360 Mild Build Questions

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KCBones

KCBones

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I just picked up a project 360 engine this past weekend. It's a 1974 block out of a van and it came with a pair of 915 casting heads. One is a J head but the other is a U head. My understanding is they are basically the same head, can I use these on the same engine or should I start looking for either a J or a U head to have a matching pair. The bores seem really nice so my plan was to maybe take it to the local machine shop for a good cleaning, and hopefully only a hone. I was planning on using the Edelbrock Performer that's on a 318 in my Dart right now and also use the Holley 4160 600 cfm carb that's on that manifold. A good fairly mild cam and I should have a cheap but fun engine. My main question is the heads, though. Will a J head and a U head work well on the same engine?
 
Yes, as long they are both 915 castings and have the same valve size your good to go. 65'
 
They worked on the engine they came off of. But there is a chance that one or both heads may have been replaced at some point during its lifetime. It wouldn't hurt to check chamber cc's, valve heights & intake valve size along with the usual magnaflux for cracks. I don't know what a normal OEM date code "spread" would be between original head castings but check that for more clues.
 
Locomotion said:
They worked on the engine they came off of. But there is a chance that one or both heads may have been replaced at some point during its lifetime. It wouldn't hurt to check chamber cc's, valve heights & intake valve size along with the usual magnaflux for cracks. I don't know what a normal OEM date code "spread" would be between original head castings but check that for more clues.
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I don't think they were ever on the '74 short block I bought. I think those heads got tossed. The J head looks identical to the U head, the U head is bare so I'll put new valves, springs, etc. on both heads. I'm also planning to go with some adjustable rockers, I had that set up on a '68 Barracuda I had over 20 years ago and it was a fun, lively car. Wish I still had it.
 
If my memory serves me correctly, they should be 72-75cc chambers. 65'
 
I've seen them mixed/matched on the same engine before. Not saying it was factory, but I saw it.
 
318willrun said:
I've seen them mixed/matched on the same engine before. Not saying it was factory, but I saw it.
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Factory went out the window on this car. I'm going for "kind of looks like it might have been factory before the guy did all the second day hop up parts".
 
KCBones said:
Factory went out the window on this car. I'm going for "kind of looks like it might have been factory before the guy did all the second day hop up parts".
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my point was i think they'll work just fine for ya
 
894/X and 915/J,U,O are the same port some of the 915 had 202 intakes and some have 188 intakes.. The difference is the 894 heads had a smaller chamber due to the deck surface shorter. Always have heads CC'd when they are mismatched to insure one isn't cut farther then the other from being used from another engine that may have been cut. 68-70's 340's were advertised at 10.5-1 with 894 castings. 70-71's were 10.3-1 with 915 castings. This was noted in any engine manual but only quoted for 71 cars. when the compression loss was shown

This is why it was always an issue installing the bolts on a factory SixPack on a 68- 69 340 engine back in early 70's that had 894/X heads. Been down that road many times in the past. You could get them on but they were a ***** to get the bolts started.
 
318willrun said:
my point was i think they'll work just fine for ya
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Yeah, I understood, I was just blabbing. That is kind of what I'm going for, though. Like a lot of other old guys, I want something like I saw a lot of but couldn't afford in high school. I like your YouTube channel, by the way. I've watched a ton of your videos.
 
Equal compression means equal balance. Means much more then you think in performance. Run an engine with a dead cylinder and feel the vibration. Lower compression in one cylinder may not be felt by your butt. But the crank feels just a tad difference. Every little bit counts when on the bottom on a hard pull. And at the top in RPM's. Balancing is the most crucial of an engine performance.

Take any Engine or electric motor and just through the balance off a bit and see if it reaches the same RPM's . I remember when I was young balancing my slot cars engines on two level razor blades.

Put 1 drastically different smaller CC head on an engine and see what happens to the performance. It will not increase from the higher compression from the one smaller CC head it will decrease.
 
Oldmanmopar said:
Equal compression means equal balance. Means much more then you think in performance. Run an engine with a dead cylinder and feel the vibration. Lower compression in one cylinder may not be felt by your butt. But the crank feels just a tad difference. Every little bit counts when on the bottom on a hard pull. And at the top in RPM's. Balancing is the most crucial of an engine performance.

