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Discussion Starter #1
Hello everybody,

Im brand new to the forum and excited to get to be here. I recently just bought my first GTO ( been saving since I was 13). It’s a 72 Phs documented real GTO optioned Lemans that has a had a decent frame on restoration. It is a factory 4 speed Muncie car and still retains its original transmission but it now as I ran the numbers has a 1973 400 2brl in it with stock 4x heads that has been rebuilt.

I’m am still learning the car but I have noticed the rebuilt engine idles incredibly smooth with not a hint of a lope. Unfortunately the motor was rebuilt by the owner who the previous owner I bought it from got it from. I have no idea of internals which will make selected a cam difficult but I’m hoping you guys can give me insight.
Here’s what I know:

-the engine runs like silk and you can balance a nickel on the air cleaner
-Pulls strong and seems like make a 14 second car
-410 rear gear
  • Muncie 4 speed
  • performer intake ( yes I know the stock 72 intake is better)
  • brawler 750 carb ( yes I know not a qjet)
  • converted to hei ignition
  • headman elite headers
  • 2 1/2 pypes exhaust
here’s my issue. It’s really irking me I do not know what cam it has and it idles like a stock 400 from 73. It honestly has road manner of a stock cam but when I get over 2 grand it becomes incredibly loud and poppy and sounds rediculously nice. I don’t think a stock cam would do that even being forced to wind up. Maybe it’s a 068 cam or a performer cam? What ever it is it definitely has a short duration which make me want to step it up if it’s possible.

So here’s the typically question you have seen a million times.... ram air III cam?

assuming I have 8.5 compression would this combo work well. Also,not sure of the aftermarket support but is there any pistons that work well with the 4x heads guys like to run to obtain 9 plus compression?

I figure with my gears and manual transmission It might work. I’m also a purist and want to be able to say I put a ram air III cam in it even though I could get a much better modern cam custom ground.

thanks!
Dan
 

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What are you calling the Ram Air III cam? The 744? There was a reason why Pontiac ditched it early on.

First you want to know more about your valve springs. If you go more lift, will they have enough spring pressure to keep the valves from floating off their seats at higher RPM's. So you need to know what springs you have - unless you keep it factory lift and go more duration.

More duration pushes the RPM power band higher up into the RPM range and sacrifices bottom end - and is probably what you are experiencing right now. Go with a bigger cam and you may have a bigger disappointment. The train of thought is that a stock Pontiac head flows best up to about .450" lift and gains little going above that, thus Pontiac uses a longer duration - but this was also with higher compressions and Premium leaded gasoline with 98-100 octane.

No need to start fooling with head changes and getting higher compression with new pistons unless you are looking for an excuse to tear down & rebuild your engine. Lower compression can be your friend. You want to raise dynamic compression. A Comp Cams cam with 110LSA will do this. I ran the XE274 in a 1972 400 with about 8.0 compression, 3-angle valve job, and my own port match and a basic deburring/clean-up. Pulled like a bear, but fell off fast around 5,500 RPM's which is fine for a stock bottom end engine with cast rods and cast pistons. BUT, it had a higher lift and I purchased matching springs.

Do not know anything about your carb and the Performer is not the ideal candidate for a performance gain - so I would ditch both and begin there with a factory Q-jet and intake.

So food for thought.
 

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What are you calling the Ram Air III cam? The 744? There was a reason why Pontiac ditched it early on.

First you want to know more about your valve springs. If you go more lift, will they have enough spring pressure to keep the valves from floating off their seats at higher RPM's. So you need to know what springs you have - unless you keep it factory lift and go more duration.

More duration pushes the RPM power band higher up into the RPM range and sacrifices bottom end - and is probably what you are experiencing right now. Go with a bigger cam and you may have a bigger disappointment. The train of thought is that a stock Pontiac head flows best up to about .450" lift and gains little going above that, thus Pontiac uses a longer duration - but this was also with higher compressions and Premium leaded gasoline with 98-100 octane.

No need to start fooling with head changes and getting higher compression with new pistons unless you are looking for an excuse to tear down & rebuild your engine. Lower compression can be your friend. You want to raise dynamic compression. A Comp Cams cam with 110LSA will do this. I ran the XE274 in a 1972 400 with about 8.0 compression, 3-angle valve job, and my own port match and a basic deburring/clean-up. Pulled like a bear, but fell off fast around 5,500 RPM's which is fine for a stock bottom end engine with cast rods and cast pistons. BUT, it had a higher lift and I purchased matching springs.

Do not know anything about your carb and the Performer is not the ideal candidate for a performance gain - so I would ditch both and begin there with a factory Q-jet and intake.

So food for thought.
Yes exactly! Thats why I wanted to poke around in the forum and ask some guys with experience like yourself their thoughts. So just for clarification I was only wondering about what pistons guys run because my engine looks like someone put a lot of time and effort into it and I wouldn'tt be surprised if it was more than a basic rebuild and they added aftermarket pistons to boost compression if it were possible. I just wanted to get clarification if this was popular since most build recipes I've seen when I had my Trans Am usually included stock pistons and shaving 6x heads. I was kind of thrown off when I saw they were 4x heads on there and figured if a guy wanted a fast motor in a real gto he would not leave a 165hp engine fro 1973 stock. Anyways, I know the intake and carb are a big no no but it runs so good I am going to keep it for now.

