X heads on a 360?

[moparkid340]

Hello friends. I recently picked up a very nice set of 340 x heads that have been very nicely ported. I have a low mile 360 out of a 78 d200 I'd like to slap together and get rid of the smog heads my bottem end is in great shape and no need to rebuild. Will the x heads work well on this block? I know they will bolt on but what I'm asking is will this kill my compression? Thank you in advance

 

[74Dusted]

It’ll definitely plummet the compression into abysmal 7’s, Low 8’s if you’re lucky.

The X heads usually have combustion chambers in the 68cc Range, though I’ve measured a few that were 71-72cc

 

[273]

They should be around the same cc. Shouldn't effect cr, the extra air flow will help power wise, I wouldn't go to large of cam cause your engine is a low cr engine.
The more gear and stall will allow more cam. Probably something like xe262h to xe268h cam or similar depending on rest of combo.

 

[JBurch]

Bolt them down, you'll be about Even-Steven on compression.........if you really gotta know, measure chambers and how far down the pistons sit, do the math

 

[krazykuda]

The X heads will run great on the 360... combustion chambers should be similar cc's to the originals...

Bolt them on and go.....

 

[QuickDart360]

I did it! But did change pistons to KB107's. These bring compression up some.

 

[rumblefish360]

I did it! But did change pistons to KB107's. These bring compression up some.

Good combo.

 

[JBurch]

Here is another thought..........sell the "X" heads to some one who desperately has to have them....use that money to rework your "smog" heads; which by the way are really NOT THAT BAD OF A HEAD; the biggest difference between the two of them is intake valve size, something easily corrected.........done right, you could end up with money left over.........food for thought

 

[67Dart273]

I doubt in "real" terms that the stock X heads are any different than what is on the 360 right now. They "might" have larger valves and they might not? And something that heavy if they were might not even help you at all

 

[Cudafever]

Here is another thought..........sell the "X" heads to some one who desperately has to have them....use that money to rework your "smog" heads; which by the way are really NOT THAT BAD OF A HEAD; the biggest difference between the two of them is intake valve size, something easily corrected.........done right, you could end up with money left over.........food for thought

To the op if your not looking for max porting/hp ALL 360/340 ARE THE SAME basic casting. some have 1.88 some are cut more to except a 2.02 intake .
If your smog head have the air pump ports drilled out. You may need to drill and tap the airport in the exh port and put a plug in it.

On the ported 340 head. they may have been decked lowering the cc in the combustion chamber(this is a plus) but my cause" intake to head" fitting, an issue.

Now that you have this info.
I would bolt then on the X heads and save your "smog heads", as a spare just, incase the ported X head crack.
There should be a noticeable difference in performance.

If they were ported badly, and run badly on your car???? Pull them, sell them, and have a good 3 or 4 angle valve job done on yours and you will have a Hp improved Smog Head.

 

[moparkid340]

They should be around the same cc. Shouldn't effect cr, the extra air flow will help power wise, I wouldn't go to large of cam cause your engine is a low cr engine.
The more gear and stall will allow more cam. Probably something like xe262h to xe268h cam or similar depending on rest of combo.

I'm running a summit brand cam duration 285/285, Lift .480/.480,

 

[Cudafever]

I'm running a summit brand cam duration 285/285, Lift .480/.480,

Stick or auto?

 

[moparkid340]

Stick or auto?

Auto 727 Dana 60 rear with 390s

 

[QuickDart360]

Hey moparkid 340 do the 3.91's do on the highway? I am going from 3.55s to 3.91's.

 

[moparkid340]

Hey moparkid 340 do the 3.91's do on the highway? I am going from 3.55s to 3.91's.

I have not drivin it yet to be honest. It's in my 71 d200 sweptline pickup project

 

[j par]

I believe them to be worth more in resales than horsepower.
I don't think you'll gain anything with them that you couldn't do with any 360 head for the most part.

 

[QuickDart360]

Give @ least 15 to 20 more horsepower over 1.88 intake valve heads.

 

[j par]

You can put the 202 valves in any 360 head. Like I said with the similar work done. Some engines have been known to run better with the 188's.

 

[QuickDart360]

Give @ least 15 to 20 more horsepower over 1.88 intake valve heads.

Ok if you say so!

 

[rumblefish360]

You can put the 202 valves in any 360 head. Like I said with the similar work done. Some engines have been known to run better with the 188's.

The problem with your logic is, he already has 2.02's in the X head and doesn't have to spend a dime to upgrade the other heads which are inferior at present. Not all heads port out the same. While the early castings can be ported well, I have not seen them go as well as the XJOU.... heads. I know that doesn't mean someone can do that work......

The 2.02 can indeed make 20+ HP over a 1.88. No question. Seen more power differences between the two. HOWEVER! It is also the combo tested that shows a big or small one. Even mild builds have a good spread.

At this point, I can't see selling the X head to roll the sale cash into a smog head that starts with getting rid of 1.88 in favor of a 2.02. IMO, that is just insanity.

 

[Cudafever]

The problem with your logic is, he already has 2.02's in the X head and doesn't have to spend a dime to upgrade the other heads which are inferior at present. Not all heads port out the same. While the early castings can be ported well, I have not seen them go as well as the XJOU.... heads. I know that doesn't mean someone can do that work......

The 2.02 can indeed make 20+ HP over a 1.88. No question. Seen more power differences between the two. HOWEVER! It is also the combo tested that shows a big or small one. Even mild builds have a good spread.

At this point, I can't see selling the X head to roll the sale cash into a smog head that starts with getting rid of 1.88 in favor of a 2.02. IMO, that is just insanity.

The "bear in the room" is the type of porting that was done.
Everyone says that you can't port them head to big with out finding water.
Well my first porting job i DID. On a 340. No power until 3500-4000 rpm, then ran grate. On a street car these heads SUCKED!
Wish i still had these head, now that i have a 4200 stall in 408......I may have like them a lot!!!!!
If they are ported like my first set, in somewhat of a street car set up. They won't be on there for long.
But the only way to know is to bolt them on. and then go the back up route later if needed.

Remember, 50 to 60% of the port flow can be improved with a simple, but good 3 to 4 angle valve job.
Soooo if the 1.88 had a "standard" valve and seat cut and the 2.02 had a good 3 angle valve seat cut, with a little blending..........You bet your bottom dollar it will make 20+ HP gain.

As i said before, Try the X head, you my like it.......and if you don't.....your only out the gasket set. And it is a X head, that is re sellable because it its the X head.

 

[Cudafever]

Auto 727 Dana 60 rear with 390s

Sound like a good package. What does your converter stall at?

 

[rumblefish360]

-

I agree on extensive porting just like any other part of the package that is out of balance. If such was or is the case here, selling the X head is a possible move.

 

[thesiren74]

So your pulling off the same heads just ported and bigger valves...yeah it'll work.

 

[Robbie2734]

CC one chamber in each X head, you'll then know the chamber size on them. After you replace the old heads clean a chamber and cc it. I bet they are within 2 cc's of each other. The ported heads will be a improvement!!!!