1974 360 horsepower rating

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Dan the man

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I've been doing research on the 1974 duster / dart sport with the 360. From what I've read the 360 in 1974 was rated at 245 horsepower at 4,400 rpm's, is this over rated or under rated or accurate? The reason for this is I've been looking at a 1974 duster with the possibly of rebuilding the 360 for pure stock muscle car drag racing. The engine has to be correct for the year / horsepower claimed, heads can not be ported, gasket matched, stock size valve's have to be run. I haven't been able to find out if a comp valve job is allowed but I doubt it. Compression ratio can be 1.5 points over stock and I have found two different ratios for the '74 360, 8.4:1 and 8.7:1. Cam has to have the stock lift and duration. Factory exhaust manifolds. Curve kit is allowed as is a high performance coil as long as it is the same shape and color as the original and has to be mounted in the factory location. What horsepower would be possible with only a increase in the compression ratio and somebody who has great tuning skills? Thanks everyone for any help and advice.
 
GTX JOHN said:
NHRA rates this engine @ around 300HP
The 245 was a net rating in 1974
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thanks for confirming my suspicions, john. i had remembered reading somewhere that they were rated somewhere in the 290's and i just couldn't recall where.
 
Dan the man said:
I've been doing research on the 1974 duster / dart sport with the 360. From what I've read the 360 in 1974 was rated at 245 horsepower at 4,400 rpm's, is this over rated or under rated or accurate? The reason for this is I've been looking at a 1974 duster with the possibly of rebuilding the 360 for pure stock muscle car drag racing. The engine has to be correct for the year / horsepower claimed, heads can not be ported, gasket matched, stock size valve's have to be run. I haven't been able to find out if a comp valve job is allowed but I doubt it. Compression ratio can be 1.5 points over stock and I have found two different ratios for the '74 360, 8.4:1 and 8.7:1. Cam has to have the stock lift and duration. Factory exhaust manifolds. Curve kit is allowed as is a high performance coil as long as it is the same shape and color as the original and has to be mounted in the factory location. What horsepower would be possible with only a increase in the compression ratio and somebody who has great tuning skills? Thanks everyone for any help and advice.
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Here's a low cr 360 at various states of modifications, it starts off with a fully stock 2bbl to stock 4bbl before doing upgrades. But doesn't do with 340 cam would have to guesstimate.

 
dan, i'm *assuming* you've seen this: https://gmauthority.com/blog/2022/1...974-plymouth-duster-360-in-a-drag-race-video/

in the article they give the weight of the duster and if you run the ET/MPH/weight thru a drag calculator that maths out to 260 net horse

on back to back to back runs he averaged low 14's with a 13.8 at 99 break out.

so i'd say somebody who really knows their nuts and bolts could probably tune themselves to possibly 300 plus and probably mid 12's with some chassis work.
 
I had to read this post because I had a factory 74 360 Duster 4 speed (I wish I never sold it) that was pretty stock. No internal engine mods, stock intake & exhaust manifolds, even the factory Thermoquad carb. That car was pretty fast & with street tires on it, I got it to run 14.11 in the quarter mile at Atco, with poor traction in 1st & 2nd gear, so with good traction & a better driver (I was no professional drag racer that's for sure) I think it would run high 13s no problem. Closer to 300 hp, I would agree with that. They certainly had the potential to make that if tuned well in their stock, as delivered form, IMHO.
 
junkyardhero said:
thanks for confirming my suspicions, john. i had remembered reading somewhere that they were rated somewhere in the 290's and i just couldn't recall where.
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The factory rating was 275 through 1971 but the 340-6bbl T/A & AAR was 290. It's common knowledge that they were very conservative numbers. In 1972 the 340 lost compression and went to smaller intake valves. The factory started using a "net" rating which was advertised at 240. The '74 360 was rated at 245 which had the 340 cam, springs & heads, 20 more cubic inches and a bigger Thermoquad. Still debatable ratings for both.
 
junkyardhero said:
dan, i'm *assuming* you've seen this: https://gmauthority.com/blog/2022/1...974-plymouth-duster-360-in-a-drag-race-video/

in the article they give the weight of the duster and if you run the ET/MPH/weight thru a drag calculator that maths out to 260 net horse

on back to back to back runs he averaged low 14's with a 13.8 at 99 break out.

so i'd say somebody who really knows their nuts and bolts could probably tune themselves to possibly 300 plus and probably mid 12's with some chassis work.
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That's my duster in the video. I was having carb issues during the shootout, no secondaries on two of the runs. Car had actually gone 13.59@100 that morning. I had run 103 mph the day before. Its a new engine so I'm still sorting it out especially launch technique. The 74 360 duster and dart sport are probably the cheapest purestock mopar you can build from scratch. Dan-If you have any questions I'd be happy to answer them.
 
