[ponyakr]

Just curious, as is my custom.

Some here are always nit-pickin about EXACTLY what the CR is. I always use the Wallace CR calculator, just because it's convenient, and because I don't know how to do all the math required to figure it myself.

So, for you guys who know how to figure CR exactly, how far off is the Wallace calculator ? Can you put a percentage of error on it ? And exactly what numbers does that calculator fail to include, that determines CR ?

http://www.wallaceracing.com/cr_test2.php

For example: I've read that the volume of the area of piston-to-cyl-wall clearance, ABOVE the top ring, must be added in, as well as the volume of the portion of the head gasket bores, which are outside the base circle of that hole. So, aprox how much would the CR calculation be reduced by including these volumes ?

[65sport]

Originally Posted by steve25

Nice find no less nice price!

Machine work wise do not forget to have all the guides cut for .530" seals and then grind off the remains of the machine lip on the short turn of each Exh valve bowl then blend and polish out the bowl.

Also grind off the casting nub on the crown of each Exh port short turn.

Next gasket match each Exh port to a factory steel gasket on the top / roof only, and blend this in for 2 inches.

Thanks steve25. Yeah I plan on doing all that. Nice thing these heads don't look like they have been messed with other than being removed from an engine and stripped. Only fly in the ointment so far is a bolt broken off on the end of one of the heads. Maybe if it don't want to come out I can just put it on so that it faces the rear. Just gotta get the heater nipple in the right place.

[65sport]

[QUOTE=Jay S;6053544]Thunderstorm alarm woke my up. So I will guess i will get to go first, lol

Crane compression ratio ranges are good for a 350 cid engine. Very accurate actually for a 350 cid engine. But not for the bigger 455. For the same compression the compressed volume is more on the 455 than the 350 (350 is about 24% smaller). Look at it this way, there is more volume in the cylinder for the overlap area of the cam on the bigger engine, 455 has more air to be diluted by the intake and exhaust mixture. It takes more overlap to effect the 455. Most cam mfg ratings are based on 350 cid, unless they say otherwise.

Makes sense.

I like Paul Spott's cam recommendations the way he breaks it down for both displacement and CR.

[65sport]

Originally Posted by Jay S

If I reach my target of 9:1 CR, how do you think my 455 will idle with the 214-224-112 LS ?

204/214 is a stock cam, smaller than some of the mild OEMs. If you want a stock cam, it is fine too.[/QUOTE]

Well from all the responses and the way it's been explained to me, I won't use the 204/214 on this engine probably the 214-224. But as this is the largest engine I've ever had, I'm re-thinking cam choices.

[Jay S]

Nice score on the 6x-8s. That will work great with the 214/224 cam. There are a lot of cam options at 9:1 in a 455 that are bigger than the 214/224 that still work good. Many of my daily driven vehicles in the past had either the 204/214 or the 214/224 cam, always served me well.

I don’t usually count the volume above the compression ring on an average street engine. I had a old speed pro piston for a 455 up next to a new speed pro piston and noticed they spread the ring pack apart more on the new piston and raise top ring fair amount. It wasn’t my engine so I did not check it, but FWIW, it looked like it could have changed the compression 1 or 2 cc’s.

[65sport]

Originally Posted by Jay S

There are a lot of cam options at 9:1 in a 455 that are bigger than the 214/224 that still work good.

I don’t usually count the volume above the compression ring on an average street engine. I had a old speed pro piston for a 455 up next to a new speed pro piston and noticed they spread the ring pack apart more on the new piston and raise top ring fair amount. It wasn’t my engine so I did not check it, but FWIW, it looked like it could have changed the compression 1 or 2 cc’s.

Technically, it all counts towards swept volume, but I've never counted the area above the top piston ring. Mainly because IMO most people don't either and I tend to listen to the majority for "comparative purposes".

