Coming back around and askingthe questions we should have addressed earlier perhaps...

TH400 tranny
454 + .030
CC Magnum 270H
Stock crank
Stock replacement flat top pistons
AirGap
750 Holley Vac 2ndary

The peanut heads are getting replaced, we're considering going to closed chamber heads to up the compression a bit if we can find them (and at an affordable price!). Question is, how much of a difference will an open versus a closed chamber make on this combo and if enough, which heads would be best from a weekend cruiser standpoint? We found a set of 702's for $150, but one of them turned out to be cracked, so no deal there! Love to find another one of those prices!

REALLY don't want to go back and replace the brand-new pistons, but had I pulled my head out and thought for a moment, I'd have gone with domed pistons in the first place... graemlins/clonk.gif

So, best route at this point?

Opinions?

Figure a 98-101 CC closed chamber heads will have about 8.9 9.0 to 1 compression with flattops..alittle more with a steel shim head gasket and if the block is decked.
The 9.0 range allows you to run more cam that at 8.0 to 1 w/open chamber heads.
For max power in 9.0 to 1 454 motor in a street car,I'd use a mild flat tappet solid cam and run 3.73 gears.
There are also plenty of hydraulic cams that will fit the bill too,but stick with 225-238 @ .050 range and up to .575 lift

The cam is already in - 270H is a hydraulic flat-tappet, 270/270, 224 and 110* with a .510 lift.
Not incredibly aggressive, but shouldn't be too bad...

Right now the rears are 2.56's (GULP!), but we're looking to change them down the road. I know you've got some great times with yours, Chris, but you've got a pretty good thumper too.

We ARE hoping for 3.73's, but I'm a bit concerned about freeway driving. Maybe 3.55 or so instead?

So which heads specifically are in that 100CC range in a closed chamber? And... is closed definitely a better way to go?

I would say closed chamber is best for your application in regards to raising your compression.
Your cam should be a very good match for 9.0 to 1
Tom "mc71454" ran this cam years ago in his Monte with a flat top/closed chamber head 454 and ran a best of 12.65 with a lot of tuning and using 3.55's
check it out here:
http://www.geocities.com/mc71454/INFO.html
Heads to look for are (using the last 3 digits of the casting #)
063
702
215
290
390 (98 cc's)
Theres a few others as well,but thats all I can remember.
Thanks for the compliments too.

I'd forgotten about Tom, but yeah, now that you mention it I did know that.

I've been lurking and reading what you've done with your combo and the 2.56s for some time, so I know all is not lost. I talk to Phil (pnutkemist) periodically as he is near me and is trying to model his rebuild after your motor too. It's always nice to know what others have accomplished.

Now, all we need to do is find an affordable set of those heads. The Turlock Swap meet is at the end of January... hopefully someone will be parting with a set by then!

Curt,keepin mind you should get a convertor,it will certainly help the motor get into the powerband alot quicker and improve the general "reaction" when you hit the gas,even easing into it.
The 12.99 was my best with those 2.56's,in mindshaft air running drag radials
Typical runs where in the 13.20-13.40 range depending on weather, and track condtions (traction)
If felt pretty good with those gears..very fun on the street and it would crank out some MPH on the highway and do big,long smokey burnouts like you read about :D

yeah - figuring about a 24-2800 converter...?
Mo money...mo money... MO MONEY!
:D

2400-2800 would be perfect

-206's are another set of real early heads too.

96.7 to 97 cc's or thereabouts??

pdq67

My 290's CC'd at 104CC after a little chamber work to unshroud the valves. The early 396 heads are the smallest chambers by far.

If you were willing to change deck height or pistons or both to achieve the same static the open chamber heads would have the advantage. Apparently they breath better, no doubt due to the unshrouded intake and chamber shape...as you may know the open chamber heads were designed to reduce emissions but an added benefit was they performed better than their closed chamber counterparts :cool:

Changing the deck height was a thought at one point. Shaving the heads, right...? Then using an appropriate head gasket...?

How much would/could one remove without impacting the performace and getting to around 9 or 9-1/2 CR?

OK........first of all if you really want this thing to be responsive you really need to get the compression up at least another number,say, 10:1 Secondly, install the cam a little early if you can ,I'm sure you have more than enough running clearance.There are enough web sites for calculating compression ratios,PreStage.com for one but its really just the ratio of the swept volume of the bore plus the chamber and adding in for valve reliefs divided by the chamber.Now start changing the volumes in the chamber in the formula until you achieve 10:1....ask your machinist if you can remove the amount you'll need to achieve it.....if not, cut as much as practicle :cool: and yes a thin gasket is an option if you dont care about retaining a specific quench.....I dont think it'll matter too much for a fun street car....just do the math and you can probably achieve the numbers(compression)by a little machining, checking ..... :cool: and maybe a head gasket change

Thanks Joe;

so I'm a little new to this whole DCR/SCR thing, and the calculation of CRs in general...

What's the difference in a bore versus that of a "swept" bore? If I take a standard .030-over bore and then figure in, say, a 98-100cc head...
Then, knowing what the size of the valve reliefs are... AAAHHHG!!!

On the other hand, is there "too much" cutting off that could be done? Not from a physical damage to the heads standpoint, but rather from a performance issue? Would removing too much downgrade performance at some point? Or is it more a matter of practicality and physical possibilities of the head? Obviously if one took off too much and left the heads too thin, THAT would be an issue, but other than that...?

Thanks for the input too!!!

The swept volume is the bore over the length of its stroke.....as far as how much to cut if you choose that route,consult with an engine shop that does high performance work that is familiar with that type head.....you dont want to weaken the head...... :cool:

dittoz,
how far from vegas are you??
i might have sumthin' for you,you will be interested.
sri3850341@aol.com
shane

Shane - I'm just ouside Sacramento.

and you've got email...


-curt