Well started to assemble my short block tonight and after cleaning the block and chasing all threads and bolt holes I started to prepare to file my rings ...only to discover that the machine shop only went .003 over piston size? I think that would be ok for a NA motor but I think that would be to tight for the turbo setup, I'm thinking more like .006-.007? What do you guys suggest. I'm running Probe SRS pistons that are 2618 - T6.

Well there goes another good weekend ....guess I'll have to spend it with the wife now??

Kerry

 

I'm going to be running about .005" with my 2618 JE pistons and a 4" bore. How exactly are you measuring your skirt clearance?

You may be getting a reading tighter than it actually is if you are using a feeler gage rather than mic'ing the piston skirt at the manufacturer's specified measurement point and using a dial bore gage on the cylinder bore.

 

:withstu:

 

I miced it a half inch up from the bottom of the skirt and miced the cylinder with an inside mic. I have standards for my mics and they were checked before I started. If I remember correct the piston was 4.026 -4.0265 and the bore was 4.029. I think I will have him hone it to 4.032. Andrew are you running gas or Alc. with those clearances? Also what ring gap will you be running? I have been told three different things be three different people???

Bennett racing Which sold me the hi temp speed pro rings .030 on top and second

Speed pro paper

Speed-Pro top rings (ductile iron, 4" bore)
moderate performance .016 - .018 (.004 per inch of bore diameter)
drag racing, oval track .018 - .020 (.0045 per inch of bore diameter)
nitrous oxide - street .020 - .022 (.005 per inch of bore diameter)
nitrous oxide - drag .028 - .030 (.007 per inch of bore diameter)
supercharged .024 - .026 (.006 per inch of bore diameter)
Speed-Pro 2nd rings (cast iron, 4" bore)
moderate performance .020 - .022 (.005 per inch of bore diameter)
oval track .022 - .024 (.0055 per inch of bore diameter)
nitrous oxide - street .024 - .026 (.006 per inch of bore diameter)
nitrous oxide - drag .028 - .030 (.007 per inch of bore diameter)
supercharged .024 - .026 (.006 per inch of bore diameter)

Darren Dakota a friend of mine here that works at Cam Motion and also builds many 7 and 8 second cars. He is the one that built the engine for Carlo Catalanotto thats the car that was in the April 2004 issue of MM&FF that has in the 7's on the license plate...it's from New Orleans and he suggested .029 top ring and .025 bottom. ??????? I thought that would cause the top ring to flutter?

 

Gaps are opinionated so each builder has their own preference but generally speaking, if that engine is seeing forced induction they are certainly on the tight side.

.006" is what I would aim for if it were my assembly.

As for ring gaps these also seem to change by the year, remember a year or two ago gapless top rings were the way to go. Now they cause high RPM flutter and sealing issues.

The current concensus is to run the second gap slightly larger than the top, .003 is what we usually run.

Keep in mind that too tight of clearances result in serious failures. Higher cylinder temps in forced induction engines are not forgiving to butting rings or stuck pistons.

$.02

Brian

 

Thanks for the advice Brian and by the way I like your music

 

On the box of Probe srs pistons it says .003 NA and .006 forced induction...

 

Yea, I think that the machinist forgot I was doing a forced induction setup??? Well he said he would have it done today ???so I will find out tonight when I Mic everything.

 

Another hone and slow easy run in time ???

 

Correction. . .Just spoke with my machinist. I will have .006" piston to bore clearance. For the ring gaps, I was going to stick with the high side of Speed-Pro's/JE's recommendations. So. . .around .026" on the 1st and 2nd. I may go a bit bigger than that. I'll talk it over with my machinist who has done a number of 1000+ HP turbo cars.

I just had a custom roller ground by Cam Motion. I wonder if he or Terry Williams spec'd it out.

 

His name is Darren Dakota and he told me to feel free to send any of you'll his way He said I could give out his cell number. One of the engines that is being tested that he just built has a split duration but not only exh. and intake but cylinder to cylinder ...you know those damn front and rear lean cylinders..you know hold the valve open a little longer. I just started my assy. tonight ...I had .005 cyl to piston. I mic'd the piston a 1/2" from the lowest part of the skirt? is that the normal on Probe pistons? The ring gap I went with .030 top and second that is what Bennett racing suggest for the street and strip. He claims 90percent of their motors go out the door that way. I will start a new thread about my engine build up.

 

Subscribed. I want to see what Swtracing's machinest tells him about the ring gap since I am going to be doing mine myself. Thanks.