Hello.

Back when I started to read this site, alot of people said that the aussie heads and flat tops were the way to go. Now everybody says that it is to much comp. Well I jump on the band wagon last year and got those heads. A couple of questions. Will I have to much comp. for 93 oct? If so, can you open up the combustion chamber a little to increase the cc's? Or can you dish the flat tops a little? Is there enough material to do this? I would hate to have spent the money for nothing.

Chad

 

You can run the aussie heads and dished pistons, its a perfect setup, with a weiand 8010 intake, some 650 CFM carb, and a compcams 265DEH.

 

You can't dish the flat top pistons but you can get dished pistons. You will not be able to get any quench unless you do a lot of machine work which will push the compression even higher or get custom reverse dome pistons.

 

same question and pics, opinions.
http://www.network54.com/Hide/Forum/...eid=1077411600
i would go the piston route. prolly a break-even $$$wise with better results by not reducing the quench area. popular opinion also says that for the quench to be effective, total deck clearance should be around .050 or less. standard head gasket is about .040 so that leaves around .010 for the piston to be in the hole. what bore/stroke is this engine?

 

Whether the pistons can be dished depends on the piston. Many aftermarket pistons have extra material in the head so that they can be sold as flat tops or have dishes machined in. Dies and patterns to make pistons are expensive; the manufacturers don't have different tooling to make each piston they sell. Racers machine pistons all the time.

I would not open the chambers. The only advantage of the Aussie heads is the quench area. I would cc and polish them and either dish the pistons or buy dished pistons that match the quench area in the head. My bet is you can dish the pistons you have enough to drop compression to a livable level.

 

kb's 3434h can be machined .125 (according to the folks at KB)
no ya not gonna find it on there site

now thats a semi custom claimer series producted but customly
if ya follow me

so i don't know if that means anything but figured i would note it

and a 351m/400 will handle compression if set up to do so but it will cost ya lol coatings are great use some today

now we have been through all this before so don't start
just search any date for it you will find most tricks if you have any questions come on back or better any better ideas plase share

after ya figure out what you need
remember to add the machine costs to the piston price VS a custom piston's exacting fit exactly how far do you want to go with this(this should read see *shazam* but that aint a street engine)

>>ok any machine shop will cut a circular dish in a piston but this is not what is needed on a closed chamber this reduces efficentcy on a closed chamber head you need a dish the shape of the combustion chamber which will cost ya much more

 

Thanks for the info. This is a project truck still in the design faze. It probable will be driven daily for a while after it is done. So it has to work right. This is a 400. The plan was bored .030, stock stroke, Aussie heads ported and polished and bigger exaust valves, Flat top pistons, roller cam, roller rockers, single plane intake with pro-jection. The trans a c6 auto, and want to put low ratio planitarys in it. Its going in a F150 with 6 inch lift, 4.10 gears and 35's. That was the plan, but plans change ($$$). So I am reading alot of post an what is working and what is not. I am up for suggestion. I wanted to get close to 500 hp, but that might not happen.

Thanks
Chad

 

You should CC the heads to determine what you are dealing with as far as CR before you selact pistons.

Also what type of driving you plan to do. Do you plan to tow at highway speeds, or is it just a daily driver, or do you just want a lot of gross torque at low RPM?

Another piston option is a 300 I6 piston. There are many versions with dishes of varying sizes. The compression height is higher than required for zero deck clearance, but the top can be cut down to get quench, and a dish for lower CR.

 

I have a set of flat top pistons from Ertel that are the same as Badger or Ohio pistons. IMO they do not have enuf metal in the dome to mill out any significant dish of any shape.

 

Whats the stock dish in CCs?

 

Hello and thanks for the replys.

This project will be somewhat of a daily driver but with an attitude. It has to perform well and be steetable. Its a truck not a top fuel dragster. Thats why all the questions. If I go with the 300 i6 pistons, could a good machine shop cut it down and take a pattern of the combustion chamber and mill it in to the piston? Is this what I need? Also what do I look for in a good machine shop?
And does this set up seem feesable, this is why I am here, for opionins.

Thanks Chad

 

My best recollection for the stock dish is about 13cc.

"If I go with the 300 i6 pistons, could a good machine shop cut it down and take a pattern of the combustion chamber and mill it in to the piston?"

