J heads upgrade

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Captain, your making more of an issue of this than is worth the time for you to type it.
 
Go for the 2.02's. At minimum while he is installing those, have the bowls and everything cleaned up. Do some work on the shortside turn/pinch point. And a solid valve job. Even really basic work like this can get those heads to flow in the 230's. And can be easily done while he's in there. A good full port job will see 260-270. 230's is good for low-mid 400 horse on the right setup. 260+ is good for mid-high 400's. Maybe even 500 if you got it planned out right.

Make sure you get the heads flow tested after. See your curve. Where your flow starts to drop off. Then get a cam to suit. IE no point in getting a .650 lift cam when your heads tip over at .500. With the cam picked, you can pick your compression ratio. As you then can know your dynamic compression (DCR), which is much more important. With iron heads I'd say you want the 7.5-8 area. Depending on octane available in the area.

If you do have 10:1 compression. And keep your DCR up. And pick a cam with good duration/lift. Right exhaust, etc etc. I would not be surprised if you saw 450 out of it. As an example. A friend rebuilt a 360. Stock stroke. +.030 over. 10:1. solid roller cam (can't give away all their secrets) 2.02 valves and full port job on J heads. Made 430 horse, at the tire.
 
perfacar said:
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.
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This isn't stock where you're stuck with rules. I don't know about anyone else...but in my 4 spd car, I'm already going through 3500 rpm before I'm halfway through the pump shot. A 3.91 4spd 340 is into 6000+rpm real quick...smh A bunch of people who like to argue and talk garbage to others while preaching the mopar bible and using it to verbally backhand people meanwhile ignoring the most basic and obvious example that mopar gives...the 340. Smh Now which years did the factory 340 have more hp ? the 2.02 or 1.88 Were in which years? You talking about port velocity and 340's but using chevys as examples with valve head diameters. What are port volumes of a chevrolame sb again. Use whatever valve you want and build the motor and gear around it to make it work and prove a point, to each his own.
 
"Right" is subjective and individualistic. Do what's most cost effective, do it in concert with the augmenting work, run matching components, and enjoy yourself.
 
Captainkirk said:
Just want to get it right the first time around, Rob.
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What is right, because depending on opinions...you started wrong with those heavy pistons and wrong by not listening to your machinist or builder. If I were him and you came back with g stock advice and the other 101 ways to skin a cat... I might pass the job up to avoid the troubles of working with advice from a bunch of mostly arm chair racers on the net.
I PM'd perfracer and tried a friendly dialog and he started confusing me with someone saying you need 2.02 or big valves to turn high r's and he aint gonna waste his time talking with me about it, lol also he says velocity is what really makes a winner... so according to perfracer, you better run the shittiest flowing heads with the tiniest high velocity ports so you can be just like him and win every gd damn race because he says he knows more than everyone else here because he spoke with an old set in his ways legend that probably told him **** that went right over his head...and he runs with it. Such nice people, all these guru people on here...
 
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the original question...gains on the street?
not much unless you port your heads and routinely drive above 6000 rpm
 
That is mostly the problem. It's not that some of the advice you cross is wrong but it varies so much. And even on the far end of one persons advice is another's advice which is also fine but just not the same. Each has fine words and a good idea of what would be a good way to go but there so far apart.

I would also shy away from such a job.
 
aren't stock J or X heads basically the same... and flow stalls around 200 cfm at about .480 lift
whether you have 2.02's or 1.88's.
I'm guessing no gain for this change on the street
 
Just one more thing I can't let pass.

If you chose your cam based on where the port starts to stall, how do you chose which pressure drop to test at? This has been a pet peeve since I bought my flow bench.

If you test a head at say 10 inches, where most bench top benches still test at, your port may look good to well over .600 lift. Bump it to 25 (the Super Flow standard) the lift at which turbulence occurs will be much closer to .500 lift. Drop to 28 inches and turbulence will occur sooner. I have tested as high as 48 inches on a production head (will be doing some W-2's before the end of the year and my push it to 60 if I can) and I will tell you the port on a production head is a turd as soon as you open the valve.

The point is, you can't pick you lift based solely on flow verses lift numbers. Sometimes,you have to lift it as much as the valve gear will let you. Other times, reliability, parts and output dictate lift.

At this point, I can't see any reason EVER, to not NET .500 lift on any application. That's why you need to develop a relationship with a cam grinder.

Hope this helps someone. I'm sure others will argue.

To the OP...a bigger valve, on the heads we are discussing, will increase low lift flow, to the detriment of mid and high lift. Low lift being, in this case, .075-.175 and mid being .175 to about .250 lift. You'd be better off with a 1.88 valve, a steeper angle valve job and a faster ramp on both the intake and exhaust lobe. That may be out of you and your machinists comfort zone. If so, use the 2.02 and use a slower lobe on the intake. The longer you keep it at low-mid lift the more power you will make.

