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Username Post: Tuning issue        (Topic#347122)
Junkyardwarrior 
Contributor
Posts: 227

Loc: Yuma AZ
Reg: 02-25-15
09-13-17 02:50 PM - Post#2707579    

Yesterday I decided to use a vigorous amount of throttle to pull out into traffic. For sanity purposes, I pulled out under light throttle and when she straightened up, I gave her full stones. Apparently it didn't like that, as it spit and sputtered, puffed a bunch of smoke out the pipes (Couldn't see the color as it was night time) and went NOWHERE. I pedaled it real quick, just a quick jump off the gas then slammed it back open, ran perfectly smooth, no problem not a sputter, not a puff, pulled like all hell like nothing had just happened. I'm thinking either different accelerator pump cams or maybe I have too lazy of an advance curve. Any thoughts? (SBC, aluminum heads, 9.5:1 compression, .486 @ 303 intake .506 @ 313 exhaust, weiand nostalgia tunnel ram, single carb 750 CFM Proform 4150 style, long tube headers, aluminum roller rockers 1.5 ratio, 3k stall, th400, HORRIBLE rear gears 2.73:1.)



 




Shepherd 
Contributor
Posts: 862

Loc: Lake George, NY
Reg: 11-11-15
09-13-17 04:08 PM - Post#2707590    
    In response to Junkyardwarrior

Try getting into on a straight away, after going around the turn your float level may have lowered some, leaning it out momentarily. Or loaded it up, hence the smoke.



Edited by Shepherd on 09-13-17 04:10 PM. Reason for edit: No reason given.

 
Junkyardwarrior 
Contributor
Posts: 227

Loc: Yuma AZ
Reg: 02-25-15
09-13-17 04:21 PM - Post#2707594    
    In response to Shepherd

It's done it before in a straight line, just it kinda spits then goes. I've never had to pedal it before. I think that was probably from the fuel slosh you were referring to.



 
Rick_L 
Honored Member
Posts: 27194
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
09-14-17 05:11 PM - Post#2707664    
    In response to Junkyardwarrior

Retarded timing will cause that stumble, as will a defective or too small accelerator pump shot.

Look at the timing first. You may need to run more initial timing and less mechanical timing.

After you experiment with that and make it better, then try bigger squirters in the accelerator pump. Different pump cams may help, but I find the differences are tiny compared to changing the squirter. Think of it this way. Pump cams change when you get the shot, but not how much. How much is what makes a difference.

Of course the engine must be running on all 8 with no vacuum leaks etc.

Here's another big deal. If you were to replace the 2.73 gears with say 3.55 or 3.73 gears, you will think you gained 100 hp - and the tuning window will become much bigger.

Also your cam is very big for those gears and any expectation of low rpm throttle response.



 
IgnitionMan 
Valued Contributor
Posts: 3180

Reg: 04-15-05
09-14-17 07:28 PM - Post#2707686    
    In response to Junkyardwarrior

I just know a lot of people will come up with all sorts of remarks after I post this, but, it has worked for me more than a few times.

When I see extremely long duration hydraulic flat tappet cams in engines attempting to run on the street, I cut the intake duration down at idle.

YES, not so hard to do. (OK, moron, how do you do it?)

Well, ever hear of Rhoads bleed down lifters? I do them a bit differently, I only use them on the intake valves, NOT the exhaust.

This causes the DCR to get better from idle up, and with the regular lifters on the exhaust valves, it helps the overlap strength.

Also, no joy in the extremely large plenum tunnel ram. hind sight would be to use one of Weiand's excellent LOW RAMS.



 
Junkyardwarrior 
Contributor
Posts: 227

Loc: Yuma AZ
Reg: 02-25-15
09-15-17 10:33 AM - Post#2707730    
    In response to IgnitionMan

You know I was certainly thinking the gears might have caused the engine to bog at low RPM last night. It's one of those know it is a problem just haven't taken the time to fix it yet deals since it seems like the car and the truck just want to take turns breaking something. I also have the Proform carb with 50cc accelerator pumps so I don't think shot size is the issue. The low advance is why I was thinking I have too lazy of a curve. I have 20 degrees initial timing with 14 mechanical advance, but the springs may just be too heavy. No vacuum advance.



 
IgnitionMan 
Valued Contributor
Posts: 3180

Reg: 04-15-05
09-15-17 10:54 AM - Post#2707733    
    In response to Junkyardwarrior

I doubt you are making enough vacuum to use the Crane adjustable vacuum advance,m they run at the lowers in/hg settings of all adjustable V/A's.

What actual vacuum reading is the engine producing @ idle?



 
raycow 
Honored Member
Posts: 26530
raycow
Loc: San Francisco, CA
Reg: 11-26-02
09-15-17 02:28 PM - Post#2707738    
    In response to Junkyardwarrior

  • Junkyardwarrior Said:
You know I was certainly thinking the gears might have caused the engine to bog at low RPM last night.


If you have a real 3K converter, there is no way the rear end could cause the engine to bog. If your carb and ignition are ok, the engine should go to 3K almost instantly when you floor the throttle, no matter what your road speed or gearing. I'm not saying that shorter gears won't help your performance, because they will, but your present gearing is not the reason for your bog.

One thing you might want to try first (because it's easy) is to check the actual converter stall speed and find out if it really is 3K.

Ray

There's a line between good and evil no wider than a razor's edge - D.S. James Hathaway quoting from The Night Keeper


 
Junkyardwarrior 
Contributor
Posts: 227

Loc: Yuma AZ
Reg: 02-25-15
09-18-17 07:40 AM - Post#2707996    
    In response to raycow

She pulls about 9 in of vacuum at idle, so not much. The stall is actually 3k. I've foot braked it to 2900 staging at the drag strip. (No, it didn't go well with that gearing)



 
IgnitionMan 
Valued Contributor
Posts: 3180

Reg: 04-15-05
09-18-17 08:28 AM - Post#2708003    
    In response to Junkyardwarrior

Just for grins and giggles, you might TRY 24 deg/BTDC initial, just to see if things vacuum-wise and launch get better.

The 9.50:1 C/R and very late intake valve closing point really don't like each other, and the intake closing demands a lot of timing the engine should tolerate fairly well.



 
Junkyardwarrior 
Contributor
Posts: 227

Loc: Yuma AZ
Reg: 02-25-15
09-18-17 10:52 AM - Post#2708024    
    In response to IgnitionMan

I'll try moving up the initial advance and see what happens. I have a 10 degree limiter bushing I can put in so I don't ping like crazy. That should give me 34 total if I set at 24.



 




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