ktm Posted June 11, 2009 Share Posted June 11, 2009 I plan on building up a nice setup after I get the car up and running on a replacement block. I am torn between going with dished or a flat top pistons. I was boosting up to 22 psi on my old setup. What I want to hear is anecdotal testimony from those who have had both setups and which one they prefer and why. My car was a screamer once on boost and by peak torque you'd blow by Lone Star One at Plaid Speed. Does anyone have any such experience that they would like to share? Keep in mind, most posts that I could find only included those who built a flat top setup and not a dished one and vice versa. I am looking for testimonials from those who ran both. Thanks! Quote Link to comment Share on other sites More sharing options...
z-ya Posted June 12, 2009 Share Posted June 12, 2009 What head? What head gasket? What cam? What is your target CR? Quote Link to comment Share on other sites More sharing options...
ktm Posted June 13, 2009 Author Share Posted June 13, 2009 z-ya, I was hoping that folks who've run both setups would chime in with their own experience about which they prefer. I've done quite a bit of research regarding a flat top build. I do not know if I would be happy with its performance over the standard turbo setup. P90a head, stock 1.2mm head gasket, L28 crank, L28 rods, dishd pistons, standard 7.4 compression. I would simply use flat tops instead of the dished pistons. Both setups would be bored 1 mm over. Quote Link to comment Share on other sites More sharing options...
Daeron Posted June 13, 2009 Share Posted June 13, 2009 Well, according to my understanding the quench effect in a stock L28ET with stock N42 L28E flattop pistons would be almost nil. According to 1_fast_z the clearance between piston crown and quench pad should be in the .21-.25 mm range, and I have heard others say as far as 0.5mm (that was a SBC discussion IIRC) BUT you need it to be close. The stock L28ET but flattop combo has a deck height .050mm below the firing deck, plus your HG compressed thickness puts you pretty far away from the piston, so you have that 8.5:1 comp ratio to deal with without the "benefits of quench" (and I am hoping you understand why I am putting that phrase in quotes.) NOW, say if you could get some Z20 +1mm overbore flattops, (they have a shorter pin height,) and use L24 rods instead of L28, you wind up popping the piston out of the deck about .2mm or so and you come closer to your goal.. Or, custom ordered pistons to whatever pin/deck height you should want. But if you are just strictly talking about for a quick rebuild to get your car going again that won't make the wife tighten her grip around your already straining throat, then breaking the new ground of flattop land probably isn't worth it. It is so incredibly annoying that there were never PROPER quenching piston/rod combinations available for a reasonable compression turbo L6!!! Quote Link to comment Share on other sites More sharing options...
woldson Posted June 13, 2009 Share Posted June 13, 2009 Well, according to my understanding the quench effect in a stock L28ET with stock N42 L28E flattop pistons would be almost nil. According to 1_fast_z the clearance between piston crown and quench pad should be in the .21-.25 mm range, and I have heard others say as far as 0.5mm (that was a SBC discussion IIRC) BUT you need it to be close. The stock L28ET but flattop combo has a deck height .050mm below the firing deck, plus your HG compressed thickness puts you pretty far away from the piston, Not doughting, just where did you read this? I kinda want to know why did they even bother to peanut the heads on the N/A's? Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 13, 2009 Share Posted June 13, 2009 Methinks Daeron needs to not go metric, and change back to the english system, and then his assertation of what 1FZ was saying would be correct. Most people run 0.040", 1FZ is running his head to crown clearance closer to 0.020" Which is 1mm, and .5mm .5mm is closer to 0.020", 0.20mm is closer to 0.008" It's the scourge of the metric parrot! ERRRRACH! Wrong conversion factor! ERRRRRACH! Quote Link to comment Share on other sites More sharing options...
Daeron Posted June 14, 2009 Share Posted June 14, 2009 Methinks Daeron needs to not go metric, and change back to the english system, and then his assertation of what 1FZ was saying would be correct.Most people run 0.040", 1FZ is running his head to crown clearance closer to 0.020" Which is 1mm, and .5mm .5mm is closer to 0.020", 0.20mm is closer to 0.008" It's the scourge of the metric parrot! ERRRRACH! Wrong conversion factor! ERRRRRACH! it is, but blame me for laziness in not having my links handy, rather than blaming me for squawking! In my defense, I had sent ktm an extensive PM before what I posted publicly. That PM was predicated by a disclaimer and some pointers to help find the original posts I was referencing... and then my post was something of a continuation of that. Sloppy, I guess. I wish we could get rid of inches and pounds altogether, though. I am only attached to them because I am forced to use them so often. So yah, Sue me!!! *ducks out of the room* Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 14, 2009 Share Posted June 14, 2009 Can you whistle like a parrot after that 'errach'? I always liked the whistle better than the loud noise...LOL I figured it was a straight conversion error, just forgot it was inches, not metric. JPL missed mars under similar circumstances, you know! Quote Link to comment Share on other sites More sharing options...
Daeron Posted June 14, 2009 Share Posted June 14, 2009 Can you whistle like a parrot after that 'errach'? I always liked the whistle better than the loud noise...LOL I figured it was a straight conversion error, just forgot it was inches, not metric. JPL missed mars under similar circumstances, you know! all taken in good fun. I'm a tad sensitive (tongue in cheek) because I know durn well that I can never remember which unit corresponds to the 22, and how many decimal places are involved. If I could remember one, the other would be no problem. Here is the thread I have bookmarked, and I will quote the post from brian in particular: YOu need to Have .025" piston to head clearence. Order your pistons extra thick in the domes. Then when you get them, you need to find out where the exact mirror image is of EACH combustion chamber, usually by putting prussion blue on the head, and bumping the head, with no head gasket with the pistons installed in the bore, and on rods and on the crank. Then mark the outline of the CC with a scribe. Then go to your mill and dish the correct amount, but do NOT go outside of that scribe line. Then once you have them all dished, go back on the inside and lighten them up, since you ordered them extra thick, and make it about .200' thick everywhere in the dome. Hope that made sense. Quote Link to comment Share on other sites More sharing options...
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