Purple Shaft or NOT?

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Sportman

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Happy New Year to everyone. I am new here but have been lurking for a while. I am in the process of building a 408 stroker motor for my 74 Dart Sport. I purchased the kit and cam from Indy Cylinder Heads. I am looking for a street machine with lots of torque. I have concerns about the cam that Indy sold me for my combo any suggestion prior to me installing it are appreciated.

My combo:

1974 Dart Sport - Power Brakes
4-Speed
3:55
26" tires
Eagle 4" crank
Eagle I beam rods
Wiesco -20cc pistons (4.030) (Indy said 9.5-1 CR???????)
2.02/1.60 mildly ported J heads 71 cc (plan on running stamped arms)
Edelbroch RPM Air Gap manifold
Carb?????
TTI headers & 2.5" h exhaust
284/284 484/484 Purple shaft 108 center 68 overlap (241/241 @ .050)???? I have been told to install it at 104???
MSD Distributer and 6al ignition

The block is going to the machine shop on Monday and I hope to start assembly late next week.

Again, I am looking for a street machine that leaves the stoplights strong, and has a lopey idle. Thanks for any advice on the cam, and anything else that might help this build.

Jim at Indy Cyl Heads said that cam was an 1800-6800 rpm cam, doesn't match with my research. Thanks for any info you can give me.

Sportman
 
The cams big swing in RPM is due to the displacement it goes in. The shorter the stroke, the higher the RPM. He gave you the biggest possible spread the cam could be used in.

Cam selection is a topic that can produce as many results and opinions as the underwear isle has styles for the ladies.

BRB, I gotta run out the door. I'll fool around with some dyno sym's for idea's. It's a good tool to play with and take with a grain of salt.

DO you have your cylinder head flow specs? This would be really good to have and a huge help in a cam choice.

OH, theres nothing wrong with the Purple cam. But a cam should be choosen with more info. The Purple cam is an old design that can make great power, but a different cam can yank out more HP and TQ.
 
I'm no fan of MP only because they seem to be made by a bunch of drunken hippos. If it was me, I'd run a cam with similar duration at .050 but in terms of lift that cam will open the valves about .465" because you lose a bunch due to valvetrain design. If you have power brakes you need to keep things smaller... to a point. Assuming you don't have power brakes I'd be looking for something more modern, with a faster rate of lift, and advertised lift around .525" or more. Something like the 60405 Lunati or the XE275HL. The pistons are close to 9.5 but you have to have the block square decked and the deck height set to zero, plus have the head chambers cc'd after the valve job to make sure you have a true 9.5:1. For my builds I like the Holley Street Avenger 870 vacuum secondary.
 
Much better cams out there,i myself have used 3 different Lunati "voodoo' cams with great result, i'd go with the .494/.513 hyd. cam,and it's a 4-speed how about a Quick fuel 750..i run the 850 on my 360 and previously on my 416,best damn carb i ever bought/used..
 
Rumblefish360: I purchased these heads about 3rd down the line from the builder. They were fresh (new valves, guides, seals & springs) when I bought them and looked like the runners had been worked and polished and the intake gaskets matched. I have no idea what they flow.

moper: The more I read about the mopar purple shafts, the more I run into people that dislike them. There are also some out there that love the mopar cams. I was leaning toward the Lunati 60404 prior to talking with Indy Cyl Heads. I am running power brakes so vacum is an issue. The block is going in on Monday so should I will have them 0 deck the block? The heads are fresh and cc'd @ 71. I would like to go with different heads in the future (when $$$$$ allow) so I don't want to get CR to high at this time??

Thanks guys,
 
MP cams make power. Don't mistake lack of quality control for "useless". But they have to be degreed and generally are ground way off. My feeling is I'm only checking the intake lobe on cylinder one when I degree. If that is off a lot, how bad are the others I'm not spending the time looking at? Plus, it IS old-school. It makes power but in standard stroke engines it's a turd down low compared to modern stuff. In a stroker it wouldnt be horrid but I really think you'll be leaving a loit of usable power on the table by running it, assuming it's installed right.

Especially if you are planning to upgrade the heads to comething modern, youwant the pistons at zero deck. The dished versions are designed to be "right" with a modern closed chamber head.
With power brakes you are going to want to run a small cam, around 230-235° @ .050 to keep them functional. With a 71 chamber, std Felpro type head gasket, and a cam in the size I mention, you should be somewhere around 9.2:1 static ratio and 8.2:1 dynamic with them at 0 deck. That'ds good for pump fuel and with aan open chamber head. When you upgrade the heads, you will need to upgrade the cam too but the result with a 63cc chamber is just over 10:1 static.
 
All of the purple cams were completely redesigned in the late 80s, so their technology is not that old. Whereas many cam companies grind camshafts for Mopars, only a select few grind them with the .904 lifter bore in mind. The Mopar Performance line of purple cams is one of those who does. I like a lot of the Comp grinds, but the truth is, they are all ground on the same profile as all of their chebbie and phord cams. All you have to do is look at all the specs. I don't think Comp knows how to grind anything that ain't on a 110 degree lobe seperation. lol A lot of people swear by Hughes cams and while I believe they are some very knowledgeable people there, I haven't heard of very many people running them. Having a larger diameter lifter than any other small block and most big blocks means that they can stand more lift per an equal amount of duration in comparison. Does that make sense? So, honestly, the best and only way to get every ounce of power is to do your homework, find out all of your available specs and get something custom ground. Short of that, there are the off the shelf cams ground for the .904 lifter bore, and there ain't many. MP and hughes are the only two I know of, actually. Any of them will do it but only those two offer it off the shelf as far as I know. All camshafts should be degreed in performance applications in the end anyway, so what difference does it make there?
 
