What will this cam change do ?

[prairiehotrodder]

Learned something pretty important tonight. Been fighting with my engine to get it to run right. Got it to idle ok but had the occasional back fire. Checked everything, took it for a drive, seemed way down on power. Came home and was ready to change back to my original camshaft. Took one last look at the cam card and seen " 7/4 swap". Switched my plug wires around and amazing how much better it runs !! All my tuning issues suddenly went away !

[barnym17]

great

[Tom68]

Learned something pretty important tonight. Been fighting with my engine to get it to run right. Got it to idle ok but had the occasional back fire. Checked everything, took it for a drive, seemed way down on power. Came home and was ready to change back to my original camshaft. Took one last look at the cam card and seen " 7/4 swap". Switched my plug wires around and amazing how much better it runs !! All my tuning issues suddenly went away !

I was gunna give you a thumbs up, but this deserves an Lol. |

As to the original question, I guess the answer will come soon.

[prairiehotrodder]

For anyone who has been following my progress, I'm headed to the track for a test and tune with my 81 malibu race car. Hopefully can post some results tomorrow night. Here is where i'm at and what i've done.

Last years best 9.16 at 148

winter modifications :

new tires (hoosier 29 x 10 slicks)

used camshaft ( see specs above)

new MSD crank trigger distributor

switched to 1.7 rockers on the intake valves ( was running 1.8 with the other camshaft)

speeded up my vacuum pump a little, went from an 18 tooth crank pulley to a 22 tooth ( had 9" of vacuum with the 18)

fresh oil change (worried i may have contaminated my oil with the 4-7 cam fiasco so i changed it even though it was new oil )

hoping for 8's and 150 + mph. Last year my 60 foot suffered with 2 year old tires and more power, hoping to correct that.

Thanks for following

Brian

[prairiehotrodder]

Back to the drawing board to analyze my results. Best pass was a 9.179 at 147.5 . With shock tuning the 60 foot started to improve (1.35 best today) but the top end never improved. My gut is telling me the cam was the wrong move but have to think about it.

first pass 9.201 at 147.12 with a 1.380

2nd pass 9.179 at 147.55 with a 1.362

3rd pass got out of shape and lifted to straighten out 9.369 with a 1.353 60 foot

4th pass 9.224 at 146.23 (jetted up the carbs for these last 2 runs but was a bad idea. 60 foot was also 1.353

basically these times are in the same ball park as typical passes last year. so my winter modifications gained nothing, or some worked and some rreally didn't work.

Brian

[Tom68]

The Cam comparison lacks information, we'd need to see it at least presented like this to make a judgement, even then for most of us there'd be guessing in the evaluation.

3-s2.0-B9781845697150500091-f09-01-9781845697150.gif

[In-Tech]

Hiya Brian
The heads are a choke but the intake is a bigger choke. I am assuming a 4.250 stroke. With that Erson cam, put the ICL at 112. Port that tunnel with at least a 15 degree taper port matched to the 385, radius entry at the top, and with all of that it will pick up ~100hp
The new cam will make more power everywhere in your rpm band.

You never mentioned the carbs in this post. Put a .040" primary and secondary MAB in the tunnel carbs without jetting change, check 60ft. It will Hit harder. Tighten valve lash .004" If it picks up...make at least a 660ft, check plugs. If all looks good, make a pass... .4 minimum better. Fuel curve is the key with that camshaft change.

[frnkeore]

What carbs are you running?

[Monza355]

What converter are you running ? You say 5500 stall. But what size etc. Did you see a change in stall speed after the cam swap ?

Even With the smaller cam which is not that small …. i think that’s not enough stall speed. 6000 stall +/- 200 would be in the ball park and then you could shift around 74-7600 rpm’s

[barnym17]

your air flow issue in the front end could be a contributing factor

[canada1]

I still think your intake manifold is the choke/cork in the bottle.
Get that correctly sized and you will see gains.
Your cubic inches and peak RPM is way, way beyond what those old tunnel rams were designed/sized for.
The bigger the cam, the higher the potential RPM peak - provided there is not a cork in the induction path.