Extra hp out of my 340.

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It's making the power of a stock 340. IMO, given the camshaft, it's got issues. Not sure where the tune is on it but I would expect another 20-30hp from a well built, well tuned 340 with that cam, those pistons, manifolds and full exhaust, and the associated work I'd assume was done to get it together.
I like the 3.23 stick combos with a 340. I think you're problem is lack of performance, not gearing. Just my opinion of course.
 
yellow rose said:
That's why I asked. 252 at the wheels is 302 HP at the flywheel.

Unless you have something totally whacked out, you only lose 20% through the water pump, fan and drivetrain. No way in hell is it 33%.
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No its not. I've followed very closely MANY engines ('cuz I'm interested in this stuff) I've built and dynoed (SF-902) over the years when they wind up on the rollers or even better a chassis dyno that bolts up to the wheel hubs (my fave). They typically put down about 90-100 hundred HP less than what the engine dyno shows. He's bang on with his 340 hp estimate--I've also tested 340's that are similar to the OP's and they make 340-360 hp everytime. It scales up and down very consistently--I built a 471 BB 682 hp on dyno--in car made 587 hp at the tire with a TKO 5 spd--that's pretty close I'd say. Did a 360 with Eddy heads small cam made 402 hp and in car made 312 @ tire. J.Rob
 
OP--Your engine sounds like its a pretty good performer as it is. As other have said headers will help a good amount. Start there. If it were mine I'd be looking at a nice little solid cam next, since the 340 is known for being a revver and all. Then when the oil gets hot from your highway jaunt with 3.73's the valvetrain will still be in control and making the same power as before. A properly spec'd solid will pick up the bottom end torque a bit and carry power upstairs that a hydraulic cam could only dream about. Use the 340 as it was intended-for RPM and HP. Don't try and make the 340 into something it will never be. J.Rob
 
perhaps i missed it ...what size are your rear tires?
If you change your cam keep the duration on the low side for street use
and not too hi on the lift.Stock iron heads flow stall around .480 lift.
 
RAMM said:
471 BB 682 hp on dyno--in car made 587 hp at the tire with a TKO 5 spd,,,Did a 360 with Eddy heads small cam made 402 hp and in car made 312 @ tire. J.Rob
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Your anecdotes seem right sub 20% for manuals and mid-low 20s for Autos
471BB+6speed--14% drivetrain loss. Sounds right for a MANUAL
360--22% drivetrain loss Sounds right for a Auto

But the OPs supposed 34% drivetrain loss seems a bit off as long as its not an automatic 4x4.


Doesn't matter if its +/- 20hp. Headers and intake will be a damn good upgrade especially in $$/hp.
 
Stirring the pot here but not for evils sake....

Was the engine tested without a mechanical water pump?
Alternator (charging a system or not?)
P/S pump being driven by belt?
A/C condenser up top? I know there a zero HP loss until there actually pumping.
Smaller or larger dyno headers rather than street in car headers?

If the engine was naked, then adding the accessories on afterwards and then coupled with the trans and converter if an auto, length of driveshaft, size of ring and pinion, tire size height width etc...

Ya’ll get the picture.
 
and I must add there can be a big difference from testing with an air filter, engine driven water pump and fan, alternator, power steering, mufflers etc. - about 50 horse
 
Marcohotrod said:
and I must add there can be a big difference from testing with an air filter, engine driven water pump and fan, alternator, power steering, mufflers etc. - about 50 horse
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Exactly! I didn’t even mention air filtration but engine masters has a hilarious filter test episode that’s worth the watch!
 
Biggest problem I see here is that Glenn is going back and forth between 2 carbs and says one is more responsive than another. That instantly tells us he doesn’t have a proper fuel tune.

Glenn, gotta keep tuning these things. Preferably on a warm, high pressure day. You may be missing potential power just from your carb tune. Before you buy anything to bolt on, you have got to get your tune under control and make it rich at wot. If you’re stoichiometric or lean or too rich, you’re leaving power and efficiency behind. Best tool to tune with is an afr meter. They’re relatively cheap these days and you’re going to have to retune the carb after any bolt on anyways. So, it’ll save you time as well.

You also mentioned you have about 10k miles on this. That’s significant enough to need a good clean up of the valves from heavy coke deposits. There are many ways to do this and many products. I use water and slowly dump in a pint on a warmed up engine at about 3000rpm.
 
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I don’t think fuel line size is an issue here. Just the possible state of tune between the two carbs and the noticeable difference in performance esteem the Avenger and a DP.

The Avenger carbs are known to have an issue with there secondary opening bogs.

For myself, I would use the 750 dp with a small block 4spd performance car. Tune the smack out of it!

Also now that we know wha cam is in there, even though I wasn’t initially to keen on a 3.23 - 3.55 gear change, I will now fillip and say that would be an excellent choice and not a 3.7- gear.
 
