Should I change my cam?!

-
V

vntned

Well-Known Member
Joined
Apr 28, 2012
Messages
1,508
Reaction score
1,440
Location
Gibsonville NC
Alright so I'm about to redo the engine/trans/rear-end/brakes on my '77 D100. The truck is a single cab long bed and weighs 3800lbs without me in it. It's a 2wd with a 318/727/8.25 in it. It haos served as an on and off daily driver and my only truck for more than 5yrs now. The old original drivetrain had around 185k on it and was just totally worn out.

The goal is to make it a reliable daily driver, that performs like a truck should, and is fun to drive and hotrod around in some.

So the engine build so far consists of the following

'73 318 (measured at an actual 9.1:1scr)
Stock crank and rods
0.030" over factory replacement pistons
MP windage tray
High pressure oil pump
"302" heads (gasket matched, ported, cut 0.030, 1.88/1.60 valves, MP valve springs and retainers)
Eddy LD340 intake (gasket matched, center divider knife edged)
1" phenolic spacer
Street Demon 625cfm carb
MP electronic distributor
MSD Streetfire plug wires
Hedman block hugger headers

Fully rebuilt A727 trans
New 2200rpm torque converter

8.75" rear end with a 3.23 SureGrip

So all this is locked in. These are the parts and specs of what I already have ready to go. I'm not changing anybody the aforementioned parts.

Now here is the question: Should I keep the cam that is in it, or should I get a milder grind?!

(and for all you guys that are gonna bash off the shelf cams and say I'm an idiot for not getting a custom grind, don't waste you're time responding).

It currently has a MP P4452761 cam in it.

Style:Hydraulic flat tappet

Basic Operating RPM Range:1,500-5,800

Intake Duration at 050 inch Lift:228

Exhaust Duration at 050 inch Lift:231

Advertised Intake Duration:268

Advertised Exhaust Duration:272

Intake Valve Lift with Factory Rocker Arm Ratio:0.450 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio:0.455 in.

Lobe Separation (degrees):110
 
I like this cam. I think it fits well with what your doing.
Ii would use something a little smaller. *I think* your converter maybe a bit low on stall for the cam. I’m not 100% on that. Also the 3.23’s. What size tire is on the truck?
 
since this new build and you have the mp cam
degree any cam when installing
and you kept the lifters in order abd have checked them for being concave/ worn I'd run it and see
duration on that cam is like a 275 comp or 280 crane
get your tune right
do a compression test
see how it pulls loaded starting up a hill
etc
check your stall speed
if you then think you need a shorter cam advance that one 4 degrees and retest
of course you can get a new cam that is both shorter and has higher lift but do your homework first
 
275/60-15s are `28 tall or 88" roll-out
With the 3.23s and a 2.45 low gear, those conspire to make 60mph =6000rpm@5% slip, at the top of first gear;therefore 30@3000
Having already run this cam,the P4452761, with a probable cylinder pressure of 145psi, just ask yourself; "were you happy with the performance".
If the answer is yes, then leave it in there.

Would I run it?
not with 3.23s and a 2200.
and not with 145psi.

