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I'm testing the springs in the vac cans to get a more smooth accel with the tripower under WOT . We have now a scary big "boost" when they open , so i bought the Holley springs sets.
Anybody did this on his tripower ? results ? other things to consider ?
that will be on a 427 ( or 454 ? ) i assume..... i have it on a Merlin 540.... as build by PO in the US.
If what you mean by a "big boost" is that after opening the throttle all the way, there is a lag and then a "kick in the pants" where the power seems to go all in all at once, then you need stiffer springs in the outboard carb vacuum servos. Hard to believe you'd have that problem on a 540, but that's the diagnosis. There shouldn't be any lag or kick in the pants feeling.
Richard, I don’t think he’s experiencing a stumble or slump - his outer carbs just aren’t starting to open until 4000 rpm on the dyno and then they open quickly with a big surge. He’s trying to get them to start opening at lower rpm in hopes of a softer transition.
But with an engine that big I’m not sure anything happens too softly with it.
If what you mean by a "big boost" is that after opening the throttle all the way, there is a lag and then a "kick in the pants" where the power seems to go all in all at once, then you need stiffer springs in the outboard carb vacuum servos. Hard to believe you'd have that problem on a 540, but that's the diagnosis. There shouldn't be any lag or kick in the pants feeling.
As Dan says Richard , i have no flat spots ( stumbles) but engine keeps struggling on the center carb to open at 4000 rpm the secundaries.... with a sudden 150 HP increase !
Per Holley i must install weaker springs till i have a "stumble " and then go to the next stiffer spring. The secundairies have no pump , so they may not come in to quickly also.
I think if the secundairies start to open quicker , the transition is also smoother , all cfm the secundairies give at a certain rpm don't go though the center carb , so he is creating slower the venturi vac which opens them ( untill enough flow and their own venturi helps them open )
PS i started this thread to see if there are other things to consider besides the springs ?
Seems the Corvette secundarie metering plates are also "special" , part # 34R5113-3 .
I overhauled my carbs but forgot to take a picture of them. Don't know if i have the right ones in there. But that is only AFR related imho.
With 85% volume efficientie i see that a 540 CID can only go to 2400 rpm on the 350 cfm center carb. There should the secundairies start to open.We see it on the dyno too, after 2600 rpm we are loosing torque till the big bang at 4000 .
AFR will be our next problem , but first we need to get rid of that peak .
Looks like I completely misunderstood the symptoms. It would be worth disconnecting the actuator rod from the throttle actuator on each of the outboard carbs and checking for free movement of the throttle shaft on them. You might also have something plugging the vacuum pathway in the center carb between the hole in the venturi and the vacuum outlet port for the actuators.
Barry must be out test driving or dyno tuning. From another forum he’s on he has been through all the vacuum checks, test of the vacuum pots, disconnect linkage and check for free movement, checked vacuum pull from center carb, check throttle plates are slightly cracked and not hanging. Seems a mystery to me that that big motor won’t start opening the secondaries until 4000 rpm. But I’m sure he welcomes all input.
Assuming 3659 Holley, it uses the brown spring which is the second stiffest spring, black being the stiffest. Try a plain spring and if still too stiff purple. Next would be long yellow, short yellow, white. The larger the engine the softer you can go with the spring.
correct @MelWff
carbs had indeed the brown springs. Dyno was done with the plain ones.
Short yellow are now in the recent new sets "orange" .
Next street test ( before dyno ) is with the white ones. Just waiting for dry roads....
correct @MelWff
carbs had indeed the brown springs. Dyno was done with the plain ones.
Short yellow are now in the recent new sets "orange" .
Next street test ( before dyno ) is with the white ones. Just waiting for dry roads....
I wonder if White will be too soft, long yellow might be the best.
Tripower acceleration