We could discuss a 2.02 valve and a 50* seat, but that would tip some viewers over. And, some castings won't take it. Don't ask how I learned that.
 
MOPAROFFICIAL said:
What is right, because depending on opinions...you started wrong with those heavy pistons and wrong by not listening to your machinist or builder.
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First...my machinist is not a fan of KB pistons and cites an abnormally high failure rate compared to other makes. He did not like the weight either but at 728g they are less than 10g heavier than the stock '68-71 piston, and they are forged. My only other option besides KB were all in the 6-700 dollar range and that was not gonna happen. I chose what would work for my budget. The old pistons (L2322F) were 660g and 12.5:1...which was simply no longer an option for a street motor on pump gas.
Second...why am I not "listening to my builder"? He's on board with the .030 over pistons I've chosen along with the '69 forged crank, and has *suggested* a preference for Eagle SIR-I forged rods over reconditioning the stock forged rods...which makes sense. This should provide me with a very solid and strong bottom end IMHO.

This project is to be a solid street runner and will likely never be raced, or only to establish an ET baseline. But more likely not. Stock 340's are known to be hard, fast revvers...why should this be any different? I would rather lose a few seconds in ET than have a piston come apart or break a ring. At my age, I intend this to be the last time I will have the bottom end out of this engine.
The heads are the next item up in the batter's box, because the cam choice has to be based partially on compression and head flow...hence my question about the 1.88 valves. I have a set of 2.02 X-heads I could run on this thing but they've had no work done to them as the J's have previously. My question was not to start a range war, just to determine whether my builder was correct in stating that "for my intended purpose (street runner) the 1.88's will create more usable torque down low (6000 and below)". The time to do head work, porting and valve changes is now; before I select a cam or valve train. Also, I would like to note that while he does many, many engines yearly, he's not necessarily a Mopar guy, and moreso not necessarily a smallblock Mopar guy...(this in no way reflects anything bad on his part)...which is why I turned to the forum here; to get the answers from guys that build them and know them.
I'm not going bracket racing. I'm not gonna lose money if I run a half a second slower. I'm not running for 'pink slips'...I just want a car that starts easy and runs strong and will make me feel like a punk kid again when I wail on it.
Hope that clears the waters for some of you...and thanks for all the advice to date.
 
If you are up for buying valves and having the porting done, get the 2.02's. It's utter horseshit to say it will kill bottom end. The issue becomes (again) low lift flow numbers. Come to think of it, as is in vogue today, if you are going to use a cam on 110 or wider LSA definitely use the bigger valve. I just ported my own heads, and I only used a 2.02 valve. I have a bowl of about 92%, and I NET a bit over .600 lift. Since I wanted to kill low lift flow (not with bad porting so I should say I wanted to control low lift flow) I ended up with a 105 LSA.

There is way more than one way to get to where you want. I can't stress how important a custom cam is. It has to be from someone who is competent to discuss low lift flow, reversion (and how to minimize it...especially and specifically at overlap) and how LSA affects, and is affected by low lift flow. Too many guys want to open up the LSA, pull the @.050 number down and use a dual pattern cam to cover their poor porting and valve decisions.

For the average guy this gets to be monotonous. Even redundant. As an engine builder, it's about relationships. GM was famous for outrageously wide LSA's and big slow ramps with long seat duration and short @ .050 times. They were pigs in the gear change and overall power was down. Emissions were possibly slightly better, and possible idle and fuel mileage were better by a BCH. What they gave up was rediculous.

Think about the system. And your goals. My cam is seat timed at 281 and has an @ .050 of 255 on a 105 LSA installed at 105. I can make it idle at 900, but I keep it a bit higher than that. If you didn't know, I could tell you it was a 284 hydraulic MoPar cam by the sound of the idle. I spent several hours on the phone with the cam guy to get on the same page. I did my own valve job, with a specific goal. Before you do anything else, figure out where you want to be with your cam. If you are going with an off the shelf Comp or similar with a 110 LSA, the bigger valve won't know the difference.

BTW, make sure the top cut on the valve job is a MINIMUM of .060 and .100 would be better, if you can get it.

My .02 cents.
 
Captainkirk said:
First...my machinist is not a fan of KB pistons and cites an abnormally high failure rate compared to other makes. He did not like the weight either but at 728g they are less than 10g heavier than the stock '68-71 piston, and they are forged. My only other option besides KB were all in the 6-700 dollar range and that was not gonna happen. I chose what would work for my budget. The old pistons (L2322F) were 660g and 12.5:1...which was simply no longer an option for a street motor on pump gas.
Second...why am I not "listening to my builder"? He's on board with the .030 over pistons I've chosen along with the '69 forged crank, and has *suggested* a preference for Eagle SIR-I forged rods over reconditioning the stock forged rods...which makes sense. This should provide me with a very solid and strong bottom end IMHO.