I have an 84D100 with a smogger-teen, also at 145psi. But I run 3.55s and a 2.74 low gear with a 2800TC; no cam and just a 4bbl/dual exhaust. Oh yeah, with 275/50-15s it burns rubber all thru first.
The 2800 lets the engine spool up to where the torque peak is. The 9.73 starter gear multiplies the meager torque the smogger teen makes, and the ThermoQuad-4bbl rolls in enough power,once it opens, to keep the engine spooled up, and the tires spinning. That's how it makes fun.
Your starter is only 7.91, but because of your tall tire28 versus my 25.8s that steals another 8% off your TM. This makes your corrected starter to be 6.78 versus my corrected of 8.75, giving me 29% more TM.
My engine is spooled up at 2800, versus yours at 2200. I'm guessing that will make close to 100 ftlbs difference.
So at zero mph, and WOT you might be 100x1.29=129 ftlbs behind my smogger-teen. You'll never catch my smogger teen in first gear.
To put that into perspective, at 2200 your 268 cam will be 1.29x2200/5250=54hp down on my smogger.
Or lets say your 9.0/268* engine makes 150 ftlbs at 2200. This is 150x6.78=1017 ftlbs to the road
and say my smogger 8.0/240* cam makes 250@2800; making 250x7.91=1978 ftlbs to the road.
You see the difference there?
I'm just spitballing numbers. The accuracy is not important, the thing that counts is the difference in ftlbs to the road.
In my experience, you need a minimum of 1600 corrected ftlbs to the road to initiate a two fat tires spinning. And about 2000 to sustain it, long enough for the engine to get up on the cam. At your corrected number of 1017, you got a long way to go. You would need 5.38s with that 2200, or perhaps a 3200/3500TC with the 3.23s or simply put; more engine torque.
Given your "no other changes allowed"; the only other choice is a cam with an earlier closing intake, to make more pressure.

So I repeat;
if you have already run this cam, and were happy with it, then leave it alone.
 
Last edited:
I bought the engine used, and have gone back through it completely. I didn't have the opportunity to see it run.
 
The heads without a flow test are more than likely going to hold you back .They flow horrible with just a 3 angle cut for 1.88 and nothing else and even what seems a like a decent laying back does squat without runner work .
 
Last edited:
Yeah, the heads have been professionally ported. Gasket matched to 340/360 gaskets, ports have been opened up, minimal bowl porting though.
 
Seems a little big to me for a 318/3.23’s/28” tires in a truck.

I’d be looking at something about 10* smaller @.050.
 
I like it. Not enough to be had or worry about going to the trouble to swap it out. It's a truck, not a points race car. Maybe give it an additional few degrees from what the ICL is and call it a day.
 
That cam is actually a 220 intake - 224 exhaust @ .050" according to the paperwork that came with mine.
 
If it ain't broke don't fix it. No way would I change it. Even if it's the first grind you thought it was. Splittin hairs.
 
AJ/FormS said:
if you have already run this cam, and were happy with it, then leave it alone.
Click to expand...
The only part of the post you should have been paying attention to. It’s hang dead on. The rest is BS dribble.
 
I think you are really going to like the combination. If your driving a lot of highway miles I'd probably keep the 3.23 gears in it, but if your running more around town and back road miles you might be happier with 3.55 gears. But I wouldn't change a thing without running it first, other than advancing the installed ICL as others have recommended. There are a whole lot worse ways of doing it than your build.
 
Everything I have found on that camshaft part number suggests the original poster's specs of 228 and 231 @ .050 are correct. I am all too familiar with the MP camshaft spec conundrum, but that's what everything "says" it is. I guess you'll really not know until you put a wheel on it.
 
Agree RRR. My old MP catalogs show those specs as well. Maybe they changed them over the years??? This is the paperwork that came with my cam...

Chart1.jpg
 
The MP .050 “specs” are nothing more than 85% of the advertised number.

I def wouldn’t count on that being correct....... especially with the smaller cams.

Put a degree wheel on, see what it measures.
Regardless of what some catalog or piece of paper, or the internet says...... you measure it..... and iiwii.
 
I already wrote on that mopar cam
the 85% rule is a real approximation - BS and mopar advrtised is short compared to aftermarket
run it
advancing that cam really hurts your expansion ratio- opens the exhaust too early
I'd go 4-6 over straight up not 8 over dot to dot
 
I found from MY experience that the MP .050 are actually larger then the .85% of the advertised duration...
 
