherwise he would have headers and big exhaust pipes on it.

No PV on a street carb? Makes it way too rich for good driveability. I run PV's in race prepped Holleys.... keeps from loading up and fouling the plugs puttering thru the pits.

Before you go ripping the top of the carb of and messing with the jets and metering rods, look at the plugs. I bet the jetting is pretty close right out of the box. One hint.... turn the idle mixture screws in and out. If you screw one all the way in and it tries to die or does die, see if it idles good with both crewed out 1 1/2 to 2 turns. If that is where it is happy, then the jetting is pretty close to right on.

Now.... you have a RTR MSD distributor. Out of the box, they have a very slow mechanical advance curve built in. That is why it isn't wanting to ping on you. Dig out the springs and bushing a that came with it and go to a lighter spring. Also, if you have one use a dial back timing light so you can see how much total timing you are getting at around 3000 rpm (should max out at around 36 degrees). The little bushings that come in the kit changes the amount of mechanical advance. If it seems like it perked up a bit and isn't pinging, go to the next lighter spring setup... trial and error but that is how you tune the distributor to the car/motor. You may also be able to add some more initial timing to it... again, try it and see.

Are you running the vacuum to venturi or manifold vacuum ???

Depending on the cam etc, you may need more or less total advance, but 36 should be pretty close.

mustang6147 · Aug 26, 2013

No PV leans it, and then you re richin with the jets, and gain control with the throttle....

Try it. you will be shocked by the power gained......

When you run a high duration cam, or a low vacuum situation, especially on the street, it controls excessive gas dump when your not at WOT....

An old Drag racer showed me this back in the early 80s. That's why holley makes the plug and sells it.... Big demand among hardcore racers and fast street machines..... They where right....

You run with the Outsiders or Outlaws??? I have a buddy who runs with the Texas Outlaws

greybeard360 · Aug 26, 2013

I tried them. I know what they do. I have a few in my tool box I pulled out of carbs so I could get them to run "right".

Yes, in certain situations, you use them. Just not in this situation.

dan31 · Aug 26, 2013

There are 3 positions for the linkage,its probably in the middle now,move it to one of the others and take a ride-see if it feels better.

ago · Aug 26, 2013

The advice about plugging the power valve. You guys are talking about Holley carbs. He has an Edelbrock. Different type of power valve. You don't run an Edelbrock without a power valve. 36 deg. is too much advance for an early Hemi. You guys are thinking Chevy. Hemi combustion shape = 30 deg. total advance. (ask Hot Heads) Forget your initial advance till you know your total advance. Run vacuum advance. Get your ign. timing in order before messing with carb. No more than 30 deg. total advance, mechanical, all in by 3200 rpm. Then start messing with carb jets. I just put another of my 354 Hemi's together. Your problem might be in Ign. advance. Vacuum with make it pull pot nicer.

Ago

hoop98 · Aug 26, 2013

Check your distributor, it is set for full adv at 4000 stock, you need that at 2500.

DanBabb · Aug 27, 2013

Thanks for the suggestions. I'll dig through my notes to get all the specs asked for. Here's what I have now.

Converter - I believe it has a 2800 stall. I will have to check through my notes to see if that's right, but from memory, I think that's what it is.

Cam - here are some notes I have in an email when I bought it.  "NOS Sig Erson cam for the 354 ( original p.n. RV-10-H). 0.415" lift, and advertised duration of 256 deg (208 @ 050). The 'RV' designation was very popular in the 70's, indicating a cam with improved low speed torque characteristics. The 'H' indicates hydraulic."

The tires are 215/85/16 Firestone HT radials. Overall Diameter is 30.4 (according to TireRack). I wanted to keep a stock look, so no fancy wide low profile tires on my truck.

I will also look to see what hole the PV linkage is in. If I turn the idle screws all the way in, it will die...but at about 1 1/2 turns, it does idle fine. I did check the float levels a while ago using the instructions in that came with the carb.

I will check on the timing advance and to see when the timing is 'all in'.

GassersGarage · Aug 27, 2013

I had an old O.T. truck with a stock bbc. I was always tinkering with the tune and finally threw in the towel. Took it to a dyno-tune shop and it was money well spent. Never touched the tune after that.

greybeard360 · Aug 27, 2013

Hoop has the right stuff there for you. Those plug and plays are good distributors but like the rest of the MSD distributors, you have to calibrate it for your application (just like any distributor used in performance applications).

Does that distributor have a vacuum advance on it? If not use what Hoop has suggested.... should be pretty happy there. If it does, use what he suggested and leave the vac disconnected.

ago · Aug 27, 2013

leave the vac disconnected. __________________

Disagree on that, tried my 354 both ways, much better with vacuum advance.

Ago

hoop98 · Aug 27, 2013

The vacuum advance only affects part throttle, if it idles fine now I'd leave it hooked up like you have it. Once you step on it the vacuum advance goes away but it helps the fuel mileage.

Because you will have very high vacuum I'd change the step-up springs to the Pink 7' or the Plain 8' springs.

If you have a truck that weighs 3500, with you in it and some fuel we are talking about 3700 pounds.

With that single exhaust and the RV Cam your power is going to look something close to this. The problem is with that converter your Torque is dropping off as soon as it locks up.

Same combo with a set of headers.

