Heads issue

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Captainkirk

Captainkirk

Old School Mopar Warrior
Joined
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Here's my dilemma, guys.
I'm (re)building the 340 in my Duster (for the second time). In the original build, when the motor was torn down we found TRW 13:1 pistons in there with 1.88 J heads. The engine shop decided (correctly so) that this was wayyy too much compression for a street motor, and cc'd the J heads our to somewhere around 72 cc's (I think) to bring actual CR down to around 11:1...which is good. We kept the 1.88 valves. I'm in the process of doing the motor again now. I've read a lot about the Edelbrock Performer heads and would love to slap a set on, but not if I'd have to have them hogged out. So, my question is, can a set of ported J heads be massaged to make them perform to the level of the Edelbrocks? And if so, what will I have to do to them? They've previously been ported, polished and cc'd and have a 5 angle valve job. I have not sent them to the builder yet.
 
First off a 11.1:1 compression motor is not going to work on the street for normal every day driving.If you had a really big cam to bleed off some compression it might work.You could cut some of the dome off the pistons and get it down to 10.5 at max,then its more suited for the street.To save your self some cash,before buying 1500$ worth of heads,tell us what you intend to do with the car ,drag or street,rpm limit,just a cruiser,highway,gear and tranny set up,etc.If the motor is never going to see rpm,s above the 6000rpm range or have a cam bigger than .525,do the work on the iron heads,and have them done by Bobby joseph.You can call him at 1-770-443-8874,and he can explain the good pionts and bad pionts to the iron and eddy heads,as he does these all day long,mrmopartech
 
I compare the Edelbrock heads to a set of well preped/pocket ported heads. The same power can be had from the J heads in this manor.
So, if your J's allready have work done on them, finish work lays else where, not in the heads.
For a street bound iron headed engine, pump gas fails around/after 9.5-1. But this is dependent of a few other factors as well, but thats the general area.
Like Mr. Mopartech was saying, bigger cam which bleeds off compresion helps. Other ways of beating a "Too high" ratioed engine just simply rob power or require more work in coating pistons and polishing chambers with coatings. And theres no sense going that way.
Just refresh your heads at best.
 
Do yourself a favor and invest in the Edelbrocks,why try to work with heads that are going to cost you about the same when the work on them is done to equal the Edelbrocks out of the box ...one of the best things i did when building my 10.9 to 1 stroker was put the Edelbrocks on top of it :)
 
I would have the heads flow tested first. By a guy who isnt looking for anything other than a number. Ported and polished may mean trashed and you dont realize it. It's much easier to start with virgin and do it right, then start with ported and try to make it better. Second, if you have domes on those pistons that project more than .020", you will have issues unless you are careful with the head choise. The "340" Edelbrock RPMS have an extra .060" milled from the chamber area making them full open chambers. No the best for power, but good to lose some static compression. You can run a static of over 10.8:1 with a good engine plan. You cannot when you are "making it work" so to speak. Cometic makes thicker gaskets too, which can lower the ratio...However, they MUST have a very smooth surface (not just flat, smooth) on both heads and block to seal properly. A fully ported set of irons will (realisitcally IMO) flow slightly more than a set of stock or "cleaned up (read as Stage 1)" Edelbrocks. A set of ported Edelbrocks will leave hogged out factory castings in the dust. I always want to know where I'm starting from, so I'd have a head flow tested first. Then go from there.
 
Thanks for the insight. I have no doubt these heads will run on pump gas as long as I stick to a cam profile much like the one I ran before....or reuse it. It was a .450/.475 lift with 298/308 duration and I had no preignition (detonation) problems nor did I ever blow a head gasket. I ran stock valve train with hydraulics (Melling) and ran the advance at 32 degrees total. This motor ran well on leaded premium. I plan to run blended unleaded premium and 100LL Avgas. The car is being built as a Sunday driver and possibly a bracket racer.
The heads were done previously by a fairly reputable local shop. Although the car was extremely quick before and ran well, I don't want to box myself into doing the same build all over again; this is why I'm asking questions now while I'm in the development stage. I've made the commitment to use the same pistons and stock rods with a balanced forged crank. Everything else is still negotiable at this point. This is why I'm asking the experts for your opinions. I'd like to be able to run low 12s without nitrous. My engine machinist thinks there should be no problem. I'll try to post some pix. Thanks.

pistons.jpg


TRWs.jpg


domes.jpg


Heads.jpg


J head.jpg
 
Can you remove an intake and exh valve and post a pic or two of the port work and bowl areas?
 
