Relieving the fuel bowl edge and compression

[Big Bore]

Anyone know if relieving the edge of the fuel bowl has any measurable affect on compression numbers?

 

[907DAVE]

Barely any material is removed with a "radius job". It will decrease compression, but it will be so miniscule you will never know the difference.

 

[Hotrodtractor]

Anyone know if relieving the edge of the fuel bowl has any measurable affect on compression numbers?

The effect on compression is directly linked to the amount taken off. The more you take off, the lower the compression gets. You don't have to remove a lot of material to prevent cracking - but maybe you want to remove material to be able to get the spray in the bowl with a bit more timing perhaps.... its all a balancing act.

 

[JDub]

We generally cut pistons depending on customers overall goals and the trucks uses. Cutting the radius around the bowl to alleviate the overhang and potential hot spot for cracks to start will have a minimal affect on overall compression ratio.

 

[1BADF350]

Hotrodtractor,
How far back have your bowls been cut?
What does it cost to have the edge removed or if for a stock build, can this be done at home with sanding rolls?

 

[powerstrokenstang]

is there any advantage to leaving the lip?

 

[Hotrodtractor]

Hotrodtractor,
How far back have your bowls been cut?
What does it cost to have the edge removed or if for a stock build, can this be done at home with sanding rolls?

The bowls pictured are straight cut to the largest diameter of the factory bowl. This cost can vary - but somewhere between $10-30 per piston is what I have seen depending on the level of work your looking for (bowls opened up, radiused, valve reliefs, adjusting the deck height, etc.. all add up).

is there any advantage to leaving the lip?

There can be to a point..... maybe not so much in leaving the lip - but there are decent power gains and efficiency to be had by adjusting the bowl shape - having some of the "re-entrant" lip design built in has shown some advantages in combustion chamber turbulence. I have spent a decent amount of time looking at combustion chambers and talking with guys about combustion chambers that I know that the next engine I build for myself will have something drastically different in it.

 

[Big Bore]

Are those roller rockers I spy in the background?

 

[powerstrokenstang]

There can be to a point..... maybe not so much in leaving the lip - but there are decent power gains and efficiency to be had by adjusting the bowl shape - having some of the "re-entrant" lip design built in has shown some advantages in combustion chamber turbulence. I have spent a decent amount of time looking at combustion chambers and talking with guys about combustion chambers that I know that the next engine I build for myself will have something drastically different in it.

just wondered, i was think you were one of the ones that decide the lip should be left on my pistons.

 

[Hotrodtractor]

Are those roller rockers I spy in the background?

They sure are - brand new in 2006 and first fired in an engine in April of 2007.

 

[JDub]

is there any advantage to leaving the lip?

The pistons we cut will still have some of the lip around the bowl, we don't cut them straight down into the bowl. More of a radius edge around into the lip. Pistons machine costs will run $200-450, depending how much is being done to them.

 

[Big Bore]

They sure are -.

And those are for a 7.3 Powerstroke?

 

[Gearhead]

I have the bowls relieved about about 3/16" and it has not affected anything other than adding durability under high heat periods like towing.

 

[Hotrodtractor]

And those are for a 7.3 Powerstroke?

I think so.....

 

[Big Bore]

I think so.....

Hey now, thats the first I've even HEARD of rollers for a 7.3, much less SEEN them. Custom one of a kind or...?

 

[Dieselfever]

See pg 2: http://www.wipeoutenterprises.com/2006_pwsparts.pdf

-Michael

 

[Hotrodtractor]

Hey now, thats the first I've even HEARD of rollers for a 7.3, much less SEEN them. Custom one of a kind or...?

In 2007 - I was running them, Unlimited was running them, Sapps had them in the white regular cab OBS drag truck, and I think there was at least 2 more that I know of that year.....

I just went and looked - I first posted pictures of my parts in April of 2006 on TDS.

 

[Charles]

Mine retain the factory angle just pushed out to a larger bowl ID with a radiused lip.

When the engine came apart on the uncut factory pistons every single piston had multiple cracks of varying size, but all pretty long and ugly with piston #7 having suffered one straight down the bowl and through the bottom, which is what got that engine pulled in the first place.

When it came back apart a few months back after running for 2 to 3 years at 600+ and towing HARD at that power, I fully expected every single piston to be cracked again. And while the heads were basically annihilated with cracks all through the seats as before, the pistons looked like they did the day we set the heads on it. Somewhere between the radius and the ceramic coating the cracking stopped.

They seriously looked brand new. And they went right back in the holes too.

 

[JoeDaddy]

Hotrodtractor,
can this be done at home with sanding rolls?

Never done 7.3 pistons but i use a fletcher for sharp aluminum edges.

 

[Charles]

Never done 7.3 pistons but i use a fletcher for sharp aluminum edges.

Just about anything will work on an aluminum piston in the lathe. IIRC mine were radiused with the edge of a file and then polished up for a second with a piece of sandpaper.

Hell, I think a pocket knife would suffice.