Hi, I have a 1970 SB coupe that I purchases 3 months ago, this is my first ever V8 in 45 years of driving. The motor just doesn't seem to develop the sort of power I expected and I toyed with the idea of having the M/T milled off the valve covers and substituted with C/K (for Clark Kent - mild mannered 350 :-). The engine is not original, the block seems to have started life in a truck but the heads are smog era big valve Corvette ones (I read somewhere these are prone to cracking so expect to change these out eventually) Anyway based on various articles I had read I thought a good place to start would be the ignition and timing so I have substituted the Mallory dual point distributor for an original single point Delco one because this has the vacuum advance where the Mallory was mechanical advance only. Timing with the Mech advance only is set at about 35 deg. On my first road test quite often as you just get on the gas after cruising on closed throttle or downhill the engine would give a large cough through the carb before accelerating. Has anybody got an idea what I could try next to fix this?
I couldn't find anyone local with a machine to set up the advance curve in the dist, I was told it was old school and should fit an HEI dist but an MSD one is around $900.00 here for the correct Corvette one. I have since replaced the mech advance springs (two heavy ones) for a black and silver one from the spring kit, this has improved things but I still get the odd cough especially if I get on the gas hard so I'm sure it is a timing issue but do I try more initial advance or an adjustable can?

 

I'm not. Accelerator pump in the carb is the usual cause of the problem you describe.

 

we really need a few more specifics. For starters,what kind of carb and how big(cfm).
it could be the accelerator pump as Mike Ward said,but are the secondaries opening too soon? you may have to use a heavier spring.you might have a vacuum leak that could affect the whole works. i doubt that your timing has much to do with it from what you describe.
more info is always good.

 

Carb is a 650cfm Holley and I doubt that it is the secondaries because this occurs with just a light push on the gas pedal, say less than half throttle. FWIW the problem was not there before I changed the distributor , I have not looked at the secondaries, it is on my list because the cars acceleration is so relaxed that I wonder whether they open very much at all If it was the accelerator pump would it need more gas or less? I see it is pretty easy to adjust. No obvious vacuum leaks, headlights and wiper door functioning as they should. Most of the other vac operated devices other than the hot/cold door in the heater duct have been disappeared from this car by a po.

 

Download the papers from Lars. Papers covering timing and Holley carbs. You won't be sorry.

Bud.

 

Thanks, I reset the accelerator pump clearance to a close 15 thou per the instructions ( it was too tight) and reset the idle mixture to 1 3/8 turns out ( any less and there was a slight flat spot off idle and popping in the exhaust on overun). Off idle pickup is much improved
:-)
Next step I,m considering is taking off the old Torker inlet manifold and adding a Performer EPS.

 

Everything needs to work together as a system. The intake manifold needs to match the cam which needs to match the gearing, etc. If you have a cam designed to make power in the higher RPM range, and an intake manifold and gearing designed for lower RPMs, you will end up with a slug.
For example, the LT1 cars used a rear gearset of 3.70 or 4.11. The base cars generally used a 3.36.

 

I don't know what what cam is fitted to this engine but it sounds fairly tame. I understand that the Torker manifold was designed for a rev range of 2500 - 5500 so I figured that the Performer would be a better bet as it is supposed to be for Idle - 5500 rpm and is dual plane v's the Torker single plane. I would be keen to know if anyone has done this swap before and whether it offered much improvement!

 

edelbrock has sold over 1 million performer dual planes for a good reason- they work great on the street!
If all of them chime in, this will be a long thread!

 

Thanks Matt, so I take it that the Performer EPS will be $324.00 well spent (that's what they cost here) = cost of two tanks of fuel, that's what it COSTS here:-(

 

And GM sold multiple millions of their hi perf manifolds. Does the performer (or any aftermarket manifold) work that much better than an OEM manifold?

No.

Spend your money elsewhere.

 

I'd use the performer 2101 or a stock one like mike ward says. The Torker that you have is a single plane that will pull in exhaust from valve overlap and make it soggy under 2500. With a performance cam, that can be a problem. Use a 1/4" thick 4hole gasket only.
The EPS doesn't have the spread bore pattern, which limits carb choices.

 

what spring kit are you using? did you replace the nylon stop bushing with the bronze one that comes with the kit? You have 35 degrees mechanical at what RPM? what is the initial timing with the 35 total?

 

The only spring kit I could get locally was a Mr Gasket set, turns out I was sold a dud as it was for an HEI dist but I had already opened it so decided to try the springs anyway the rest of the kit was useless for my stock dist. A light black spring and silver intermediate one seemed to work well and 35 deg was all in by 2500 RPM. I may try a gold spring instead of the black to shift the "all in" a little higher as the motor is still a little flat off the line but this could be the single plane manifold? I haven't yet re-checked the idle timing with the vac disconnected to see what it is.
Seems based on Mike's advise a std inlet manifold would be sufficient for my use but an alloy original looks like it would cost me more than a Performer EPS, I will have a look on e bay for a 2101. There is an EPS on e bay with a broken stud in it which may sell for a reasonable price, (funny thing its the same stud as is broken on the manifold on the engine at the moment which is so hard I haven't been able to drill it out).