How should this cam work with my combo?

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MopaR&D

MopaR&D

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I scored a used Mopar Purple Shaft 284*/.484" for small blocks and was wondering how it might work with the rest of my engine/drivetrain combo.

I'm putting together a 360 with a '79 LA block, stock Magnum heads and rockers (and other stuff for conversion), KB-107 pistons (about 10.5:1 comp), 340 exh. manifolds, Air-Gap intake, and (for now) a 625 cfm Carter AFB. Headers and a bigger carb will come in the future.

Transmission is a 904 with tci internals and 2800-stall converter, and rear-end will be 3.23:1 SG either 8 1/4" or 8 3/4" haven't picked yet.
 
For an accurate answer, you need to remove the "about" from your equation. You need to know dead nuts on what your compression ratio is.
 
be prepared to tune your carb with that cam...it aint going to idle very nice..
 
OK when I used the online calculators it came out to 10.6x, I plan to have the block zero-decked and use .039"-thick head gaskets. I will try to cc the heads if I can get a hold of the materials at school.

But basically it sounds like this cam is pretty damn big... would installing it advanced help at all? Is this cam too big to work with a Carter carburetor? I already have it but if it will disappoint me on the street then I'll see about giving it back, I could definitely use the cash.
 
you should be fine with it, i would go with a holley 750vs, or if your good with carb tuning a 750 dp.
 
EL5DEMON340 i would go with a holley 750vs, or if your good with carb tuning a 750 dp.
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YEP!

70aarcuda be prepared to tune your carb with that cam...it aint going to idle very nice..
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YEP!
More than likely. Being that a CArter is being employed. The Carter will idle better when warm. Otherwise, the 110 C-line is a nornmal lopey idle.

Kid, theres a few issues with the combo at hand. The cam is wrong for this set up. Your use of exhaust manifolds is going to hurt. The carb is to small and yur gear is not loose enuff.

IMO, give the cam back and look into a split duration cam of approx a stock 340 spec'd to one +6* larger at most. Your exhaust duration IMO should be at least 8* more than the intake duration.

Another thing, your compresion ratio looks way off. Something not jivin there. The Cylinder heads must be low on cc's. A stock 360 head should have about 72 cc's, give or take 2 on ethier side. If it is 72 cc's, then it is a 9.8-1 ratio with the gasket used, give or take a .10 on ethier side due to exactness of the gasket missing.
 
I almost went with that cam in my 360 build.I slammed in the 280-474 purple cam,no problem tuning my 600 Holley,all tho a 750 will work better,she is a shaker.Good luck you will be fine.
 
rumblefish360 said:
YEP!



YEP!
More than likely. Being that a CArter is being employed. The Carter will idle better when warm. Otherwise, the 110 C-line is a nornmal lopey idle.

Kid, theres a few issues with the combo at hand. The cam is wrong for this set up. Your use of exhaust manifolds is going to hurt. The carb is to small and yur gear is not loose enuff.

IMO, give the cam back and look into a split duration cam of approx a stock 340 spec'd to one +6* larger at most. Your exhaust duration IMO should be at least 8* more than the intake duration.

Another thing, your compresion ratio looks way off. Something not jivin there. The Cylinder heads must be low on cc's. A stock 360 head should have about 72 cc's, give or take 2 on ethier side. If it is 72 cc's, then it is a 9.8-1 ratio with the gasket used, give or take a .10 on ethier side due to exactness of the gasket missing.
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I mentioned that I was using Magnum heads, not LAs... And it looks like I'm getting some mixed replies here. The guy I bought it from had it in a 360 for his '66 Barracuda, had the same tranny I'm about to use and 3.55 gears. He said it ran great on the street and wasn't too radical, he claims he even could get 18 MPG if he really tried. And I don't think he's stretching the truth to sell stuff because he's given me a lot of nice parts for super cheap (sometimes free). On that note I'm pretty sure he has several Holley carbs lying around that he'd be willing to sell me.

Another issue I'm wondering about is max lift for stock Magnum heads... With 1.6 rockers the valve lift comes out to .516", is this too much?

And how much power am I giving up by using exhaust manifolds?
 
I think magnum heads max lift is about .520+ so you are close, I would check your heads to be sure,
 
OH! Sorry Kid. My bad. Lift is close. Check it before fireing it up. Worst case....ya wait while the retainer to guide clearance is fixed. On the exhaust maifold use/loss, I'll "Guess" at 30+ HP. At least.