Yes, within reason. The depth will be limited by the minimum thickness required to maintain strength. Unless the piston maker can recommend how much that is, it's a bit of a guessing game.

"Is this what I need?"

Lately, I been re-thinking this option because the modifications may cost too much. The I6 engine doesn't have canted valve heads like the 335/385 series.

You'll have to remove some of the I6 piston top to reduce CH. Cut new valve reliefs so the intake valves clear. Remove some material in the center of the piston to reduce compression and it would be a good idea to make sure the I6 piston is reasonably close to the same weight of the 400 to avoid any rebalancing problems.

"Also what do I look for in a good machine shop?"

I always thought the best place to find a good machine shop was at a local drag strip on amatuer night. Ask around, racers love bragging about their cars.

"And does this set up seem feesable."

Yes, but shop around and get other opinions. It's your engine, your vehicle & your money.
Personally, I like these semi-custom KBs for the best, all around price and performance.

"kb's 3434h can be machined .125 (according to the folks at KB)"

I had not heard this before. It's a good information for me since all they gave me in the past was a minimum thickness.

"In a message dated 1/23/03 8:10:06 AM, tech@kb-silvolite.com writes:
The dome thickness has to be at least .190 thick and valve relief at the
deepest part a minimum of .090 material to maintain strength."

This info was almost useless, unless I already have the pistons to measure, but based on a .125" depth, I estimate up to 20cc can be removed from the piston center to lower compression, when modifying for quench chambers.
---------------------------------------------------------

When we refer to Aussie heads, 95% of the time we're talking about the 302C quench heads. You'll see a wide range of chamber sizes. Accurate or not, the AU Factory Shop Manual I have shows the chamber volume to be 56.4-59.4cc.
The other AU stock head rarely mentioned is the 351C. The same manual lists these at 72.2-75.2cc.
Most people say these are the same as the US 351C/400 heads, but I'm working on a different theory.

I've come across a couple images that suggest they are a semi-quench design. That could account for the 3cc difference from the US heads. The valves look like they have plenty of room to breath, and if they were milled slightly, the quench effect should improve slightly without hurting airflow. I can think of a few applications where a 68-70cc chamber may be just what we're looking for. I don't think they are in high demand so they should be reasonably priced. Any Aussies out there who could look into this?

Lets see if this image will load so you can see what I'm seeing.
http://home.iprimus.com.au/bwill/100_1723.JPG

 

Hello

Thanks for indepth info. With those KB's are they a flat or dished? And do you know what the total cc's (with combustion and piston") you need for the quench to work. I need this to run on 93 octane. Is a 10.5 to 1 compression ratio okay with 93 and the quench and can I get down to that with these heads and the KB's? Sorry for all the questions. Trying to do the build before the build. Keep the ideas coming.

Thanks
Chad

 

You say that you have a truck and not a top fuel dragster, but you want 10.5:1 CR and 93 Octane fuel. You want your cake and to eat it too.

In order to run a motor, any high compression motor on 93 Octane, you need a cam with an Intake Valve Closing (IVC) late enough to keep the cylinder pressure low. This requires a long duration cam, or a retarded cam. Either of these cam features will reduce your low end torque. This is not much of a problem for a light car with a stall converter, but it is self defeating for a truck.

I have such a truck, but it is used as a street rod, not as a truck. In fact I have 10.35:1 CR, and no quench.

If you still want to use your truck as a truck, don't go any higher than 9.0:1 with your CR. Spend your money on porting your heads.

It has been said that head porting is only for high RPM. While it may be true that porting is needed for high RPM, it offers benefits any time you are at WOT. Porting is like increasing the carb size, without all the negative effects of large venturis.

 

I've repeated most of this so many times already but briefly the 3434H KBs I mentioned are flat tops for my infamous 427/400 stroker combo.

Quench doesn't have anything to do with CCs, Try reading the S-o-M building tips.
http://www.speedomotive.com/Building%20Tips.htm

There are volumes of info in the archived posts about compression and octane, static vs dynamic compression. I can't explain it in a few words.

You can also try my home page.

Just to clarify, since email address' are automatically deleted, this information was provided by the KB TECH Dept.

"In a message dated 1/23/03 8:10:06 AM, KB TECH writes:
The dome thickness has to be at least .190 thick and valve relief at the
deepest part a minimum of .090 material to maintain strength."

You can also try my home page.