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Horsepower Hunt


Dave M

I love this hobby, the mere thought of "hopping up" my Corvette or any Corvette really excites me. Give me a good ol' fashioned horsepower hunt any day of the week. I have recently put together an engine for my Corvette, as when I purchased it, it had no engine at all. I searched and managed to get mostly good parts, but sadly some not so good. The engine I put together is basically stock. I have used flat top pistons, a std crank + rods and heads from a '81 Corvette. The block is a 4 bolt 350 reconditioned to 30 thous. The cam is from Cam Dynamics (Crane Cams) # 975848.
The inlet manifold is an Edelbrock Performer, the carburetor a Rochester and the ignition HEI. It has a proper twin exhaust with "rams horn" exhaust manifolds.
All of this sounds pretty impressive to me. However, I have discovered the motor for my 1979 Corvette is meant to have an EGR + many other disagreeable emission control systems. Actually I think emission controls are good if they work, but that's another debate, some other time.
The problem I have is, No EGR and the carburetor and HEI distributor are designed for a motor equiped with an EGR valve. I believe EGR distributors produce far too much vacuum advance and an EGR carburetor will need rejetting & rodding to the same specs. as a pre EGR carb. if no EGR installed.
What I need to know is, what is a good set up for the distributor? regarding mechanical and vacuum advance. And what mods should be done to the carburetor?
I have got to say at this stage, a big thankyou to those that have assisted me with their knowledge and welcome to the CAC. including 79 toy, 69myway, Rare81, Vigman, 75shark, Silver, Barb, Lemonpeeland Patti ! And ofcourse Rob and any others I've missed , you all deserve a pat on the back for keepin' this show on the road!
Keep cool,
Dave M
You can get an adjustable vacuum advance unit from Crane for the dist. for under 25.00 here in the U.S. Your cam part number does not relate to any one avaiable here. Do you have the specs. on it? If it is a radical cam you may want to not run any vacuum advance anyway.
The mechanical advance should give you 20 degrees of advance. Use an aftermarket weight set if needed to get there. With the vacuum advance disconnected set your timing at 36 degrees of full advance. That should give you 16 degrees at idle. If your car is hard to start the you will have to back off the timing a bit. My car starts like a stock motor at 12 degrees but requires a bit of cranking at 16.
Quadrajet needles, jets and rods are hard to get here. I don't have a clue how to help you there. We order them from Summit and hope that we at least get close to what we need. Stock for a '79 should have been #40 primary rod, 72 primary jet and CH secondary rods on a J hanger. The basic setting for the mixture screws is 4 full turns out from seated but I've never seen a 350 that needed more than 3 turns, so that's where I start.
I hope this will get you started.
MY opinion is don't waste your time. Get a Holley 750 and be done with it. They work and don't let anyone tell you differently.
Thanks for your help 79toy, the cam that I've installed has the following specs.
Intake Exhaust
ADV.DUR 280 290
.050"DUR 214 224
VALVE LIFT 0.443 0.465

So I think it is pretty tame and is designed to run in the 2000-4800 rpm range. I've set the ignition timing at about 10degrees @900 rpm and have disconnected the vacuum advance completely. The vacuum advance was causing the motor to "ping". You recommend running the Total Advance at 36 degrees, to do this, do I adjust the engine revs to, say, 3000rpm and then set the distributor advance to 36degrees ?
The fuel here is only 98 octane and fuel additives seem to only foul the spark plugs and make my Corvettes carburetor dirty! Bring back the 100 octane soon I say.

And Hey Redmist, you have convinced me, mmm.. I really want that Holley 750 ! ! I don't know what I was thinking when I purchased the Rochester. Yes, I do, I thought the pollution police would get me at the car registration office ! They always seem to sneak up on me when my back is turned. Mind you the laws seem to get more relaxed every year for old cars, and was surprised when my '79 Corvette was passed for registration with no air pump, no EGR, no catalytic converter and true twin exhausts. I probably should keep quiet about it. I believe the pollution authorities have found a lot of emission controls if not properly maintained cause more pollutants than a well tuned engine without.
Dave...I think you'd be very lucky to find any petrol out here that's even close to 98 RON. The closest you could hope to get would be PULP with an octane booster and even then you'd be pushing the proverbial uphill to get past 97 and a bit.
The idiocy of it all is that any vehicle running unleaded fuel without a cat is producing more carcenogens that any leaded car ever did.
I've still got my original Q jet too but I'm still not sure which way I'll be going after I finally put the new motor together. I've been collecting bits and pieces over the years now to finally put a decent donk together. The crowning bits were some new AFR aluminium heads that I brought back from the US last time I was over there. Can't wait to see them finally go to work.
Hey Brutus,
Isn't premium unleaded or Shell ultra rated at 98 octane? Or is it true it's mixed with paint thinner ? ! I swear that is the octane rating they advertise it at (98) . I was using avgas but as you probably know, leaded fuel is no longer available to the general public. What is happening with todays fuels? do you think we will ever see 100 octane fuel again? I believe they sell higher octane fuels in Japan, why not here? Is it because of our refineries? I believe this is the case.
Dave...I work for Caltex refinery and as such haven't seen anything that high for quite a while and also there is no way known in the forseeable future that there'll ever be any juice that high again.
I just had a quick look in my outdated Gregory's and couldn't find Oatlands........where is it? I saw some streets named that that were out in the west of Sydney. Is there a suburb out there now as well?
Your cam should be a great street cam. You did install new valve springs that match the cam didn't you? Stock springs go in to coil bind at about .460 lift. 98 octane gas is only a fond memory here.
To set the full advance timing you need to have an adjustable timing light or mark the balancer at 36 degrees. Rev the engine until you have full mechanical advance. If you don't have full mechanical advance by 3000 RPM you are going to want to replace the advance weight springs with lighter springs. I'm too nervous to set the timing while the engine is running that fast so it becomes a bit of hit and miss, but it sure is worth it when the timing is set. Be sure that you take careful note of which way the dist. needs to be turned to advance and retard the timing in case the engine won't fire back up after an adjustment. All of the above is with the vacuum advance diconnected and plugged.
I just discovered that I can attach files. I've included a timing tutorial by a great guy that understands how things work.
79...Lars is the best when it comes to HEI distributors and a lot of other things mechanical as well. I bought his kit when I was over there last July. I'll be putting it in my dist. when the engine comes out for it's major rebuild.
Dave M
Desktop Dyno says:
293 Horsepower at 5000 RPM
335 Ft. pounds of torque at 4000 RPM
Brutus. Oatlands is near North Parramatta or West Dundas. I think it used to be called West Dundas but another suburb was made now Oatlands. Sort of corner of Pennant Hills Road and Kissing Point Road.

Toy79, Great info you got on tap there Man! I'll get my address of to you. You mentioned the valve springs, something I never even considered. (I'm learning!) I did have the heads serviced by my local machine shop and they replaced two valves, one exhaust and one inlet, don't know which ones. The cam is recommended for 2000-4800 rpm but seems to run out of puff at about 4200rpm. The power falls off at about 4200 rpm but will rev to 5000rpm. I dare not push it any further.
From a stand still, Wide open throttle the motor will falter or hesitate and not accelerate smoothly. A smooth operation of the gas pedal is required to get away from a standstill.
You are loosing some power somewhere. Your cam should be good until 5500 RPM or so. Back up a bit on this thread and look at Redmist's reply about carburation. He may be correct if you are going to cure your problem completely. There are some adjustments that can be done before you toss it though. If you have a manual on the carb. check the setting for the secondary inlet door adjustment. The idle mixture also plays an important part in inital take off.

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