Don't have a valve spring compressor at the moment, but I'll try to post some pix of the intake port and valve shroud areas.

Heads1.jpg


Heads2.jpg


Heads3.jpg


Heads4.jpg
 
Hi, I'm presently building a 340 also and your pistons look like flat tops. How did you get 13 to 1 ratio out of them. my pistons are positive decked about .030 over the deck. I have stock X heads. Am I going to have to much compression to run on weekends to shows? We though i would have about 10.5 to 1 with .040 felpro head gasket. We put the crank in yesterday and I haven't measured the deck height for possitive yet. I just remember when i bought the short block the pistons were out of the deck and I tore it down. What do you think, am I in trouble for street. I plan on mixing racing fuel to 91 as needed. thnsks for any reply. walt :toothy7:
 
Walt, Fel-Pro makes a .054 thick gasket.
Cometic makes them thicker if needed.
Your going to have to do the math and measure the pistons to know for sure.
 
Thanks rumblefish I had hoped you would say I'll be just fine. I read about cc'ing the heads and hoped I wouldn't have to do that. Too much money invested not to do it right though. thanks your mopar brother Walt, :toothy7:
 
No problem Walt. I wish I cold have said, heh, don't worry, just slap it together.
CCing the heads is easy and worth while.
 
Have your machinist measure the thickness of the dome on the pistons. You should be able to mill quite a bit off of them. They're old school TRW's. they had thick domes. Much cheaper to mill the pistons.

don
 
Men. my eyes are bad and I have my acceleration turned on so they looked like flat tops to me, sorry. RUMBLEFISH, thanks for taking the time to respond to many posts and taking the time to explain in detail, its peole like you that make this site GREAT, keep up the good work, Walt :)
 
dusterdon said:
Have your machinist measure the thickness of the dome on the pistons. You should be able to mill quite a bit off of them. They're old school TRW's. they had thick domes. Much cheaper to mill the pistons.

don
Click to expand...
Thanks for the info, Don. I'll keep that in mind if I need to drop the CR any. As it is, they ran fine on pump gas in this motor's last reincarnation (probably due to the long duration/overlap cam) and while gas ain't what it used to be, I figure the 15:1 blend I'm planning to run should be sufficient to support an 11:1 CR. If not, I'll know in a hurry.
 
If you are planning on seriously running 100 LL av gas dont worry about the CR. You wont have a problem up to anything around 13 :1, Buddy of mine ran a ford 390 with this kind of CR and 100 LL and never had any issues with detonation.

For the heads. If they are in good enough shape why not finish whatever porting needs to be done, throw in 2.02 and stainless 1.60's and call it a day ?
 
My engine guy says the 1.88's will give better low end torque on the street than the 2.02's below 7000 RPM.
 
Looking at those ports...It doesnt look like too much has been done really. I'm sure they can be improved on. As far as valve size, I wouldnt waste my time with 1.88s at this point. 2.02s will site further out without replaceing seats, and IMO you will not notice any "loss" of low end with anything over 10:1 true compression. That's just my opinion tho.
 
Captiankirk,
I'd listen to my engine guy, sounds like he's on the right track, bigger isn't always better IMO.
 
IMO, I'd just bowl hog under the valve and port match. Your not drag racing this. If you were, I'd say 2.02 and a full blown yak yak yak yak....
 
I agree with Pagilma. Those arent domed pistons. They are flat tops and dont look like they even stick out of the bore. My 340 has Ross flat tops tha are + .020" deck height. The heads needed to be milled to get the compression to 11:1. I bet you are closer to 9.5 or 10:1.

Here is a pictures of my exhaust ports. They flow around 170 @.550"

IM000609.jpg
 
What head is that Adam? Valve size?
 
They are are 587s with Mopar Perf 202, 160s in them and lots of porting.
 
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