Well I finally got around to swapping cams in my truck.

Old cam: .502/.511 236/242 @ .050"
New cam: .555/.555 260/260 @ .050"

Combo is a 9.5:1 440 with stage V heads.

The PTC that’s in it now flashed approx. 4000 with the old cam, with the new cam it flashes 3800.

Last time I had the truck out with the old cam was November (great DA…) and last night was the first time I’ve made a pass with the new cam. I’m a little disappointed in the fact the truck didn’t really ET all that well compared to the old cam - lost 9 numbers in the 60ft. I know the fact that the DA was 2200 doesn’t help matters much.

My suspicion is that with the old cam the tight-ish TC didn’t really effect it due to the lower torque peak and that moving the torque peak up with the new cam has resulted in it not tolerating a lower flash. The positive take away from this is that the MPH was basically identical to the old cam’s best mph at great DA – so I know it’s making more power.

So, before I call PTC what’s everyone’s thoughts on the flash I need to shoot for on this combo?

Gratuitous photo…

I would wait to see how it runs in comparable air before changing anything but the tune up
Did you look at the plugs to see if they are rich now ?
How much difference in density altitude from the last time until the current run?
To much squirter and to rich on the idle, transition and WOT will slow it down also, it needs to be crisp on the leave to 60 ft. well
Did you degree the new cam in? If so what is the lobe separation angle and where did you install the intake lobe centers?

I did check the plugs - that was a big goal of mine for last night's TnT. Plugs looked a tad lean imho and I should have taken some pictures of them. Gotta get my wideband installed soon tho...The 850dp set up is 3.5pv in the front with 82s, rear pv blocked with 88s. Squirtters are 35s. It's pretty crisp but I'm positive It could be better with more tweaking.

DA in November was -37ft, last night was 2209ft

I didn't degree the cam - just went dot to dot with it...probably will get flamed for that..

With all the timing you added you gave up some torque and that effectively tightens up the converter.

Send it back to PTC and have them fix it. You'll get back what you lost and then some.

IMO, 260@.050 with 9.5cr is "too much" cam..... Especially since its not a light weight vehicle.

Depending on what size the converter is, it either is or isn't a good candidate for loosening it enough to provide the desired increase in stall speed without loosing a bunch of efficiency.

I would say if its larger than a 9.5" unit, leave it alone and save fore a different one.

9.5cr, 260@.050, heavy vehicle...... Needs 4500 flash(minimum), which is going to be a fairly loose 9.5" behind that motor.

Looking at the specs, it appears you went from a xs274s up to a 306s Magum cam.
Not what you want to hear, but there would have been better options for a cam IMO.

I'll keep my thoughts to myself after reading the cam was installed dot to dot. To me that's worse than not knowing what your rear tire pressure is. I see 5 pages of guessing about ready to start.

Dewayne I was hoping you'd chime in! I know you have tons of experience in this realm.

It's actually a 9.5" and you are dead on with the cam #s.

I went with this cam due to the fact a lot of my friends have had great results with the 306s cam in stock stroke 3500-3700lb cars and it also helped that they had a spare one lying around...

I appreciate the honesty - that's what I'm looking for! What kind of cam #s would you like to see in this street/strip combo?

I love reading through the stuff you've posted over the years - especially the latest on the Promaxx sbm heads. With that said, I get that you disapprove of the dot to dot thing. But it's easy for you sit back with 40+ years of experience and say that. I'm sure you've made your fair share of "rookie" mistakes long ago.

If you have constructive thoughts please feel free to jump in.

One thing I'd do to get a feel for how "off" the cam could be, (installed position and size)..... Is do a cranking compression test.

What's the elevation where you race?

And what are the performance numbers for the truck?

Thanks for the advice! I will try and do that soon and report back.

The track elevation is 702ft

With the old cam it went 7.57 @ 89.0 with a 1.663 60ft. Last night it went 7.77 @ 89.9 with a 1.759 60ft. Also last night was a "street" night so track prep was dismal to say the least.

Put a BB carb on that thing instead of that baby 850......small-blocks run those and some bigger.........

Missed that part.........when you fix that THEN give it more carb..........

If you're primarily running 1/8 mile, then I think it's going to be tough for that 306 cam to show much improvement over the old cam, in that combo.

The speed improvement is somewhat promising though.

I'm sorry if what I posted upset you but to properly diagnose an issues you got to know the facts. Cam timing can and will make the difference between a dog or a race horse. Again I'm sorry and will butt out now.

The speed improvement is certainly hopeful. It may be more advantageous to look at a different cam rather than re-stalling the converter?



It takes more than a comment on the internet to upset me.

Get a looser converter and watch the ET's drop. It's not making the grunt down low to flash that converter anymore. Let it rev and it'll fly.

edit...I also strongly encourage you to tear the front back off the motor and degree the cam.

I too wasn't trying to offend you but it's best maybe to get the cam squared away to verify accuracy, or fix it then onto tuning...........And I'm a 56 year old rookie..........learnin every day..........

You didn't make a "rookie" mistake, you just made progress of your learning curve.

Degree'ing a cam is one of the checks you do to make sure everything is right.
I have only degree'd about 8 cams in 40 years, some were dead on, some needed a 2*-4* offset bushing to get them where I wanted.
There was one exception where the cam was so far retarded, I had to advance the cam a tooth and use a 8* bushing to retard it back! If I hadn't have degree'd it, the motor would have been a dog and I would have spent hours and $$$ trying to figure out why.

I still say before anything on the front gets unbolted...... Do the compression test.

There are several different ways to learn, the hard way stumbling through all the things you do, another is to look, listen and apply what others(with knowledge of that subject) are willing to share with you to help you from repeating the rooky mistakes we have all made
The first solid roller cam I installed was a old(in 1971) Sig Erson special marine grind for S/K boat racing that they didn't stock in there inventory in their warehouse, I had to wait 6 weeks for it and it ended up having the cam dowel alignment pin mislocated by 8 degrees retarded That motor(392 hemi) was a real turd with that cam retarded
I learned a lot about not trusting the after market cam makers cams with out degreeing them at that time
Murphy lurks ,ready to pounce on us hot rodders and racers
Buy the tools needed and degree every cam you install so you don't wonder about where the cams intake center line is
I've moved intake lobe centers on engines in the car and on the engine dynos, I've seen over 40 HP and similar torque loss by moving the cam from 2 degrees retarded to 4, 5 or 6 degrees advanced on the intake lobe center
If your truck is spinning the tires on the starting line retarding the cam will help stop that