340 Piston to valve clearance w/RHS heads

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goldduster318

goldduster318

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*EDIT...should say piston to HEAD clearance*


I'm in the process of procuring all the parts to build up my 340.

I'm starting with a 1970 340 with the forged crank, stock bushed rods, etc.

One of the big parts of my build will be the RHS LA-X heads from Brian at IMM. Since these are closed chamber, and as many of you know, the off the shelf pistons for 340's that are Forged are the TRW L2316F pistons, which tend to stick out 0.016-0.018" out of the hole.

I'm planning on replacing the rod and main bolts with ARP's, but other than that, it will be stock. I would like to run the 0.055" thick felpro gaskets (can't remember the PN), but this would give me around 0.037" piston to head clearance. Is this enough? I could order some cometics but they would be custom at 0.060", but I don't plan to get the block decked (its still within flatness specs and I don't need the pistons to stick out farther), and I'm somewhat concerned by their roughness spec.

Your thoughts?
 
Best thing to do is assemble the short block and check EACH piston and measure how much it sticks out. You may find some that are too tall requiring a different gasket. You won't know what you need for sure until you do this. It only takes one to ruin the party!!
 
Yes, that's definitely good advice. Before I took it apart, I measured the #1 and #5 pistons using a dial indicator with its 1.824 compression height cast pistons. With piston rock the worst measurement I could get anywhere was +0.002". The L2316F's are 1.840 compression height so that's where I was getting the general idea from.

So, with that being said, would you run the engine at 0.037" clearance? 0.035?

I started doing a stackup using metal expansion coefficents at the max surface temperature it could see(600 deg F), large pin and main clearances, and wasn't even getting close to that distance...haven't calculated possible rod stretch, etc.

I did however, see an article by Steve Dulicich where they used the 0.055" head gaskets with the same pistons sticking out of the deck +0.018" and closed chamber heads, and it worked...but then again I don't want have this thing get ruined.
 
goldduster318 said:
Yes, that's definitely good advice. Before I took it apart, I measured the #1 and #5 pistons using a dial indicator with its 1.824 compression height cast pistons. With piston rock the worst measurement I could get anywhere was +0.002". The L2316F's are 1.840 compression height so that's where I was getting the general idea from.

So, with that being said, would you run the engine at 0.037" clearance? 0.035?

I started doing a stackup using metal expansion coefficents at the max surface temperature it could see(600 deg F), large pin and main clearances, and wasn't even getting close to that distance...haven't calculated possible rod stretch, etc.

I did however, see an article by Steve Dulicich where they used the 0.055" head gaskets with the same pistons sticking out of the deck +0.018" and closed chamber heads, and it worked...but then again I don't want have this thing get ruined.
Click to expand...

Given your not going to turn the engine much past 6000rpm, I would be OK with .035. Measure all of them to be sure. I've run .030 to 7000rpm but it was with H beams, forged crank/pistons.
Brian
 
I've always heard that .040" - .045" is about the minumum. That's what they guys at United Engine say, anyway. Brian may have more insight. I'm sure it also varies from engine to engine and also depends on which parts you use.
 
I have exactly the same build. Same crank and Pistons, same RHS Heads.
I milled .021" down the top of the Piston to zerodeck. ( depends on your deckheight!)
Then i had the clearance of the standard felpro Headgasket of .039.
Runs very strong and very good!
I ran the Lunati 60402 in it and clearance was no problem!
Change now to the 60403. Will hope the clearance is still ok.
 
Yep...I do have a rev limiter. My build would have zero reason to go above 6500 ever, but I'm not sure I wanted to go that high, so I was planning for a 6000 limit.

With that being said, If its too bad, I think the custom head gasket route is preferable to milling the pistons.

I have some J heads, I have no intentions of using them. The cost to rebuild them and get them near the flow of the RHS heads from Brian and have the same springs would meet/exceed the cost (and if I home ported them, this engine would be finished in 2035).

Planning on running the Comp XE274HR hydraulic roller cam, Air Gap, & Edelbrock AVS 800.
 
ou812 said:
Best thing to do is assemble the short block and check EACH piston and measure how much it sticks out. You may find some that are too tall requiring a different gasket. You won't know what you need for sure until you do this. It only takes one to ruin the party!!
Click to expand...

Yep, I would not try to run close chamber heads on a 340 with pistons sticking out .018. I have the same thing but milled .030 open chamber iron heads and I went with the .055 fel- pro's to play it safe.

