Magnum 360 heads "best" for my build?

[octanejunkie]

So I have a set of Magnum heads ready to bolt on. After some careful consideration looks like I can do about a .510 lift with the right springs.

Considering the XE268H cam http://www.summitracing.com/parts/CCA-20-223-3/

Block is a .030 over '99 magnum.

Will be going into a '71 Scamp in place of the tired 318 in there now.

Rear is 2.76 geared, thinking about 2.94s, 3.21s or 3.55s, but fwy cruise rpm is a concern

Trans is a 904 with stock converter, upgrade pending based on overall build

Car will be street/strip driven, 85% street, spirited driving

While I know I can drop $$$ on heads, will the magnum heads suffice?
Should I consider doing any work on them?
How can I expect the car to perform with these heads and Hooker Super Comp headers?
Would 340 manifolds be better?
What would be the overall compromise in performance running these heads?

 

[rumblefish360]

Well, with that cam, I think 3.55's is what I'd look at and possibly 235/60/15 on the back. At Hwy speed, (Somewhere in the 65-70 mph range I assume) you should be cruiseing right in the power band, which cam manufactures recomend doing, at about 3000 - 3200 rpm.

You'll want a stall converter so it's not so slow outta the hole.

Now, on to the heads....and exhaust;

The Magnum heads will work fine as cast, a good valve job and back cut of the valves is more than enuff. I don't think porting is needed. The heads, as cast, delivered 400+ HP on the create engines. So, IMO, the ponential (SP) is there for you without extra work. Stock as cast OE valve sizes will work fine. The cam your looking at, the Comp cam is alot smaller than the MoPar roller cam in the create engines.

Powerwise, headers win hands down. However, they really suck to install. There worth the power. The exhaust manifolds are great for installing and lasting halfway to forever without issues later on.

The down side? The Magnum head valve train is not as stable as the "LA" system and the attaching bolts are weak, but can be upgraded to a larger size and use Chevy rockers for an inexpensive upgrade. 1.7 rockers are also available.

Then again, your not stressing the engine/valve train enuff to care about it.

Keep the head cool to avoid cracks inbetween the valves.

 

[WackoWilly]

I agree with Rumblefish360, there is a possible 30 + H.P. increase with magnum heads. Draw back are the head bolts (I would use studs, have to if alum. heads), the R/A gear is close to the same as Chevy and the intake manifolds available are - single plane Mopar Performance or dual plane Mopar Performance or Edelbrock. Engine Quest has magnum heads with magnum R/A, flow better than most other magnum heads and come with either "A" engine intake bolt latout or magnum intake bolt layout; with this you can use the "A" engine layout and use a 6-pak intake, tunnel ram intake or the rare Street Tunnel Ram intake, along with single or dual plane.

 

[octanejunkie]

Well, with that cam, I think 3.55's is what I'd look at and possibly 235/60/15 on the back. At Hwy speed, (Somewhere in the 65-70 mph range I assume) you should be cruiseing right in the power band, which cam manufactures recomend doing, at about 3000 - 3200 rpm.

I am running 245/60/14s in the back. I have calculated highway speeds 65mph & 80mph respectively as follows:

2.94 - 2714 @ 65mph, 3340 @ 80mph
3.21 - 2963 @ 65mph, 3647 @ 80mph
3.55 - 3227 @ 65mph, 4033 @ 80mph - nice launch, but ouch on the fwy
​

My other option is the 3.91 gear set in the SG equipped 741 I have for my 8.75 - if only the car were 100% strip I'd run those...

The Magnum heads will work fine as cast, a good valve job and back cut of the valves is more than enuff. I don't think porting is needed. The heads, as cast, delivered 400+ HP on the create engines. So, IMO, the ponential (SP) is there for you without extra work. Stock as cast OE valve sizes will work fine.

Good news there, just got them back from surfacing, seals, seats and stems - aside from springs they are ready to bolt on

The cam your looking at, the Comp cam is alot smaller than the MoPar roller cam in the create engines.

I am not "sold" on this cam, but it does seem like a good compromise in power with mild lift. Not sure if I wll run 1.6 or 1.5 ratio rockers yet... I am open to other cam choices, comp suggested a custom grind, waiting to hear back from them as to why they suggest it over the 20-223-3 XE268H, here are the specs they sent me:

265/273 adv dur (@ .006)
216/224 dur @ .050
.3170/.3170 lobe lift
.4755 valve lift with 1.5s
.5072 valve lift with 1.6s
110 LSA
-install dot to dot for a 106 IC (4 deg adv ground in)
​

Would love to know what the logic in suggesting this cam is...

