Don Terrill’s Speed-Talk

I just bought a 3 keyway adjustable timing set for my Chevy 350, the application is street/strip. Horsepower range is 300-325ish what are the advantages of advancing the cam 2 or 4 degrees verses running straight up? Will it effect mileage any? I'm looking for more power than mileage but I'm curious as to how it well effect it. Also when advancing the cam does it have any effect on the timing curve? Like if your timing is set at 32 degrees straight up would it change it to 34? Also should the timing be adjusted at all with a cam that's been advanced?

What makes you think the cam is actually "straight up" now.

Most all catalog cams are manufacured so that they are 4 to 5deg advanced when installed with a
normal timing gear set.
Your cam is probabily already "advanced".
You have to degree the cam to know where it is now in order to move it with any accuracy.
The multiple keay way timing gears are not necessarily going to move the cam by
4deg or 8deg as marked.

Ignition timing is set independently. Yes you would need to readjust the spark timing using a timing light.

As a general trend advancing the cam tends to add a bit of bottom end torque by closing the intake valve a bit earlier.

its does not make a big cam into a small cam. Its just rocks the torque curve a bit. Biasing the low end of the rpm range usually at th cost of a bit of top end.
The effect on the running motor is not 100% absolute. There are many other factors.
Same with gas mileage. There many factors. 2degrees is a waste of time.

Any real in car gain-loss in performance wether its quicker acceleration or better net fuel mileage
can only be determined by accurate A-B testing.

I played around with the camshaft timing on my 302 cleveland some years ago, 290 degree cam (advertised), performer manifold, running l.p.g. through a holley 600 (dual fuel). Advancing the cam 4-6 degrees gave back some bottom end,(not a lot) but then I had to retard ignition timing to avoid pinging, retarding the cam 4-6 degrees gave a better top end (4000 to 7000), with no ignition retard required . I tried open chamber and closed heads on this engine, the closed chamber heads were miles ahead as far as pre-ignition goes, what compression ratio are you running?

Everything F-bird said is good advice. As he mentioned, you can't assume the multi-keyway sets are correct. Not too long ago, I used one of the more expensive Cloyes sets with 9 positions - varied all over the damn map from their labeling.

The cam isn't aftermarket. It's the stock cam used in the 300 hp 69 350's I've got a degree wheel coming from summit to degree it. Compression is 9 to 1. So for longevity because of the pinging I would see better advantage running straight up? This is my current set up right now. 1971 short block with the cam that was mentioned. World Products S/R Torquer heads 67cc 170cc intake runners. Comp Cam 1.6 ratio roller rockers. HEI distributor. The timing set mentioned earlier. Factory aluminum intake non EGR. 1 5/8inch Flowtech headers. I've also got two carbs an edelbrock performer 650cfm and a worked over quadrajet. I'm not for sure which carb I'll be running.

I'm not to familiar with degreeing a cam. But you bring number 1 to TDC and then bring the cam to 180 degrees correct? Or am I doing that wrong?

Your ride, your time and money, you decide how to spend it. If asked what I thought about spending a bunch of effort fiddling with advancing a stock cam, I'd say spend your time and money on a chassis dyno tune of timing and A/F. If pinging is a problem, also consider a cold air induction and blocking the intake manifold exhaust heat.

jack vines

MPac wrote:I'm not to familiar with degreeing a cam.

Your Summit purchase may come with instructions, and the web has many video and text descriptions.
Unless you bought a kit from Summit, you'll need to make and/or buy a few more pieces.
I sincerely wish you good luck as you go through this. You may be enough of a masochist to enjoy it.
But as Mr. Vines often says:

PackardV8 wrote:Your ride, your time and money, you decide how to spend it.

mpac,
Dizzy timing and cam timing are 2 completely separate but related items.

Dizzy timing is when the spark hits the plug in relation to the crankshaft usually 25-35* BTDC before top dead center. The more advance needed to make power the crappier the heads are, if you can make power with less advance you will be eliminating a lot of HP drag on the engine as the sooner you light the fire in the cylinder the harder the piston has to work to get up the cylinder that list couple inches...That is why pre-ignition and / or detonation will kill an engine as it is even more premature or deadly than too much timing.

Cam timing is the relation of the valve timing event to the crankshaft or piston location. As you advance the cam you open and close both intake and exhaust earlier in relation to the crank / piston position. In my world I have not seen a SBC Intake open too early so I have come to advance cams as much as 10-12*. You also have to consider that the exhaust sequence will be advance the same amount and in most cases engines don't like this. That is one reason cam manufacturers run 5-10* bigger on exhaust duration so the event will be long enough to get the exhaust out.

I personally like to get the timing events as close to ideal for a given engine as possible. I did a lot of the original work on a 4 cyl Fiat which has the same rod length and stroke as a Chevy with a smaller bore. DOHC allowed me to play with cam positions in relation to piston position and the numbers are almost identical to what a SBC likes. One of the Ferrari engineers really like Duntovs piston speed and rod to stroke ration so they copied it...Works pretty good cause a stock 124 Fiat engine can turn 8500 from the factory and with aftermarket cams and some decent springs 10,500.
Pistons, rods and crank are awesome forged pieces capable of 100HP / CYL.

From that work I was able to move the cams to where I wanted on the engine dyno and in a couple days I hit a sweet spot I have been working with ever since. In my way of thinking piston speed and peak head flow determine the valve events, and they all revolve around how efficient the head is at accelerating the flow off the seat and getting the port up and moving air.

