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post #1 of 5 (permalink) Old 12-05-2017, 07:02 AM Thread Starter
 
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Frankenmotor :)

I am dealing with a lot of unknowns with my 1965 tripower convertible and wanted to see if you could share your opinions and knowledge.

Essentially I have an unknown motor in my car. It appears to be a 400 with "14" heads and a correct 1965 tripower setup. According to my research the "14" heads with the 400 should be a low compression ~265 hp motor , yet my actual motor feels much much stronger. If I were to guess, I'd say maybe it is ~350 hp. (Motor seems very happy north of 4000 RPM and 5500 feels like it is still pulling.)

Do you know if it is possible to make the "14" heads more like 9.X : 1 compression (milled that much)? Or do you know signs that I should look for to get a guess to the compression ratio ? What about cams - other than pulling the cam, are there any tricks to identify what might be in the motor ? The pistons appear to be flat top.

I really don't want to pull the heads just to calculate an exact CR ratio.

Thanks in advance!

Chris

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #2 of 5 (permalink) Old 12-05-2017, 02:16 PM
 
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Without pulling the '68 model 14 heads & disassembling them, & having a pair of seasoned eyes carefully examine the ports, if they have been ported, will be very hard to tell to extent what head work has been performed. Such a small valve mid 90's cc '68 cyl headed 400 shouldnt run that well up top, instead it would rely on moderate torque to get the job done by 4500 RPM.

For a few decades, it was fairly common to upgrade the late '60's usage 46 & 47 casting heads, as well as '70 model 15 casting heads through proper port & seat work, 2.11-1.77 valves, & conversions to screw in studs. Ive yet to run across a pair of '68 model 14's that received that treatment, but am sure there are some out there. A lot of such upgraded cast iron Dport head work has slowed down over the last 10 years with higher machine shop prices, what was a poor economy, & with so many head choices out there.
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post #3 of 5 (permalink) Old 12-05-2017, 06:11 PM
 
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You do not need high compression to get horsepower gains. There is static compression (actual compression) and there is dynamic compression - the pressure built up within the cylinders based on cam timing.

Comp Cams have several good cams that will boost dynamic compression. My last 400CI build was a '72 engine with 7K3 heads and I used the aftermarket kit cast pistons which were stock compression or possibly less - factory is 8.2 compression.

The 7K3 have the larger valves and I gasket matched the intakes and a 3-angle valve job. Used a Comp Cams Extreme Energy 274 cam. Pulled like a freight train - I was real happy with the cam.

So you might have an aftermarket cam which works with lower compression engines to build up more cylinder pressure and act like a higher static compression engine. The smaller valves will develop more velocity and the engine should be pretty responsive.

So why not leave well enough alone?
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post #4 of 5 (permalink) Old 12-05-2017, 09:08 PM Thread Starter
 
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Originally Posted by Pinion head View Post
Without pulling the '68 model 14 heads & disassembling them, & having a pair of seasoned eyes carefully examine the ports, if they have been ported, will be very hard to tell to extent what head work has been performed. Such a small valve mid 90's cc '68 cyl headed 400 shouldnt run that well up top, instead it would rely on moderate torque to get the job done by 4500 RPM.

For a few decades, it was fairly common to upgrade the late '60's usage 46 & 47 casting heads, as well as '70 model 15 casting heads through proper port & seat work, 2.11-1.77 valves, & conversions to screw in studs. Ive yet to run across a pair of '68 model 14's that received that treatment, but am sure there are some out there. A lot of such upgraded cast iron Dport head work has slowed down over the last 10 years with higher machine shop prices, what was a poor economy, & with so many head choices out there.
Thanks for the help....It definitely is very strong above 4500 so I am guessing there is a cam involved...

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #5 of 5 (permalink) Old 12-05-2017, 09:10 PM Thread Starter
 
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Quote:
Originally Posted by Pinion head View Post
Without pulling the '68 model 14 heads & disassembling them, & having a pair of seasoned eyes carefully examine the ports, if they have been ported, will be very hard to tell to extent what head work has been performed. Such a small valve mid 90's cc '68 cyl headed 400 shouldnt run that well up top, instead it would rely on moderate torque to get the job done by 4500 RPM.

For a few decades, it was fairly common to upgrade the late '60's usage 46 & 47 casting heads, as well as '70 model 15 casting heads through proper port & seat work, 2.11-1.77 valves, & conversions to screw in studs. Ive yet to run across a pair of '68 model 14's that received that treatment, but am sure there are some out there. A lot of such upgraded cast iron Dport head work has slowed down over the last 10 years with higher machine shop prices, what was a poor economy, & with so many head choices out there.
Quote:
Originally Posted by PontiacJim View Post
You do not need high compression to get horsepower gains. There is static compression (actual compression) and there is dynamic compression - the pressure built up within the cylinders based on cam timing.

Comp Cams have several good cams that will boost dynamic compression. My last 400CI build was a '72 engine with 7K3 heads and I used the aftermarket kit cast pistons which were stock compression or possibly less - factory is 8.2 compression.

The 7K3 have the larger valves and I gasket matched the intakes and a 3-angle valve job. Used a Comp Cams Extreme Energy 274 cam. Pulled like a freight train - I was real happy with the cam.

So you might have an aftermarket cam which works with lower compression engines to build up more cylinder pressure and act like a higher static compression engine. The smaller valves will develop more velocity and the engine should be pretty responsive.

So why not leave well enough alone?
Jim - Thanks....I am guessing there may be a cam involved. I want to put the car on the dyno and see where it is. At this point, regardless of the number, I'll probably just drive the tires off it ....Thanks again for your help.

Chris

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
cij911 is offline  
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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