I'd also lke to mention that gear ratio + tire size has an effect on how the engine will be able to release the power made. More ratio, more power released. OK we knew that, but also, the tire size is like a helper or hinderance. Larger, hinderance. Smaller, helper, but less traction.
 
i got to agree with rumble on this one.you need more gear.that cam also has a 108 lsa,and is a single pattern.if you take both of those things into account the the exhaust manifolds are wrong for that combo.i had a copy of that cam (custom ground) in a 318 years ago.it ran killer with a radical idle,however i also had headers,the cheap one with zero ground clearance.they met their demise on a speed bump and i replaced them with 340 manifolds.i lost so much power and throttle response it was like i had castrated the car.with alot of tuning i got some of the power back,but the car was never the same.
 
Yeah I think I'll look into getting a different cam, I really want the car to be practical for long-distance driving without any hassles. The car this .484 was previously in I feel was set up better for it. I have a Lunati Voodoo 60401 from my old 318 but I think it would build too much cylinder pressure at low speed, it's only 256/262 adv. duration and .454/.475" lift. What are some good cams with more duration that have around .460" lift (with 1.5 rockers)?
 
OK I'm eyeing the Crane 272-H, split pattern 272/284* and .454/.480"... here's a LINK Anybody here used this cam before?
 
MOPEkidD-3 said:
OK when I used the online calculators it came out to 10.6x, I plan to have the block zero-decked and use .039"-thick head gaskets. I will try to cc the heads if I can get a hold of the materials at school.

But basically it sounds like this cam is pretty damn big... would installing it advanced help at all?

No. It already has 4* advance ground into it. Use a degree wheel and get it right.

Is this cam too big to work with a Carter carburetor? I already have it but if it will disappoint me on the street then I'll see about giving it back, I could definitely use the cash.
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Not too big to use with a Carter...but as others have eluded, there are other carburetors that will work better. Overall, I think it's a good camshaft choice. Long as you run a converter and gear to match it will be nice.
 
MOPEkidD-3 said:
OK I'm eyeing the Crane 272-H, split pattern 272/284* and .454/.480"... here's a LINK Anybody here used this cam before?
Click to expand...

If you're runnin headers, stick with the Mopar single pattern camshaft.
 
I think anything is going to be a compromise when you talk about building for changes later. You will be higher static with Magnum heads, but you also will be using 1.6 ratio rockers, so you want to keep the lobe lift under .320 (advertised .480 with 1.5s) or so. I would say Crane is the (much) better cam, regardless of the exh system. Single pattern cams generally will make more power at specific rpms with matched components. But dplit patter will make better average power with almost any components (meaning best for compromise builds).

I should add I have that cam for my truck 360 that is getting Magnum heads but has about 2 points less compression (stock pistons way down in the bore).
 
I've used that cam twice before. I like it alot for pepping up a street ride. If your rear tire stays small with those gears, it will make for a good ride. It's capable of high 14's in a dead compresion 318, in my Duster with the same gear, stock stall & headers.
 
I'm pretty set on having 3.23 or numerically lower gears in the rear end so I can go on long highway cruises. For tires I'm looking at 235/60-15 Firestones which are about 26" tall. I also have a 2800-stall TCI converter I'm going to use.

My main concern is drivability and ease-of-use. I want it to be able to start on cold winter days (30*F or colder) and be ready to go in 5 minutes, cruise hundreds of miles while getting at least 18-20 MPG, and be able to withstand 2000'+ altitude changes without running like crap and needing a full re-tune. I was able to do all this before with my stock-bottom-end 318 with Voodoo 256/262 cam, duals, and same 625 AFB carb. If running the 284/.484 cam will make that difficult then I'll choose something else.
 
You are gearing for torque. SO using a cam that makes a torque peak higher than about 2400 is going to lose you efficiency. The problem I see is the interplay between the static compression ratio and the cylinder pressure. The .484 will certainly help with that, but it's boarderline too tall for the Magnum springs. So the trick might be to find something with similar duration but less lift. Engle has one, a hydraulic E420221. It's [email protected] and 310° advertised but only has .462 lift (all with 1.5 rockers). That's a fairly mild rate of lift too, so the springs dont have to be crazy even with 1.6s.
 
Doesnt wider lobe seperation allow somewhat higher compression ratios also?
What about something like an engle EP-18hyd? specs are 260 adv 216 at .050
.456 lift and a 113 lobe seperation?
 
OK looks like I need to check my retainer-to-guide clearance before I go any further, because if I have .520" clearance or more than I can run a .480-lift cam... Would it be good enough just to remove a valvespring (1 intake, 1 exhaust?) and put on the retainer and locks, then measure with dial calipers with the valve closed solid?
 
just remember magnum rocker arms are 1.6 ratio....

almost all cams are listed with 1.5 rocker ratio...

.480 cam with 1.5 is a .512 with 1.6
 
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