This project is to be a solid street runner and will likely never be raced, or only to establish an ET baseline. But more likely not. Stock 340's are known to be hard, fast revvers...why should this be any different? I would rather lose a few seconds in ET than have a piston come apart or break a ring. At my age, I intend this to be the last time I will have the bottom end out of this engine.
The heads are the next item up in the batter's box, because the cam choice has to be based partially on compression and head flow...hence my question about the 1.88 valves. I have a set of 2.02 X-heads I could run on this thing but they've had no work done to them as the J's have previously. My question was not to start a range war, just to determine whether my builder was correct in stating that "for my intended purpose (street runner) the 1.88's will create more usable torque down low (6000 and below)". The time to do head work, porting and valve changes is now; before I select a cam or valve train. Also, I would like to note that while he does many, many engines yearly, he's not necessarily a Mopar guy, and moreso not necessarily a smallblock Mopar guy...(this in no way reflects anything bad on his part)...which is why I turned to the forum here; to get the answers from guys that build them and know them.
I'm not going bracket racing. I'm not gonna lose money if I run a half a second slower. I'm not running for 'pink slips'...I just want a car that starts easy and runs strong and will make me feel like a punk kid again when I wail on it.
Hope that clears the waters for some of you...and thanks for all the advice to date.
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Hey you're good, as I said ...opinions. Technically you said you asked the builder and he told you to stay at 1.88 int valve.LOL
The guy is afraid of the kb's hyper pistons from the experience of not enough top ring gap or bozos playing with nitrous and bad tune, they work fine if the top ring is at a minimum gap of .028-.030 for nat aspr..
The kb have gotten heavier over the years, they used to be lighter than stock by a decent amount for that level, around 574 w/o pin . They switched manufacturing to Mexico and got about 7 grams heavier...all moot, and irrelevant now.
What you want to do sounds like what many of us have done, keep the small valve though it is a heavy pos, ski jump, multi keepers n all, have the heads flow tested when he is done. This is basic street build w/3.91 gears...lol with all the advice everyone has given...that's hard to screw up. say a cam with .050 more lift than heads flow peak/where it starts to fall off and don't go bigger than 280ish adv degrees and 240'[email protected] 110 if you can help it...or just get more gear .lol
Have the guy flow the heads with the intake for fun, Maybe throw the carb on it while you're at it.
 
MOPAROFFICIAL said:
...Have the guy flow the heads with the intake for fun.....
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Well, now that you mention it...
He doesn't have a flow bench and does only cleanup port work (gasket matching) which a monkey and Dremel could accomplish. No; if the heads are gonna get worked. other than simple reconditioning, they're gonna have to go outside the loop, or I'll have to do them myself. I have no idea how to work heads other than the monkey-thing. As finicky as Mopar heads appear to be, I wouldn't want anyone who's not a pro grinding on them anyway, much less without a flow bench to check their work. It's either send them out or run them stock.
 
This is where,I miss Justin... He knew his sh&t,and could explain it....(Wild & Crazy guy....).
 
Captainkirk said:
True, but don't forget the cam and compression changes, which probably make up the lion's share of the HP difference.
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340 cams were all the same except the 68 manual transmission 340's. And they changed the way they measured Horse Power starting in 1972.
 
66fs said:
340 cams were all the same except the 68 manual transmission 340's. And they changed the way they measured Horse Power starting in 1972.
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Correct. The '68 340 with it's flat top 10.5:1's and the cam netted 275 HP. I'm striving for somewhere in the 300-400HP range.
 
Big range, 100 hp is a lot in difference to each other.

300hp? Dead stock OE everything except headers and a 2-1/2 exhaust, muffler of your choice. Upgrade the ignition.
 
rumblefish360 said:
Big range, 100 hp is a lot in difference to each other.

300hp? Dead stock OE everything except headers and a 2-1/2 exhaust, muffler of your choice. Upgrade the ignition.
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Well, my builder says 400HP no problem, but he hasn't recommended a cam yet so not sure where he's going with this.
I don't think I should cross that bridge until I have the heads figured out.
 
Captainkirk said:
Correct. The '68 340 with it's flat top 10.5:1's and the cam netted 275 HP. I'm striving for somewhere in the 300-400HP range.
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68-71 340's make more than 275 HP. They were Factored up to 325 and higher by NHRA. My only point is to look at NHRA factored HP numbers and not advertised numbers. They are closer to comparable. If you pay attention to YR, Moper, and Perfacar, that level of machining works great on the street with no bad side effects. Few people understand what great machining will do for output (HP).
 
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