Powerwise, headers win hands down. However, they really suck to install. There worth the power. The exhaust manifolds are great for installing and lasting halfway to forever without issues later on.

I'll see if the struggle with the headers is worth it. I have the coveted 340 manifolds now...

The down side? The Magnum head valve train is not as stable as the "LA" system and the attaching bolts are weak, but can be upgraded to a larger size and use Chevy rockers for an inexpensive upgrade. 1.7 rockers are also available.

Then again, your not stressing the engine/valve train enuff to care about it.

I was looking at a set of stud-mounted self-aligning roller rockers, SBC in origin, as long as the length and geometry were correct; no guideplates. Obviously the pushrods are of concern too

Keep the head cool to avoid cracks in between the valves.

Cooling was my next concern. I have a 22" radiator on the 318 now, not sure if it will be sufficient for the 360 - but I was probably going to go to an electric fan/shroud/relay as I really like this setup on my '59

Thanks for the advice!

 

[octanejunkie]

I agree with Rumblefish360, there is a possible 30 + H.P. increase with magnum heads. Draw back are the head bolts (I would use studs, have to if alum. heads), the R/A gear is close to the same as Chevy and the intake manifolds available are - single plane Mopar Performance or dual plane Mopar Performance or Edelbrock. Engine Quest has magnum heads with magnum R/A, flow better than most other magnum heads and come with either "A" engine intake bolt latout or magnum intake bolt layout; with this you can use the "A" engine layout and use a 6-pak intake, tunnel ram intake or the rare Street Tunnel Ram intake, along with single or dual plane.

Forgot to mention the Eddy Air Gap RPM for magnum I have too along with a 625cfm AFB

 

[64physhy]

Hughes now has shaft mounted rockers for Magnum heads. It's 1 short shaft per cylinder with both rockers on it. Not badly priced at $475 for a set. http://www.hughesengines.com/Index/products.php?partid=25628

 

[octanejunkie]

Hughes now has shaft mounted rockers for Magnum heads. It's 1 short shaft per cylinder with both rockers on it. Not badly priced at $475 for a set. http://www.hughesengines.com/Index/products.php?partid=25628

Now THOSE are SEXY! I like...

1.65 ratio would take my lift to 0.52305 on the custom cam or 0.528 max on the XE268H - not sure I can tolerate that much lift without cutting the seats/guide stems

For mild lift/performance I have had good luck with the ProForm SA roller rockers, at only $160 per set, like these, got 'em on my '59 too

 

[moper]

That is a very good looking rocker setup... Just what the RHS/Indy's NEEDED. As far as the cam... Comp probably thinks the XE268 will have problems with the stock valve/spring package and 1.6 ratio rockers (comes to .512 lift at the lifter... prob closer to .490 in reality at the valve but they don't want to risk it). So they gave you basically the XE262 spec lobes.

 

[rumblefish360]

64physhy Good link! I forgot about those. Nice system.

I am not "sold" on this cam, but it does seem like a good compromise in power with mild lift. Not sure if I wll run 1.6 or 1.5 ratio rockers yet... I am open to other cam choices, comp suggested a custom grind, waiting to hear back from them as to why they suggest it over the 20-223-3 XE268H, here are the specs they sent me:
265/273 adv dur (@ .006)
216/224 dur @ .050
.3170/.3170 lobe lift
.4755 valve lift with 1.5s
.5072 valve lift with 1.6s
110 LSA
-install dot to dot for a 106 IC (4 deg adv ground in)

Would love to know what the logic in suggesting this cam is...

The cam is more suited to the small carb size, gear ratio/tire size and stock head set up than a larger cam is. This is why I also suggested a 3.55 gear with a 26 inch tire.

I run a very similar Crane cam in my 318 with 3.21 gears and a small tire. (I need to refresh my memory on it's exact size. I think there 225/70/14, about the same diameter as your wider tires.
It's a preety good combo.
(Crane specs; 216/228-.454/.480/112)

With a Magnum head, your ratio for the rockers start at 1.6 and the 1.7 is the extra lift arm.

The "LA" heads have a 1.5 and a 1.6 as the extra lift arm. As far as I know, you can not get a 1.5 rocker for the Magnum head.

The exhaust manifolds are a restriction now matter what exhaust manifolds you have. Period.

A slant 6 rad. is not enuff to cool the engine well and constantly. While it is possible for use, it is best used as a short term runner or a track car that see extremely limited running time.
Best bet, Advanced Auto/AutoZone, for a new V-8 rad.
A electric cooling fan and shroud is a nice (but expensive) move that will free up some good HP.

(Edit, I also agree with Moper.)

