MP .474 purple cam

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Brambles

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Who's running this cam, how do you like it? A guy I was talking to who claims to build custom mopar engines was really talking this cam up and claimed it was a much better cam than the MP .484.

I got magnum heads and am leaning towards the single pattern cam since the exhaust flows at almost optimum %.

The only concern is that i hear Ma mopars actual dur .050 is not accurate

Any feedback.
 
MoPar says to do there duration @ .050 via, multiply by .850.

280 X .850 = 238
284 = 241.4
 
That is what Mopar says. But with the magnum heads he will be running 1.6 rockers so wouldn't he gain about 6 or 7 degrees of duration as compared to 1.5 rockers?

Jack
 
Anyone running this cam, done some looking around and can't seem to find anyone with timeslips faster then low 14's - high 13's with this cam. You'd figure with 238 @ .050 you could go mid to high 12's. This makes me wonder if the cam is tamer than advertised, especially if they say you can run a stock converter with it.......
 
I agree that rocker ratio changes lift. But wouldn't you get to the @50 point a little quicker and stay there a little longer than you would with 1.5 rockers.

Jack
 
Redfastback is correct. The increased rocker ratio just creates a higher lift. The duration figure that is ground on the cam stays as is. The valve still opens and closes at the same degree on the cam.
 
I agree with Coyote Jack. The total duration does remain the same but with the higher rocker ratio lifting the valve faster the duration at .050 is increased somewhat. I don't think it makes a tremendous difference, probably only 1-2 degrees but it does change. I was recently speaking with Jim at Racer Brown cams and he confirmed this.

I think what Brambles was referring too as far as the mopar duration not being accurate is because the bad angle the lifter is in comparison to the rocker arm. This causes a little lift and duration to be lost. I've heard lift loss is close to .020" but haven't measured it to confirm it but the next time I rebuild an engine I plan on checking it. If everything was aligned up straight (lifter to pushrod to rocker arm) there wouldn't be any loss.
 
What I"m interested to find out is if you have a mopar 238 deg @.050 and a cam from another manufacturer with 238 deg @.050 will they be similar behaving cams.

I think not, Mopar even says that you can only use their Duration at .050 to compare mopar cams and that its not accurate to compare to other brands. I'm guessing because its a mathematic formula to get their duration numbers rather than actually measuring them.

Guys seem to be running much faster with say a comp 280H/ 230 deg .050 than a mopar cam .474 238 deg @.050.

It goes back to them making the statement that their .474/ 238 @ .050 cam can be run effectivly with a stock convertor when another manufacturer claims that a cam with 8 degrees less duration needs a 2500 RPM stall.
Everything else being equal the mopar cam should need a 2800 RPM stall.

Something is fishy with their duration numbers.
 
It actually does change duration slightly "at the valve" when basing off a certain lift.

Duration at the lifter doesn't change.
 
JUNK! JUNK! JUNK! I have this grind in my 340. It sucks. It has sucked since day one. It's noisy, has no bottom end because it's a 30 year old crap design. The duration is too long for the lift. I had mine checked by a local cam grinder to see what the real specs are. It's actually 288 duration by SAE specs, (which is @ .006 lift) with 238 @ .050.

Run away from this grind as fast as you can and buy a Lunati VooDoo or a Comp Cam.

I intend to put a Lunati VooDoo in my 340 at some point in the future.
 
redfastback said:
well, guess i was wrong.
Click to expand...

Actually you are right to a degree, LOL.

Depends on where you are considering duration changes. If you degree the cam, use a standard .050 lift, duration doesn't change at all.

If you take it at the retainer you will have a very minimal increase when going up in ratio. If you took a standard 1.5 SB you'd have .075 theoretical lift at the retainer when at .050 cam lift. Now take that same lift point at the retainer of .075 and divide it by the new 1.6 ratio. Your .075 lift requires, .046875, which makes duration slightly longer to each of those points on the lobe. It's really insignificant, maybe a degree or two at the most, yet it's there.
 
Brambles said:
What I"m interested to find out is if you have a mopar 238 deg @.050 and a cam from another manufacturer with 238 deg @.050 will they be similar behaving cams.

