I think I have created a possible ego problem here.. I have a 1969 Bird Vert.. I am trying to make a Trans Am Clone.. The heads are #48 close chamber high compression heads.. the block is a 400 cu. out of a 1969 GTO 4 speed with the build date two weeks after my car was born... The problem I have is did I do the rebuild with two low of compression pistons for what I have,???? The thing I'm afraid is it won't have the power or the torque and especially the sound... The guy that built my engine used 9 to 1 compression forged pistons, 30 over,, the heads were shaved 20 thousance to clean them up,, does anybody have an idea what horse power I will have and what the torque should be on 92 octane pump gas,???.. that is the reason for the lower compression pistons, so I could use pump gas.. also stainless valves... should I take out those brand new pistons and replace with higher comp. and a better cam,?? or will it eat me up for high octane gas,?????.. What would you guys/gals do,,????... I want to be able to cruise this mad machine and not have to rob a bank to do so,, but I want it all,, the best of both worlds, you know,, just like everyone else...

I'm assuming that the pistons were 9-1 with stock heads. You had them shaved .020 which will raise the compression a little, probably to around 9.4 to 1. You are right on the line for using 92 octane. As far as power, in my opinion, you are just right for the cruiser.
I would continue with your plans and see how it turns out.

Do you think I'm going to sacrfice power/torque FUN!, for the sake of saving gas $$$,, Does anybody have an idea what HP I should have now with this set up,????... Yes they are stock #48 1969 pontiac heads...

What piston did your machine shop install? With the 48 heads (stock 72 cc's?), and as Jim noted, shaving 0.020", you will have pretty high compression with 0.030" over stock replacement pistons - probably close to 10.5:1, maybe a little higher.

I was not aware of a "9.0:1" replacement, off the shelf piston. Did the the machine shop dish the pistons to get the 9:1?

Tom

We would need the exact piston specs to get really specific. I used your figures to calculate the resultant 9.4 to 1. It depends on what you want to do and what gas you want to burn whether you have enough comp./torque/HP. I run stock compression and high octane gas because I would rather pay for gas and get all the BANG.

Here's a likely aftermarket piston:
http://store.summitracing.com/partdetail.asp?Ntt=l2262f&N=0&part=TRW%2DL2262F&autoview=sku&Ntk=KeywordSearch

I don't know,, I'll have to check the paper work or call the Machine shop guy.. All I know is what he told me,, '9.0:1' comp. ratio, forged pistons... The pistons in the motor are brand new flat top..

Well, your options are to keep it like your machine shop guy planned with about 250 HP or go with stock compression. Stock compression(around 10.5 to 1) would make it so your have to burn a mixture of 92/93 and 110 octane racing fuel. It would also give you another 75-100 HP. This is all very general to keep it simple to make your decision easier. Once you make the decision to go with the higher compression you will ALWAYS have to use high octane.

How is it with todays motors that they can get 350 to 550 horse power using pump gas???.. why can't I do the same with this motor,???.. should I change to Aluminum heads and change cam.. is it not possible to do this with the older engines??????..

Aluminum heads will get you the ability to use 92/93 octane with higher compression. You should be able to run 10.5 without detonations.

do you mean I can leave the pistons that I have in there now 9.0.1 compression, and add aluminum heads and it will jack up the compression, but I still will be able to use 92-93 octane gas.. or will I have to use higher compr. pistons along with using alum. heads??????

Yes, you should be able to use the pistons you have. You would have to order the heads with your specific piston and bore information. They would calculate the cc of the heads to get you to the compression you want.

I guess it would be cheaper short term to replace pistons vs. buying new heads, but long term gasoline costs.. do you have any idea what a new set of aluminum heads would cost me.???

A nice set of Edelbrocks set up with the best parts will cost you around a $2000. Unless the prices have come down.......
Reference:
Street Edelbrock heads, includes everything above (except Ferrea 5000 series valves + chrome moly 7 deg retainers are used and a flow chart of 2 ports is included), pocket ported to flow 295+cfm @ .600” lift @ 28”, no extra cost valve size options, 2.11” intake valves, 1.66” or 1.77” exhaust valves. More flow throughout all valve lifts compared to out of the box Edelbrock heads with better components installed for only a few dollars more!!!!
72cc $997.50 each
87cc $1072.50 each

I guess what I could do is try it as it is and see if I'm satisfied, and if not it will be easier to change heads than it would be to pull motor out and change pistons.. If I change heads will I need to change cam too????

We need to know your exact piston specs first...dish AND how far "down in the hole" they are at TDC. Then we'll be able to more accurately calculate your CR.

Then, decide what you want to do. I'll be glad to send you info on my recent "upgrade" but, its only one of many possibly less expensive directions to take.

You can buy an awful lot of premium gas for the cost of a set of aluminum heads.

20 thousandths is 4 CC. Holding true, those heads were virgin at 72cc, you are now at 68 cc. Those pistons would have to sit in the hole pretty deep or have a nominal 18 cc valve dish/relief with a .020 deck.

Without throwing a bunch of crap at you. I need piston part numbers and deck height. Without those, all anyone is doing for you is guessing.

Where are the part #'s on the pistons? Can they be found w/ the pistons installed?

The numbers are right on the face of aftermarket pistons.

What about stock? Tried looking them up (Autozone) w/ no luck.

To clarify a few things, if you have flattops they will give you very close to the same compression as the factory rating for the heads you are using. In the case of the #48s, that would be 10.5:1. If you have dished pistons, the volume of the dish will be added into the total volume to tell you your "new" compression ratio. As stated, no compression numbers without piston and deck height numbers.