HOWEVER

Wouldn't hurt subtracting 1 or 2 cc's of SV for that. I used a set of KB pistons on another car that had the high location which required a wider top ring gap due to the extra heat expansion of the higher location.

As for cam selection, I am now taking the larger displacement into account. I'm thinking the 214-224 in a 400 or 455 is similar to a 204-214 in a 326 or 350.

Yup, that's why I'm here. Thanks for the advice.

[65sport]

Originally Posted by ponyakr

Just curious, as is my custom.

Some here are always nit-pickin about EXACTLY what the CR is. I always use the Wallace CR calculator, just because it's convenient, and because I don't know how to do all the math required to figure it myself.

So, for you guys who know how to figure CR exactly, how far off is the Wallace calculator ? Can you put a percentage of error on it ? And exactly what numbers does that calculator fail to include, that determines CR ?

http://www.wallaceracing.com/cr_test2.php

For example: I've read that the volume of the area of piston-to-cyl-wall clearance, ABOVE the top ring, must be added in, as well as the volume of the portion of the head gasket bores, which are outside the base circle of that hole. So, aprox how much would the CR calculation be reduced by including these volumes ?

I DO know the math, but I use the Wallace table because it's accurate and easy. If my head gasket volume or quench volume is different I either add or subtract.

I wouldn't bother with the above the ring volume. You might subtract a little swept volume for the KB high ring pistons but not sure it's enough to be of concern.

What I don't have figured out is how to come up with dynamic compression ratio and how it relates to static compression ratio. I do know that cylinder pressure changes throughout the RPM spectrum, and different valvetrain/heads flow different for different RPM situations.

What I think could be a total disaster is someone thinking that they can "cam away" too much compression which could result in higher RPM detonation. I'm thinking dynamic compression figures would protect against that, but it's not in my wheelhouse yet so for now I'll just use common sense.

[54nomore]

Aren't the #66 valves shorter than the 6X valves?

[65sport]

Originally Posted by b-man

When you add up the cost of tapping for screw in studs and the added cost of conversion studs with 1/2-13 threads on the bottom ($100) plus the heavy milling to try to get 9:1 compression and expensive Cometic .027” gaskets ($200) the 6X-8 heads are a better way to go.

No expensive conversion studs and no tapping needed for the 6X-8 heads and no heavy milling requiring a cut on the intake side of the head. .

So on your advice I found an unworn bare set of 6X-8's, planning to use valves, retainers, and guide-plates from the 66's so hopefully the valves are the same lengths or at least close enough to shim or not shim the springs.

This is going to save me a lot of money, thanks for the good advice.

[b-man]

The factory put the fairly long duration ‘323’ cam in the low-compression (8.4:1) 455 SD engines, about 224 intake and 230 exhaust at .050”. They originally wanted to use the ‘041’ RAIV cam (231/240 at .050”) but it wouldn’t pass emissions testing. These cars left the factory with a 3.42 gear most of the time in auto trans form if I’m not mistaken.

You might be surprised at how much cam you can put in a low-compression 455 and still maintain good street manners.

I used to bracket race a low-compression (8.6:1) 455 running the H-O Racing HC-02 cam (244/252 at .050”) in a fairly light weight (3330# w/o driver) car. That cam required the use of a good 10” 3400 stall converter and a low rear end gear to get any decent performance out of it, I was using a 3.89 gear and 28” tall slicks. Probably a bit too much gear but it’s what I had and it worked fine for racing in the brackets.

Use a mild cam such as the 214/224 if you’re going to use a tall highway gear (3.08, 2.73 or 2.56) and a stock converter. Step up to a bigger 224/234 if you go for a little more gear such as a 3.23 and maybe a 2500 converter. For more serious performance go even further with a 230/240 cam and a 3.42 or 3.55 gear. Nothing hard and fast here, just some general guidelines.

A 455 will pull a very tall (low numerical) gear and still perform amazingly, some very hard running street 455s have dipped into the 10s in the 1/4 mile using 3.08 to 3.42 years.

