Selecting Pistons

Go down

Selecting Pistons

Post  75truck on May 4th 2015, 3:15 pm

How to select pistons?

Here is what I am planning:
429 .030 over
Flat tops that sit almost flush
Heads - low compression 72 tbird
Compression ratio  9:8:1
Cam  1500 - 4500 range
edelbrock intake w 700 ish cfm carb
Headers shorties

in a 75 f250 Supercab with a zf 5 speed.

So question is how do i select pistons?
I want to make sure that I am getting pistons that will sit almost flush and not down in the hole.  How do I confirm this with the piston dealer?

Thanx for all the help! Always

Bob
Tucson

75truck

Posts : 97
Join date : 2015-03-26

View user profile

Back to top Go down

Re: Selecting Pistons

Post  dfree383 on May 4th 2015, 3:20 pm

I know this isn't what your asking for.....

But spending a few extra $$ on a stroker kit would be money well spent IMO.
avatar
dfree383
BBF CONTRIBUTOR
BBF CONTRIBUTOR

Posts : 14160
Join date : 2009-07-09
Location : Home Wif Da Wife.....

View user profile

Back to top Go down

Re: Selecting Pistons

Post  supervel45 on May 4th 2015, 3:38 pm

It not supposed to be a good idea to run that much compression on D2 heads with pump gas. The blocks came in at least two deck heights, from 10.30" to 10.32" and some say a 10.31" also. What year is your block?

supervel45

Posts : 3084
Join date : 2013-09-04

View user profile

Back to top Go down

Re: Selecting Pistons

Post  supervel45 on May 4th 2015, 4:12 pm

You can see the different compression ratios with the different year blocks and heads with a flat top pistons. http://www.flatlanderracing.com/trwford429460.html

supervel45

Posts : 3084
Join date : 2013-09-04

View user profile

Back to top Go down

Re: Selecting Pistons

Post  Carl on May 5th 2015, 11:26 am

75truck wrote:
I want to make sure that I am getting pistons that will sit almost flush and not down in the hole.  How do I confirm this with the piston dealer?

You'll need to know the deck height on your block (measured, not just factory spec), then have the pistons made with a compression distance that will set the piston/deck where you want it. There are also going to be variances in rod length and crank throw, especially with factory parts. It's going to be less expensive to choose an off the shelf piston, and machine the block as needed....unless you don't have access to a machine shop.


.

Carl

Posts : 261
Join date : 2008-12-03
Location : Colorado

View user profile

Back to top Go down

Re: Selecting Pistons

Post  gt350hr on May 5th 2015, 11:52 am

Aftermarket piston manufacturers do not have a crystal ball to see what every customer has for a block height. ( the major factor here). So the make pistons "little short" to allow for block decking and year to year block height variation. For instance 429-460 blocks are listed from 10.300 to 10.322 in height. If the piston is made for a 10.322 but the block is 10.300 , the piston will be out of the bore. As Carl said it's cheaper to get the off the shelf piston and have the machine shop machine the block to the desired clearance. 1.890 is a common compression height for aftermarket forged pistons like the Autotec pistons I have for my engine. Knowing the block height in advance would allow the piston company to make them to your specification on a custom basis. Companies like Autotec often do this at no additional charge in some cases.

gt350hr

Posts : 465
Join date : 2014-08-20
Location : Anaheim , CA

View user profile

Back to top Go down

Re: Selecting Pistons

Post  supervel45 on May 5th 2015, 1:01 pm

The point I was trying to make to the OP is from the chart was that his 9.8/1 compression ratio was incorrect with flattop pistons even with around a 0" deck height. If you look at the chart with a 97cc head and a early block it lists 9.05C/R and 8.67C/R with a late 72/73 block. That is a .38" C/R increase. No quench pad on a D2 head and less than a 1/2 point of C/R gain. Is it worth the hassle? Like Carl said he would be well advised to deck the block, for his 0 deck height, for the reasons he listed.

