400 motor with 16 or 62 big valve heads - Pontiac GTO Forum
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post #1 of 29 (permalink) Old 01-12-2018, 07:56 AM Thread Starter
 
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400 motor with 16 or 62 big valve heads

I currently have a 400 with 14 heads and the original tri power setup. I have a set of 16 heads from a 68 Firebird - big valves, screw in studs, and small chamber ~72 cc (need to get exact). I also have a set of 62 heads, but have been told the 16s flow better. I would also like to add a camshaft if swapping the heads. (My goal is to get the motor to 350+ hp with a nice broad power curve.) My concern is the compression ratio and 91 octane here in socal.

My questions are:
(1) Can I effectively lower the CR enough with a thick head gasket?

(2) Is there a popular camshaft that would not only make more power but also lower the CR? Any specific recommendations would be great!

(3) If options 1 & 2 won't be sufficient in lowering CR enough (to ~9.25:1), I guess I need to build the bottom end with dished pistons ?

Thanks

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 29 (permalink) Old 01-12-2018, 11:20 PM
 
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Originally Posted by cij911 View Post
I currently have a 400 with 14 heads and the original tri power setup. I have a set of 16 heads from a 68 Firebird - big valves, screw in studs, and small chamber ~72 cc (need to get exact). I also have a set of 62 heads, but have been told the 16s flow better. I would also like to add a camshaft if swapping the heads. (My goal is to get the motor to 350+ hp with a nice broad power curve.) My concern is the compression ratio and 91 octane here in socal.

My questions are:
(1) Can I effectively lower the CR enough with a thick head gasket?

(2) Is there a popular camshaft that would not only make more power but also lower the CR? Any specific recommendations would be great!

(3) If options 1 & 2 won't be sufficient in lowering CR enough (to ~9.25:1), I guess I need to build the bottom end with dished pistons ?

Thanks
All D-port heads with the big valves basically flow the same, so its your choice. Best improvements would be gasket match the intakes & 3-angle valve job. Add ARP 7/16" BB screw-in rocker arm studs and poly-locks.

Do not go with thicker head gaskets -band aide fix. Get the correct dished pistons to give you 9.0-9.3 compression.

Cams with a nice broad power curve will be those like factory - 114 LSA. Narrower LSA will typically narrow the power curve, boost cylinder pressure, and are more "explosive" but run out of steam early.
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post #3 of 29 (permalink) Old 09-19-2019, 07:28 AM Thread Starter
 
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Originally Posted by PontiacJim View Post
All D-port heads with the big valves basically flow the same, so its your choice. Best improvements would be gasket match the intakes & 3-angle valve job. Add ARP 7/16" BB screw-in rocker arm studs and poly-locks.

Do not go with thicker head gaskets -band aide fix. Get the correct dished pistons to give you 9.0-9.3 compression.

Cams with a nice broad power curve will be those like factory - 114 LSA. Narrower LSA will typically narrow the power curve, boost cylinder pressure, and are more "explosive" but run out of steam early.
Jim, I am coming back to this as I have the car pretty much done now and running well. Fundamentally what I am struggling with is what to do with the motor. Currently the motor runs fine - no smoke on acceleration or engine braking, but just is not a monster. The motor appears to be out of a 1968 Catalina (400 with #14 heads) and according to Wallace Racing's site should have a ~8.6:1 CR. I don't have any pinging (that I can hear) using 91 octane and when I did a compression test on the motor the numbers were all low but consistent, so I suspect it is a low compression motor. From what I have read the Catalina had a small cam, although I haven't found details other than what apparent stock replacement cams advertise. Is there really a huge difference between 8.6:1 and 9:1 ?

Given that all D-port heads flow close to the same, why not just replace the HFT cam with a better suited cam for the tri power and displacement and see if I am happy with the power results? It sure seems better (financially), than buying a built motor and heads. Worst case scenario I blow the motor and have to buy the built motor anyway..... I am sure I am missing something....Thanks in advance

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 #4 of 29 (permalink) Old 09-19-2019, 07:49 AM
 
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"... why not just replace the HFT cam with a better suited cam for the tri power and displacement and see if I am happy with the power results?..."