All of these different cams mentioned will work in a street 455 with 9:1 compression or less. The longer duration cams will be better optimized when used with higher compression ratios but that doesn’t mean they won’t run and run strong in low compression 455s.

My bracket race 8.6:1 455 was built using what I had laying around in my garage. It was not a perfectly optimized engine combo but that didn’t stop it from being a very competitive car that was fun to drive and performed well, running in the 12.0s at over 110 mph.

[b-man]

Originally Posted by 65sport

So on your advice I found an unworn bare set of 6X-8's, planning to use valves, retainers, and guide-plates from the 66's so hopefully the valves are the same lengths or at least close enough to shim or not shim the springs.

This is going to save me a lot of money, thanks for the good advice.

You’re going to need valves that are the correct length for the 6X-8 heads. The deep chambers of the #66 heads required the use of very short valves that won’t work in the 6X heads.

You’re best off going to a stainless steel one piece valve anyway, the factory 2-piece units (friction welded head to stem) are known for coming apart and destroying engines. Your 455 will thank you, they’re not making them anymore.

[65sport]

Originally Posted by 54nomore

Aren't the #66 valves shorter than the 6X valves?

My #66 head"s valves measure 4.86" intake and 4.847" exhaust on average. Not sure if the stems have ever been re-faced or if the valves have been replaced; the engine had been rebuilt.

Wallace racing is showing the 6X-8 valves as being 4.86" both intake and exhaust. So the 66's exhaust valves are approximately .040" shorter in this case.

I'm thinking after the valves are seated, measure the retainer height and see how close I am. Order springs to give me close to the right pressures, maybe remove the metal umbrellas to help add .020 assembled height if needed, shim the intake side if needed. IF I had to I could try some off-set keepers.

I also want to use the rockers, pushrods and guide-plates that came with the 66's as long as the rockers contact the valves close to center, if they don't I'll get a pushrod checker. I already used the 66's valves to check the guides on the 6X-8 heads, they are surprisingly tight.

Would a new set of 4.970" valves be too long ?

I appreciate your input.

Do you think is this a plausible plan?

[65sport]

Originally Posted by 54nomore

Aren't the #66 valves shorter than the 6X valves?

My #66 head"s valves measure 4.86" intake and 4.847" exhaust on average. Not sure if the stems have ever been re-faced or if the valves have been replaced; the engine had been rebuilt.

Wallace racing is showing the 6X-8 valves as being 4.86" both intake and exhaust. So the 66's exhaust valves are approximately .040" shorter in this case.

I'm thinking after the valves are seated, measure the retainer height and see how close I am. Order springs to give me close to the right pressures, maybe remove the metal umbrellas to help add .020 assembled height if needed, shim the intake side if needed. IF I had to I could try some off-set keepers.

I also want to use the rockers, pushrods and guide-plates that came with the 66's as long as the rockers contact the valves close to center, if they don't I'll get a pushrod checker. I already used the 66's valves to check the guides on the 6X-8 heads, they are surprisingly tight.

Would 4.980" valves be too long? I'm capable of installing longer push-rods if needed and I have not ordered needed rocker studs or valve springs.

I appreciate your input.

Do you think is this a plausible plan?

[54nomore]

Originally Posted by 65sport

My #66 head"s valves measure 4.86" intake and 4.847" exhaust on average. Not sure if the stems have ever been re-faced or if the valves have been replaced; the engine had been rebuilt.

Wallace racing is showing the 6X-8 valves as being 4.86" both intake and exhaust. So the 66's exhaust valves are approximately .040" shorter in this case.

I'm thinking after the valves are seated, measure the retainer height and see how close I am. Order springs to give me close to the right pressures, maybe remove the metal umbrellas to help add .020 assembled height if needed, shim the intake side if needed. IF I had to I could try some off-set keepers.