AJ/FormS said:
Would I run it?
not with 3.23s and a 2200.
and not with 145psi.
Click to expand...
Do the math.
(268+272)/2 less 2x 108= 54, obviously the posted numbers are in error.
More likely that is a 110 LSA cam. Then
(268+272)/2 less (2x110)= 50 overlap

here it is installed at split overlap
Static compression ratio of 9.1:1.
Effective stroke is 2.59 inches.
Your dynamic compression ratio is 7.33:1 .
Your dynamic cranking pressure is 141.85 PSI. ............. 141
V/P (Volume to Pressure Index) is 106 ........................ 106... like a slanty

and at 8* advanced
Static compression ratio of 9.1:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 7.70:1 .
Your dynamic cranking pressure is 151.59 PSI. .................... 152
V/P (Volume to Pressure Index) is 120 ................................ 120 like a stock smogger teen
And like wyrmrider says; this reduces the power extraction from 113* (in at 109) to 106* (in at 102), making it very inefficient especially at hiway speed .... When the exhaust opens this early, there is still a lot of energy in it, that a streeter could really use to propel the vehicle at cruising speed, rather than make little worthless dust devils in the dirt......
plus this KILLs the overlap, from a generous 50 advertised/Effective 50@ 109* install, to an Effective 36*,in at 102*, stunting it to being worthless. Which was the whole reason you chose that 268/272/110

But ya know, you can swap out that 2200Tc for a 3200, and skip right over the soft part. Now you only have the fuel-hog issue( in at 102) to deal with. So make it a week-end warrior, and budget your gas. Once she's up to~3800 she'll start to giddy-up, Lessee 3800 with 3.23s and say 28s is oh gee lookitthat 38 mph. Can you wait until 38 mph for the cam to wake up?

Like I said , for me;
not with a 2200, and not with 3.23s and not with 145psi or 9.1Scr; something has got to go.

Since you say you have no experience with this cam,I would leave it in the box. By the time you add the cost of the TC and proper gears for it, and now it really sucks gas, it's gonna cost you a lotta money to continue to run it.
 
AJ/FormS said:
Do the math.
(268+272)/2 less 2x 108= 54, obviously the posted numbers are in error.
More likely that is a 110 LSA cam. Then
(268+272)/2 less (2x110)= 50 overlap

here it is installed at split overlap
Static compression ratio of 9.1:1.
Effective stroke is 2.59 inches.
Your dynamic compression ratio is 7.33:1 .
Your dynamic cranking pressure is 141.85 PSI. ............. 141
V/P (Volume to Pressure Index) is 106 ........................ 106... like a slanty

and at 8* advanced
Static compression ratio of 9.1:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 7.70:1 .
Your dynamic cranking pressure is 151.59 PSI. .................... 152
V/P (Volume to Pressure Index) is 120 ................................ 120 like a stock smogger teen
And like wyrmrider says; this reduces the power extraction from 113* (in at 109) to 106* (in at 102), making it very inefficient especially at hiway speed .... When the exhaust opens this early, there is still a lot of energy in it, that a streeter could really use to propel the vehicle at cruising speed, rather than make little worthless dust devils in the dirt......
plus this KILLs the overlap, from a generous 50 advertised/Effective 50@ 109* install, to an Effective 36*,in at 102*, stunting it to being worthless. Which was the whole reason you chose that 268/272/110

But ya know, you can swap out that 2200Tc for a 3200, and skip right over the soft part. Now you only have the fuel-hog issue( in at 102) to deal with. So make it a week-end warrior, and budget your gas. Once she's up to~3800 she'll start to giddy-up, Lessee 3800 with 3.23s and say 28s is oh gee lookitthat 38 mph. Can you wait until 38 mph for the cam to wake up?

Like I said , for me;
not with a 2200, and not with 3.23s and not with 145psi or 9.1Scr; something has got to go.

Since you say you have no experience with this cam,I would leave it in the box. By the time you add the cost of the TC and proper gears for it, and now it really sucks gas, it's gonna cost you a lotta money to continue to run it.
Click to expand...

Have you used this particular cam in an engine just like his?
 
Bottom line it has a lot of duration for his build and no easy fix
70aarcuda - what I was trying to say and each vendor of these cams changes the equation over the years. some series even change with the duration
 
You must log in or register to reply here.
-

Back
Top