Horsepower Estimate?

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crackedback said:
The magazines create unrealistic expectation. An xe268 will likely be a high side of 1.1hp/ci stick in an oem style/stock headed 340-360 with a great tune up.

If I told you Billy Barty was 7 feet tall and had a tape out (dyno) that showed he was 7 feet tall, would that be ok? What if you met him and he was really 3ft 9in. Just because it's the data you see or read doesn't make it valid, nor supportable when other data shows the build is way off base.
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That's all the info most people have access to, millions upon millions only knows those numbers, majority becomes the standard, officially or unofficially. If your 7 feet was equal to my 3.9 feet we can convert for that. So if a magazine 390 hp equals your 360 hp we can convert for that. All I'm say most don't have access or knowledge of your dyno numbers better or not they ain't the one most are gonna go by.
crackedback said:
I've said it many times, built a couple 360's with a xe268, rpm/ld, 750dp, dougs/tti/5204's and good OEM heads (equivalent to the dyno derby pieces) and NONE of them made more than 360hp. NOT ONE.
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I'm not arguing they don't, I would agree that that sounds like an reasonable number for that combo.
I don't think of a xe268h cam as anything more.
crackedback said:
I'm not going to engage in this with you, carry on if you like.

Selling parts is job one for them.
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Yes magazine and such obviously rely on the aftermarket, there glorified ad's for the most part.
 
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All I know if I asked builder to build me a run of a mill 400 hp sbm and he asked what was that to me and I'd say Around 10:1, 235° cam, air gap, 1 3/4" headers, 750 and like 225 cfm heads and the builder said that only a 375 hp engine on his dyno, then I'd I want your 375 hp engine then, what I wanted hasn't changed whatever dyno numbers you give it.
 
273 said:
All I know if I asked builder to build me a run of a mill 400 hp sbm and he asked what was that to me and I'd say Around 10:1, 235° cam, air gap, 1 3/4" headers, 750 and like 225 cfm heads and the builder said that only a 375 hp engine on his dyno, then I'd I want your 375 hp engine then, what I wanted hasn't changed whatever dyno numbers you give it.
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Cubic Inch Displacement ?
 
autoxcuda said:
Cubic Inch Displacement ?
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I don't see cubic inch as an automatic gain in hp.

That's the basic Magazine 400 hp 318 build recipe and most magazine 400 hp 340/360 seem to be similar too and even engines from other manufacturers, even seen similar spec NA 400 ish hp 4 cylinders.
 
Sounds to me like someone wanted to build a blower motor got halfway there and quit. Many years ago I built one and had to drop the cp down to at least 8.5 to 1. went a full 8to1 ran it three times before I sold it. Was great on strip no good for street.
 
mad mike said:
Sounds to me like someone wanted to build a blower motor got halfway there and quit. Many years ago I built one and had to drop the cp down to at least 8.5 to 1. went a full 8to1 ran it three times before I sold it. Was great on strip no good for street.
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I believe the compression the original posted in his 73 340 is the original compression for that motor.
 
Ok I did not know they built a motor with that low of a compression ratio. Thank you for informing me.
 
pittsburghracer said:
Why is what??? You gotta give me more than that as I’m not going back and rereading this post. Once was hard enough.
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" it’s not hard to make a stock crank 340 or 360 run low 10’s. But you’re not doing it with a small hydraulic cam."

I was just asking about this quote, nothing more. I thought it was enough to stand on it's own.

I thought it was possible (and historically typical with hydraulic flat tappet cams), but honestly I totally missed the " 'SMALL' <part of the> hydraulic cam."
I was curious as to what loose-guess size cam would get an A body owner in that ball park.
 
3RD Duster said:
Anyone want to give me a horsepower estimate? This is all I know about the 340.
1973 block
Bored 30 over
J Heads (probably not ported)
New pistons and rods (no idea what they are)
New lifters (?)
8.5:1 compression (could be higher...not sure about head gasket thickness)
474/280 purple cam
RPM Air Gap intake
Holley 650
Hooker Headers

I probably won't be able to answer any other questions until I can find the guy who built the engine. Thank you.
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Sorry, but in my humble opinion, we don’t have enough data, and you said that some of it was second hand. J heads can accept 2.02 heads, but I believe they came with 1.88 intakes. It could be anywhere between 250 and 300HP.
4mulas said:
250-260 ish
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Probably pretty close, maybe a bit higher.
273 said:
Mid high 300's.
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I kind of doubt that. With low compression and unknown valve sizes
273 said:
So it's got less than stock ?
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Probably; with low compression and smaller valve J heads.
 
harrisonm said:
I kind of doubt that. With low compression and unknown valve sizes

Probably; with low compression and smaller valve J heads.
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That's fine, everyone has their own opinions, I think your over valuing cr and 2.02 valves on a mild build, guess we'll never know :)
 
273 said:
That's fine, everyone has their own opinions, I think your over valuing cr and 2.02 valves on a mild build, guess we'll never know :)
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That is the problem with these "guess my horsepower" questions that have incomplete data.
Isn't there a formula where you can estimate the HP based on a quarter mile run given the car's weight and other factors like gear ratio and .......
 
harrisonm said:
That is the problem with these "guess my horsepower" questions that have incomplete data.
Isn't there a formula where you can estimate the HP based on a quarter mile run given the car's weight and other factors like gear ratio and .......
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True, best you can do is best guess based on what similar engines generally dyno.
 
One of the biggest variables is how is it tuned, just cause it can make 340 or 290 or whatever hp on the dyno, who knows what hp it's making net in the car, go get it chassis dyno tuned you'll get the most out of that combo and know what hp it's putting to the ground.
 
PRH said:
The motor makes what it makes…….regardless of what the guesses are.
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That we can agree on.
I have a 800hp big block, what will it run. Don't ask me any questions because I don't know.
 
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harrisonm said:
That is the problem with these "guess my horsepower" questions that have incomplete data.
Isn't there a formula where you can estimate the HP based on a quarter mile run given the car's weight and other factors like gear ratio and .......
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Its weight and mph=hp period
Everything else is just about et gears/verter/traction/tunning
mph might change abit if it does you refigure it
you take your weight and mph= hp
Then look up weight and that hp will tell you the quickest et you can run if everything is perfect aka traction/gearing/verter /tunning
At some point when everythings perfect and you get that best et for that mph, at that point you need more power to go quicker
 
a-bodyguy said:
Its weight and mph=hp period
Everything else is just about et gears/verter/traction/tunning
mph might change abit if it does you refigure it
you take your weight and mph= hp
Then look up weight and that hp will tell you the quickest et you can run if everything is perfect aka traction/gearing/verter /tunning
At some point when everythings perfect and you get that best et for that mph, at that point you need more power to go quicker
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These charts and graphs are all ok but there can be things that kinda mess up the numbers. Example my duster with my 422 Indy headed 422 ran [email protected]
[email protected]

My Edelbrock headed 408 has gone [email protected]

My 422 had a solid lifter cam, 4 year old springs, and an 850 carb. This engine was out of steam at or before 1000 foot with my 4:88 gears

My 408 has the same size lift cam but it’s a roller cam. I also upgraded to a 1000 cfm carb. I never have ran it 1/4 mile as every track runs my class 1/8 mile. But it is pulling like a mule up top compared to my 422. I know it would probably run 9.28-9.32 but if you would run the numbers on an 1/8 mile chart I’m thinking the horsepower numbers would be off. So gearing has to be a factor I’m sure. So wouldn’t carb size play into this too.
 
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