 

[octanejunkie]

That is a very good looking rocker setup... Just what the RHS/Indy's NEEDED. As far as the cam... Comp probably thinks the XE268 will have problems with the stock valve/spring package and 1.6 ratio rockers (comes to .512 lift at the lifter... prob closer to .490 in reality at the valve but they don't want to risk it). So they gave you basically the XE262 spec lobes.

I was planning on new valve springs anyway, the 901 springs they recommend will tolerate about .510 lift but I don't want to go that high. The installed height of my current springs/retainers is 1.670 (with .060 safety margin already figured in,) the 901 springs will bind at 1.160 - seems they will work for up to .512 lift, or less wtih the 20-223-3 cam; if I go that route with 1.6 rockers

The cam is more suited to the small carb size, gear ratio/tire size and stock head set up than a larger cam is. This is why I also suggested a 3.55 gear with a 26 inch tire.

I am seriously leaning towards the 2.94 or 3.21 gears, converter stall TBD, purely from a fwy economy point of view. If I had an OD trans, 3.73 would be my choice ratio, but I do have those 3.91s ready to bolt in... tempting

The "LA" heads have a 1.5 and a 1.6 as the extra lift arm. As far as I know, you can not get a 1.5 rocker for the Magnum head.

I could if I use SBC rockers. I have a set of stock vortec 1.5 SA stamped rockers off my 906 vortec heads... Hmmm

A slant 6 rad. is not enuff to cool the engine well and constantly. While it is possible for use, it is best used as a short term runner or a track car that see extremely limited running time. Best bet, Advanced Auto/AutoZone, for a new V-8 rad.
A electric cooling fan and shroud is a nice (but expensive) move that will free up some good HP.

Not worried about the cost of cooling, it is a necessary evil for hp and HP. Ironically my car was a factory V8 car, I thought my rad was stock. I am looking at an 22" alu on ebay, wish it were cross flo tho...

 

[64physhy]

What's the formula for figuring the difference in lift on 1.6 and 1.65 rockers? Doesn't seem like the extra .05 in ratio would raise the lift by .020".

 

[rumblefish360]

I am seriously leaning towards the 2.94 or 3.21 gears, converter stall TBD, purely from a fwy economy point of view. If I had an OD trans, 3.73 would be my choice ratio, but I do have those 3.91s ready to bolt in... tempting

I hear ya.

I could if I use SBC rockers. I have a set of stock vortec 1.5 SA stamped rockers off my 906 vortec heads... Hmmm...

Hummmm, INdeed!

What's the formula for figuring the difference in lift on 1.6 and 1.65 rockers? Doesn't seem like the extra .05 in ratio would raise the lift by .020".

Lift divided by rocker ratio mulitply new rocker ratio
For a Magnum head going to a 1.5 from a 1.6;
500 / 1.6 = 3.12 x's 1.5 = 468.75

An "LA" head going from 1.5 to 1.6 or "LA" head to Magnum head if you will;
500/1.5 = 333.333 X's 1.6 = .533.333

 

[octanejunkie]

What's the formula for figuring the difference in lift on 1.6 and 1.65 rockers? Doesn't seem like the extra .05 in ratio would raise the lift by .020".

If you don't know the lobe lift you have to find it
Valve lift / 1.5 = lobe lift

With that just multiply the lobe lift by the rocker ratio
Lobe lift x rocker ratio = valve lift w new rocker ratio

Seems simle enough, I'm sure someone else will chime in if I overlooked something

 

[1wild&crazyguy]

I agree with Rumblefish360, there is a possible 30 + H.P. increase with magnum heads. Draw back are the head bolts (I would use studs, have to if alum. heads), the R/A gear is close to the same as Chevy and the intake manifolds available are - single plane Mopar Performance or dual plane Mopar Performance or Edelbrock. Engine Quest has magnum heads with magnum R/A, flow better than most other magnum heads and come with either "A" engine intake bolt latout or magnum intake bolt layout; with this you can use the "A" engine layout and use a 6-pak intake, tunnel ram intake or the rare Street Tunnel Ram intake, along with single or dual plane.

30 hp increase over what?

 

[1wild&crazyguy]

3.23 gear at the least.jmo

polish anything that might be crack prone=between valves around chamber, yes they crack there too, and you'll be good.jmo
Especially in the bowl between the valves, I've seen them crack from the seat down almost to the bowl roof.

you should be good though with what you are doing as long as you have enough capacity in the rad.

 

[octanejunkie]

3.23 gear at the least.jmo

polish anything that might be crack prone=between valves around chamber, yes they crack there too, and you'll be good.jmo
Especially in the bowl between the valves, I've seen them crack from the seat down almost to the bowl roof.

you should be good though with what you are doing as long as you have enough capacity in the rad.