If the heads have press-in studs, you are limited on cam choice. Anything bigger than an 068 clone, such as a Melling SPC-7, is a gamble. And, if the springs are original, you'd need new springs.

https://www.autozone.com/internal-en...07135_705947_0

https://www.ebay.com/itm/Pontiac-V8-...AAAOSwmrlU0mJ9

From a performance standpoint, a 262 Voodoo would probably be best for your low CR 400, to meet your goal. But, with it's steeper ramps, more lift, & stronger springs needed, it would very likely pull some studs.

https://www.lunatipower.com/voodoo-h...8-262-268.html

https://www.summitracing.com/parts/c...oaAgLIEALw_wcB

Some have been lucky, using larger cams, with press-in studs. If I was gonna try to get by with a cam larger than the 068, I might try something like a Lunati 10510312. It has only .454 lift, and the ramps are not as steep as on a Voodoo. And I'd use the stock springs from Ebay, linked above.

Cams like a 744 clone adds more duration, without adding lift more than the 068. But the 744 was designed for high CR engines. Actually the 068 was also used mostly in high CR engines. The only low CR engine the 068 came in was the 455HO, & the only low CR engine the 744 specs were used in was the SD455.

https://www.ebay.com/itm/Engine-Cams...-/292730769560

The Lunati version of the 744 has less duration @ .050 lift, but has more total lift, at .424, and a lower LSA of 110.

https://www.lunatipower.com/factory-...8-301-313.html

If you wanna try .450 lift, here's a possibility. Should make more power in a low CR engine than the 068. But, the ramps don't appear to be quite as steep as the Voodoo ramps.

https://www.summitracing.com/parts/h...w/make/pontiac
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Last edited by bigD; 09-19-2019 at 08:45 AM.
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post #5 of 29 (permalink) Old 09-19-2019, 09:06 AM Thread Starter
 
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BigD - Thanks a ton for all the help. How would I know if I had press in studs. If I recall correctly they appeared to have nuts on the end. (Sorry for the noob question. I really know almost nothing about camshaft design or selection, rocker arms, and/or lifters.)

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 #6 of 29 (permalink) Old 09-19-2019, 09:53 AM
 
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"...How would I know if I had press in studs. If I recall correctly they appeared to have nuts on the end..."

Screw-in studs have a hex that holds the pushrod guide plate down. Press-in studs do not have a hex. The bottoms are smooth all the way into the head. The guide plates are held down by bolts.

Here's a pic of #11 heads with press-in studs. You can see the head of the bolts that hold the guide plates down. The 2nd pic shows how the screw-in stud hex holds the guide plate down.
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Last edited by bigD; 09-19-2019 at 10:12 AM.
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post #7 of 29 (permalink) Old 09-22-2019, 08:57 AM Thread Starter
 
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OK, why not put my big valve #16 heads on with a nice HFT cam and run 50/50 e85/91 octane for an effective octane of ~98 octane ? From what I have read, e85 loves timing and runs cooler too.

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 #8 of 29 (permalink) Old 09-22-2019, 09:20 AM
 
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Originally Posted by cij911 View Post
OK, why not put my big valve #16 heads on with a nice HFT cam and run 50/50 e85/91 octane for an effective octane of ~98 octane ? From what I have read, e85 loves timing and runs cooler too.
The carb must be modified to run E85. So, getting it calibrated correctly for running some mixture of E85 & pump gas might be difficult. If you want more octane, you can either mix in some race gas, or add Torco Accelerator octane booster.

https://www.summitracing.com/parts/t...010t?rrec=true
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post #9 of 29 (permalink) Old 09-22-2019, 09:34 AM
 