I did want to ask you a big question here about your cam suggestion because I think I am missing something. Did Pontiac advertise their cams specs differently so I am not understanding the geometry correctly? When I compare the two, the xe 274 has .80 more lift on the intake and exh and is also has a higher duration. I know that extreme energy cams are made for low compression engines which is why I suspect it works so well, but why did your mention that the 744 cam would require new springs because of lift when the comp cam has in noticeably higher? 410 lift is less than a tinny edelbrock performer cam. I must be missing something.

Here's what I am looking at

744- 224/236 dur .410 intake .410 exh 119 lsa
xe 274 230/236 dur .488 intake .491 exh 110lsa

Thanks for you help!
 

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The 068 was 212/225 with 0.407" lift. LSA is 116. The 744 is 224/236 with 0.407 lift on a 115.5 LSA. There's no telling what cam is in your engine since it is not original.
 

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I forgot to mention about the valve springs for the 744 cam. It has nothing to do with the lift of that cam. The 744 was the last cam Pontiac made that had a fixed ramp angle (lift profile) on the lobes. The duration was long enough that they ran out of ramp to maintain the 0.407" lift. That made the nose of the cam flat. That caused valve spring problems that required taller and stronger springs. IIRC the factory installed height of springs for the 068 cam is 1.56". For the later 744 cams it was 1.714", and 1.8" for the 041 cam.
 

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Thered72 - "I did want to ask you a big question here about your cam suggestion because I think I am missing something. Did Pontiac advertise their cams specs differently so I am not understanding the geometry correctly? When I compare the two, the xe 274 has .80 more lift on the intake and exh and is also has a higher duration. I know that extreme energy cams are made for low compression engines which is why I suspect it works so well, but why did your mention that the 744 cam would require new springs because of lift when the comp cam has in noticeably higher? 410 lift is less than a tinny edelbrock performer cam. I must be missing something.

Here's what I am looking at

744- 224/236 dur .410 intake .410 exh 119 lsa
xe 274 230/236 dur .488 intake .491 exh 110lsa"

PJ - Here goes. Yes, Pontiac, as well as any cam manufacturer can use different lift points on the cam, and this is why they can be confusing when comparing. So the way to compare, and even this can be slightly deceiving, is to compare each cam at its .050" lift spec.

The factory cams were generally spec'd at .006" where it was considered that all the slack in the valve train, ie lifter, pushrod, rocker arm, was taken up and the valve would then begin to raise off the valve seat and duration/lift numbers began. This was essentially an AMA spec which all car manufacturers adhered to as their industry standard. Aftermarket cam grinders were all over the place - and rightly so in an effort to keep secret how they ground their cams and sometimes to sound better on paper than the next guy.

The "744" as Jim Taylor explained it is correct. The lobe actually looks like a roller cam lobe, kinda flat on the top. Milt Schornack ran a RA car with this cam and hated it. He went back to the 068 cam as I recall and the factory seemed to follow his lead shortly thereafter. I enclosed a photo I have showing the differences in the ramps, 744 on the left.

I was thinking off the top of my head and thought the 744 was more inline with the larger lift RA IV cam. Lift is .406" like most all Pontiac cams. I have read that you can go up to about .45-" lift with the stock springs. However, you numbers seem off. The duration Int/Exh is shown to be 301/313. LSA is 115.5. Overlap, another big consideration, is shown as 76 degrees. The 068 for comparison is 63 and the RA IV being 87.

The XE Cam has a higher lift and a faster ramp opening so it requires stronger springs. When I purchased my cam/lifters, I also purchased matching springs. I said the head basically flows up to .450" and may flow slightly more at higher lifts, but there seems to be little gain.

So doing some basic head work will improve flow and take advantage of the higher XE 274 lift. My thinking, and I may be wrong, is that even though the heads don't benefit from lift over .450", that the higher lift cam reaches the .450" faster/earlier on the lobe profile and is then kept open longer as the lobe reaches the high side of .488" and as it drops off on the closing ramp. So if I were to draw a cam lobe and view it from the side and mark at what point on the cam lobe .450" is reached, then went up and over the top of the lobe at .488" and then went down the lobe until I reached .450" lift, and drew a line between those 2 points and looked at the cam lobe, it would look flat on top like a roller cam profile, but I still effectively have a typical flat hydraulic cam lobe. I would then be able to calculate the duration that my valve is being effectively kept openedat its apex Versus simply climbing the lobe ramp gradually to reach the apex of .450" and then drop down the ramp backside. The valve would only momentarily stay at .450" while the higher lift cam would hold the valve open at .450" for a much longer period- understanding that any lift above .450" lift is doing nothing for flow because my heads stopped flowing at .450", but I got more valve lift duration (not cam duration) at which .450" lift was effective.

Hope that makes sense?

original Pontiac 744 cam on left.jpg
 
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