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There’s some good potential there with 10.2: and 974 heads with the e58 360 cam. Is extrusion honing of the ports, intake, and exhaust manifolds allowed?
 
E58 360 4 Bbl cam is reported to have the same specs as the ‘68 340 four speed cam.

360

4 barrel

Hydraulic

430/444

268/276
 
Seth Jones said:
That's my duster in the video. I was having carb issues during the shootout, no secondaries on two of the runs. Car had actually gone 13.59@100 that morning. I had run 103 mph the day before. Its a new engine so I'm still sorting it out especially launch technique. The 74 360 duster and dart sport are probably the cheapest purestock mopar you can build from scratch. Dan-If you have any questions I'd be happy to answer them.
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Thanks, I appreciate it and I'm sure that I will have questions.
 
Garrett Ellison said:
There’s some good potential there with 10.2: and 974 heads with the e58 360 cam. Is extrusion honing of the ports, intake, and exhaust manifolds allowed?
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NO porting allowed of any kind. 74 360 uses 587 heads and 340 auto cam. 9.9:1 is the compression limit as the factory rating was 8.4:1
 
Seth Jones said:
That's my duster in the video. I was having carb issues during the shootout, no secondaries on two of the runs. Car had actually gone 13.59@100 that morning. I had run 103 mph the day before. Its a new engine so I'm still sorting it out especially launch technique. The 74 360 duster and dart sport are probably the cheapest purestock mopar you can build from scratch. Dan-If you have any questions I'd be happy to answer them.
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Still running a TQ? I remember selling you one years ago when you you were building your car.
 
Yes a 6453 850 TQ. The one I bought from you is the one giving me problems lol! Its been flawless on the old motor but this new engine is giving it fits. We'll get it figured out though.
 
Seth Jones said:
Yes a 6453 850 TQ. The one I bought from you is the one giving me problems lol! Its been flawless on the old motor but this new engine is giving it fits. We'll get it figured out though.
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Glad to hear it was at least ok on the old motor. I was afraid it was the same one I sold you when you said you were having carb problems. :)

What's the new motor? Step it up any?
 
DionR said:
Glad to hear it was at least ok on the old motor. I was afraid it was the same one I sold you when you said you were having carb problems. :)

What's the new motor? Step it up any?
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New motor has KB 107 flat tops .003 in the hole, 9.9:1 calculated. Dwayne Porter prepped 587 heads (1.88's), Mr. Sixpack cam. Nothing special really.
 
Seth Jones said:
New motor has KB 107 flat tops .003 in the hole, 9.9:1 calculated. Dwayne Porter prepped 587 heads (1.88's), Mr. Sixpack cam. Nothing special really.
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That 13.84 et in that with 3.55 gears is pretty impressive. I’m thinking of a few factory optioned 340 cars optioned with 3.91 gears that would be very competitive in that class.
 
Does the cam have to be 100% stock or just have to have the same lift advertised duration lsa but can be ground with more aggressive profile ? compression generally gives 3-4% for every point of cr, with a bias to gains at lower end of cr like going 8.4 to 9.9 than 12.4 to 13.9 the hp gain % is slightly higher for the !st. Valve job and tuning is probably where it's at engine wise, anything you can do to lower friction, pumping loss, efficiency etc..
It's all the little things you can do to add up to improve e.t.s, probably more comes down to the rest of the car, drivetrain suspension etc.. since performance is somewhat fixed.
 
