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HP pondering - 271 or 306 HP

Discussion in '1965-1970 Shelby Mustang GT350 & GT500' started by KenAsh, Jun 4, 2008.

  1. Jun 4, 2008 #1
    KenAsh

    KenAsh Member

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    Hi,
    This question has plagued me for a few years. Back in the day, the early GT cars were touted as having either 271 or 306 HP, depending on the tune, I guess. Knowing today what we know about heads (small'ish valves, cam), induction, has any of this been documented? having dynoed my "warmed" up 333 mustang, I will assume these claims were flywheel stabs, obviousley.
     
    KenAsh, Jun 4, 2008
    KenAsh, Jun 4, 2008
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  2. Jun 4, 2008 #2
    shelby6t5

    shelby6t5 Well-Known Member

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    Re: HP pondering

    The 271 figure was for a "Standard" HiPo, 306 was the claimed HP after the Shelby mods (intake, carb, headers, etc) With a little work it is easy to get 350, and 400 is about what we expect to get from the one being re-built for the 65. Flywheel is correct as well.

    Mike
     
    shelby6t5, Jun 4, 2008
    shelby6t5, Jun 4, 2008
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  3. Jun 4, 2008 #3
    crzy4shelbys

    crzy4shelbys Well-Known Member

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    Re: HP pondering

    The early GT cars were offered with either an A code or a K code engine, advertised at 225HP and 271HP respectively. As Mike stated, the 306 HP number was associated only with the GT350 Mustangs (Shelby's), which was a further modified K code engine (started life at 271HP). You are absoultely correct that engine tuning has come a long way since then, but things have also gotten a lot more complicated (smog equipment, exhaust systems, etc.). Things were much simpler then. Aggressive cam, tall intake with a four barrel and some headers could make a respectable amount of power and there wasn't all sorts of ARB regulations to deal with. The Shelby modified engines also weren't as well mannered as newer cars. They were loud and rough.

    It only takes driving a solid lifter 289 once to believe the numbers were either accurate or very close. Of course every engine will dyno a little differently, but I don't think the numbers were very far off (at the flywheel as Mike stated).

    Josh
     
    crzy4shelbys, Jun 4, 2008
    crzy4shelbys, Jun 4, 2008
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  4. Jun 4, 2008 #4
    KenAsh

    KenAsh Member

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    Re: HP pondering

    Hey guys,

    I do agree with alot of what your saying. In the late 60's early 70's I was an avid SCCA racer. We saw many of those rough riding "B" production shelbys in those days. One of the guys who frequented our shop owned a 350GT, who'd a thunk, they would have the kind of following they have today.
    Still, I would like to see dyno specs on a GT 350, to see the HP, torque, AFR graph. This would "make or break" my beliefs in those numbers?
    The 338 RWHP, I get, is running 1.94/1.60 valves, 600 CFM Eddy, TriYs, 2.5 "X" exhaust, through a c4, no less, and a custom designed Hyda roller cam.
    Thanks for your replies.
    ^_^
     
    KenAsh, Jun 4, 2008
    KenAsh, Jun 4, 2008
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  5. Jun 4, 2008 #5
    crzy4shelbys

    crzy4shelbys Well-Known Member

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    Re: HP pondering

    Hi Ken,

    With the kind of horsepower you're making AT THE REAR WHEELS, that'd be a big increase over the old Shelby's. You didn't state what kind of rear end you have, but for a 64 1/2 with the power you're talking about, I'm guessing you've slipped in a 9"? Those things are bullet proof as we all know, but they are also major power robbers in terms of frictional horsepower loss. If you're running an 8" or a modern 8.8", you'll see a lot more of that flywheel HP making it to the rear wheels. Back to the 9", though... assuming that's what you're running, those are some very impressive numbers. Do you have any pictures to share?

    Like you, I'd be curious if anyone has done any dyno pulls on a "stock" Hipo and/or a Shelby modified Hipo rebuilt to original specs.

    Josh
     
    crzy4shelbys, Jun 4, 2008
    crzy4shelbys, Jun 4, 2008
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  6. Jun 4, 2008 #6
    KenAsh

    KenAsh Member

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    Re: HP pondering

    Hi Josh,

    Actually, currently, I'm running a Currie built 8" 3:25 torque lock rear, or whatever they call their posi units. Although I have a huge amount of torque, this rear has not showed any signs of failure...."yet". I'm pretty easy on my cars, though. I have a 3:55 posi waiting in the wings. With the 3:55 at 70 mph, I'll be right at the start of my power band which is 3200 RPM, or so. One of the ideas, I've been beating around is adding a "GV" (GearVendor under/over drive) unit to my C4. This will offer 3 additional gear ratios for a total of 6 including the 3 in the C4. But, I need to see how it will fit in my cvt tunnel with that body tie plate there and the "x" of my exhaust sysem routed through that tunnel area.
    I'm happy to share any of my findings, fixes, breakages etc.:thumbsup:
    I've added a couple of pics. Being new to this forum, Im not sure if they'll post OK.
     