supervel45

Posts : 3084
Join date : 2013-09-04

View user profile

Back to top Go down

Re: Selecting Pistons

Post  gt350hr on May 6th 2015, 11:00 am

supervel45 wrote:The point I was trying to make to the OP is from the chart was that his 9.8/1 compression ratio was incorrect with flattop pistons even with around a 0" deck height. If you look at the chart with a 97cc head and a early block it lists 9.05C/R and 8.67C/R with a late 72/73 block. That is a .38" C/R increase. No quench pad on a D2 head and less than a 1/2 point of C/R gain. Is it worth the hassle? Like Carl said he would be well advised to deck the block, for his 0 deck height, for the reasons he listed.


I agree! To get to 9.8 at "0" deck would require a -18cc dished piston , a flat top would be almost 11.7 and 11.2 at .020 below the deck. You can't get there with a flat top.

gt350hr

Posts : 465
Join date : 2014-08-20
Location : Anaheim , CA

View user profile

Back to top Go down

Re: Selecting Pistons

Post  supervel45 on May 6th 2015, 5:15 pm

gt350hr wrote:
supervel45 wrote:The point I was trying to make to the OP is from the chart was that his 9.8/1 compression ratio was incorrect with flattop pistons even with around a 0" deck height. If you look at the chart with a 97cc head and a early block it lists 9.05C/R and 8.67C/R with a late 72/73 block. That is a .38" C/R increase. No quench pad on a D2 head and less than a 1/2 point of C/R gain. Is it worth the hassle? Like Carl said he would be well advised to deck the block, for his 0 deck height, for the reasons he listed.


I agree!  To get to 9.8 at "0" deck would require a -18cc dished piston , a flat top would be almost 11.7 and 11.2 at .020 below the deck. You can't get there with a flat top.
I think he has open chamber heads. I agree with your post if you where refering to closed chamber heads and trying to lower compression. I think he is trying to get the compression up into the 9/1 range with the open chambers.

supervel45

Posts : 3084
Join date : 2013-09-04

View user profile

Back to top Go down

Re: Selecting Pistons

Post  IDT-572 on May 6th 2015, 5:42 pm

Put a rod and piston on the crank in the block and check the deck height. Then measure the pin height on the piston.

Allow your self about .010 and then buy the pistons you need, and that will allow a cut on the deck to put your piston to deck where you need it. Be it zero deck or .005 in the hole or what ever.

Also if you do have the D2ve heads find a set of D3ve's and run them with a flat top or a set of Dove's with a dish piston around 19-20 cc.

That way you can have a good quench and have the compression right where you want it.
avatar
IDT-572
BBF CONTRIBUTOR
BBF CONTRIBUTOR

Posts : 4604
Join date : 2008-12-02
Age : 57
Location : Shelbyville Tn.

View user profile

Back to top Go down

Re: Selecting Pistons

Post  gt350hr on May 7th 2015, 1:59 pm

supervel45 wrote:
gt350hr wrote:
supervel45 wrote:The point I was trying to make to the OP is from the chart was that his 9.8/1 compression ratio was incorrect with flattop pistons even with around a 0" deck height. If you look at the chart with a 97cc head and a early block it lists 9.05C/R and 8.67C/R with a late 72/73 block. That is a .38" C/R increase. No quench pad on a D2 head and less than a 1/2 point of C/R gain. Is it worth the hassle? Like Carl said he would be well advised to deck the block, for his 0 deck height, for the reasons he listed.


I agree!  To get to 9.8 at "0" deck would require a -18cc dished piston , a flat top would be almost 11.7 and 11.2 at .020 below the deck. You can't get there with a flat top.
                                                                                                                                                                               I think he has open chamber heads. I agree with your post if you where refering to closed chamber heads and trying to lower compression. I think he is trying to get the compression up into the 9/1 range with the open chambers.

Sorry , you're right , guess I misread it. FT+ 97cc head = approx. 9.6c/r

gt350hr

Posts : 465
Join date : 2014-08-20
Location : Anaheim , CA

View user profile

Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum