Captainkirk
Old School Mopar Warrior
My 340 has a set of late '72 1.88 "J" heads. Would I experience any issues upgrading these to 2.02 intakes, and how much will it buy me on a HP street motor?
J heads upgrade
- Thread starter Captainkirk
- Start date
-
txstang84
Well-Known Member
This should be fun to watch the replies... 
txstang84
Well-Known Member
What does the rest of the build look like?
cam
intake
carb
compression ratio
exhaust
etc...
cam
intake
carb
compression ratio
exhaust
etc...
Captainkirk
Old School Mopar Warrior
So far....
+.030 Speed Pro forged L2316F 10:1, forged crank. No decisions on cam or valve train yet.
Intake, Air Gap with either Holley 650 DP or TQ
All negotiable except the pistons and crank
Last edited:
stroked340
Well-Known Member
Deffinately...................
yellow rose
Overnight Sensation
If the piston isn't .045 out of the hole you won't be near 10:1
txstang84
Well-Known Member
If the block is milled to blueprint height and the crank is properly indexed those pistons should be .018" out of the hole @ TDC. Making some relatively well placed guesses on the valve relief volume and what gaskets you'll likely use, the compression should be around 9.7:1 with ~68cc chamber, which is about on par with J heads. That could go either way depending on what type of valve you use.
Another question is:
Do you need to replace the valves?
If you haven't decided on the end goal of the engine, or what cam you wanna use...
Another question is:
Do you need to replace the valves?
If you haven't decided on the end goal of the engine, or what cam you wanna use...
yellow rose
Overnight Sensation
Which is why I said he would be at 10:1. He would need to be up another .019 just to make up for the gasket thickness he is giving up over OEM. That would make it .037 out and I doubt his heads will be anywhere near as small as 68 cc's. You could deck .040-.060 off the heads but you already need to deck the block. Just stick the piston out and leave the head gasket surface as thick as you can.
As for the valve size...a bigger valve will increase flow at low lifts. Unless you do some porting, the 2.02 won't do much better than a 1.88 above .300 lift. And since I detest low lift flow, I try not to gain it without getting the flow curve up in the higher lift ranges for THAT port. That should be a big hint on valve jobs, so I'm giving that out for those that care.
MOPAROFFICIAL
Oogliboogli
More of this...Okie dokie.
And or if the chambers are milled down, the new 2.02/1.60 valves eating up 4-7 cc's ....the piston can stay where is.
Captain, get the short block together, have the valve work done and then cc the heads before cutting them...then you can dial in the best you can get without reinventing the wheel. You can take the heads down to 60 cc if you want, Damn near closed chamber and plenty deck thickness, I do it a lot to know.
MOPAROFFICIAL
Oogliboogli
Without being properly blended, not much more...but if bowl blended right you should see around 225-230 cfm @or between .450-.500 lift. It can be a good thing to build around the heads...
yellow rose
Overnight Sensation
Dude, how many heads have you cc'd that were anywhere NEAR 68? The answer is zero. NONE. Get the book out and READ. The piece of **** was designed to be out of the hole.
Yes you can mill them down so they are closed chambered. They won't flow worth a ****, be very sensitive to the top cut on the valve job and be thinner than they need to be. I spent more hours trying to fix the junk chamber on my W-5's than I care to remember. That is what you are doing when you mill the head like that. I used to use a 1 inch cutter in the mill to do it. I quit when I learned better.
But since you do it, it must be right. Geebus, you ain't building a Chevy. Stick the piston out of the hole. Better off at 11:1 with some quench than 10.1 with the piston so far from the head.
MOPAROFFICIAL
Oogliboogli
Didn't get past the 1st line of yellows post... Most are 72-73 cc a few have been 69cc, the valves are a big part of how large they are, port volumes as well. 1.88 are larger P.V than 2.02 ports from the factory. I know we all like to make points...but you can't leave the rest out...or is exactly like saying .."you can only do it this way".
You would have in search of flow around 290 cfm or better and at .600+ to have an issue with loading on the side of the port induced by heavy milling.
Last I checked...the captain isn't doing anything of the sort. You gotta attack it for what it is...
You would have in search of flow around 290 cfm or better and at .600+ to have an issue with loading on the side of the port induced by heavy milling.
Last I checked...the captain isn't doing anything of the sort. You gotta attack it for what it is...
Captainkirk
Old School Mopar Warrior
OK...my bad. Forgot to mention:
1) These heads were previously cc'd...67ccs
2) Block has not been decked or heads milled. I can check "out of the hole" once it's assembled, just trying to get my ducks in a row.
My machinist tells me 2.02's won't do me any good below 6k and may actually hurt bottom end torque but every Mopar pub I've read says "if ya got 'em, flaunt 'em" WRT 2.02's
This will be a A833/3.91 gear car...
1) These heads were previously cc'd...67ccs
2) Block has not been decked or heads milled. I can check "out of the hole" once it's assembled, just trying to get my ducks in a row.
My machinist tells me 2.02's won't do me any good below 6k and may actually hurt bottom end torque but every Mopar pub I've read says "if ya got 'em, flaunt 'em" WRT 2.02's
This will be a A833/3.91 gear car...
yellow rose
Overnight Sensation
That's where you went wrong. You stopped reading. And you are full of **** with your lift and flow numbers.
Right, attack it for what it is.
yellow rose
Overnight Sensation
Your machinist I'd nuttier than a jar of goobers. The 2.02 valve won't kill bottom end. What a bunch of 1970's and 80's CRAPOLA. If you want the bigger valve, use it. Or, you could send you machinist to the funny farm and tell him to use the 1.88 valve with a 50 degree seat. That will make more power than a 2.02 with a 45.
Now we can all wait for moparofficial to come in and correct us. He is official because the toy in the Cracker Jack box says so.
MOPAROFFICIAL
Oogliboogli
He is speaking from a general point of view that is misunderstood, what is comes down to in this case is....flow is power, the bigger valves give more airflow when cut and blended right, and especially the lower lift that is handy in filling the cylinder. These ports are small...so small that even if you opened them to be .060 thick in the entire port walls,floor,roof...the fps/air speed would be huge. Your machinist is not a this or that...he is just a machinist. The numbers I post are not BS, anyone who plays with sb mopars knows the x, j, o, u, blah blah are easy to get to 240 cfm, its not rocket science or a secret and yes you remove a bit...but It's no secret to those who work with these that the real work is getting up past that and controlling fps/air speed so it holds at lift.
Listen to who you'd like, I want you to be happy and care not about living vicariously through your build.
txstang84
Well-Known Member
Wow...that got a little heated...
I renew my first post in this thread:
I renew my first post in this thread:
This should be fun to watch the replies...
Your machinist has a point and he is thinking about air flownslowing down and causing a muddy soft response at the gas pedal.
This is a possible side effect of a small cam in a big headed/valves engine. To illustrate on a stupid level, use a towing cam in a otherwise fully worked head.
Matters become worse with low compression.
In a loose follow of your build, I would not worry about a 2.02 valve. The factory cams were very small compared to today's mild upgrade cams. Even the OE 340 cam.
Generally in the past, build dependent, inwould tell people that a 1.88 valve would be fine. And it would be. There is little HP difference in the 2 valves in mild street builds. But it is there. The smaller valves offers a snappier response. The difference is small. But it is there.
This is a possible side effect of a small cam in a big headed/valves engine. To illustrate on a stupid level, use a towing cam in a otherwise fully worked head.
Matters become worse with low compression.
In a loose follow of your build, I would not worry about a 2.02 valve. The factory cams were very small compared to today's mild upgrade cams. Even the OE 340 cam.
Generally in the past, build dependent, inwould tell people that a 1.88 valve would be fine. And it would be. There is little HP difference in the 2 valves in mild street builds. But it is there. The smaller valves offers a snappier response. The difference is small. But it is there.
Captainkirk
Old School Mopar Warrior
Not necessarily.
DieWilde13
Well-Known Member
So i would let them in.
Your machinist is right when he said it only hurts you under 6k rpm.
I made the same mistake.
Build a 340 with RHS Indy heads with 2.02 heads.
After i sold the engine, i build exactly the same setup again and choose 1.94 valves.
It pulls stronger under 5k rpm as the big valves.
It´s only really remarkable over 5500rpm with the big valves!
So if you want to rev like 7500rpm, it´s ok with the big ones. Otherwise, let the small ones in it. Gives you more power from the lower rpms.
Your machinist is right when he said it only hurts you under 6k rpm.
I made the same mistake.
Build a 340 with RHS Indy heads with 2.02 heads.
After i sold the engine, i build exactly the same setup again and choose 1.94 valves.
It pulls stronger under 5k rpm as the big valves.
It´s only really remarkable over 5500rpm with the big valves!
So if you want to rev like 7500rpm, it´s ok with the big ones. Otherwise, let the small ones in it. Gives you more power from the lower rpms.
perfacar
Well-Known Member
ok, port velocity and shape are everything, port speed fills the cylinder, not valve size!! as for power, we have tested 2.02 and 1.88 valves on real flow bench. the 1.88 has more port velocity, vs the 2.02. flow is close. the X head was designed for 2.02 valve, the others were designed for 1.88 valve. now, to compare power, in stockers, the 1.88 headed engines are as fast as 2.02 headed engines. some exceptions are there. Chevrolet, went to 2.02 valves years ago. it was a marketing ploy! we tested a chev head with 1.94 and then he opened up bowl , installed 2.02 valve and retested, flow and velocity loss. imagine that!! valve type and seat angles are important to flow gains. I realize you can't brag on 1.88 valves. 2.02 , you can. lol. BTW, a 1.88 valve 340 runs to 7300 rpm in traps, doesn't lose power. 283 chev super stockers, with 1.75 valves run 9200 RPM. no power loss.
Captainkirk
Old School Mopar Warrior
So you guys are saying, keep the 1.88's but have the heads flowed?
moper
Well-Known Member
Anyone that gets in one of my cars and can tell me by driving it what intake valve is used can keep the car. By this logic the 2.02s or (gasp) 2.05s I use should ruin them entirely. It's about the combination. Not the valve size. It's cheaper to go larger rather than putting in seats, and with the 5 angle valve job they get anyway the bowl gets properly "prepped" to make use of them. This is one of those way over-thought things...
yellow rose
Overnight Sensation
seabee
Well-Known Member
-