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    KenAsh, Jun 4, 2008
    KenAsh, Jun 4, 2008
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  7. Jun 4, 2008 #7
    shelby6t5

    shelby6t5 Well-Known Member

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    Re: HP pondering

    Ken,
    Very nice ride. Love Poppy and Rangoon cars.
    The one thing I would change would be the Monte Carlo bar (the ones with the bend like yours are really more for show - the bend is the flex point, unlike the straight units), but it looks like you would have clearance issues with the dist cap.
    Are you driving up to SAAC 33 in August?

    Mike
     
    shelby6t5, Jun 4, 2008
    shelby6t5, Jun 4, 2008
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  8. Jun 4, 2008 #8
    crzy4shelbys

    crzy4shelbys Well-Known Member

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    Re: HP pondering

    Ken,

    That 3.55 will make a big difference when you put it in. I'm running a 9" with 3.89 gears in my GT coupe. I have a T-5 in it so I can keep the RPM's at a decent level on the freeway. That tunnel can be restrictive, that's for sure. When I was looking around for a 5 speed I found a good deal on a TKO, but when I researched it more I found out the crossmembers that are designed to put a TKO in a '65 without cutting the tunnel put the drivetrain at an unacceptable angle, so I had to pass on it and go with the T-5. I wasn't really looking to cut up the trans tunnel in the swap. The coupe's just a fun driver. I've heard similar stories about some of the AOD units, but a gearvendor unit might fit in there okay.

    Nice pic's. You did the galley up right... that's a nice detail.

    Josh
     
    crzy4shelbys, Jun 4, 2008
    crzy4shelbys, Jun 4, 2008
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  9. Jun 4, 2008 #9
    KenAsh

    KenAsh Member

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    Hey Mike,
    Very observant! Yes, I used the curved bar for those reasons, when I was tuning. I have the straight bar, as well. I have no plans to pull the cap, so I should go ahead go back to the straight. But, at the same time, I haven't challenged the front end suspension lately with a bunch of twisties. Although, I set it up for road racing in the event I have to make a few "moon-shine" runs. :guitar:
    What where is SAAC 33?


    By the way, that Poppy Red was covered by two subsequent coats of paint - Caspian Blue, and me thinks, Rangoon Red. When I purchased it in 1984 it was red with a black interior and top. It should have been Poppy red with a white interior. So, there were major restoration issues.
    Thanks for the nice comments. But, then again, our mustang community is always pleasant to converse with.
    :D
     
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    KenAsh, Jun 4, 2008
    KenAsh, Jun 4, 2008
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  10. Jun 4, 2008 #10
    shelby6t5

    shelby6t5 Well-Known Member

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    Re: HP pondering

    go to www.SAAC.com

    Millville NJ should not be too far for you, just over the Del Bridge.

    Mike
     
    shelby6t5, Jun 4, 2008
    shelby6t5, Jun 4, 2008
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  11. Jun 4, 2008 #11
    KenAsh

    KenAsh Member

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    Re: HP pondering

    Hey Mike,

    Yes , I located Millville, NJ.It's about 2 1/2 hours from me. Any folks caravaning from DC, AA County, Md, or?
    :)
     
    KenAsh, Jun 4, 2008
    KenAsh, Jun 4, 2008
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  12. Jun 7, 2008 #12
    GT52

    GT52 Active Member

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    Because horsepower ratings were notoriously unreliable, the NHRA "factors" horsepower ratings for virtually every engine to level the playing field in Stock and Super Stock competition. These numbers are available on the NHRA.com website. They are extremely accurate for comparing one engine to another, and fairly closely approximate the SAE gross horsepower you'd expect to get by testing...not to be confused with the SAE net numbers used by manufacturers today. The Mustang 289/271 is factored at 271 hp, and the Shelby 289/306 is factored at 306 hp...exactly as they were originally rated. If you wander around the site you'll see that that is often not the case.
     
    GT52, Jun 7, 2008
    GT52, Jun 7, 2008
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