X heads on a 340 HP potential???

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swinger340

swinger340

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Have a fresh set of X heads that flow 240/165 @ .500 on the bench. Been gasket matched w bowls blended a little. What kind of HP potential may these heads have on a 10.3:1 340 w/ a, MP .509, RPM air gap, and a 750 holley. Machine shop told me around 325, but i was hoping for more than that. I thought they were under rated and more like 325 stock. When these heads were bone stock they flowed 220/140 @ .500
 
I can't speak to the specific number but I would expect it to be higher than that as well! I thought they were close to 325 stock or with very mild mods.
 
A stock engine with headers will dyno 325 or better.

If your useing headers ..... I'd bet 400 HP at the flywheel.
I get this quick number from the oldMP create engine, the Comando 360 pumping out 360 HP with stock 308 heads & 2.02's (Approx. 200+ cfm) and a Purple 284/484 cam. Between the porting, larger cam and the better HP making shorter stroke of the 340, you'll be at 400 or better HP.

The create engine also use's the MP M1 single plane and 1-3/4 tube sized headers. The newer RPM (Relitive) should produce as much HP as the single M1 at this stage of the game.

The newer Magnum create engines use the .509 cam and above mentioned parts and make over 400+ on the dyno, no matter who dyno'd it.

Considering a (?!) 25% loss through a 727 trans .... you'll get 300 HP at the rear wheels. So, depending on what he is thinking ...........
 
I don't mean to jack the tread but since we're talking 340s, I hope you don't mind if I ask about my 340. It has a 509 ultradyne, M1 intake, J-heads with the 2.02s, headers, 650 mighty demon. What you think for hp/tq?
 
Swinger - I think your guy is a little low, but hard to say. I don't see it making big numbers with that cam either. I think 380-400 is closer to reality assuming the engine is really 10.3:1, and not just put togetehr without blueprinting. If it's not blueprinted, I'd say it's closer to 330-350.
 
swinger, what pistons are you using? because to my knowledge (which is admittedly limited) TRW is the only one that makes a true 1.84 compression height piston to actually get over 10:1 in a 340. the rest are 1.80 and yield closer to 9.4:1 comp
 
Baxter61 said:
swinger, what pistons are you using? because to my knowledge (which is admittedly limited) TRW is the only one that makes a true 1.84 compression height piston to actually get over 10:1 in a 340. the rest are 1.80 and yield closer to 9.4:1 comp
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It's a combination of the piston and tall factory deck heghts. That' why I mentioned the blueprinting step. Even the TRWs are "low" in most blocks unless the block is square decked during blueprinting.
 
Tuned right, should make right in the 390-400hp range and 400 tq

A stock 340 can make 325-340 with a good carb, intake and headers.
 
Baxter61 said:
swinger, what pistons are you using? because to my knowledge (which is admittedly limited) TRW is the only one that makes a true 1.84 compression height piston to actually get over 10:1 in a 340. the rest are 1.80 and yield closer to 9.4:1 comp
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The pistons are TRW 2316s that are sticking .015 out of the block and the heads are 67 cc had planned on using fel pro 1008s (.039 compressed @ 4.18 Machine shop told me it would be 10.3:1 Are they close?
 
without doing the math it sounds about right to me. just wondering because I have been shopping for some 340 pistons and TRWs seem to be the tallest and the only ones to get at or over 10:1 without going dome or semi-custom.
 
This engine would be going in my 4 speed swinger for street use only. I was hoping for @ least 375. When machinest said 325 I kinda scratched my head. This guy is a die hard chevy nut.
 
Well, he may just be a diehard chevy experienced builder. Doesn't mean he sucks and the engine will be underpowered. He just doesnt do a lot of them and doesnt have a good grasp on what a "typical" deal might do. That would make sense if it was him that recommended the MP .509 cam too.
 
moper said:
Well, he may just be a diehard chevy experienced builder. Doesn't mean he sucks and the engine will be underpowered. He just doesnt do a lot of them and doesnt have a good grasp on what a "typical" deal might do. That would make sense if it was him that recommended the MP .509 cam too.
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He is actualy a good friend of mine. We are always harrasing each other. He is comparing it to a 9.5:1 (chevy) 350 w .202 heads he just built. He does good work and is very particulal, but dont do many mopars. Would you recomend a diff. Cam?
 
just make sure you did your home work are going o take the engin over 5500 rpm and did you do any oiling mods if not you can starve you nice new engin.
 
robert 68 cuda said:
just make sure you did your home work are going o take the engin over 5500 rpm and did you do any oiling mods if not you can starve you nice new engin.
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Oiling mods have been done along w/ 7 qt. pan. Probably wont see much more than 6500. Mopar drag racer/rebuilder up this way w/ stroked 340 that he turns 7500 gave me his oiling mods. Check him out if interested, Bob from Outrageouslyvintage.com Vintage Mopar only machine shop. He is the one I had do my heads. He could have done alot more port work but i think it would have been an overkill for a street motor. All other machine work and balancing was done by my buddy I work with @ his machine shop. Its kinda nice knowing 2 guys w machine shops.
 
Baxter61 said:
swinger, what pistons are you using? because to my knowledge (which is admittedly limited) TRW is the only one that makes a true 1.84 compression height piston to actually get over 10:1 in a 340. the rest are 1.80 and yield closer to 9.4:1 comp
Click to expand...

I'm using mahle pistons and have 10:5.1 compression , a similar build to Swinger and am getting 412 HP 398 torque with lunati # 60403 cam

268/276 226/234 .494/513 @110 degree


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jerry6 said:
I'm using mahle pistons and have 10:5.1 compression , a similar build to Swinger and am getting 412 HP 398 torque with lunati # 60403 cam

268/276 226/234 .494/513 @110 degree


.
Click to expand...
I was actualy considering that cam. Do you like it? I thought it sounded good because my x heads are lacking flow on the exhaust side so the extra lift and duration may help the engine breathe a little better.
 
I like it , numbers speak for themselves 412 hp 398 torque . Have just about the same set up , heads done just like yours by a real mopar guru . He's been doing mopars for over 35 years . Was thinking of going with the 60404 , but not with an auto and the converter I have , with a 4 speed maybe .
Combo works well , everybody was pleased with the numbers it pulled on the dyno . Pulls well at any speed , punch it at 20 and it will smoke the tires , punch it at 60 and your hitting jail illegal in no time .
 
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