I think not, Mopar even says that you can only use their Duration at .050 to compare mopar cams and that its not accurate to compare to other brands. I'm guessing because its a mathematic formula to get their duration numbers rather than actually measuring them.

Guys seem to be running much faster with say a comp 280H/ 230 deg .050 than a mopar cam .474 238 deg @.050.

It goes back to them making the statement that their .474/ 238 @ .050 cam can be run effectivly with a stock convertor when another manufacturer claims that a cam with 8 degrees less duration needs a 2500 RPM stall.
Everything else being equal the mopar cam should need a 2800 RPM stall.

Something is fishy with their duration numbers.
Click to expand...

The reason guys are running faster with Comp 280H is because it's a better grind. Lots of guys talk about how great the MP grinds are. They probably were -- in 1978. But it's 2008 now. Time to move on to newer technology.

All I can say is good luck running this grind with a stock convertor. I'm running it with a 4 speed and it's a dog until 2500 rpm. That's with 9.75:1 compression and I degreed the cam in @ 106 ATDC. My gears are 3.55

Don't waste any more energy thinking about this grind. Look elswhere. One more thing - Mopar doesn't parkerize their cams. I guess they save a buck on each one. I paid to have mine parkerized before I installed it, just to be sure it survived break-in.
 
I run the 280H in my magnum headed LA360. But I also run 10.58 compression, headers, 2800 conv. and 4:10 gears. It runs very good for me. I think it woud be a dog in an everything else stock situation.

Jack
 
Coyote Jack said:
I run the 280H in my magnum headed LA360. But I also run 10.58 compression, headers, 2800 conv. and 4:10 gears. It runs very good for me. I think it woud be a dog in an everything else stock situation.

Jack
Click to expand...


What kind of times is that combo putting out? Mine is also a magnum head engine, but with 9.5:1 comp and 3.91's haven't decided on stall but 2600- 2800 was in the back of my mind. I might mill the head for another .5 point in compression but I haven't decided on that yet.

Brambles
 
I havn't had it to a track yet. Maybe later this summer. But the car was designed to run 12.0 Not sure whether it will or not but the calculators say it should do a little better than that. I do know it is a real fun ride for the street.

Jack
 
Brambles said:
Anyone running this cam, done some looking around and can't seem to find anyone with timeslips faster then low 14's - high 13's with this cam. You'd figure with 238 @ .050 you could go mid to high 12's. This makes me wonder if the cam is tamer than advertised, especially if they say you can run a stock converter with it.......
Click to expand...

I have ran 12.50's with this cam in a 360
 
It seemed to me that the lift figure @ .050 was taken at the lifter. If this were the case, rocker ratio would have no effect on duration @ .050. Are the Mopar pieces measured differently?
 
i was taught that lift @ lobe did NOT affect duration. but i was wrong once.................
 
doktor_x said:
It seemed to me that the lift figure @ .050 was taken at the lifter. If this were the case, rocker ratio would have no effect on duration @ .050. Are the Mopar pieces measured differently?
Click to expand...

The rocker ratio would not affect the cam duration at .050,what it would do is hang the valve open a little longer by opening a liitle sooner and closing a little later.The engine would act as if it had about a 2-3 degree larger camshaft,which isnt a drastic change.Also mopars cams are rated like everyone else in the industry,.050 is the standard,the only real difference is when comparing the .050 numbers to the .006 or advertised.You can have two advertised 280 cams and one will be 230 @ .050 and the other one will be rated at 238 @ .050,this indicates a more agressive lobe profile.Mopars are old but they were a pioneer of agressive ramps,their lift numbers were kept low to compensate for stock heads which generally peak in the lower lifts.
 
well, back to the original poster.... go with a modern dual pattern cam. you will be happy. i just yanked my 80's mullet haircut, hijacker airshock, 284/484 mp purple shaft cam and put in a 274 xe comp cams. it woke up the bottom end.
 
redfastback said:
well, back to the original poster.... go with a modern dual pattern cam. you will be happy. i just yanked my 80's mullet haircut, hijacker airshock, 284/484 mp purple shaft cam and put in a 274 xe comp cams. it woke up the bottom end.
Click to expand...

Oh man-I already cut my hair!-now I have to get rid my hi jackers too!:supz:fwiw I agree ,modern grinds are better.
 
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