318 replacement cams....

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cudaracer said:
I have a related cam question.

Since my stage two engine rebuild is on hold due to funds, and I still suffer with poor low end from too much cam in my stock bottom end 72 318 (360 heads, comp XE268H cam, DP Al Intake, 600 Eddy, Dakota exh manifolds, 904 auto & TC, back to 3.23 gears).....I am now down to just fixing the cam for now. So here are my choices:

Option I: Cheap summit cam like the 6900
Option II: Not so cheap Whiplash Hughes cam

Looking at the overlap with my current cam, I am at about 50 deg. That siginificantly hurts my effective CR, right?

With the Whiplash cam, I am at nearly zero overlap, with huge rapid lift (.485/.518 for a stock setup. I am above stock of course, so I am seeking advice then. What should I expect with either cam?

Thanks all.
Man I love this site, but wish I found it a long time ago :(
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Like most things with poor low end, what is the timing profile?

A 318 with an xe268 should run really well.

Overlap does nothing for CR. The overlap numbers you are getting from the hughes site are misleading. They are .050 lift numbers.
 
crackedback said:
Like most things with poor low end, what is the timing profile?

A 318 with an xe268 should run really well.

Overlap does nothing for CR. The overlap numbers you are getting from the hughes site are misleading. They are .050 lift numbers.
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Ooops, yeah it was at 50 lift. From their site:
Camshaft Technical Details
Intake Valve Lift 1.5
Exhaust Valve Lift 1.5.485"
.518"
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Intake Valve Lift 1.6
Exhaust Valve Lift 1.6.517"
.552"
x.gif
Intake Duration at .050"
Exhaust Duration at .050"213°
226°
x.gif
Lobe Separation Angle109º
x.gif
Intake Centerline 104ºIntake Opening at .050"
Exhaust Opening at .050"2.5° BTC
47° BBC
x.gif
Intake Closing at .050"
Exhaust Closing at .050"30.5° ABC
-1° ATC
x.gif
Min. Suggested Cylinder PSI
x.gif
Sweet Spot RPMidle-4200
 
Wait a minute, too much overlap robs you of your effective CR, right? If you have have a late intake valve close event as the piston is compressing....does that not take away your CR???
 
Overlap is on the intake opening side. That has nothing to do with when the valve closes the chamber to create compression.

Installed centerline will have more to do with dynamic compression.

Ignition timing?
 
crackedback said:
Overlap is on the intake opening side. That has nothing to do with when the valve closes the chamber to create compression.

Installed centerline will have more to do with dynamic compression.

Ignition timing?
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I have moved the needle on ignition timing everywhere, Sometimes it helps a bit at the best scenario, and runds like crap at the other end of the spectrum. I am at the helps a bit scenario with about 10 deg advance.

And my cam was degreed by what I would call a very capable builder who has done it for years.
 
318 with a xe268 will run like crap down low with 10 degrees initial timing.

It needs ~16 minimum and the distributor needs to be altered so your total timing number is in range. The reason it runs poorly up top is because when the engine has the proper initial timing, it likely pings like crazy from too much total timing up top.

It's a multi-piece puzzle to get it right. You can't just drop in a distributor and have it run right out of the box. Unless you get extremely lucky and that almost never happens.

If the timing mark disappears, search hillbilly timing tape to solve that issue.

I bet it's really stinky out the exhaust the way it's timed now.
 
Not terribly stinky, and thanks for the advice.
I have had it advanced to about 16 before, and she seemed to run better…..but no matter what I do, tires do not spin easily when I mash the pedal. I can’t tell you how many times I have read that people just add a good cam, little else, and they can burn rubber all day long if they like. Well, I have a pretty hot cam, good heads and a gearing that is smoke friendly…..and I am lucky to break traction. WTF? And I refuse to believe it is my converter, although I am sure it would help.

So frustrated.
Just when I think I hear a solution, I hear a conflicting argument that sets me right back to square one.

Should have never sold that Boss 302 L
 
A stock converter? That's not the best choice for a 318 with a smaller decent camshaft. Correct ignition timing will help the engine make more low end tq, and increase stall speed.

Advance the initial timing to where the engine wants it. Simple test. If your turn the distributor a bit CCW and the engine picks up rpm, it wants the timing. Reset idle speed and do it again.

Use a vacuum gauge, same deal, advance timing, picks up rpm, reset idle see where the vacuum reads. More, do it again until it peaks. Then back off timing so it drops 1".

As long as it doesn't kick back on the starter trying to start when hot, you're good.

If someone tells you to total time it... RUN!!!! Terrible method to time a street driven car.

Initial timing is REALLY important.
 
Yes, reset idle speed.

Say it idles at 800 rpm, twist distributor. Picks up to 850, turn idle speed screw back down to 800. do it again. At some point it's not going to pick up or very little

I wouldn't be surprised if it likes initial timing in the 20-22 range.

All this needs to be done at operating temps.
 
Be careful, if you take it out and drive it as the total is likely to be way out there. If it pings, get out of it.

Then the distributor altering part of the show takes place. If it's an MSD, easy fix. Stock mopar stuff, maybe, then maybe not.
 
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