Good advice on the polish, easy enough to do while the rest of the build is simmering on low ;)

I will probably start out with the current converter and gears just to see how it runs, feels, launches, etc. Then I'll make some decisions and upgrade the gears and the converter - might as well get the experience while I can.

On second thought, best time to change the converter is when I swap the 360 in place of the 318, no reason to pull the trans twice

Honestly 3.2X gearing is a compromise, I do really prefer to drop in 3.55s but not on the fwy at 80mph with 1:1 top trans ratio.

 

[WackoWilly]

30 hp increase over what?

A 30 H.P. over stock heads and if you put in 2.02 valves (Int.) better than 340 heads. Their castings just flow better and are new castings. Hughes rocker arms set up is great, low expense and will work if you decide to increase h.p. gains (bigger cam, torque convertor, pistons, carb, etc...)

 

[1wild&crazyguy]

A 30 H.P. over stock heads and if you put in 2.02 valves (Int.) better than 340 heads. Their castings just flow better and are new castings. Hughes rocker arms set up is great, low expense and will work if you decide to increase h.p. gains (bigger cam, torque convertor, pistons, carb, etc...)

30 hp huh?

every 5 cfm in worth 10 hp....

Stock 1.88 j heads w/ a good valve job flow 195cfm-200cfm @28
I have a flow sheet from J&J machine from my 1st set of j's.
They were flowed 189cfm at 25, converted to 28 200cfm

Now stock 2.02 J/X with stock or 3 angle stone valve job went anywhere from 200-205cfm
Same head with a serdi 'multi angle' VJ and new valves[say wide margin valves heads =210-220

the kicker is that there is way more potential left in the older heads.
Magnum heads-cost effective, thin lite castings with low emissions in mind, and the exhaust ports only flow maybe 10cfm more than a j head, as in the shape got better but the port became smaller and restrictive in that lite.

I have actually flowed something before, have you?

 

[dgc333]

FWIW, I am running the XE268H cam in a 360 with stock magnum heads. My set up is making approx. 370HP based on 102 mph trap speeds in the 1/4. The engine pulls strong from 1500 to 6000+ rpm.
The XE268H is a great street cam IMHO.

 

[MopaR&D]

Nobody's mentioned it yet BUT since you are using a 904 trans why not put in the lower 1st/2nd gearset from the A-999 transmission so you can run a higher rear ratio for the freeway? I think from what rumblefish360 said you could use a 3.23:1 ratio and from a stop it would accelerate more like it had 3.55:1 gears. If I don't swap a 4-speed and 3.23:1 rear into my Duster I'll probably rebuild the 904 with a ~2500 RPM converter, A-999 gears, and shift kit and put in a 2.94:1 rear.

To put it in perspective I'm going to rebuild my 318 at the same time with its current cam but with RHS Magnum heads (LA intake bolt angle), 1.6:1 rockers on the intakes for around .480" lift (cam is already dual-pattern so exhaust lift will be around .475" with 1.5:1 rockers, from what I've read is plenty for Magnum heads), headers (Doug's or TTI), zero-deck pistons for around 10:1 compression, and a port-matched Edelbrock Performer (non-RPM) intake for better gas mileage and low-end torque with the auto trans. I'll probably run a DemonSizzler-tuned SB ThermoQuad as well. Then if I want to take it to the track I can swap in 3.55s or 3.91s as well as an RPM Air-Gap intake and 650 cfm Holley and see its true potential.

 

[octanejunkie]

FWIW, I am running the XE268H cam in a 360 with stock magnum heads. My set up is making approx. 370HP based on 102 mph trap speeds in the 1/4. The engine pulls strong from 1500 to 6000+ rpm.
The XE268H is a great street cam IMHO.

I am leaning heavily towards this cam, a few questions:
What carb and intake are you running?
What rocker ratio/valve springs too?
What is your static compression ratio?
What trans are you running?
What is your rear gear ratio?

Would love to know so I can tailor my build, thanks!

Nobody's mentioned it yet BUT since you are using a 904 trans why not put in the lower 1st/2nd gearset from the A-999 transmission so you can run a higher rear ratio for the freeway? I think from what rumblefish360 said you could use a 3.23:1 ratio and from a stop it would accelerate more like it had 3.55:1 gears. If I don't swap a 4-speed and 3.23:1 rear into my Duster I'll probably rebuild the 904 with a ~2500 RPM converter, A-999 gears, and shift kit and put in a 2.94:1 rear.

