Hello ! Wanted to put this out there and see what people thought. I have a 68 Vette 327/300 that currently has an aftermarket cam and valvetrain. I am going to pull the aftermarket equiptment and put the engine back to factory specs. I know , there are a lot of people out there that are saying WHAT ?? 🤦🏻‍♂️ There is a problem with this cam I believe either with the installation or with the cam itself and as I have done cams in the past , this one I decided I want to put back to factory specs . Here’s the issue : WHO if anyone knows can I get the factory cam and lifters from for that Vette 327/300 engine . Appreciate any info anyone can give thank you !

 

I would get the specs for the camshaft you are looking for and compare it with Cams being made today. A good cross search could find the closest to the original. Comp Cams has a huge library of camshaft designs and might be a good place to start.

 

Elgin sells the cams separate or in a kit with the lifters. Low cost.
They sell the stock "929" hydraulic cam as well as the "151" 327/350 hydraulic cam. I would run the 327/350 cam any day. Can't comment on the Elgin quality either way. The low prices worry me.

Howards sells the kits as well but they cost a lot more. The lifters are known good in my experience so thats a plus.

You can get a good deal on these from Competition Products. I have used them many times.

 

I know it unfortunately is such a risk today picking not only the correct cam and lifter set but the possibility that it is a quality cam and lifters is a bit daunting, because the last thing we all want is to have to go through this whole process and end up having a set destroy our motor because of a poor quality , failed cam or lifter set. Back in the day this was unheard of, now it seems I hear this happening a whole lot .

 

Jebbysan's excellent write up regarding flat tappet cam break in. Post #10https://www.corvetteforum.com/forums...-failures.html

 

I totally understand wanting to go back to a camshaft with oem specs.
I do have to ask, what if any other modifications have been made to the engine?
If other modifications have been made, going to a cam with oem specs could greatly affect how the engine runs and could cause the engine to have very poor performance.
You might be better off looking at more than just stock spec cams and find a cam that may be close to stock specs, that will give you better performance and drivability where you want it.
Look at where the cam comes on, what it’s operating range is and not just lift and duration specs.
If your engine is all stock original, then an oem spec cam may work fine for your needs.

 

If you’re worried about flat tappet lifter failure I would consider going to a hydraulic roller. No more zinc oil/additives, and you can still have a better than stock spec cam with good driveability.

 

I totally understand wanting to go back to a camshaft with oem specs.
I do have to ask, what if any other modifications have been made to the engine?



One of the issues is that no one has any idea what exactly this cam is that is in the engine currently . I don’t have a problem with aftermarket cams . I suppose if I really want to find out what exactly this cam is I will have to degree the cam and record the specs , not sure if that will be enough to actually set the cam up so it runs appropriately. I have tried everything to get this engine to run like it should , but it just won’t . Falls flat on its face cannot accelerate (literally) 30 mph is its best no matter what you do to this thing . Ive gone through EVERYTHING on this engine trying to find issues and adjust for the fact that I CANNOT adjust the timing to a point where it will actually run even half way decently . This is why I have come to the conclusion either the cam was installed wrong or there is something drastically wrong with the cam itself . Not looking for a hot rod , just want to drive it and enjoy it . It’s got to be a roller cam with roller rockers (comp cam ) I don’t believe there are any other modifications besides headers . Looks like just the top end was done but I’m in the process of taking it down to see if I can see something set wrong . Or problems .

 

Besides a new carb I just put on the car , to repair a few fuel management issues the car was having (including setting the timing ) I replaced the distributor with a factory Corvette tach drive single point distributor in excellent condition, removing the old distributor which was an Accel dual point racing distributor which was converted to electronic with a pertronix set up ( no vacuum advance on it ) . The new carb definitely solved some issues I had with the fuel management , at that point I turned to the ignition/timing issue figuring I could now solve the issue and set up the timing and at least make it run halfway decent but nope . I have basically minimum 15-18 degrees initial timing without the vacuum advance. With it I’m at 25-28 degrees of advance. Full advance timing at 2500-3000 rpm is about 45-48 degrees which is insane at this point . Don’t know if that helps explain a little more what’s going on .