Any chance the head can be machined open?
 
goldduster318 said:
Yep...I do have a rev limiter. My build would have zero reason to go above 6500 ever, but I'm not sure I wanted to go that high, so I was planning for a 6000 limit.

With that being said, If its too bad, I think the custom head gasket route is preferable to milling the pistons.

I have some J heads, I have no intentions of using them. The cost to rebuild them and get them near the flow of the RHS heads from Brian and have the same springs would meet/exceed the cost (and if I home ported them, this engine would be finished in 2035).

Planning on running the Comp XE274HR hydraulic roller cam, Air Gap, & Edelbrock AVS 800.
Click to expand...

i don't get the logic, you want high flowing heads yet aren't going to spin it past 6,000? A basic rebuild J heads with 2.02 intakes could flow past 6,500 rpm's. If your not going to spin it, you won't get the benefits of high flowing heads. Why the 273/318's came with small port heads, they flow BETTER at low flow demands. If the air moves too slow the fuel is going to drop out of the airstream and power goes down

Now the Chevy boy's do run .030 quench, so maybe it be fine but too close for my comfy leve

l. The old Mopar bible claim .060 was min.

Forged pistons are looser in the bore when the motor is cool and will rock more than hyper pistons. When the pistons rock the clearance goes down. Why the bible went for .060 clearance
 
I won't machine the heads into open chambers...lots of $$$ and the effects probably aren't good as the castings aren't designed for that.. I'd much rather spend the money on custom zero deck pistons than that.

With a thick enough head gasket, the pistons sticking out of the deck is irrelevant. I know it would work at 0.040+, just wondering if the 0.005" tighter clearance is a make or break dimension.
 
ou812 said:
Best thing to do is assemble the short block and check EACH piston and measure how much it sticks out. You may find some that are too tall requiring a different gasket. You won't know what you need for sure until you do this. It only takes one to ruin the party!!
Click to expand...

That and don't forget those old trw pistons fit loose in the bore and will rock while the engine is warming up. The clearance will decreases when the motor is warming up.

Hyper pistons, while weaker won't rock much and can run tighter clearances.
 
dodge freak said:
i don't get the logic, you want high flowing heads yet aren't going to spin it past 6,000? A basic rebuild J heads with 2.02 intakes could flow past 6,500 rpm's.

Now the Chevy boy's do run .030 quench, so maybe it be fine but too close for my comfy level. The old Mopar bible claim .060 was min.
Click to expand...

Just because a head can support 6500 rpm doesn't mean that I'm setting everything else up to work best at that rpm level. Good head flow should help everywhere. Like I said, getting the J heads cut with a valve job, spring pockets machined, decks trued, and CC's down far enough to get a true 9.5 to 10:1 compression with a standard gasket, $800 in machine work + springs+retainers+valves...getting awfully close to the price for the RHS heads, and in the end, the J heads would still be inferior.

You get pretty much zero quench effect at 0.060" clearance.

I'm trying to build an engine that has good streetability, hence the lower RPM range.

Not that I use it at a bible, but my planned combo looks damn good in desktop dyno 2000. The extra head flow seems to help everywhere.

This is the results dyno 2000 gave me.

RPM HP TQ
2000 146 384
2500 192 403
3000 241 422
3500 294 441
4000 346 454
4500 390 455
5000 422 443
5500 440 420
6000 430 377
6500 412 332
 
goldduster318 said:
I won't machine the heads into open chambers...lots of $$$ and the effects probably aren't good as the castings aren't designed for that.. I'd much rather spend the money on custom zero deck pistons than that.

With a thick enough head gasket, the pistons sticking out of the deck is irrelevant. I know it would work at 0.040+, just wondering if the 0.005" tighter clearance is a make or break dimension.
Click to expand...


I think the common ross, srp, diamond pistons are zero deck. It was just the factory replacement pistons that had a .018 deck height.

Those trw are HEAVY, you should just get new pistons, that are lighter--can spin faster, lol--and they are stronger.

.060 is just what Mopar/Direct Connection used to recommend
 
Around .018-.020 out of the hole for a stock replacement 340 piston, so run a .060 head gasket, they aren't even a custom order btw.
 
dodge freak said:
i don't get the logic, you want high flowing heads yet aren't going to spin it past 6,000? A basic rebuild J heads with 2.02 intakes could flow past 6,500 rpm's. If your not going to spin it, you won't get the benefits of high flowing heads. Why the 273/318's came with small port heads, they flow BETTER at low flow demands. If the air moves too slow the fuel is going to drop out of the airstream and power goes down

Now the Chevy boy's do run .030 quench, so maybe it be fine but too close for my comfy leve

l. The old Mopar bible claim .060 was min.