To put it in perspective I'm going to rebuild my 318 at the same time with its current cam but with RHS Magnum heads (LA intake bolt angle), 1.6:1 rockers on the intakes for around .480" lift (cam is already dual-pattern so exhaust lift will be around .475" with 1.5:1 rockers, from what I've read is plenty for Magnum heads), headers (Doug's or TTI), zero-deck pistons for around 10:1 compression, and a port-matched Edelbrock Performer (non-RPM) intake for better gas mileage and low-end torque with the auto trans. I'll probably run a DemonSizzler-tuned SB ThermoQuad as well. Then if I want to take it to the track I can swap in 3.55s or 3.91s as well as an RPM Air-Gap intake and 650 cfm Holley and see its true potential.

Nice strategy on the 904 - I am not sure what the status of it is yet, I got it "built" with the car. I guess I'd have to get it into the shop to find out what it's got; but I like the gear swap idea - just like we are doing with my buddy's 67 mustang - swapping an AOD with 4R70W gear set in place of a stock C4 - go for the gearing that makes the biggest difference, rear gears are easy to swap. And a new stall converter is definitely in my future...

 

[Coyote Jack]

I am leaning heavily towards this cam, a few questions:
What carb and intake are you running?
What rocker ratio/valve springs too?
What is your static compression ratio?
What trans are you running?
What is your rear gear ratio?

Would love to know so I can tailor my build, thanks!



Dave and I have very similar engines. I use a Comp Cams Magnum 280H.

1. I have a 650 Speed Demon, 1 inch spacer on top of a M1 dual plane.
2. I have Crane rollers, 1.6 ratio with Mopar springs. good to .550 lift I believe.
3. 10.58 to 1
4. 727 manual reverse, 2800 stall conv.
5. rear is 4.10

Tires are 255-60-15, headers, X-pipe 2.5 inch exhaust MSD ignition

My heads are ported and have 2.02 valves. I would reccomend at least gasket matching the intakes.

My combo dyno'd over 400 hp and over 400 ft lbs torque.

Jack

 

[octanejunkie]

Dave and I have very similar engines. I use a Comp Cams Magnum 280H.

1. I have a 650 Speed Demon, 1 inch spacer on top of a M1 dual plane.
2. I have Crane rollers, 1.6 ratio with Mopar springs. good to .550 lift I believe.
3. 10.58 to 1
4. 727 manual reverse, 2800 stall conv.
5. rear is 4.10

Tires are 255-60-15, headers, X-pipe 2.5 inch exhaust MSD ignition

My heads are ported and have 2.02 valves. I would reccomend at least gasket matching the intakes.

My combo dyno'd over 400 hp and over 400 ft lbs torque.

Jack

Thanks for the reply Jack, what do you do with the car? Driver, street/strip, etc? Got any ETs to share? You running magnum heads too?

 

[Coyote Jack]

It is my toy that I drive a couple of times a week in the summer months. I built it to run 12.00 but the HP to weight ratio says I should do a little better. Yes I have the Magnum heads. It is a real fun ride when I put my foot in it. Scares the hell out of the wife. LOL

Jack

 

[dgc333]

I am leaning heavily towards this cam, a few questions:
What carb and intake are you running?
What rocker ratio/valve springs too?
What is your static compression ratio?
What trans are you running?
What is your rear gear ratio?

Would love to know so I can tailor my build, thanks!

I currently have a Holley 670 on the car but the 370HP based off a 102 mph trap speed was with a 600 Holley. The car is stronger with the 670 but I do not have any times.

The intake is a Professional Products CrossWind open plenum dual plane (similar to the Edelbrock AirGap).

I am using stock 1.6 ratio magnum rockers with Mopar Performance springs (the R/T which is good for .525 lift).

The static compression ratio is a measured 10.6:1 and the cranking pressure is 185-195 psi.

The tranny is an A833OD 4spd.

The rear end ratio is 3.55 with 27" tall tires (255/60-15).

When I had it to the track I was running smaller tires (235/60-14) and the leaf springs were tapped out and I had real bad wheel hop when I launched it hard. So, my best time was a very traction limited 13.7 @ 102 mph with a miserable 2.2 sec 60'. With better tires and new springs the car should easily run low 13's maybe even a high 12.

My car is a nice weather daily driver. I put about 7500 miles a year on it between April 1 and the first time they slat the roads in Nov/Dec. Since I drive this car a lot mileage is important to me and my set up gets 16.5-18 mpg around town and 21-22 mpg on the hiway. The car also runs on 89 octane and I have used 87 in a pinch, I just have to be careful below 3000 rpm or it pings.