 

Take it to a local shop whose bread and butter includes Both building carbureted race SBC motors And tuning carbureted race cars. If you don't know where to start searching; begin by asking local auto machine shops.

 

As to original brands, look into Melling. They were a long-time GM supplier of all sorts of engine parts. Last fall, I had a Melling stock replacement cam and their lifters put into my '67's 427, broken-in/dyno'd by the builder, and reinstalled the engine this summer. It's running fine and strong. He also installed a flat-tappet camshaft in my '72's 454 about 5 years ago and like my 427's engine, is running great.

Roller cam & lifters are very expensive in comparison and very often require block machining.

The key to running flat-tappets is to ensure the lifters are rotating as the cam rotates. This interaction between the cam and lifters is super important as that is what keeps lobe and foot wear to a minimum for long life. The rotation should be evident after the heads/pushrods/rockers but before the intake is bolted on.

 

Ok I see you were a fleet tech.
This could be just a carb & distributor tuning issue. Or not.

What kind of symptoms are you getting?

One of the best ways to kind of identity how big a cam is is to measure the manifold vacuum at idle. Example 18" Hg or 10"?
Performance cams with less than 12" at idle get progressively more difficult to tune.

Let us know those two things and we can give you more specific tuning advice.

 

Timing curve does sound odd. 15 ish initial sounds ok. But 28 total sounds way low. Make sure to rev it up and make sure you have topped it out, or pull one spring to check it.All-in should be 36* near 3000. Not 5500 like factory.

50 total with mech & vacuum actually sounds about right. IF the total centrif is all in.

The vac can, at idle, should add 10-12* for today's gas. Many add 20+. Just plug it in and off and measure.

Getting the timing correct, or at least close, is more important than the carb. If it is off 8 or 10* it will run like crap, no matter what.

 

Ok I see you were a fleet tech.
This could be just a carb & distributor tuning issue. Or not.

What kind of symptoms are you getting?


The symptoms are this . Engine runs good at idle a tad rough but runs good sounds good accelerates and does 12-14” vacuum. Setting the timing is difficult , won’t run at 8-10 degrees as long as it is is advanced to 15-18 degrees seems to idle well. If a plug vac advance there is about an additional 10-12 degrees advance .idle it up to 3000 rpm for full advance with the centrifugal weights and you can be at anywhere between 45-48 degrees total advance, depending on where initial timing is placed . I have had as much as 60 degrees of advance which I think is nuts . Anyway no matter where the timing is set it will barely drive , kicking back , bucking , popping back thru exhaust and carb you can def tell timing isn’t correct . If pushed you can get to about 25-30 mph but the bucking and popping just gets to violent . Fuel pressure for some reason is usually consistent at 41/2 to 5 lbs but it does tend to drop off at times to 2 lbs it’s running an AC Delco factory style pump and a Holley pressure regulator .

 

I have had cats in the past plenty of times where you just can’t get the timing correct using a timing light for whatever reason . They may have good vacuum advance and centrifugal weights work correctly but timing with the light just doesn’t work well, so you set it by ear and take it out on the road and time the engine by ear/performance. I have done this many times over the years with great success . Between carb tuning and road timing you can get it pretty damn close , but not this car . It is just undrivable however the timing or carb tuning is set up . With the new carb it has eliminated a few fuel management issues I had before and runs much better now . The difference is when you drive it the bucking, spitting, and popping back are just too violent and NO adjusting of the timing out on the road makes it any better tuning wise . All external vacuum assessors have been disconnected from the engine to eliminate any sort of vacuum leaks affecting the running of the engine , and there are no vacuum leaks in the engine , like from gaskets or anywhere else I can find . Distributor has been inspected multiple times for tightness and centrifugal weight performance and vacuum advance performance …. All good . Plugs of course are black and sooty because it not burning the fuel in the chamber as it should be . With the violent bucking and popping back you would assume the engine would not be able to properly burn fuel in the chamber, hence the ignition timing problem. Everything external seems to be working as it should . Which leads me to believe that it could be an issue with the cam installation or the cam set up that is not allowing proper ignition timing . I am pulling the pan and timing cover to see if I can tell if something was installed incorrectly .