Lastly, you need to remember, comparing the MP cams at .050" is useless because they grind using .850 as a standard for .050" figures, while the rest of the industry uses either .750 or .777. That's why the Mopar Engine book says to disregard the .050" figures and only compare advertised figures.
 
I too am thinking about the MP 231 cam. How rough an idle with is cam and what would you consider minmiun engine specs for a 360? Not to steal the thread but very interested in the cam choice. Anyone running this cam?
 
IIRC

The XE comp line is ground using the Ford lifter ramp rates, the HL series is ground using the more aggressive .904 lifter ramps.

That 284/484 will be pretty tame in a 400+ inch engine. They sound and run real good in 340/360, but a 408 will eat up that duration. My general feel, if you know how something runs in a 360, add 12-15* to it at .050 and it will run about the same in a 408. I'd look for something like Moper suggest, the voodoos and Comp XE- HL series cams work really well.

410 with a Comp XE295hl
http://img192.imageshack.us/my.php?image=irwindalevids002.mp4
http://img13.imageshack.us/my.php?image=irwindalevids003.mp4
 
I have the MP 280-474 cam in my 360 idles strong and pulls hard from 800 rpms to 55oo love that cam.
 
Mp cams were not redesigned with anything more than idle quality and it was only a few part numbers. And my point is if they cant get the intake centerline of one lobe within 8° of where THEY spec, it screams to me problems. They do make power, but there'sa lot better out there. The bs about "designed for Mopar lifters" is media hype from hughes engines. Ultradyne had fast rates of lift for everyone back in the 70s, but for any application with a lot of idle time, that ultra fast rates that the larger lifter give can't be safely used. Which is why the XE lobes and Lunati's lobes are closer to the "max rate" for the Ford lifter, which is .875 vs .825 for chevys. It should also be noted that the fast rate .825 lobes are faster by several degrees throughout the lift range than the MP stuff.
 
Go full roller setup, Hughes roller lifters, comp pro mag roller rockers and (I used crane) roller cam just make sure the cam as a cast iron gear on it.
 
Sportman said:
Rumblefish360: I purchased these heads about 3rd down the line from the builder. They were fresh (new valves, guides, seals & springs) when I bought them and looked like the runners had been worked and polished and the intake gaskets matched. I have no idea what they flow.
Click to expand...

OK, sounds good. On builds like this, I like to know where the heads stand. It helps in cam selection. Also, what your idea is for what you want, the target goal of the build is really helpful.

I like to run a split duration cam to help the engine breath better and extend the power band. Duration in the RPM range of the intended operating perameters of what your doing. As much lift as the head will take until the port stalls. Centerline goes down with engine size.

moper: The more I read about the mopar purple shafts, the more I run into people that dislike them. There are also some out there that love the mopar cams. I was leaning toward the Lunati 60404 prior to talking with Indy Cyl Heads. I am running power brakes so vacum is an issue. The block is going in on Monday so should I will have them 0 deck the block? The heads are fresh and cc'd @ 71. I would like to go with different heads in the future (when $$$$$ allow) so I don't want to get CR to high at this time??
Click to expand...

I like the Lunati line as well as a couple of others. As long as you can run pump gas with the iron heads, you'll be fine when the switch to aluminum comes around. The bigger the cam, the more C-ratio you can run. Lower the centerline, the more ratio you can run. These two factors bleed off compresion at low RPM.

What ever you end up with, the distributors timieing is what will allow you to run 91/93 octane without issues. You have to take the time to dial in the distrib & carb to get it to run not just well, but at it's best!

It is possible to run a 10-1 on 91 octane with big-ish street cams if you take the time to dial it all in.
 
Thanks everyone for your input. I think I will try the MP cam as long as it degrees properly. I am also going to get the block 0 decked and possibly take a bit off the J heads to bump up the CR a bit (around 68cc). This should give me 9.6:1CR? Do you think that combo would work OK?
 
I've got a purple cam...I stick it in the door jamb to hold the door open on windy days...
Back when they were $19.95 they were good value next to the $79.95 Crane Fireball cam and they made better power too.
Now there is no excuse to use one unless your going with the all mopar theme ...
Call up Engle Cams and get something comparable from their catalog...
 
I think over 30 yrs I have everyone of the small block version...and dont ever remembering having problems degreeing one in...and never had one flatten a lobe...

currently got a MP590 cam in one car...
 
I have a BRAND NEW MP .509 hyd cam for sale??? Also have the springs and lifters!!!!
PM if your interested.

Im not saying MP cams are the best out there but they do work!!!
 
Alot of good info,there really is not a bad cam between the ones talked about and there is nothing wrong with running a 110 a 108 or what ever lobe separation,it all depends on your combo.As mentioned the mopar cams are off,I have installed a couple and they were both off by 4-6 degrees,I was able to get them degree'd within a couple degrees of were i wanted them using an adjustable chain.I do agree that in your case something like the lunati would be a much better fit considering the cubic inch and vaccum brakes,you will also get more lift and in your case I would prefer the 110 lobe separation.The lunatis have a cool sound at idle and still have good vaccum.If you have not heard the lunatis here is a sample,I know its a chevy but it is a 408,the mopar design is a bit more aggressive yet.
[ame="http://www.youtube.com/watch?v=jaQiF7ZBWFs"]YouTube - 1970 Chevelle 500 HP[/ame]
 
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