RAMM said:
No its not. I've followed very closely MANY engines ('cuz I'm interested in this stuff) I've built and dynoed (SF-902) over the years when they wind up on the rollers or even better a chassis dyno that bolts up to the wheel hubs (my fave). They typically put down about 90-100 hundred HP less than what the engine dyno shows. He's bang on with his 340 hp estimate--I've also tested 340's that are similar to the OP's and they make 340-360 hp everytime. It scales up and down very consistently--I built a 471 BB 682 hp on dyno--in car made 587 hp at the tire with a TKO 5 spd--that's pretty close I'd say. Did a 360 with Eddy heads small cam made 402 hp and in car made 312 @ tire. J.Rob
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You'd be the only one getting that much drive train loss. If you think that essentially stock 340 is making that HP you can buy that.

He doesn't have a 33% drive train loss. Don't lie to him. Take it to the track and watch it MPH like it has 295-300 HP because that's what it has.
 
crackedback said:
Total BS HP claims in that article. No way does a stock headed 340 and an xe268H camshaft make 390hp... LOL NO WAY, NO HOW!!! 350hp if it's lucky!

Been beat to death in here so many times and I'll say it every time that POS article comes up. Much like many of the HP claims that have been pushed by that mag over the years... 600+ HP 3500 pound cars running 120mph... yep that's about right. :) Get the F outta here.
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Yeah BS is the word, I'll give some on track hp no's with my 340>
3600lbs stock '71 340 Cuda, 2.02 heads, ally dual plane, 750DP, .484 purple hyd. 1.5/8" hdrs, = best of 101mph = 303fly hp.
Add> Holley Strip Dominator int., DC.590 purple sft cam, 1.75" race hdrs, 850DP = best of 108mph = 373fly hp.
 
yellow rose said:
You'd be the only one getting that much drive train loss. If you think that essentially stock 340 is making that HP you can buy that.

He doesn't have a 33% drive train loss. Don't lie to him. Take it to the track and watch it MPH like it has 295-300 HP because that's what it has.
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Sorry RAMM. What YR said. For an engine that was totally gone through and has a .500" lift cam it's down on power. Could be tuning. Could be something else. It sure isn't the calculations. If there's a chassis dyno losing 30+% because of driveline loss the dyno's broken.
If it were me, and I owned the car, and saw the cam card, I would be tuning the hell out of it and if it didn't improve digging into it over the winter.
 
moper said:
Sorry RAMM. What YR said. For an engine that was totally gone through and has a .500" lift cam it's down on power. Could be tuning. Could be something else. It sure isn't the calculations. If there's a chassis dyno losing 30+% because of driveline loss the dyno's broken.
If it were me, and I owned the car, and saw the cam card, I would be tuning the hell out of it and if it didn't improve digging into it over the winter.
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I don't think we can say anything about it at this point. Its a dyno number which in my book is really only useful for comparing to itself (until proven to correspond with something else).

yellow rose said:
Take it to the track and watch it MPH like it has 295-300 HP because that's what it has.
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Hot Metal said:
I'll give some on track hp no's with my 340
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I agree that's the type of performance I'd expect at the track. We ran a best of 99.5mph with my 3450 lb Barracuda; 340 with Compcam's H280 (.480 lift), Street dominator, 340 exhaust manifolds, Stock12" air cleaner (but K&N filter).
That setup showed 240 to 250 rear wheel Hp on a Dynojet depending on which correction factor you want to go by. (trans 727 with T/A converter - 3000 rpm stall)

I've also had opportunities with my new engine to use the same chassis dyno , along with two others dynojets. One was so different it wasn't even funny - or useful. Something wrong with the setup or operation. Dunno, don't care. All I care about is understanding the changes made to my setup and tuning.

That said, if the OP is really most interested in the Hp on the dyno, far be it from me to change his desires! That is what some people like to do.
IMO its only IF he's says he's interested in some sort of driving test is all of this relevant. By driving test I mean any sort of use that requires high Hp such as standing 1/4 mile or mile, or a long distance high speed timed event like our Silver State.
 
moper said:
Sorry RAMM. What YR said. For an engine that was totally gone through and has a .500" lift cam it's down on power. Could be tuning. Could be something else. It sure isn't the calculations. If there's a chassis dyno losing 30+% because of driveline loss the dyno's broken.
If it were me, and I owned the car, and saw the cam card, I would be tuning the hell out of it and if it didn't improve digging into it over the winter.
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I don't actually care what the percentage is--I have very little faith in chassis dynoes anyways--they are only a comparator at best. As usual communicating over the internet is a clusterfuck. My point was that my observations are just what I said--about 90-100hp less on a chassis dyno than an engine dyno-BFD. I've seen extreme examples of a chassis dyno showing 150-200 HP less than an engine dyno. What I haven't seen is only a 50 hp loss ever.