Take any Engine or electric motor and just through the balance off a bit and see if it reaches the same RPM's . I remember when I was young balancing my slot cars engines on two level razor blades.

Put 1 drastically different smaller CC head on an engine and see what happens to the performance. It will not increase from the higher compression from the one smaller CC head it will decrease.
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Yeah, that was a concern of mine and why I posted the original question. I think I'll CC the heads and see where I stand before I spend any money on them. I want both banks of cylinders to be as close as possible to each other. I think they look identical buy my eyeballs may not be calibrated as much as they used to be.
 
Neutral balance the engine at a good shop with a digital balancer within at least 2 grams or less . Do it with a neutral balance damper. You'll thank yourself down the road when you need a converter or trans work. I have not seen one externally balanced engine balanced correctly. If they don't vibrate the car they are assumed OK.

If you don't want to spend the money on a Damper. Have it balanced with a after market 360 flex plate to run a neutral balance torque converter

If its a 4 speed car throw the external flywheel away and get a Neutral Damper and flywheel.
 
You could say that. In my opinion the op doesnt have to cc the heads. He or she should be able to check the part numbers and verify what the chamber size is and if they are the same they should work. There are stories of the factory running two heads one with a U on it one with a J or O etc. For the OP to cc the heads and come up with .4 of a cc variation then what come here and have you all blow more smoke up his ***? c mon man...that's a whole 'nother issue the variation in the casting of the combustion chambers.. You all are just giving the guy the runaround and it is unnecessary. This is 50-60 year old automotive technology it isn't rocket science...OP, check out this thread, Look up your casting numbers and Combustion chamber size with the chart in post #8.

Combustion chamber CC's Chart ??
 
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Dartswinger70 said:
You could say that. In my opinion the op doesnt have to cc the heads. He or she should be able to check the part numbers and verify what the chamber size is and if they are the same they should work. There are stories of the factory running two heads one with a U on it one with a J or O etc. For the OP to cc the heads and come up with .4 of a cc variation then what come here and have you all blow more smoke up his ***? c mon man...that's a whole 'nother issue the variation in the casting of the combustion chambers.. You all are just giving the guy the runaround and it is unnecessary. This is 50-60 year old automotive technology it isn't rocket science...OP, check out this thread, Look up your casting numbers and Combustion chamber size with the chart in post #8.

Combustion chamber CC's Chart ??
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Also the factory block deck height was not all that great. If your building a race engine or a spec engine then you should have everything squared up but for a mild fun street motor 50 year old factory tolerances will get you there.
 
mod5v said:
Also the factory block deck height was not all that great. If your building a race engine or a spec engine then you should have everything squared up but for a mild fun street motor 50 year old factory tolerances will get you there.
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I looked down the 408 stroker rabbit hole and backed out pretty quickly. I think if I ever do one of those, it'll be based on a 360 Magnum block with a roller cam. For now, the 50 year old factory stuff will be a lot of fun. The other thing is, I'm pushing 60 years old and have never built an engine. I figured refreshing an old 360 LA motor would be a good first build.
 
The word mild is the key take away here. As far as the worst offender I've seen on a factory 360 was a 1972 Windsor foundry casting with 587 heads with a -7 on one side and a -12 on the other side. There was an average of 5 cc's of difference in chamber colume from one head to the other. If you could find some 974 heads, have the chambers equalized, and install 1.94/1.60 stainless valves with a four angle valve job and clean up the rough edges in the bowls and ports (most an be removed with emery cloth roll) you would have one of the better iron heads available. The 318/360 performer intake will work well if you do a deep port match on it.
 
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65-73 is a pretty big margin to be playing with... 65 on one side 73 on the other. It's not hard to check things out and see where you are.

Doesn't require fancy tools. As simple as a medicine syringes for kids from your local pharmacy and a flat piece of plastic with a hole in it.

Get a large syringe, like a 50 CC if they have one and a 10 or 5 cc one. Don't forget the cup of water.
 
Are you going to run headers and what kind of HP are you looking for?
 
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