[ponyakr]

Originally Posted by Slick

Digging up an old thread.

I'd like to change the cam in my own 74 GTO 350. Understand they have pistons without valve reliefs. Given that, how much lift can one safely run?

Thanks,

Stuart

That's a really good question. I too, would like to know the answer.

Because of the size of the chambers, I'd assume that .450 or a little more lift would be perfectly safe. Especially if the pistons are still .020 or more in the hole.

If it'll clear the pistons, I like the looks of the 256 Voodoo, for a low CR 350.

http://www.lunatipower.com/Product.aspx?id=1774

If you are concerned only with low & mid range power, the 250 Voodoo looks even better, to me.

http://www.lunatipower.com/Product.aspx?id=1773&gid=287

Will probably need new matching valve springs.

[Slick]

Thanks for the quick reply Ponyakr!

I want all the power I can get from this, cheaply. I have another engine to go in eventually, but the car has to be ready (fuel system, cooling, rear, suspension, transmission.......). For now, I'd just like as much of "that great GM feelin'" as I can get without digging farther into the engine. Nothing I can do about the 7.6 compression, except look for a cam with tight lobe centers.

I'll have a look at the VooDoo 256 specs. Was looking at a 2801 Summit (did I mention cheap?)

Stuart

[Slick]

I guess the sensible thing to do is locate maximum lift on my stock cam, then measure piston to valve at that point with a dial indicator, repeat measurement at TDC. Thoughts?

[Rocky Rotella]

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.

[unruhjonny]

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...

[ponyakr]

"...Was looking at a 2801 Summit (did I mention cheap?)"

Guessing that the 2801 would be a little too much for a 7.6 CR 350, unless you have a 4-speed or a converter that will flash above 2600 rpm.

For that CR, I'd use a 2800 before I'd use a 2801, especially if I had a 3-speed auto, with a stock converter.

The Summit cams are definitely the best bang for the buck, if you want a low budget build.

If I had to run a 2801 in a 7.6 CR 350, I'd do so ONLY with Rhoads lifters. And that takes some of the "cheap" out of using a Summit cam.

Not much difference in the price of the 2801/Rhoads VS a small Voodoo/Spotts $59 lifters. Even tho I love Rhoads lifters, with a 7.6 CR 350 I'd go with the Voodoo.

2801 = $73 + Rhoads 9518 @ $116 = $189

256 Voodoo = $125 + Spotts lifters @ $59 = $184

https://www.ebay.com/itm/Lunati-Vood...wAAOSwLFBbGwRt

https://www.ebay.com/itm/New-Hydraul...oAAOSww9xZODlz

Or, you can really cheap out & go with the Summit K2800 cam/lifters @ $115 shipped. Some have said the cheap Summit lifters work OK for mild builds.

https://www.summitracing.com/parts/s...UaArmaEALw_wcB

[Greg Reid]

I have a Summit 2800 cam and lifter set in the box that I'm not going to use...just in case you're interested.

[Slick]

Thank you for lots of good suggestions.

Rocky Rotella, I'm not sure that 90k+ miles qualifies as "low mileage", but I guess in the context of a 44 year old car, it is. Engine looks excellent inside, better than I hoped. I may give your idea a try first, use 1.65s on the stock cam (with BBC studs and polylocks), since that is by far the easiest. Love your Avatar car by the way, my first car was a 70-1/2 Lucerne Blue Trans Am. The absolute best car ever!

Ponyakr, your advice is well taken. I'll avoid the Rhoads lifters and wilder cam, it is probably unnecessary. I knew about the Crower cool face lifters. Please tells me about the (Paul?) Spotts lifters? Price seems very reasonable. Didn't realize Spotts was still in operation, and was unaware of the lifters he sells.

I guess, of the cams mentioned, the VooDoo (which should have a great ramp design) would be my 1st choice. Followed by the factory cams, then the 2800. Are the factory cams actually available somewhere? I seem to recall, way back when, replicas of factory cams being sold that performed like crap compared to actual GM cams.....

Curious that no one has suggested the old standby, Tripower, "S" or 068 cam? Certainly lift isn't an issue. Is the cam timing so long that cylinder pressure/dynamic compression will be too far too low?

This is a temporary measure until I can "correct the factory defect"; the 350. There is a 511 sitting on the engine stand, waiting for a prepared car. So a compromise here is okay.