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Originally Posted by cij911 View Post
Jim, I am coming back to this as I have the car pretty much done now and running well. Fundamentally what I am struggling with is what to do with the motor. Currently the motor runs fine - no smoke on acceleration or engine braking, but just is not a monster. The motor appears to be out of a 1968 Catalina (400 with #14 heads) and according to Wallace Racing's site should have a ~8.6:1 CR. I don't have any pinging (that I can hear) using 91 octane and when I did a compression test on the motor the numbers were all low but consistent, so I suspect it is a low compression motor. From what I have read the Catalina had a small cam, although I haven't found details other than what apparent stock replacement cams advertise. Is there really a huge difference between 8.6:1 and 9:1 ?

Given that all D-port heads flow close to the same, why not just replace the HFT cam with a better suited cam for the tri power and displacement and see if I am happy with the power results? It sure seems better (financially), than buying a built motor and heads. Worst case scenario I blow the motor and have to buy the built motor anyway..... I am sure I am missing something....Thanks in advance

The #14 heads are press-in studs & small valves. 8.6 compression can be worked with. The draw back will be the press-in studs which will limit your lift. You probably don't want to go more than .440" lift to be safe. Factory lift is .406" and the H-O blueprint manual says that coil bind can occur at .446". Obviously larger lift cams can be used, but changes are in order and you want to use your stock heads "as is."

To take advantage of the 8.6 compression ratio, you want to build up Dynamic Compression. This adds more cylinder pressure in loosely the same way a higher compression ratio does. The factory cam in your engine now is very mild - and 7.6 seconds for the 0-60MPH most likely reflects that. The valve overlap is at 47 degrees - not a very "hot" cam.

You can use the Wallace Dynamic Compression Calculator to get an idea of what it will take to raise the Dynamic Compression. However, this may require a custom ground cam. I did play around with a couple cams offered on line, but nothing really fit the bill with the limits of the stock heads.

I went with a Comp Cams XE cam on my previous 1972 400CI build with its stock 8.2 compression, maybe less with the aftermarket 8-eyebrow cast pistons I used. The heads were the 7K3 which had the big intakes and screw-in studs so I could use a high lift cam. The cam really made that engine perform - I was impressed. Ran on regular octane gas all day long.

The Comp Cams use a tighter 110 LSA vs the factory 113-116LSA. The tighter LSA can build more cylinder pressure. These cams have "explosive" power, but peak early as opposed to a factory grind that has a broader and more even power range for longer.

The XE series has steep ramps that throw the valve open faster, so be advised that heavier springs may be needed to keep the lifter on the cam lobe - depending on type of cam grind/series some companies offer.

That said, and in my opinion in keeping the stock heads and wanting to do just the cam/lifter swap, I would inquire about a custom ground cam that will build cylinder pressure (Dynamic Compression) to work with the 8.6 ratio you presently have.


So using the Dynamic Compression Calculator, and as an example, you see how the Intake closing point affects Dynamic (cylinder) pressure.

67 degrees - 6.75 ratio (yours now)
64 degrees - 6.90 ratio
60 degrees - 7.10 ratio

So this is why I say you may need a custom ground cam to maximize your combination using the stock #14 heads. I think I might give it a try and then start saving for the "new" engine. You may even like the new installed cam in your present engine and just go with that.
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post #10 of 29 (permalink) Old 09-22-2019, 09:51 AM Thread Starter
 
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The carb must be modified to run E85. So, getting it calibrated correctly for running some mixture of E85 & pump gas might be difficult. If you want more octane, you can either mix in some race gas, or add Torco Accelerator octane booster.

https://www.summitracing.com/parts/t...010t?rrec=true
I am struggling with what would need to be modified as the accelerator pump uses ethanol friendly rubber and all of the other bits are metal....Maybe you mean jetting needs to be increased?

I have read that some pumps and fuel lines need to be changed, but I suspect this is more internet myth. I have new fuel line which I believe to be ethanol friendly as well. The seals in the fuel pump (mechanical), I am not sure of.....Other than that, what am I missing??

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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