340 improvements with dyno numbers

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canyncarvr

canyncarvr

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I haven't noticed this posted, but I certainly don't read everything here.

This link lists a reasonable step-by-step modification list for the 340 complete with dyno HP and torque numbers for each step. That the link was on the top of a google search about the 340 likely means it's commonly read. Just 'cuz it's new to me doesn't mean a whole lot. It may well be a, 'Yeah...everybody knows this already,' sort of thing.

It was of particular interest to me due to their choices of modification, more than one of them fitting very well into choices I've made for my 340.

1970 340 High Performance Mill Dyno - Mopar Muscle Magazine
 
Build it and be disappointed when it acts like a 330-340hp engine. :)
 
I think you guys are too hard on magazine builds. Even if it's on the generous side it still a helpful guide and pretty sure most people would be happy with that 340 in their car.
 
273 said:
I think you guys are too hard on magazine builds. Even if it's on the generous side it still a helpful guide and pretty sure most people would be happy with that 340 in their car.
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I call into question ANY numbers where the sponsors are throwin parts at the builders and editors. End of story.
 
ir3333 said:
you realize that is a magazine article.
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I do. That is a problem somehow? The link is attributed to the owner.

crackedback said:
Build it and be disappointed when it acts like a 330-340hp engine.
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That is intended as a response to something? I don't know what that might be.

It's not a 'build'. It's a stepped process with performance numbers attached to each step. And having ended up with close to 400hp, how does that related to the stated disappointment?

This sure got off the rails quick! The link is simply a list of some common modifications with dyno results. There is no indication of the link having an intent of 'building' a 10-second car...or anything else.

What is all the angst about?
 
So you guys really don't think a 340. Bored .030 over. 10:1 compression (stock pop up pistons). Edelbrock RPM intake. X heads. Dialed in edelbrock 800. Comp XE268H. And 1-5/8 headers can do 390 horse/411 torque? C'mon. That's a well known combo for 400 horse out of a small block. At least read the article before you slam it.
 
Lustle said:
So you guys really don't think a 340. Bored .030 over. 10:1 compression (stock pop up pistons). Edelbrock RPM intake. X heads. Dialed in edelbrock 800. Comp XE268H. And 1-5/8 headers can do 390 horse/411 torque? C'mon. That's a well known combo for 400 horse out of a small block. At least read the article before you slam it.
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I never said that. It may very well make the power they claimed. It damn well should make a lot more than a stock 340.

I always call into question any mods or builds done by magazines when they are obviously using sponsors' parts that have been thrown at them for the cost of being published and bragged about. I much prefer independent tests.

I don't think anybody is showing angst, but merely saying to not necessarily believe everything you read.

Do yall not think the numbers could be inflated for the sake of making parts look good? Parts that were probably donated? Parts that you or I would have to pay for?

We're simply saying look at it from all perspectives.
 
And I never said I believe every horsepower claim ever. Reminds me of a time on horsepower TV when they switched fluids in the entire drive train and "found" something like 20 horse. I just don't see it. And of course I prefer independent tests. Guys with nothing to lose have nothing to prove.

What I am saying is read it, watch it, whatever, and judge for yourself if you believe it or not. Don't always assume it's going to be biased. That makes you biased. Use your head, judge from your experience. Don't let someone else give you your opinion. And most of all, educate yourself.

Back on topic. These articles are from 2001, so a lot of guys have run a combo very similar to this (Infact I run almost the same with an XE274H cam). It's a solid way to go. If you are interested, here is the second part of that article.
340 X Head Buildup - Mopar Muscle Magazine

They end up at 477hp/431tr with a port job, custom solid grind, new carb and spacer. Judge for yourself if you believe it.
 
Lustle said:
So you guys really don't think a 340. Bored .030 over. 10:1 compression (stock pop up pistons). Edelbrock RPM intake. X heads. Dialed in edelbrock 800. Comp XE268H. And 1-5/8 headers can do 390 horse/411 torque? C'mon. That's a well known combo for 400 horse out of a small block. At least read the article before you slam it.
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The simple answer with a set of X heads with stock ports... NO!!!!

Isn't going to happen. Seen 3 or 4 built this exact way and NONE of them ever made more than 345hp. They ran like they had 345 at the track. Nowhere close to a 390-400hp engine in regards to MPH/ET and weight of car.
 