Isky has some of the best towing cams in the biz I would think 200-210@.050" on 105 intake on 100* would get you making monster torque, I would not go much more than 9:1 with todays crap gas. You will make plenty of cylinder pressure with a small cam, efficient ports and big inches from the stroke portion of the engine.

Do yourself a favor and find a decent set of used vortec steel heads, you can buy them new for about $350ea from GM with valves and all. Same heads as on a GM602 crate engine. They are better than almost any steel head out there and will outperform them in the range you are talking about hands down. They make more power than the old GM Bowtie head up to about 6000rpm's.

I never seen anyone have any luck advancing a small or smallish cam beyond what is ground into them. Any I have seen pinged under load and power seemed to be down.

PackardV8 wrote:Your ride, your time and money, you decide how to spend it. If asked what I thought about spending a bunch of effort fiddling with advancing a stock cam, I'd say spend your time and money on a chassis dyno tune of timing and A/F. If pinging is a problem, also consider a cold air induction and blocking the intake manifold exhaust heat.

jack vines

I'm glad you commented Jack! I always appreicate your knowleage. So basicly I'd be wasting my time worrying about degreeing it? The exhaust heat is blocked on the intake, I have a question for you Jack I've got the edelbrock and quadrajet I mentioned which carb would you recommend I run? This will be a first time fiddling with a quadrajet for me I'm used to working with Holleys, Edelys, and Motorcraft. With my intake I've got now I've got to run a space on both carbs for seperate reasons. The manifold is spread bore and the edelbrock is square bore. But the quadrajet hits the block off so I need to raise it half an inch. Do you think I'd have more of an advantage with running an open spacer and the quadrajet since it's the same bore as the intake?

Those who claim to know carburetors say while the Edelbrock is nice and shiny, the Quadrajet is the most advanced design 4-bbl ever and is the best all-around for street/strip/fuel economy on an engine such as yours. Since you have the OEM spread bore manifold, the Quadrajet what I'd run on it. Rather than an open spacer, use an insulating stock 4-hole spacer.

If you can tune Holley/Edelbrock/Motocraft, you can figure out a Quadrajet. Build a cold air intake system and book some time on a chassis dyno.

jack vines

X2 on QJ.

If you degree that stock cam in that 350, I bet you find it is retarded a bit.
I did what you are doing many years ago.
It was a 350 in a 76 work truck.
Stock chain was tired. Replaced it then a month later decided to advance it.
It was 8 degrees retarded, advance it to 4 advanced. Really helped THAT motor. Started better, mileage did improve too.
If I was you, I'd NOW change that cam for a modern one and degree it in as advised.

Thanks Jack that has been bugging me for a bit.

John- I was debating on swapping the cam out for aftermarket but it just wasn't in the budget right now. Evently it will get swapped out for something that's a little more power friendly. Something along the lines of a 292 Isky mega cam lol I figured it was probably retarded atleast 4 degrees due to the engine is a 71 and that's when all the emmission crap started. I know with the Ford 351M's and 400's they were retarded 8 degrees from the factory. When I had one of those in a old 70's F250 threw in a new straight up timing set cam headers and 4 barrel she really woke up and I couldn't understand how people couldn't like those engines then.

A 1971 350 Chevy truck would not be emissions hampered unless it came from California. Trucks were a couple years behind all that emissions stuff.

Advancing cam timing on a Chevy v-8 would be the same on just about every one ever made because there is not much difference in piston speed and compression from a 265 to a 400. Like I said in my earlier post you almost cannot get the intake advanced too far on an SBC and especially on a street engine as the compromise is in top end power above 5000rpms.

How many stock pick-up trucks hit 5000rpms on a regular basis?

I built a 400SBC with 9.5 compression, 305 #601's I think on the heads, dished KB pistons, 5.56 rods, and a 390 BGN 4-bbl carb with pretty rare 2 stage power valves ( they really work ). It was in a 1989 Suburban that I drove back and forth to Charlotte as my Serdi Service vehicle. It made over 500ft/# RWTQ and about 325RWHP @ 4500rpm. From red light to red light it would keep up with most 5.0 Mustangs and Z-28's it was a blast to drive. It had a Reed hydraulic cam in it that was 214-224@.050 on a 106 lobe separation .390/.410 lift. I installed the cam with the intake on 96 and the thing ran like a top for almost 250,000 miles. I kept a log book on that truck for every mile I ran for tax purposes and it got 20-21mpg on the hiway and 18mpg around town.

I would still have it today but it was stolen from my shop while I was at Talladega. They caught the thiefs about 5 years later on an ATF / DEA deal, I did get about $50K worth of tools and tool boxes back but the truck was long gone. The group of them got 20+ years no parole ( cause of the guns and drugs ).

If I built that same engine today and put a 4L80E behind it she might get 25mpg, especially with the better 16" Michelin XPS ribs I run on my truck now. They run at 90psi and give a great ride and the old Kelly Springfields ran only 35psi, there is about 2-3 mpg right there.

I agree with most everything you guys have said about tuning and cold air and all the rest, but I also know there are huge gains to be made in advancing any camshaft, and if it does kill power and you want it back you just have to go bigger on you .050" duration to get it back. Basing power production on advancing and retarding a camshaft is just not knowing where the proper intake and exhaust event need to be.

Folks that have never tried it just don't know.