 

Have you checked the harmonic balancer to see if it has slipped or come apart?
Are you 100% positive the distributor isn’t off 180 degrees?

Lets also back up a little bit.
Did you just purchase this car?
Did you just rebuild the engine?
What recent modifications have you made?
Did you install the modifications?
Was it running good before you made any modifications and now you are seeing these problems?

 

The 12-14" vac at idle reading you measured indicates to me you have some kind of street level performance cam. (~225-230* duration at .050").
It will like 18* at idle. It will like the 10* vac can.
It should be perfectly tuneable and is not the source of your trailer hitching problem.
The distributor is.

If the 45-48* degrees max advance @ 3000 occurs with the vac can disconnected, and running centrifugal only, then you have 30* centrifugal advance in the distributor and you have a distributor problem.
60* tends to support this (with vacuum?)
Severely over-advanced timing will give you the trailer-hitching syndrome, which could be what you are describing.
Many factory distributors and some new ones do have this much centrifigal advance built into the distributor.

It should never go past ~45* with the vac can on.
And never go past 36* with the can off.
In your case, with the can off, it should swing between 18* and 36*, and never go anywhere else.

Easiest way to check is to plug the vac advance, and then test it and drive it.
Do your testing with the vac can unplugged first, and get the centrifugal curve correct, first.
It should run good past 1/3-throttle.
Then worry about the vac can.
Then the carb.

I agree the numbers you are quoting just do not make sense. They indicate the distrib is bad. And then you say the distrib is "good".

Do you know how to change a centrifugal advance curve to something non-stock?
Many techs have never done that.
I worked in a speed shop and engine shop for years tho. Not many have.
I can supply a procedure if needed.

 

Have you checked the harmonic balancer to see if it has slipped or come apart?
Are you 100% positive the distributor isn’t off 180 degrees?


Yes just bought this car a short time ago . Car was running but wasn’t running very good at all. Found out afterwards the engine has been rebuilt in like the last couple of years . It sounds good , runs good at idle and snapping throttle , engine is strong , no blow by , nothing seems out of the ordinary . The only thing I have done to it since I got it was take out the Accel 37100A distributor and replaced it with a factory stock and correct tach drive point distributor with new points condenser cap rotor wires and test the coil . I knew the car had serious fuel management issues because the quadrajet that was on it had multiple issues . I put another rebuilt quadrajet on it from the correct time period a 7022212 D8 and it was still having issues . Also at the time was having fuel pressure issues the pump would jump to 9-10 lbs of pressure causing the carb to overflow . Replaced the pump with a new one installed the Holley regulator making the pressure steady but the carb still had issues . So I bought a new Edelbrock carb put that on with a bit of tuning and the carb still ran great . Take it out on the road tho and with a load car will not run right as stated above .

 

The 15-18* advance is initial timing set with distributor can disconnected . Connect the can and you are at 24-28* advance. Rev the engine with the can connected and initial timing set to 15-18* and you get total timing including initial, vac can, and centrifugal of about 44-48* total advance .
I have NOT ever had to change the timing curve of the distributor through the weights except but maybe once long ago . You are referring to the changing of the springs that control the weights and slow or speed up the timing of advance coming into the picture yes ? Plugging the vac can to eliminate some of the advance to the engine may be a way to see if it affects the timing to the engine positively , something I was thinking about where I had removed the Accel racing distributor without a can to a factory dist with vac can

 

Did you actually drive the car with the Accel distributor in it?
You might swap back to the Accel distributor and see how it runs?
Leigh knows his business and he is giving you great advice.
I’m just simply reminding you to check the simple stuff first.