why J heads, why not x heads?????

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christineman

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I can buy J heads with 202 intakes or 188 intakes,, which ones are better for a HP engine??? can I put 202 intakes in the 188 heads easy? or am I better off to just find 202 factory heads... please,,, some advice from the pros out there

christineman
 
x heads are more money, and are harder to find. for h.p, the 2:02 flow better, but what kind of h.p are you looking for? like i stated in my p.m, i was told that it was better to go with 1:88 j-heads, due to if you have a set of 2:02 heads and the valves are "sunk" then it costs too much in the long run. but if you buy a used set of 1:88 j heads, you can just get them fitted for 2:02 valves while you are getting them rebuilt. just what i was told. someone correct me if i was mi-informed
 
For one the "J" heads are more abundant, yes you can open to 2.02".
Depending on the year of the "J" head, they may not require hardened seats, as they were used on 360's in the late '70's.
I personally prefer "J's" over "X" heads, they were designed for the T/A's.
 
so what would be the h.p difference between the 1:88 and the 2:02 j heads?
 
The X heads are only better if you just want to say you have X heads. For all practical purposes the Js and Xs head are the same except some Js had the smaller 1.88 intake which can easily be machines for 2.02. The Js with 1.88 are the exact same casting as the Js with 2.02 except they are machined differently for the respective valves after they were cast. Same goes for the TA and AAR six pack J heads, same casting, just machined differently.
 
ive got a set of heads on a 360, there cast no is 4027569 I believe,,, what if I just put 202s in them? can this be done and will they be as good as the factory J 202s?
 
340plot said:
so what would be the h.p difference between the 1:88 and the 2:02 j heads?
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Unless you are going to bowl blend and do a little clean up of the port not a lot of difference. But if you bowl blend and clean the ports up so the port can take advantage of the bigger valve then you will put up some power.
 
christineman said:
ive got a set of heads on a 360, there cast no is 4027569 I believe,,, what if I just put 202s in them? can this be done and will they be as good as the factory J 202s?
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did i not read somewhere else that those are not j heads, and are not worth the effort?
 
christineman said:
ive got a set of heads on a 360, there cast no is 4027569 I believe,,, what if I just put 202s in them? can this be done and will they be as good as the factory J 202s?
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I think you mean casting number 4027596..and those are "smog" heads i wouldn't put any money into those...
 
340plot said:
did i not read somewhere else that those are not j heads, and are not worth the effort?
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They may have a J on them, they are basically the same. Effort just depends on what you want to do. The 596's have some advantages over the 915 J heads.

IMO, put in a 1.94 Chevy valve, blend them in your 596's and you have a really good working iron head. Not hard to get 400 hp out of them with the right choice of other parts. A really mild build will get 350-370, XE268H, performer rpm/LD340, 750DP, headers.
 
stroked 340 said:
I think you mean casting number 4027596..and those are "smog" heads i wouldn't put any money into those...
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All open chamber 340/360 heads with the expeception of the 308 head (these have the improved exhaust port of the magnum head) have the same chamber and port design, the air injection holes in the latter heads have no impact on the potential of the head (just plug them with epoxy or pipe plugs).
 
1st The x heads have less material in the roof compared to J heads.
2nd T he exhaust floors of the X heads seem to have more short turn height, or maybe it;s just my eyes..
3rd The j heads DO have minor differences over the span of production, like the smog heads have a lil less int ssr/floor hump, the smog heads do have floor bumps/air injection bosses with some undrilled. I don't believe the bump is really worth much if any.jmo
4th The 1.88 head as a start is better to work with when porting due to the far side throat cut from the factory-they removed a lil too much on the 2.02 heads JMO I'd rather start fresh.
The diff between the later j and earlier J is in full ported form..the early J head will make a peek of around 20cfm int over the later in most cases.
as in...all the ported later 70's heads quit around 250's while J heads go 270+, at least from what I've seen
 
A nice race valve like a Frerra Stainless Steel valve on both sides in a well preped head and valve job will go along way. Go for the early J head if you can. There cheaper but can be ported very well and flow like crazy for an iron head. (if need be of course)
 
I wouldn't be afraid of any of them, INCLUDING the the ones with air port bump in the port!!!!

Why J over X.... Cost less, and easer to find.
 
Cudafever is right about the bump. It has nearly no effect on the port flow.
 
even 10 years ago we started with the 1.88 heads, conversion guides, lighter chevy valves, you still have to blend the bowls or more to get any advantage of the larger valve except at low lifts
 
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