Another question: if I measure piston-to-valve clearance, and find that with the chosen cam/rocker combination, there is adequate clearance with a cushion, can I substitute a thinner head gasket and pick up a bit of compression? I know that Cometic sells thin (0.026"?) 3.95" bore gaskets, which should net a bit compared to the factory (0.046", right?) gaskets, but Cometics require a mirror finish on the deck and heads if I understand correctly AND they are way more expensive than this project is worth. Is there another, more affordable, thin gasket choice? 0.020" thinner, even if the gasket diameter is 4.3", gives me about 4 tenths of a point in compression.

In any event, I don't mind replacing valve springs.

Greg Reid, I'll send you a PM.

[Rocky Rotella]

Originally Posted by Slick

Rocky Rotella, I'm not sure that 90k+ miles qualifies as "low mileage", but I guess in the context of a 44 year old car, it is. Engine looks excellent inside, better than I hoped. I may give your idea a try first, use 1.65s on the stock cam (with BBC studs and polylocks), since that is by far the easiest. Love your Avatar car by the way, my first car was a 70-1/2 Lucerne Blue Trans Am. The absolute best car ever!

I'm sorry, Slick. I mistook your example and confused it with that of the original poster's. His car has 28,000 miles.

I think you'll likely see a gain of 10 to 15 horsepower from the rocker arm swap.

And while the 068 is an ideal camshaft for street driven 400 and all 455 applications, I think you'll find it a bit ragged in a low-compression 350.

[ponyakr]

First, I'll say again that I'm no expert, like some of these other guys here. So, these are just my opinions, which may not be worth much.

Thinner, but cheaper than Cometic, head gaskets were mentioned. The FP 1016 gaskets are thinner than the cheap FP head gaskets. Won't help much tho.

1.65 rockers were mentioned. I assume some grinding is required to clear the pushrods, and that everybody involved here knows that ?

"...the 068 is an ideal camshaft for street driven 400 and all 455 applications..."

With all due respect: ideal for "all 455 applications" ???

"...Are the factory cams actually available somewhere?..."

It's my understanding that the Melling SPC-4, SPC-5, & SPC-7 cams are clones of the 066, 067, & 068 Pontiac cams. if this is not correct, I'd appreciate it if someone would post exactly what these 3 cams are.

https://butlerperformance.com/c-1234...ment-cams.html

The cheapest source for these cams are usually from Ebay sellers. Sometimes Auto Zone will have the lowest price for the SPC-7, even with having to pay tax. Have never understood that.

It has also been said that several of the popular Pontiac cams are actually made & ground by a company called CMC, & these cams are then sold by several different vendors, under different brand names. I assume that the 041 clone is the most popular, and is sold by most of the major brand name cam companies. SPC-8 is the Melling number.

This Spotts cam is the same cam as the Summit 2801.

https://www.ebay.com/itm/Pontiac-068...sAAOSw0e9UwqDI

"...Please tells me about the (Paul?) Spotts lifters? Price seems very reasonable. Didn't realize Spotts was still in operation, and was unaware of the lifters he sells..."

He says they are USA made. He says they're the best. He says he has used 'em for years with no failures. Someone here has posted who makes his lifters, but I forget who it is. Maybe somebody will post that info in this thread. Others here have disagreed with his opinion of these lifters. These Melling lifters have the low groove, just like the Spotts lifters have. So, I assume they're the same lifters. Not sure.

https://www.ebay.com/itm/Melling-Hyd...ty!71251!US!-1

Some here say that the Hylift Johnson "R" lifters are by far the best Pontiac lifters. Opinions differ.

The regular Hylift Johnson lifters are sold on Ebay for a very reasonable price. But I've never seen the "R" lifters advertised. They can be bought from member Paul Knippen.

[Rocky Rotella]

Originally Posted by ponyakr

"...the 068 is an ideal camshaft for street driven 400 and all 455 applications..."

With all due respect: ideal for "all 455 applications" ???

Dammit! That was supposed to say "all street driven 400 and 455 applications."

And by that, I mean that the 068 camshaft after all these years still remains a great choice that provides excellent street manners and good performance for all street driven 400 and 455s. Yes, there are better choices, but for an economic solution, it still works!

[ponyakr]

"...there are better choices, but for an economic solution, it still works!"


Yes, I agree that it would be an "economic solution" for a street 455, for fuel mileage.

But, the high lift version of the 068, the Summit 2801, and the Summit 2802, would both make more power & cost less than an 068 clone.

Not trying to argue. Just wanting to get the facts out there for any who are interested.

Except for the SD455, the 068 was the biggest cam used in a factory 455. I think that is a shame. All the HO & SD 455's would have made lots more power with an 041, especially that high compression '70 model.

