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#1
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Original 74 GTO 350 Cam Specs
This is my first post on this site; seems like there are 74 GTO fans/owners in this forum with some excellent experience and knowledge about 74's. I've had my 74 GTO since November 1973, it has about 28,000 original miles on it and the original 350 in it. It has had very little street time in the last 35-40 years, mostly resting in the garage, until about a year ago. Anyway, mostly stock, no plans for any major machining of the engine, since it is low miles and runs pretty well for a basically stock 350.
I have undone some mods I did as a kid in the 70s. Now it has the stock Pontiac intake back on, and I rebuilt the Qjet; has light springs in the distributor, so mechanical advance is all in at about 2,800 rpm; 3.08 posi rear; TH350 with TransGo shift kit; aluminum radiator; 1.65 rockers and pushrods, old headers and dual exhaust in poor shape (that will be getting replaced). It would be helpful to know the duration specs on the stock cam as I plan for the future. I believe the stock 74 GTO has the Pontiac 483555 cam, with 269 int. /277 exh. advertised duration. I'm curious if anyone knows the duration at .050 inch lift for the stock 74 GTO 350 cam? Thanks in advance for any insight. |
#2
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All 200 HP '74 GTO 350 engines used the 9779066 cam.
Advertised duration 273/283, .407"/.407" lift, duration @ .050" 197/206. Nice that the factory saw fit to put a fairly decent cam in the GTO 350. to the PY Forums. Bart
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1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
#3
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Bart, I'm not sure that's correct. I'm showing the W-coded 483555 camshaft that the OP mentions. I'd be interested in knowing if that's wrong.
Regardless, according to the original blueprint for the 555 cam, its advertised duration is 269/277 degrees, duration at 0.050-inch is 189/202 degrees, the intake centerline is at 109 degrees, and the LSA is at 111 degrees. Valve overlap is 51 degrees and valve lift with 1.5:1 ratio rockers is 0.374/0.399". |
#4
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I'm going by information from Pete McCarthy's book.
Makes sense seeing the 170 HP 4-barrel 350 with the 555 cam shown in the listing.
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
#5
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Bart/Rocky,
Thanks for the quick replies. The info on the 48355 duration at 0.050" lift is helpful. After getting some interior work done (sagging headliner) and the exhaust, I might look for a mild cam for the engine. It runs strong, from 2,000 rpm to 5,000, but a bit slow coming on at WOT from a stop. It has the original 7.6 #46 heads. Not looking for any racing here with this car, just a little more on the very bottom end. Do you think something like the Summit 2800 or mild XE might be appropriate and make a difference? The car is just driven on nice days, needs dependability and pleasant street manners. Thanks again! Dan |
#6
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I'd stick a new 066 cam in it.
The Summit 2800 is also a good match.
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1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
#7
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Welcome to the forums! I can't help with your questions, but we need to see pictures of your car!
Importsmasher
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Scott Baggiore 66 GTO convertible 389/4 speed (parents bought new) 73 Firebird Formula 400/4 speed 74 GTO 455/4 speed 74 Grand Am |
#8
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Thanks for the welcome Scott.
Here are a couple of pics. Dan |
#9
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Dan,
Let us know when you pull out the original cam from your '74 GTO. If it has an 'N' stamped on the nose it's the 066, if not it's the 555. That will help us to solve this mystery. Nice GTO! Bart
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
#10
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Bart,
I'll check the nose of the cam and let you know what I find when I get around to the cam. I appreciate for the cam suggestions, welcome to the forum, and the comment on my car pics. Thanks, Dan |
#11
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Here are the docs. Rocky is correct. Don't know where the @0.050" values are published though.
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#12
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I like the 2800 cam in a 350. Fun, but easily streetable. It made my 400 with 066 cam seem a bit slow.
Welcome! I'm not a Ventura guy, but I'm a fan of people who run 350's. Stumbled across this thread.
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"...ridge reamer and ring compressor? Do they have tools like that?" |
#13
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Helpful input about the 2800 in a 350 and great to see positive comment about 350's; it may not have tons of displacement, but still a Pontiac blue-blood (or is that blue-paint? )
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#14
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And the lift is sedate enough that you can run it with press in rocker studs with little fear that you will start pulling one out. I buzzed my .030 over 350 with stock bottom end and press in studs to 5k rpm shift points. I had 25+ quarter mile blasts and a few thousand street miles before parking that engine and moving to a hotter setup. It was most definitely low dollar fun.
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"...ridge reamer and ring compressor? Do they have tools like that?" |
#15
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Quote:
That's good to hear about the performance increase you experienced. The good thing about the 74 GTO 350 with the #46 heads, is they come with screwed in studs. Dan |
#16
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I appreciate those docs, I haven't seen the two docs with the 1974 250 vs. 350 cams. Also liked the pic with the W-coded cam.
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#17
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Cams
Red,
If you decide to go with the 2800 you will like the bottom end. It is a smooth take low end power cam. I run it in a 455 with 1.65 rockers and I really like it. I was also suggest the Crower cam saver lifters due to the pitiful oil off the self's these days. They run when I purchased mine a little over a hundred bucks from Summit Racing but well worth it. Laters Terry link:: http://www.summitracing.com/search/m...aver%20lifters |
#18
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Quote:
Appreciate hearing your experience with the 2800 and the suggestion about the Crower cam saver lifters, never heard that suggestion before. Dan |
#19
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Assuming that the engine is completely stock, I'm certain you can get darn close to .500-inch valve lift, or even more without fear of a valve smacking a piston.
The real concern is the condition of the original valve springs and how much lift they can tolerate. Then there's also the question about sufficient clearance between the retainer and the valve guide. You will also likely have to change rocker studs because the bottle-neck 3/8-inch studs can sheer off under the stress of higher valve lift. The most important point to consider is that stock d-port heads, particularly those with 1.96-inch valves generally don't show any airflow increase past about .450-inch valve lift, so lifting the valve any higher than that is futile. As opposed to tearing the low-mile engine apart, you might find a noticeable performance increase by simply installing 1.65:1 ratio rocker arms on the stock camshaft. You're gross valve lift will increase some 10 percent and you can likely retain the original valve springs. You'll need the 7/16" rocker studs, which is an easy install, and lashing the valves manually may also add some top end charge. |
#20
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call me kinda funny, but I would stick to a Pontiac 066 or 067 cam;
Either of these cams should do away with concerns about too much lift or duration, and should provide a bump from the original 555, while retaining all the positive attributes of a factory grind...
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1970 Formula 400 Carousel Red paint on Black standard interior A no-engine, no-transmission, no-wheel option car. Quite likely one of few '70 Muncie three speed Formula 400's left. 1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing) 2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs) |
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