I also want to use the rockers, pushrods and guide-plates that came with the 66's as long as the rockers contact the valves close to center, if they don't I'll get a pushrod checker. I already used the 66's valves to check the guides on the 6X-8 heads, they are surprisingly tight.

Would 4.980" valves be too long? I'm capable of installing longer push-rods if needed and I have not ordered needed rocker studs or valve springs.

I appreciate your input.

Do you think is this a plausible plan?

That's only .013" difference and that's probably just in the head of the valve, so you should be fine. The only problem I see with offset keepers is that Pontiacs don't have much tip sitting above the retainer as it is, so you can get into interference problems with the rocker after grinding the valve tips. Otherwise, I am all for using them to fine tune spring installed height. Using the longer valves (4.970 or 80) has some benefits too. They will certainly allow for more lift and may open up some spring options too. Sounds like you have a pretty good grasp of the situation already!!! I'm impressed!

[65sport]

Originally Posted by 54nomore

That's only .013" difference and that's probably just in the head of the valve, so you should be fine. The only problem I see with offset keepers is that Pontiacs don't have much tip sitting above the retainer as it is, so you can get into interference problems with the rocker after grinding the valve tips. Otherwise, I am all for using them to fine tune spring installed height. Using the longer valves (4.970 or 80) has some benefits too. They will certainly allow for more lift and may open up some spring options too. Sounds like you have a pretty good grasp of the situation already!!! I'm impressed!

Well I've been doing valve jobs since the late 70's and worked at GM dealers as a heavyline tech 15 years. ZERO Pontiac experience and I've learned a lot from you guys here on the forum. My first car was a 65 Lemans Sport 326 HO 3 speed 3.55 posi. Always regretted letting that car slip through my hands, and I never thought I would ever find another one. Then I found a survivor here in Arizona that had been here since it was delivered Oct. 1st 1964 at Mecham Pontiac. NO rust, all original 326 2 bbl 2 speed ST300. Buckets, console, rear speaker and rear electric antenna.

[54nomore]

[Jay S]

Originally Posted by 65sport

Well I've been doing valve jobs since the late 70's and worked at GM dealers as a heavyline tech 15 years. ZERO Pontiac experience and I've learned a lot from you guys here on the forum. My first car was a 65 Lemans Sport 326 HO 3 speed 3.55 posi. Always regretted letting that car slip through my hands, and I never thought I would ever find another one. Then I found a survivor here in Arizona that had been here since it was delivered Oct. 1st 1964 at Mecham Pontiac. NO rust, all original 326 2 bbl 2 speed ST300. Buckets, console, rear speaker and rear electric antenna.

Sounds like a great car. Very cool car project!

What your plans are for the 455 are starting to resemble a 455 budget build we did for a friend years back. Started with a used 455 short block. We honed it, reused the cast pistons, gave it new rings and bearings, rods received arp rod bolts. 60 psi oil pump. It had the rods resized, mains and crank were checked, and the crank polished. No other machine work on the short block. We used 6X-8 heads, I ported them, mostly the valve pockets and removed the places Steve25 mentioned. I ground and reused the stock valves, kept the 1.66 valves in it. On our flow bench it flowed mid 230s cfm on the intake, and around 10% gains on the exhaust. It had a melling Ram air 4 cam with 1.5s, q jet, stock intake with log manifolds. Went in a 70 GTO with 3.23s. Ran decent, i think it would have ran better with less cam, more in the 224/234 range. But with an open rear end it had no issues lighting up the back wheel.

If the 66 heads have some newer 1 piece stainless valve installed I would reuse them, but, FWIW, being budget oriented, if I was given a choice, used valves and pay for the machining to install 1.77 exh valves. Or just new valves and retain the 1.66 exh valves. I would spend the $170 and do the new ferrea 4.98” valves and run 1.66s. Used 2 piece valve are not worth using when new 1 piece are reasonably priced. The carnage from a broken two piece valve is not pretty either...