Forged pistons are looser in the bore when the motor is cool and will rock more than hyper pistons. When the pistons rock the clearance goes down. Why the bible went for .060 clearance
Click to expand...

You need to get out more...and leave that MP junk info out on the curb for the trash man. If MP knew anything about making power they'd screw it up way before the public could ever get a chance to use it.

Remember....when I give advice I'm also putting my reputation on the line...NO WAY I would jeopordize that with bunk info....Nobody has to take my advice as I never force anyone into anything. I let my rep and my happy customers back up my advice.

If you always play it "safe" you'll be missing out on alot of "possible" power IMO...
 
Yeah but he isn't going for 7000 rpm max power levels. Its just a strong street build. He is going to leave power on the table.

I agree Mopar played it too safe, that is how things were done back then--too safe was better than not safe enough. Those old pistons were loose at 100,000 miles.

These newer pistons are much better than the old trw's, he should change the pistons, IMO. 9.5-10 to 1 compression is easy with 63 heads. In fact he might be closer to 10.5 to 1.
 
I was reading something about special cuts of gaskets for the RHS heads.

I'd rather not use hypereutectic cast pistons (stronger than cast but very brittle), just a personal preference. I haven't been able to locate any zero deck forged 340 pistons that are any size other than +0.030. I'm going to be needing +0.040".

Brian told me the heads CC out at 67 most of the time. add the valve reliefs and I'm at about 9.5:1 with a 0.060 gasket.

I'm not going for the ultimate potential of the 340...but I am going with a hydraulic roller cam, good heads, etc to still get a strong build. I'm just willing to trade some top end HP for a flat torque curve (its going in a full interior, 4-speed stick, 3.23 geared car).

We live in the age of the chevy "LS" engine. I'm trying to keep up with these, even with this block that was made in 1970. If I can truly make the numbers DD2000 was giving me and have great streetability and durability, then I will be a very happy fellow.
 
dodge freak said:
i don't get the logic, you want high flowing heads yet aren't going to spin it past 6,000? A basic rebuild J heads with 2.02 intakes could flow past 6,500 rpm's. If your not going to spin it, you won't get the benefits of high flowing heads. Why the 273/318's came with small port heads, they flow BETTER at low flow demands. If the air moves too slow the fuel is going to drop out of the airstream and power goes down

Now the Chevy boy's do run .030 quench, so maybe it be fine but too close for my comfy leve

l. The old Mopar bible claim .060 was min.

Forged pistons are looser in the bore when the motor is cool and will rock more than hyper pistons. When the pistons rock the clearance goes down. Why the bible went for .060 clearance
Click to expand...

The one thing that I noticed is you did not mention port velocity or low lift numbers,both essential in building an efficient engine.Those heads will have both those assets and make for a very responsive,powerful street engine.Add that with the superior combustion chamber and they are a far superior head-in fact by design they come out being the ultimate street head.The other thing is port size plays a bigger role in conjunction with cubic inch so a smaller engine could use less port size unless spinning higher rpm,a 340 to 273/318 is apples and oranges when comparing similar build up's
 
.035 on the quench should be fine. .080 on the intakes and .100 on the exhausts. Do the mock up with clay to be sure.
 
goldduster318 said:
Yep...I do have a rev limiter. My build would have zero reason to go above 6500 ever, but I'm not sure I wanted to go that high, so I was planning for a 6000 limit.

With that being said, If its too bad, I think the custom head gasket route is preferable to milling the pistons.

I have some J heads, I have no intentions of using them. The cost to rebuild them and get them near the flow of the RHS heads from Brian and have the same springs would meet/exceed the cost (and if I home ported them, this engine would be finished in 2035).

Planning on running the Comp XE274HR hydraulic roller cam, Air Gap, & Edelbrock AVS 800.
Click to expand...

JMO but buy a Holley carb
 
goldduster318 said:
I was reading something about special cuts of gaskets for the RHS heads.

I'd rather not use hypereutectic cast pistons (stronger than cast but very brittle), just a personal preference. I haven't been able to locate any zero deck forged 340 pistons that are any size other than +0.030. I'm going to be needing +0.040".

Brian told me the heads CC out at 67 most of the time. add the valve reliefs and I'm at about 9.5:1 with a 0.060 gasket.