We can use the road for a dyno; be sure you have an accurate 1/8 mile marked off and calibrate your speedo using mileage markers so you know how much it is off. Now go see what MPH you get in the 1/8.

This will tell you about where you are power wise;

67 182
69 200
71 216
73 235
75 255
77 275

If you are on the low side then a dyno tune will probably be a good investment.

DanBabb · Aug 27, 2013

The dizzy has vac advance and it's hooked up to the base of the carb (the port that is above the butterflies). The other vac port is routed to the transmission and the big one is to a PCV valve that's in the valley cover. I have a breather on the front of the valley cover (oil fill port). No breathers on the valve covers.

Vac reading on the engine at idle is in the 15 or 16 range...but it's steady...not bouncing around.

If I could find a good dyno tune shop around here that knows carbs, I'd drop it off in a heartbeat.

31Vicky with a hemi · Aug 27, 2013

Man ,,,,, they have been tuning carbs and ignitions without chassis dynos for ever.

So hook up your timing light, plug the advance hose and get her up to 2500 RPM.
You want to see it around 30*. ( I'm guessing its not close & less)
If its less than 30 pick up your rpm in 500 increments and note the rpm and degrees advance. See what that looks like plotted on graph paper compared to hoops post.

Try and set the timing at 2500-3000 Rpms to 30*. This will be your total set.
Chances are that your initial will be way off and give you starting troubles. Maybe not???
This is where the recurve comes in, softer springs, heavier weights, and different vac cans.

Really want to get fancy pick up a wide band 02 and dual in the carb.

That 2800 rpm stall converter does not match an RV cam profile at all.
The RV cam will give power off idle up to 3500 and rapidly fall on its face. Your converter is just sitting thru most of the power band of that cam.

hoop98 · Aug 27, 2013

DanBabb said: ↑

The dizzy has vac advance and it's hooked up to the base of the carb (the port that is above the butterflies). The other vac port is routed to the transmission and the big one is to a PCV valve that's in the valley cover. I have a breather on the front of the valley cover (oil fill port). No breathers on the valve covers.

Vac reading on the engine at idle is in the 15 or 16 range...but it's steady...not bouncing around.

If I could find a good dyno tune shop around here that knows carbs, I'd drop it off in a heartbeat.
Click to expand...

Dyno tune is a good choice for "getting it done" and if you watch closely you can learn a lot.

The satisfaction of doing it yourself is also a factor that varies.

Make the changes on the springs I indicated above, go to 3,000 and check your advance, set to 30.

The "660" foot dyno works well for timing changes.

1. Make 2 runs, advance 2 degrees and see if you gain 50 RPM, about 5 HP, or 1 MPH, more like 8 HP . Repeat until you hit 38 total or it stops going faster. Then back up 2. If it starts pinging about 3000-3500 go back 2.

It's unusual for the carb to be lean on full power, we usually need to work more on part throttle.

You can use the tip in method to check part throttle.

Block the throttle to 2500 RPM.

Tip the choke in slowly, it should pick up 25 RPM or so. If it picks up 50 or more you are lean, go up one step on the primary jet.

If it doesn't, pull off a 1/4 inch vacuum line (not from one runner), if it picks up 25 or more RPM it's rich, go down one step.

This will get you very close, the dyno will be closer.

If you get an A/F ratio sensor, shoot for 12.5 WOT, 15 part throttle.

Check Part throttle 2 " above the Step up spring value. So for a 5''HG spring do it at 7.

Btw, my sig means, I think, therefore I tune!

MBog · Aug 27, 2013

Timing timing timing,,Those msd distributors are horrible out of the box. I typically use one of the lightest springs and the next one up and leave the bushing they installed. Also you should regap plugs to 0.045 with electronic ignition. I know it was all said before but they were right...

DanBabb · Sep 22, 2013

Thanks everyone again for all the feedback. I found the paperwork that came with the distributor and it is set to advance out to 4000rpms. I'll grab a tuning kit and change the springs to get that down to 2500rpm.

I will also check the gap on the plugs. I know they aren't at 45...probably closer to 30 or 35.

I don't think I'll want to pull the transmission to change the converter...but if I got motivated over the winter to do that...which one would be a good fit with the cam I have in the truck?

DanBabb · Sep 26, 2013

I got the MSD Timing Advance kit and changed the springs to get timing all in by 2500 rpms. It seems to be a lot more responsive when I blip the throttle, but couldn't get the truck out at lunch for a spin (MIL's car had me blocked in).

Will report back when I get a chance to take it out for a spin.

KoolKat-57 · Sep 26, 2013

Had a friend who had basically the same setup on his 354 hemi.
The setup was in a 56 Dodge 2 dr sedan, turbo 350, 3:54 rear gear.
In all honesty the car was not really that quick and he was quite disappointed with the performance!
It looked really good in the engine bay, but just wasn't all that impressive on the road.
Hopefully you will find a way to wake yours up.
KK

DanBabb · Sep 26, 2013

Seems to have helped. If feels like it moves a little better and even spun the tire when leaving a light (and I wasn't trying to spin it).

Might still be some extra power I can gain by messing around with it more, but the timing curve was a great first step.

Thanks again for all the help.

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Edelbrock Carb on a 354 hemi...tuning questions

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