340 SHP question

[Jim C.]

Mine is a 1963. Question:


When at WOT, all 4 bbls open , should the rate of RPM rise slow a bit over 4000 RPM? I know this sounds very subjective but it is as articulate as I can be describing the action.
I have checked all tune up items including insuring the AFB is jetted properly. I do have Crower rods , KB pistons at about a 10:1 compression ratio. 3.70 rear. .097 cam.
I don't know anyone with a similar car to compare it to. It pulls like hell up about 4000 and then seems to flatten out but continue to rise more slowly.


Thanks

[Bob H.]

Re: 340 SHP question

Hi Jim

Mine pulled strong from about 3200 on up. Passing through 4k , it was like just really getting started! I THINK I had an all original build

[Larry B.]

Re: 340 SHP question

Check the advance in the distributor and your total advance. If that checks out bolt on another carb and try it. Check your compression and vacuum one is going to be low.

[William C.]

Re: 340 SHP question

Are you sure the throttles and the air flapper in the secondary is really opening all the way? It Should pull like a freight train from about 3500-6000

[Timothy B.]

Re: 340 SHP question

I agree with all the above posts, could the fuel pump be suspect?

[Stuart F.]

Re: 340 SHP question

I too am in agreement. Mine pulls strong to the redline in both 1st and 2nd, then takes a little longer in 3rd and of course 4th. Mine has a 3.36 final. The 097 (Duntov) turns on (so to speak) at around 3500 rpm. It was explained to me that at that rpm it begins to multiply horsepower, specially when compared to an L-75. With an L-84 fuelie, it is even more noticeable when you gradually advance the throttle you can actually feel it push you back in the seat as you pass through 3500 rpm.

You didn't say whether or not your engine will continue to pull up from 4000 to redline, albiet flat. Does it shut down at a particular rpm or stumble?

Stu Fox

[Jim R.]

Re: 340 SHP question

Jim there is a better rotor for the for the ingnition with a longer tip for high rpm that has been talked about and also a article in the restorer magazine, and what your engine is doing was one of the symptoms if you don't have the extended tip rotor, not being able to pull high rpm, something else to try if the other replies do not fix your problem.

[Jim C.]

Re: 340 SHP question

I too am in agreement. Mine pulls strong to the redline in both 1st and 2nd, then takes a little longer in 3rd and of course 4th. Mine has a 3.36 final. The 097 (Duntov) turns on (so to speak) at around 3500 rpm. It was explained to me that at that rpm it begins to multiply horsepower, specially when compared to an L-75. With an L-84 fuelie, it is even more noticeable when you gradually advance the throttle you can actually feel it push you back in the seat as you pass through 3500 rpm.

You didn't say whether or not your engine will continue to pull up from 4000 to redline, albiet flat. Does it shut down at a particular rpm or stumble?

Stu Fox

Stu, it continues to climb RPM albeit flat.

[Jim C.]

Re: 340 SHP question

Are you sure the throttles and the air flapper in the secondary is really opening all the way? It Should pull like a freight train from about 3500-6000

i can hear them open. Whether it is fully I will try to check if I can figure out how when driving

[Jim C.]

Re: 340 SHP question

I agree with all the above posts, could the fuel pump be suspect?

it seems to ok and I have changed it to sure.

[Jim C.]

Re: 340 SHP question

I am going to begin a step by step process starting at all aspects of fuel delivery, ignition and air. I will check the secondaries tomorrow, give me some extra fun on Fathers Day. Then a carb swap. I'll move on to the ignition. I had Dave Fielder curve the distributor so that is fine, coil maybe ? I'll try a rotor cap. I am running Lectric limited plug wires so they get checked.
Eventually I'll get to checking the lobe lift if all else fails. I want this thing to run like it should. BTW it TF at the Nationals five years ago and now I just want to drive it and enjoy the car . But it has to be "right" !
I will figure this out with help...thanks to all

[William C.]

Re: 340 SHP question

What rotor are you using in the distributor?

[Jim C.]

Re: 340 SHP question

Bill, I think it is generic? Been a while since I looked. What do you recommend?

[William C.]

Re: 340 SHP question

Well. here is one problem I have found with modern rotor configurations in the SHP engines. Around 1971 or so GM shortened the tip of the rotor used in the OEM distributors, under the theory that it would help with emissions. Subsequently, almost if not all the rotor manufacturers did the same, and if used in the low compression engines being built at that time, it is no problem, but with ANY smallblock of the 11-1 compression configuration, it places a real strain on getting proper firing at high rpm. I'm assuming you have high performance points and a good cap, and that you have checked the resistance of all your wires to make sure they are in spec, if so, what I have done is to scrounge eBay and swapmeets for NOS or NORS (packaged pre 1972) rotors and used them in my cars. Fixed the problem for me. Something to look at AFTER you have checked fuel pressure @ rpm, High peformance points, good wires, and set the plug gaps at .030. Don't get crazy, but something to consider if you run out of ideas. BTW, don't wast money on "high performance" stuff built in the last 15 years or so as all I have checked are built to the newer spec also. Most of the "high Perf" outfits are hiring ad writers rather than engineers.

[Jim C.]

Re: 340 SHP question

Well. here is one problem I have found with modern rotor configurations in the SHP engines. Around 1971 or so GM shortened the tip of the rotor used in the OEM distributors, under the theory that it would help with emissions. Subsequently, almost if not all the rotor manufacturers did the same, and if used in the low compression engines being built at that time, it is no problem, but with ANY smallblock of the 11-1 compression configuration, it places a real strain on getting proper firing at high rpm. I'm assuming you have high performance points and a good cap, and that you have checked the resistance of all your wires to make sure they are in spec, if so, what I have done is to scrounge eBay and swapmeets for NOS or NORS (packaged pre 1972) rotors and used them in my cars. Fixed the problem for me. Something to look at AFTER you have checked fuel pressure @ rpm, High peformance points, good wires, and set the plug gaps at .030. Don't get crazy, but something to consider if you run out of ideas. BTW, don't wast money on "high performance" stuff built in the last 15 years or so as all I have checked are built to the newer spec also. Most of the "high Perf" outfits are hiring ad writers rather than engineers.

Thanks Bill, right now I am running a single wire electronic points set up. I wonder if a new/modern distributor cap with with a new rotor would make a difference?
I will take this journey one step at a time and see if I find success . I sure hope I don't have a wiped out cam.