308 or RHS on a 408

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TheDeputy

TheDeputy

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Hi Guys,

I'm planning a budget 408 360 stroker build.
I was thinking about using the new indy RHS head. However I have a chance now to buy a pair of 308 heads locally. I expect they need to be gone through totally.
Which head would be best (without porting and stock valve size) for a budget 408, mostly set-up for low end torque, four speed 3.23 rear axle.

I don't have a cam yet, and I might be using an old edelbrock D66 dual quad.

Thanks,

Antoon
 
If you need to go through the other heads anyway, you might as well just get the the rhs heads and have them done by IMM. This way they are ALL new, they are done right, and without any real porting they flow really good.

You wont regret it.
 
If the shop actually does go thru them properly, the prices will be similar to RHS heads. Shipping heavy iron accross country isnt cheap so factor that into the cost too. And if you go with RHS heads, use the LA-X versions so you can run the cheaper rockers and any intake.
 
The 308s are junk. They crack if you look at um sideways. What good are they even if they flow like gangbusters if they crack real easy? Get the RHS.
 
308s are prone to cracking? Hmmm, never heard that before. Anyway, I have a set of ported 308s on my 408, but I already owned them and the RHS heads were not available at the time. I have total of about $800 in my heads. If I were to build another 408 or 416 then I would seriously consider the LA-X RHS heads prepped by Brian and IMM (member ID OU812).
 
Just an opinion, but I believe since low end torque and budget are major factors, the 308 heads may be a better choice over the bigger port RHS heads. A dual four barrel intake may look cool also, but it is harder to tune and isn't helpful towards your goals, especially with a 3.23 gear. True, a 4 speed and stroker helps, but it is a street car. Higher velocity ports and a single 4 barrel set up to work with them at lower rpm's may be the way to go.

Personally I can't wait to try out the RHS LA-X heads. But they would need to be approved for my race-only combo before building an engine for my class with them. I've run mid 11's with 308, 576 and 587 heads and the RHS heads should be a big improvement.
 
I never heard of the 308 "Prone" to cracking. Any head will if it can not be cooled, I just remember the 308 being any different than any other head. OE Magnums seem to have this issue.

I just priced a set of J heads to go from NYC to Washington state. Approx. $63 per head.

Loco, do you remember the port cc amount of the Indy head?
 
rumblefish360 said:
I never heard of the 308 "Prone" to cracking. Any head will if it can not be cooled, I just remember the 308 being any different than any other head. OE Magnums seem to have this issue.

I just priced a set of J heads to go from NYC to Washington state. Approx. $63 per head.

Loco, do you remember the port cc amount of the Indy head?
Click to expand...

Intakes are advertised at 179cc and exhausts at 67cc.
The intake numbers are 17-21 cc more than the OEM 340 and 360 heads as listed in the NHRA specs. But I haven't actually cc'ed any heads myself to confirm the actual as-cast numbers, so I am curious to know how close they are. I believe Brian said the chambers are somewhere around 65cc as cast even though they are advertised at 62cc. I wonder if he has measured any ports as cast.

http://www.autopressreleases.com/_uploads/docs/RHS Indy 360 X Heads.pdf
 
OK cool, thanks. Just wondering for the port velocity thing. Kind of get a feel/idea/forcast it all thing in my head. The new head is indeed a nice looking part with good reports about it. When Brian did the Mag (M-Muscle) and dyno'd it, I thought I'd see a true 500 like writin on the cover. (LIARS, Shakes fist @ mag!)

I don't remember all the specs, but I was thinking the ports small for some reason.

Non the less...... The real bottom line is how well the 308's will do and there cost vs. the Indy heads as prep'd by Brian for the job at hand, not a full on HP build with 3.23's. Though that D66 and cube size ought to be real cool down low and mid range and scream up top with those gears.
 
Yes sir, they sure are known for it. Now, I never said they didn't flow well. But they are known for cracking. They're a very light weight casting....as cast iron goes anyway. Ask around some machine shops that pay attention to casting numbers. You'll see. Last shop where I did cylinder head repair we had a pile of 308 and 062 chevy vortec and 915 chevy vortec heads that were junk. The ford stuff from about the same period didn't have near the trouble for whatever reason.
 
Seems I read somewhere that the RHS/Indy intake port opening is somewhere between an LA and OEM Magnum size. But the not-so-obvious volume is more.

408 c.i. is plenty big, but I tend to lean on the conservative side because of the street application and gear. Same with the carb/intake combo. If multiple carbs are used, hopefully they will be properly tuned.
 
Same thinking going on here Loco.

Thanks strokerscamp.
 
Going through my RHS/Indy head links, I see that Brian notes that these heads "have incredible intake port speed" on his website.
http://www.immengines.com/rhsheads.html

Obviously, a good trait. Perhaps my conservative tendencies leaned me too far over!:p
Since I've offered as much opinion and info as I can for this particular combo, I'll sit back and hopefully learn more about the heads myself.
 
TheDeputy said:
Hi Guys,

I'm planning a budget 408 360 stroker build.
I was thinking about using the new indy RHS head. However I have a chance now to buy a pair of 308 heads locally. I expect they need to be gone through totally.
Which head would be best (without porting and stock valve size) for a budget 408, mostly set-up for low end torque, four speed 3.23 rear axle.

I don't have a cam yet, and I might be using an old edelbrock D66 dual quad.