I'm not going for the ultimate potential of the 340...but I am going with a hydraulic roller cam, good heads, etc to still get a strong build. I'm just willing to trade some top end HP for a flat torque curve (its going in a full interior, 4-speed stick, 3.23 geared car).

We live in the age of the chevy "LS" engine. I'm trying to keep up with these, even with this block that was made in 1970. If I can truly make the numbers DD2000 was giving me and have great streetability and durability, then I will be a very happy fellow.
Click to expand...

Good luck finding any forged pistons .040 for a 340.

As for the carb, that is another mis match, IMO. Why go with the 800 if you aren't going to rev the piss out of it? A 750 or even a grasp 650 avs would be find for your use. I used holley's for years, one Holley will outperform one Edlebrock but the Carter/Edlebrock give better street manners and since he is comparing these new cars I think he be more than happy with a decent running 340 in a light weight duster. Plus I think he rather get 12 to 15 mpg than 8 to 12 mpg.

Yes those heads RHS might be better than the normal J heads but I don't think Edelbrock makes a special 340 head for nothing. .030 might clear but too close for me.
 
Mr Hemi said:
.035 on the quench should be fine. .080 on the intakes and .100 on the exhausts. Do the mock up with clay to be sure.
Click to expand...

Yeah I believe the Chevy guys run it that close too. It would just stink thou to have a great running engine for awhile and then one day showing off on the freeway to your GF--or better yet--your GF winding out the engine in 2 gear on the freeway and bang, boom and white smoke goes pouring out the rear while the engine gets weak while your foot is still down on the gas--I blew a head gasket once like that.

I wasn't thinking of making the heads open chamber, just grinding .015 in for extra space. Or take it off the pistons. Most pistons should have valve reliefs already in. Maybe it be open but i can't see the harm .015 would do

So far my kb 340 hypers been holding up, only 2,500 miles on the engine but hard miles. I stayed on the 6,500 rev limiter for a good 10 seconds last summer. All was fine. Not a wiff of smoke either in back. Hyper pistons run tight and seal great. If you don't ping the engine--by too much timing, too lean, it should work fine.

I was all against hyper's too but for $250 for a new set at Summit it got my engine going and I now think its going to last. I'm getting taller tires for sure and maybe stick my 3.21 gears back in. If $4 a gallon gas shows up this spring, yuk. I'm going for mileage over performance
 
The TRW/Federal Mogul L2316F Forged pistons do come in +0.040. They always have, that's why I would be using them...seem to be the only one. With how much the rest of this engine is going to cost, I'd rather not cheap out on hypereutectic pistons. Its only $150 more anyway.

The 800cfm edelbrock AVS will work fine. Its much more tunable than your average Holley 3310 on the primary side anyway with its replaceable jets, metering rods, & step up springs. I have an Innovate LC-1 wideband and adjusted the crap out of the holley 600 on my 360 and its just not anywhere near a mileage machine....it has never gotten better than 13 mpg.

Also, read this article: http://www.moparmusclemagazine.com/...ocks_thunder_series_avs_carburetor/index.html He has a similar combo and was getting 16.6 MPG. If you know how to tune it, the car does not know the difference between Holley & edelbrock...only that its not choking on lack of CFM and getting the proper A/F mixture.

I wouldn't even attempt running it at under 0.035" clearance. Lots of people running 0.039" (Zero deck+closed chambers+standard gasket).
 
goldduster318 said:
The TRW/Federal Mogul L2316F Forged pistons do come in +0.040. They always have, that's why I would be using them...seem to be the only one. With how much the rest of this engine is going to cost, I'd rather not cheap out on hypereutectic pistons. Its only $150 more anyway.

The 800cfm edelbrock AVS will work fine. Its much more tunable than your average Holley 3310 on the primary side anyway with its replaceable jets, metering rods, & step up springs. I have an Innovate LC-1 wideband and adjusted the crap out of the holley 600 on my 360 and its just not anywhere near a mileage machine....it has never gotten better than 13 mpg.

Also, read this article: http://www.moparmusclemagazine.com/...ocks_thunder_series_avs_carburetor/index.html He has a similar combo and was getting 16.6 MPG. If you know how to tune it, the car does not know the difference between Holley & edelbrock...only that its not choking on lack of CFM and getting the proper A/F mixture.

I wouldn't even attempt running it at under 0.035" clearance. Lots of people running 0.039" (Zero deck+closed chambers+standard gasket).
Click to expand...

That 800 carb is actually a good peice.
 
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