273 said:
Does the cam have to be 100% stock or just have to have the same lift advertised duration lsa but can be ground with more aggressive profile ? compression generally gives 3-4% for every point of cr, with a bias to gains at lower end of cr like going 8.4 to 9.9 than 12.4 to 13.9 the hp gain % is slightly higher for the !st. Valve job and tuning is probably where it's at engine wise, anything you can do to lower friction, pumping loss, efficiency etc..
It's all the little things you can do to add up to improve e.t.s, probably more comes down to the rest of the car, drivetrain suspension etc.. since performance is somewhat fixed.
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this type racing is where the adage of ounces add up to pounds is really magnified. all the little inane details suddenly become more items of interest.

i'm not sure how tightly controlled the cam is beyond lift & duration, but if i were competing you can bet your sweet patootie i'd have some kind of a custom grind in there.
 
Beyond the easy/obvious

If you do a 100 things that gain average 1/2 a hp that's 50 hp, same with the rest of the car 100 things that gain 0.01 of a second gains a second in the quartermile problem is each mod could cost an average of hundreds $$ each :)
 
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junkyardhero said:
this type racing is where the adage of ounces add up to pounds is really magnified. all the little inane details suddenly become more items of interest.

i'm not sure how tightly controlled the cam is beyond lift & duration, but if i were competing you can bet your sweet patootie i'd have some kind of a custom grind in there.
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No custom grind cams are allowed. Interior has to be as it left the factory and the spare tire and bumper Jack has to be in their correct location. Even the radio has to work. No cylinder head porting is allowed, stock size valve's are required, I don't think that a comp valve job is allowed. Rocker arm's have to be factory stamped steel or cast iron so rocker arms from a 273 are allowed. A maximum of a 0.070" over bore is allowed. Heads can be milled and aftermarket pistons are allowed to help with the increase in the compression ratio which is 1.5 over factory. The actual cost isn't much more than doing a rebuild because of the Strict rules. The biggest cost most likely would be the cylinder heads since stock valve size has to be used would mean having to replace the intake and exhaust valve seats. Carburetor has to be stock but jet sizes can be changed. Ignition system, curve kit is allowed as well as a performance coil as long as it's the same color and size as the factory coil. Any gear ratio is allowed and the converter can't be any smaller than 1" of the stock converter.
 
Dan the man said:
No custom grind cams are allowed. Interior has to be as it left the factory and the spare tire and bumper Jack has to be in their correct location. Even the radio has to work. No cylinder head porting is allowed, stock size valve's are required, I don't think that a comp valve job is allowed. Rocker arm's have to be factory stamped steel or cast iron so rocker arms from a 273 are allowed. A maximum of a 0.070" over bore is allowed. Heads can be milled and aftermarket pistons are allowed to help with the increase in the compression ratio which is 1.5 over factory. The actual cost isn't much more than doing a rebuild because of the Strict rules. The biggest cost most likely would be the cylinder heads since stock valve size has to be used would mean having to replace the intake and exhaust valve seats. Carburetor has to be stock but jet sizes can be changed. Ignition system, curve kit is allowed as well as a performance coil as long as it's the same color and size as the factory coil. Any gear ratio is allowed and the converter can't be any smaller than 1" of the stock converter.
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You sure you can’t run a custom cam? I thought there was a lift rule and that was it.
 
Dan the man said:
No custom grind cams are allowed. Interior has to be as it left the factory and the spare tire and bumper Jack has to be in their correct location. Even the radio has to work. No cylinder head porting is allowed, stock size valve's are required, I don't think that a comp valve job is allowed. Rocker arm's have to be factory stamped steel or cast iron so rocker arms from a 273 are allowed. A maximum of a 0.070" over bore is allowed. Heads can be milled and aftermarket pistons are allowed to help with the increase in the compression ratio which is 1.5 over factory. The actual cost isn't much more than doing a rebuild because of the Strict rules. The biggest cost most likely would be the cylinder heads since stock valve size has to be used would mean having to replace the intake and exhaust valve seats. Carburetor has to be stock but jet sizes can be changed. Ignition system, curve kit is allowed as well as a performance coil as long as it's the same color and size as the factory coil. Any gear ratio is allowed and the converter can't be any smaller than 1" of the stock converter.
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Yes cause everyone follows the rules a 100%, depends how they check things ? Eg. I doubt they pull your cam a put it on Cam Analyzer.
 
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