Aluminum heads will allow you to run a higher compression ratio on the otherwise same engine combo and the same octane gas as with iron heads. That extra is .4-.5, not 1 point or higher. A more modern chamber design on an aluminum heads will allow higher than that but the rest of the engine needs to be considered before counting on being able to run pump gas.

The extra 1 1/2 points of compression will add only about 8-10% to the power output or about 30 hp, not 75-100hp. A fairly stock 400 with 8:1 compression and a mild cam will make about 300hp, a better cam about 320-330hp, a 400 built strictly to '69 RAIII specs will make about 360hp, add properly ported heads for another 30-40 hp, and finally another step up in flow to the Edelbrock heads for about 450hp. Proper cam selection and engine prep is assumed (but not always easy to find).

Stock piston numbers are visible from the bottom. Just flip 'er over and pull the oil pan.

Thanks, Vikki.

I also noticed, James, that your mid-70s engine had pistons with beveled edges, and were stamped "S" on the face. Valve notches looked normal, not compression-reducing.

Thanks for the effort.. I checked the numbers on the piston tops and they are { L2262F .030 }... below that are the numbers {05-176-01B }... I did not see any name on the piston top... As far as I can tell measuring from the top of the deck to the top of the lowest piston is 3 3/4" of an inch.... hope this helps....as far as the cam goes it's a Comp Cam,, { Part # 51-314-4 },,.. { grind P8 280AH-10 }......... {Gross Valve lift intake .481 ,, exhaust .481 }... Duration @ .050 intake 232.. exhaust 237 .... Stainless valves with dual springs & hyd. lifters... Thanks again... Dale

http://store.summitracing.com/partdetail.asp?part=TRW%2DL2262F&autoview=sku

If block is not zero decked, you are at 10.2 to 1 with those pistons and 68 cc #48 heads.

About 6/10th higher CR for a 0 decked block (400)

Zero Decked,????????????.. as far as I can remember the block was not decked, if it was it was just enough to clean it up, but i'm sure he did'nt do that.. like I posted earlier the heads were shaved just 20 thous. to clean them up.. If you need I can take a pic of the top of the piston, but I don't know how to post a pic on here yet...

With a piston produced to sit deeper in the bore, you do not want to 0 deck block or mill heads excessively. Defeats intended purpose of the piston. I believe there is another piston out there that is right around 9.2 to 1 with a 72 cc head.

Do not need a picture of the piston top, the part number was fine. If you just had a deck mill to true, I believe your CR is right around 10.2

Do you need to know if piston comes right to the top of the block/deck, or from top of deck to top of piston with the piston down as far as it will go,???????

I kinda like the idea of a 450 HP trans am clone.. in a convertable,, boy now that would be a Screamer!!!!

I know Brent will jump all over me on this...

Your block deck (stroke) is a given distance. As a rule, .020 piston top to deck is typical for that era of block. When you 0 deck the block (or mill heads) you take away that .020 and increase compression by removing volume of the combustion area.

Knowing your piston numbers (specs tell me how far your pistons sit in the hole), just a clean up on block (maybe a few thousandths clean up) and knowing 20 thou was taken off gives me a rough number of 10.2 to 1.

That is all. No pics needed at all.

Brent will give you the MIT/Oxford explanation....

Those pistons with those heads should do just fine. Plan on using a mixture of 92 and 110 octane. It's very close to the same build as my 79 TA. I have those pistons and 62's that are not shaved. I think you will be very happy with the performance.

Will I have to buy higher octane than pump gas if the compression is over 10cr..????... maybe I should use the aluminum heads on my 1969 vert 400 block and replace the # 6X heads on my 1968 firebird w/ a 1974 455cu.in in it with the #48 heads to jack the compression up on it...

Do you have any idea how much horse power I will have, and what mix ratio should I do the gas.??????

You do not want to put the #48s on a 455.

What about the size of the cam,, is it going to perform pretty good and is it going to sound cool,????,, or can I do or should do better..?????

Okay,, now the most obvious question from me is 'Why',, What will happen,,????.. This is why I am here.. to learn

I suggest buying Jim Hands book on engine rebuilding or a Chiltons manual or Sunnens guide to engine machining before you try to "jack it up".

You'll jack it up allright. The wrong way.

A 455 has a bore of 4.151 and a stroke of 4.210. A 400 has a bore of 4.12 and a stroke of 3.75. 6X heads have huge chambers 110 CC (GRAPEFRUIT) bigger. #48 heads have volume of 72 cc (ORANGE).

You put grapefruit heads on a 400...7.8 compression, bad.
You put grapefruit heads on a 455...eh, so so. 8.6 to 1

You put Orange heads on a 455..squish..need 110 octane.
Orange heads on a 400, 100 octane.

It is all about area/volume when piston reaches TDC of the stroke. This area includes some ring area, valve relief cc, chamber volume and deck height clearance.

When I say read about it...it will be better if you had a diagram and read up on it rather than reading schmucks like me explain it.

In essence, most good heads are 72 cc..On a 400, they are fine with the proper piston and a blend of fuel if a stock piston.

The smaller the volume at TDC, the higher the compession, the higher the grade of fuel.

Jim Hand's book is an excellent primer, and it gives many suggested recipes for successful engine builds.

If you are going to vary from stock parts, it is important to know what to choose. Sometimes what looks on paper to be a lower performance part will develop more power in a particular configuration.

If you are borderline on a compression ratio increase/decrease, head gaskets are available in different thicknesses.

These are low compression heads..look at the size of chamber and depth where valves are..

http://cgi.ebay.com/ebaymotors/Pont...categoryZ140686QQitemZ160099174642QQrdZ1

These are high compression heads...

http://cgi.ebay.com/ebaymotors/1967...categoryZ140686QQitemZ270103356068QQrdZ1

Look at the chamber size difference..