Pontiac reduced the advertised hp rating of the SD455, from 310 to 290, when they decided to use the 744 specs cam instead of the 041 specs cam. That's a 20hp drop, with only the cam change. Don't know if this rating change was because of dyno testing results, or not. Anybody know for sure ?

[Rocky Rotella]

Originally Posted by Slick

Curious that no one has suggested the old standby, Tripower, "S" or 068 cam? Certainly lift isn't an issue. Is the cam timing so long that cylinder pressure/dynamic compression will be too far too low?

I don't take it that you're arguing, but thanks just the same for the clarification.

The only reason I brought up the 068 was because of the comment above. It'd be interesting to see how the 068 with 1.65:1 ratio rockers would compare to the Summit grinds from a power production standpoint. Considering that airflow doesn't continue increasing beyond about .450-inch lift on a stock d-port head, there isn't much to gain lifting the valve much beyond .450, which is about where the 068 comes in. I'd bet they'd probably all perform pretty closely. No doubt the Summit grinds have the edge on cost though!

[Slick]

Originally Posted by Rocky Rotella

I don't take it that you're arguing, but thanks just the same for the clarification.

The only reason I brought up the 068 was because of the comment above. It'd be interesting to see how the 068 with 1.65:1 ratio rockers would compare to the Summit grinds from a power production standpoint. Considering that airflow doesn't continue increasing beyond about .450-inch lift on a stock d-port head, there isn't much to gain lifting the valve much beyond .450, which is about where the 068 comes in. I'd bet they'd probably all perform pretty closely. No doubt the Summit grinds have the edge on cost though!

Definitely not trying to be argumentative! My experience has always been with 400/428/455 (lots of 455 builds). The 068 cam is a great cam, but too mild for my own tastes. I do like a little "snotty" sound, and the extra power from a wilder camshaft.

A soft low end won't be a big deal for me, since I have no intentions of standing start racing with this combination. Just looking for a bit more power. And I do need a bit of guidance when dealing with a "no compression" 350!

Thanks again, you've been a big help. Now, first to find a set of 1.65 rockers and studs..........

Stuart

[ponyakr]

"...first to find a set of 1.65 rockers and studs."


May have already been mentioned. Don't know & not gonna reread. But, keep in mind that with 1.65 rockers, the pushrods will rub, unless you remove some material for clearance. At least that's what I've always read. Never used any 1.65's. I'm sure some of these guys who've done it can tell you exactly what to do.

As for the studs, all you need are some BBC studs. Standard Pontiac length is about 1.75". BBC studs are available in several lengths. Cheap studs are under $40 shipped. Or you can go with ARP studs & pay a few bucks more.

https://www.ebay.com/itm/New-Set-7-1...ty!71251!US!-1

https://www.jegs.com/i/Milodon/697/8...oaAmehEALw_wcB

https://www.summitracing.com/parts/arp-135-7101

https://www.ebay.com/p/Arp-135-7101-...7888674&chn=ps

[SD455DJ]

Personally, I would go with the 2800 cam & lifter kit (204/214/112 @ .422"/.444") and forgo the 1.65 rockers. That will be plenty of cam with the 7.6 compression you have. My '74 GTO's 350 (built by others before I bought it) has a CC XE256 (212/218/110@.456"/.456") with 8.2 compression and it's really soggy for low end power, even with the tight lobe center. I have a 2800 cam to put in it. I do like the 066/067 cams for a low compression 350, but the 2800 is a higher lift version of the factory cams and have higher lift so no need for the 1.65's....just a thought for you to consider.

Dennis

[se428bandit]

I actually had good luck with a 068 adv 4 degrees in my 1972 Ventura. We took a few cc's off the 7H1 heads, it had the crappy center dump stock manifolds, original factory stock short block. It ran 9.80s in the 1/8 with the 2.73 gear and stock convertor and went 9.24 with a 2400 convertor and a 3.23 gear with the single track rear. Here is my car with the 3.23 gear, ***warning do not listen to it with the volume up***, a friend film it with his Obama phone. https://youtu.be/P7S38kFsIq8

[SD455DJ]

se428bandit- Impressive one-wheel peel! What does a 9.24 ET in the 1/8 convert to 1/4 mile ET? Mid-14's?

Dennis

[se428bandit]

Between a 14.36 to mid 14.40s. The track I ran at that day was a 1/8 track. I wish a had the chance to run my Long Branch manifolds on the 350 and the posi in it.

[Greg Reid]

I just noticed this 'defect' in the Summit 2800 I've had for a few years. Does anyone think it's a problem?
It seems to be a tiny void in the casting that was exposed during the grind. About the size of a pin head right at the edge of one lobe..