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Better to underestimate and find out you have more than you thought rather than less.
 
it's logic...a cam,carburetor and headers just won't add 125hp to a small block.
perhaps 50 hp.
i'm betting most 408 strokers with stock heads won't hit 375hp.
..but i've been wrong before
 
ir3333 said:
it's logic...a cam,carburetor and headers just won't add 125hp to a small block.
perhaps 50 hp.
i'm betting most 408 strokers with stock heads won't hit 375hp.
..but i've been wrong before
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Your basically listed all the main things that make power besides CR and heads and speaking of which 340 has both maybe not the 10.5:1 advertised. If you go by the 2hp per cfm rule of thumb X heads have 440 hp potential. So yes a cam, carb/intake and headers can add a lot of power. Question does this combo, I think it's maybe a little generous at 390hp, to me a 400 hp combo is 10:1, 280 ish cam, 750/air gap, 220 cfm heads and headers. And that combo is two steps down on cam and a half cr down so should be 30-40 hp less not 10 less but even if there dyno is a little happy still useful info.
And for us not in the racing world probably we get our sense of engine hp is from magazine builds and even if it's a little askew it's actually probably more of the norm since a greater number get our info that way. And really there's so many variables it hard to get an accurate hp number of your engine anyways even the run it down the track method.

And of course the 408 gonna make 15 hp less (375 vs 390) cause it eats it up in friction. lol
 
...just read comp cams own dyno test on a 356 sm blk chev
i know..i know,but it did have nice Dart alum. heads

XE268
Dart alum heads
2" intake valves
Dual plane intake
Holley 3310
headers
... 342 hp and 413 torque
 
ir3333 said:
...just read comp cams own dyno test on a 356 sm blk chev
i know..i know,but it did have nice Dart alum. heads

XE268
Dart alum heads
2" intake valves
Dual plane intake
Holley 3310
headers
... 342 hp and 413 torque
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What compression though?
 
ir3333 said:
9.25:1
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On alum heads? So basically 8.25:1 given how alum heads don't heat as well as iron. With that cam makes for a dynamic compression ratio of 7.52 (at 0 feet elevation, less is more, in my area that would be 7:1 dynamic). Which once again with alum heads is more like 6.52. Yeah sorry if this sounds rude, but that's just stupid. Mismatched components for sure. Pump gas dynamic on alum heads is in the area of 8.5. They are leaving a ton of power on the table in that build.
 
Stock 340 comp was lo 9's
..would the x heads make more power than the aluminum Dart heads?
 
You're talking 1972 or later than. Stock 340 up to 71 was 10.5:1 compression. The engine mentioned in the article is a 1970. With 10.5:1 pop up pistons.

And yes, X heads can make more power than aluminum dart heads. It's never as simple as "bolt on new heads make power!" it's about matching your components. For example, running 9.25:1 compression on aluminum heads doesn't make sense. With the higher heat tolerance of aluminum heads, you have to up the compression. Or you lose power. Running less than 10:1 compression on aluminum heads is a waste. In my opinion running less than 10.5:1 on aluminum heads is a waste. Why run iron head compression on an aluminum head? You'll make less power.
 
Lustle said:
On alum heads? So basically 8.25:1 given how alum heads don't heat as well as iron. With that cam makes for a dynamic compression ratio of 7.52 (at 0 feet elevation, less is more, in my area that would be 7:1 dynamic). Which once again with alum heads is more like 6.52. Yeah sorry if this sounds rude, but that's just stupid. Mismatched components for sure. Pump gas dynamic on alum heads is in the area of 8.5. They are leaving a ton of power on the table in that build.
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No, 9.25:1 is 9.25:1. All day long. Aluminum heads do not take compression away. Period.
 
If you do the math using 72 cc heads i think you'll find the early 340's were about 9.4 or so.They were rated at 10.5:1 so you could build them to 10.5:1 and be NHRA legal.
I thought the alum Dart heads would be far superior to the 45 yr old X's.
 
Actually, the early 340 was specced out at 10.2:1. The later ones 8.2:1. Though they blueprinted around 9:1 and 7.5:1 respectively.
 
Most of them I checked were in the 9.00 to 9.50 range but it's not the head volume that was the issue. With a shim gasket, the piston has to be out of the bore at least .017-.018 and most are .010-.015 down the bore.

My current build is 11.08:1 actually measured with a small dome and out of the bore .045 IIRC I'd have to pull the but it's all that and STILL only 11:1. I can get to 11.25:1 with a gasket change if I want to.


Most guys who don't downfill the bore and do the math don't have near the compression they think they have.
 
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