I'b building a 455 for my 67 Firebird. I have 2 different sets of heads.
The first set is a #62 from a 69 Grand Prix. They have screw-in type studs, have 2.11/1.77 valves but have a tiny combustion chamber. To use these I will have to buy dished pistons. They are supposed to be 72cc.
The 2nd set is 6X-4 from a 75 Firebird. They have screw-in type studs, have 2.11/1.66 valves and have NOT been to the machine shop. To use these I would have them machined to accept larger valves and I could go with flat top pistons (94 cc) or domed pistons (101cc).
My question is which would be less expensive? Dished pistons or machine work on the 6X heads?
I have toyed with the idea of selling them both and getting aluminum heads but I just don't have the budget for that.
(1) If the #62 heads have 1-piece stainless valves & hardened seats, and are ready to bolt on, then the dished piston route is probably better.
(2) But, if the #62 heads are not as I described then, IMO, the 6x-4 heads & flat pistons are the better way to go.
--(A) The Speed-Pro L2359NF forged pistons, are still only a little over $300. Dish pistons are twice that. Some buy the SP pistons & have a dish machined into the piston tops. They're plenty thick for that. Many have done it. Some say a D-shaped dish is best. That will cost more, since most machine shops can easily cut a round dish, but not a D-shaped dish.
--(C) Some like the Icon pistons, which are made of the 2618 material, same as racing pistons. These require more piston to cyl wall clearance, since they expand more. These come in both flat top & dished.
--(D) I recommend Auto Tec pistons, BECAUSE they are made of the 4032 material, & can be ordered with the pin location of your choice. This allows you to order the pin height you need, to achieve near zero deck height, WITHOUT having to have extra material removed from the block deck. The machine shop will just do the needed square-up deck machining, then measure to see what piston pin height is needed to put the piston top even with the deck, @ TDC, & you or the shop can order the pistons. From everything I've read, Auto Tec will not charge extra to put the pin hole where you want it. Yes, Auto Tec pistons cost more than Speed Pro. BUT, you save the cost of the extra machining, in order to achieve zero deck height. Always better to machine away only the material that must be removed to square the deck up with the crank centerline.
When I called Auto Tec, they told me I could buy pistons cheaper from one of their hi volume dealers. They recommended Shannon's Engineering. He claims that he'll beat anybody's price on Auto Tec pistons.
(3) You mentioned going with bigger valves in the 6X heads. No need to do that ! They work just fine, unless you plan to have the heads fully ported, for max flow & power. There are 2 reasons you don't need to do it.
--(A) Valve seats in the 6X heads were factory hardened for use with unleaded gas. Many have posted that when you cut the exhaust seats for the larger 1.77 valves, you cut down passed the hardened metal, meaning that if you wanna keep hardened seats, you'll have to pay to have hardened seats installed. That's extra cost. Some say the hardened seats are not needed, & they've been running without 'em for 30 years or more, without any problems. Others say they've seen sunken valves because of soft seats. So, take your pick.
--(B) Many have probably gone with 1.77 valves because the very popular Ferrea brand 5000 series valves do not come in a 1.66 size in the correct length. Butler machines some of the 1.77 valves down to 1.66, then sells 'em for about double the price. So, most just go with 1.77's.
But, SI valves sells 1.66 valves. Part number is 6001SG. One of their salesman even told me that their cheaper replacement 1.66 exhaust valves are 1-piece stainless, with the factory type 2-groove tips. The lower groove is for the factory type rubber O-ring seals. But, I think most everybody nowadays goes with 1-groove valves & has positive valve stem seals installed.
Many say they have spent over $1000 having iron heads built correctly. But, the correctly built new alum heads are around $3000, with bolts & shipping charges. Some say the valves & springs that come in E-heads are of poor quality, so that you need to have a competent Pontiac head shop build the heads, starting with bare cores, then adding the good parts & doing the correct machine work. But when you say that, some will usually say they bought out-of-the-box E-heads & they are just fine. Again, take your pick.
