ACN super squishies

[Ohio Tom]

Piston/valve interference doesn't happen at full lift.
don't go thinking if you have .100" less lift, that gives you .100" more clearance.

The proximity from piston to valve happens at relatively low lifts. Not a full lift.
So you might only gain .050" clearance with lower ratio rockers (not the full .100").

You really need to mock it up and use clay to be sure what clearance you have.

It' more duration dependent than lift.

[txoval]

Tom:

Good point, I will be checking clearances, just thinking out loud.

The 86B and W125 have similar durations as well, total and 50.

Only one way to know though. Looking forward to mock up

[Steve Arndt]

[Alstrup]

[theastronaut]

I would think it would be best to cut mirrored/matching reliefs into the quench pads of the chamber instead of cutting the dome to fit the quench pads... you'd want the dome's shape to affect the direction the mixture mixing instead of having flat quench pads with a bump on the piston top, no? The dome's shape, and therefore the reshaped quench pad's shape adds a new "direction" of quench pad mixing in to the chamber- the quench pad isn't on a single plane then. That's maybe not the best way to explain but it should make sense if you've seen the pistons. Cutting the chamber would give all the benefit of the dome pushing the mixture into a smaller area, and add the benefit of having two quench pad planes pushing the mixture in different directions for better mixing.

If I'm correct in that line of thinking, then maybe these would be nearly as effective set up that way even with a valve pocket added, since the valve pocket won't affect the "new" quench pad area.
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[txoval]

Couple lessons for me on the switch to 92mm SS pistons;

1) 92mm SS pistons have the same 35mm pin height as 94mm pistons. I assumed (even though John’s add is clear) they had a 34mm pin height. Not a huge deal, but just info for the next guy.

2) 92mm Thickwall AA cylinders are 114mm in length from seat surface to top, 2mm longer than standard 90.5 cylinders

3) I switched to 5.4 h-beam rods (78.8 crank) which meant I need to trim the cylinders or deck the case. I chose to do both, .010” trim at case deck, and .046” from the cylinder base. This provides a .040” deck height with no shims. My aluminum case measured 100mm from crank centerline to case deck before cutting.

I have also switched from Panchitos to Tim’s Stage 2 heads with 55cc chambers.

Cam will be a Web 86A on 112 LC’s.

[Dan Ruddock]

[txoval]

I bit of an update and as a reminder, my heads are Tim’s Stage 2, with the chambers cut to 55cc.

Current deck is .040” and after claying the pistons to check chamber clearance, I was basically at zero clearance in a few spots. I chose to mill the domed part of the piston, because I didn’t want to hand clearance my chambers. My neither has a nice mill and we trimmed the dome at the perimeter where it was tightest. At first I clearanced for .040” clearance and then chickened out and went to .060”. These were relatively minor cuts, probably a total of .2cc per piston.

With that set, I moved to check valve to piston clearance. I have two cams, the Web86a on 112 LC’s and a CB2288 (K on 112 LC’s.

I performed this with both clay and a dial indicator. The Web86a has .123” clearance on the intake valve and the 2288 has .115”

This is with 1.5 rockers. I have .575” lift with the 2288

I may increase my deck to .050” to obtain more cushion...still undecided

.040” is 10.1 CR and .050” is 9.8 CR

[txoval]

Also, want to thank the following for your assistance getting to this point:

John@ACN, thank you for answering my emails and questions!

Steve, thank for responding to my PM’s on your experience with the SS pistons

Torben, thank you for answering my PM’s and helping with my head and cam selections

Dan, thank for you taking my calls and helping with the cam, rockers, and pushrods (forthcoming)

Tabari, thank you for sharing your knowledge with me, machining my case and pistons to achieve a .040” deck with my 78.8 crank and 5.4 rods. You saved my bacon on the case/cylinder measurements.

Will close up the short block this week and the top end will follow shortly

[sled]

I would definitely do whatever you need to do to keep the deck tight and compression high...thats the whole point of running squishes.

all the guys successfully running squishes run REALLY high compression in NA applications (as well as forced).
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[txoval]

Sled, I had the conversation with John because I was confused with every SS build I read about. Everyone had wide LC’s (114 and 115) and were retarding the cams 4 degrees. Yet, when I asked John for cam advice he would always say run them straight up on 108 LC’s.

He told me in the beginning everyone, including him was trying to see how far they could go with compression, which led to super tight decks and small combustion chambers. This required the cams above and had others notching their pistons for valve clearance.

He said since then, he has found that the benefits of the pistons are there without going to these extremes.

I had to trim the piston domes because my chambers do not match original VW chambers, which is what the pistons were designed around.

[sled]

shim it and let 'er rip!
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drive your split.

[txoval]

Well, crazy me is looking at a Web 252 Cam as well.

If I get similar valve clearance with it, I’ll probably leave it at .040”

[sled]

[evanfrucht]

I second that smiling devil
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[modok]

It would make more sense if the rockers were progressive ratio, and IMO they should be.
I think once Mr. Ruddock realizes this, he will want to make some progressive rockers to match his camshaft philosophy. It is all that is missing

[jason]

I got 10.5 out of mine with an 86b retarded 2 degrees. Its a bit close on the intakes but the valve is chasing the piston. Exhaust are miles away. Haven’t run it yet. Thought about shaving the dome a bit but figured thats the whole point of them.

[txoval]

What LC for the 86b?

For me, I was either going to hand curve the chambers or neatly machine the piston. I chose the piston because I could hold it easily in the mill and precisely cut what was needed. If I posted pictures of the pistons, you would be be able to tell without hold a non-machined to me next to it

[txoval]

Going with the 252 on 110 LC’s

Having to change valves springs too

[jason]

Mine is 108lc. I have 44 mm valves, 42 would give me a lot more clearance.