Thanks,

Antoon
Click to expand...

Is that intake real restrictive? If it is, then use the 308 heads you'll save money. Complete heads should run about 650-700 with GOOD parts.
Now if you want power, leave the 308 head alone...with NO porting the RHS head should be at least 30HP better and probably more like 45HP better unless you use a stock cam.
A really good cam for the 408's is Comp's 275HL...MONSTER TQ and a little bit of pep up top.

I haven't poured an intake port sorry guys.
 
ou812 said:
Is that intake real restrictive?
Click to expand...


Well here is some pictures--but no flow numbers. Some ports are very short--all are small 273-318 size.

D66 001 (Small).jpg


D66 002 (Small).jpg
 
I'm useing the RHS heads in stock trim, They have "plenty" of torque, I'll have to agree with StrokerScamp on the cracking issue, most all of those light casting magnum heads had this problem, your lucky if you get a good set, I'll listen to the machinest that get them in all the time cracked (in some fashion) around the seat area, my magnum heads were toast, so in the trash they went. I spent right around 60.00 shipping for "both" my heads, 936.00 to the door, best $$$$ i've spent.
 
308s are an LA head with "high swirl" intake ports and a magnum-esque exh port. They are no more prone to cracking than any other LA based head. I've seen more cracked X/J/915 heads than 308s. I've never seen a cracked 308 come to think of it. That's owning or using around 10 pairs. Magnum heads will almost always show cracks, some are not an issue other than visual/emotional, but most factory Magnums show cracks. The last set of 308s done properly and with good parts (albeit in CT...lol) were $1100. That includes milling the decks and intake side for the intake fit.
 
I had a set of cracked 308 heads, cracked between the valves just like the mag heads I had, though the mag heads also cracked at the edge of the chamber and down into the exhaust port. oh well...
I've had 1 pair of j's that were cracked around the outside of the head by the center exhaust ports [really weird] , it was in a 360 truck that had been abused to death and had a rod hanging out the side of the block and crack all the way across the valley.

If you treat something like that and you'll have cracks for sure.

it is fact that the later cast heads had less meat in them to save a lil $ here and there.

with good attention paid to cooling system and mixture they will last, but slip a lil and or turn up the wick to the edge ...and they give.

I like to have a lil room between running a lil warmer than usual and melt down.

I rumage threw the junk yard a lot and pull a lot of heads.


btw hang that intake on the wall and go buy something good.jmo
 
TheDeputy said:
Hi Guys,

I'm planning a budget 408 360 stroker build.
I was thinking about using the new indy RHS head. However I have a chance now to buy a pair of 308 heads locally. I expect they need to be gone through totally.
Which head would be best (without porting and stock valve size) for a budget 408, mostly set-up for low end torque, four speed 3.23 rear axle.

I don't have a cam yet, and I might be using an old edelbrock D66 dual quad.

Thanks,

Antoon
Click to expand...

Here are a set of Brians "IMM Engines" Indy/Rhs heads Running on my 410!

More info the better so you can make your choice!

http://www.forabodiesonly.com/mopar/showthread.php?t=105913
 
Thanks for all the replies so far,

Let me give some more details about the build.
First, I live in the netherlands, so that's a cost factor as well, since shipping a pair of steel heads from the usa will cost around 200$ and then there's always taxes and custums.
The engine will go in a 1970 challenger as mentioned with a four speed (this is a slant-six four speed with the 3.09 first) and a 3.23 rear with 27" tires.
Since it will only be street driven, no track time whatsoever, it needs to run smooth and reliable. There's no need for it to make 7000 rpm.
a 408 around the 400-450 hp range would be more than enough for me.
Also with the prices of gas around 1,5 euro per liter (+/- 8,5$ per gallon) it would be nice that it can be driven a bit economically as well.

So my goal's are:
-high torque
-reliable
-gas effecient
-around 400-450
-good parts for good money

could this be accomplished with the 308's and what would have to be done to them?
can I use the awesome D66, and make the carb linkage progressive so it'll run on the rear carb when cruising, and opens fully above 3500 rpm?
I've got the rockers and shafts from a solid 273. can I use them on the 308's?
I would like to run a solid cam. Is this a good or bad idea?

I know, a lot of questions, so I could really use all your input. If you see something that's conflicting, don't hesitate to give your opinion.

Thanks,

Antoon
 
I forgot to mention that I will be running 340 hp exhaust manifolds and a TTI 2,5" exhaust with dynomax mufflers.

Antoon
 
Any 360 heads on a stroke 360 motor will run ok.

And yes the D66 is a great intake but beware the D66 intake has small ports like the 273-318 heads. Really no problem power wise I believe since the ports are short. I am using two 500 cfm Carters on my 340.

Get this Fel-Pro intake gasket ! It has a steel core and will not rip / split if tighten hard. You can just barely see the print-o-seal rings but twice now I have had no intake leaks using this gasket.

Fel Pro 1213S.....the S is for steel core, you do not want the 1213 gasket without the S cause the small ports may crack the gaskets. Some places you get like only a 1/8 inch to seal--but it seals good with just some high tack / Indian head sealer just on the head side. The gasket is so nice you can remove the intake, even after a few years and reuse the gasket. It sticks to the heads only. Use rtv on the end rails only.

I drill a small hole on each gasket for the exhaust heat.

http://www.summitracing.com/parts/FPP-1213S-3/
 
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