Besides the OP states that he doesn't really know much about the engine and judging from that cam card if a 340 can't make 1hp/ci I'd be VERY disappointed. J.Rob
 
RAMM said:
I don't actually care what the percentage is--I have very little faith in chassis dynoes anyways--they are only a comparator at best. As usual communicating over the internet is a clusterfuck. My point was that my observations are just what I said--about 90-100hp less on a chassis dyno than an engine dyno-BFD. I've seen extreme examples of a chassis dyno showing 150-200 HP less than an engine dyno. What I haven't seen is only a 50 hp loss ever.

Besides the OP states that he doesn't really know much about the engine and judging from that cam card if a 340 can't make 1hp/ci I'd be VERY disappointed. J.Rob
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One reason why wheel dynos produce lower than expected numbers is turning the water pump, actually using headers for the car and the same carb and ignition.

An engine dyno will produce just as shitty results using a dyno carb, ignition, headers and the dyno water pump. Engine dyno testing without the same **** you use in the car is idiotic, unless you are trying to find as issue. All it does is cause people to doubt the results.
 
hux340 said:
Hi All,
I've got a 71 Dodge Demon 340. Don't know what's been done to the motor as it was rebuilt before I bought it. Seems very strong though & with maybe 10,000 miles on it. We put it on the dyno recently & it's getting 340 hp at the flywheel. I would like to get some extra hp without tearing down the motor. Has no after market mods on it besides a 670 holley street avenger. Was looking at doing the following -
1. Alloy Heads
2. Dual plane alloy intake manifold &
3. Headers (or as we call them here in Aust. extractors).
Not sure about a cam change as I don't want to sacrifice torque which it's got plenty of.
With the alloy heads I would like them to fit under the factory rocker covers. I will also paint the inlet manifold the hemi orange. Trying to keep the engine bay as original as possible.
If I do the above what hp increase would I see?
Cheers,
Glenn.

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Lose that carburetor, it's air bleeds are too small, nothing you can easily do to fix it.
Get a quick fuel/Holley hp/proform 700-780 dbl pumper to start.
An edelbrok Rpm dual plane would help.
Headers, yes!

If you get an air fuel meter setup, you'll see.
 
RAMM said:
I don't actually care what the percentage is--I have very little faith in chassis dynoes anyways--they are only a comparator at best. As usual communicating over the internet is a clusterfuck. My point was that my observations are just what I said--about 90-100hp less on a chassis dyno than an engine dyno-BFD. I've seen extreme examples of a chassis dyno showing 150-200 HP less than an engine dyno. What I haven't seen is only a 50 hp loss ever.

Besides the OP states that he doesn't really know much about the engine and judging from that cam card if a 340 can't make 1hp/ci I'd be VERY disappointed. J.Rob
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Completely agree, I've seen it.
 
yellow rose said:
One reason why wheel dynos produce lower than expected numbers is turning the water pump, actually using headers for the car and the same carb and ignition.
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Another reason besides water pump, air cleaner, power steering, drive train dadada is wheel slippage on a chassis dyno. I would be very surprised when there was NO loss at all...
Just my 2 cents.
 
Why does everyone except RAMM think that drivetrain loss is a fixed percentage? Say I have a stock 318 that makes 150 HP . At say 22 percent loss I would lose 33 horsepower. Now if I build a mild 360, and because of budget, have to use the same drivetrain. We will say I internally balanced the the 360 so I even use the same converter. If my 360 makes 320 HP and I still have a 22 percent loss, now I would lose 70 horsepower from the same drivetrain! To me, that is just faulty thinking.
 
I don’t think it is a fixed number but in general numbers are an OK assumption. Like an engine build, two identical engine equipment wise can turn out to different graphs. Same holds true for the equipment used on the engine and behind it. IMO, a general rule of thumb is a certain amount of power lost for useage of certain equipment.
 
Mopar Sam said:
Why does everyone except RAMM think that drivetrain loss is a fixed percentage? Say I have a stock 318 that makes 150 HP . At say 22 percent loss I would lose 33 horsepower. Now if I build a mild 360, and because of budget, have to use the same drivetrain. We will say I internally balanced the the 360 so I even use the same converter. If my 360 makes 320 HP and I still have a 22 percent loss, now I would lose 70 horsepower from the same drivetrain! To me, that is just faulty thinking.
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Engine all hooked in a car is different and has many variables to account for accessory wise, working condition and also slippage be it tire or trans etc.
 
rumblefish360 said:
I don’t think it is a fixed number but in general numbers are an OK assumption. Like an engine build, two identical engine equipment wise can turn out to different graphs. Same holds true for the equipment used on the engine and behind it. IMO, a general rule of thumb is a certain amount of power lost for useage of certain equipment.
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I guess I should not have used the word " fixed". I just think people get too caught up in percentages as a blanket rule. As my examples above point out. Lets look at it another way. If the drivetrain above cost, say., 70 horespower at 4500 RPM there would be a huge percentage differance between the 2 engines. If the 318 made it's peak 150 at 4500 RPM and lost 70 through the drivetrain that is a around 47 percent loss. If the 360 was making 250 horsepower at the same 4500 RPM , the same 70 horespower loss is 28 percent.
 
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