PS: If you're actually building a 400 block stroker, rather than using a 455 block/crank, the stroker assembly can be ordered with whatever custom pistons you need.
Don't believe all the old world internet claims of the CC of all these heads, they are not exactly 72 cc My 1968 #16 heads are actually 77 CC I have these on my +.030 455 with a 24cc dished piston to give me exactly 9.4:1 compression. Even if you have to completely do a set of factory Pontiac heads with valve job,guides, new valves and springs....etc you are still saving $1000 over the cost of buying new aluminium heads. People always forget to add in the extra cost of the required head bolts and new push rods and other little goodies when they buy aftermarket heads.
I agree, once you go for the aftermarket stuff the snowballing starts, been there/done that. If I could do mine over I wouldn't put anything aftermarket on my car. GM already did all the trial and error before they went to the assembly line.
If you do go for dished and have a machine shop do it, rather than buy dished pistons, try for the D shaped dish if not too much more. May help with quench.
I was playing around with the compression ratio calculator over at Butler Performance.
If I have an unmolested block, what would the deck height be? The calculator told me if I had 0.090†deck and used a gasket that crushed to 0.045†that my CR would fall right in around 9.5:1 using the 62 heads. Is there any down side to having a slight deck height and basically flat top pistons?
I was playing around with the compression ratio calculator over at Butler Performance.
If I have an unmolested block, what would the deck height be? The calculator told me if I had 0.090†deck and used a gasket that crushed to 0.045†that my CR would fall right in around 9.5:1 using the 62 heads. Is there any down side to having a slight deck height and basically flat top pistons?
I've read that the factory deck height ranged from around .010 to .023., and even more, depending on who you believe.
You want around .040 quench distance. No more than .045. The quench distance is the distance from the flat part of the piston top, @ TDC, to the head. So, a zero deck height piston + a .045 thick head gasket would give you .045 quench distance. Or, if you use the higher priced FP #1016 head gaskets, they are .039 thick. So, if using these you'd get that same.045 quench distance, with .006 deck height pistons. Would be better to use the .039 gaskets & zero deck height, for .039 quench. The smaller quench distance helps prevent detonation.
So, I'd consider the quench distance more important than trying to get the max CR you can get by with. Obviously, I'm talkin about pump gas street engines. If you're gonna race, with high octane gas, run all the CR you want.
I wouldn't wanna run a piston .090 in the hole, in any normal Pontiac street engine. The best way to reduce CR is with bigger chambers in the heads, or dish pistons, NOT by more deck height.
As soon as you say something won't work, somebody will post that it worked very well for them, for many years, with no problems at all. So, you'll just have to decide what to believe & what to not believe.
I agree with Oldskool, don't use deck/piston height to attain C/R. Try to get the most quench you can. A zero deck clearance and a 40 thou compressed gasket will get you good quench, better to buy dished pistons or have yours milled. A 3" dia 80-100 thou dish should net you around 1 to 1.5 drop in compression ratio. A D shape is even better for increased quench area but I'm not sure what it would cost to get that done. Good quench will improve fuel air mix, result in a faster burn and should lower chances of detonation.
Back in the 'good old days' when gas was going from 100 octane rating to the crap we now have, it was common practice to put in thicker head gaskets or even double them up to try and reduce detonation, the reduced quench offset any benefit of lowering the compression ratio and it failed as a cure.
Don't believe all the old world internet claims of the CC of all these heads, they are not exactly 72 cc My 1968 #16 heads are actually 77 CC
Since I am down to using the 62 heads I thought I'd cc them just to see what I am working with. All of them came in around 71 cc. Granted I wasn't using super expensive or super accurate equipment (plexiglass with 2 holes in it, a smear of vasoline, and a syringe)I was just curious given what Bigchief said.
I have a set of #62 sitting on the shelf. When I have some time I will check and see where they are at with chamber size. Would be interesting to see since they have not been surfaced at all in there life.