3.1 Short Stroke Build 66 X 100
 

Started on my 3.1 short stroke engine. I have been looking at all the parts for almost a year. This build will be based off a 930/02 early 3.0 Carrera case. Ollie's went through the case and Pauter modified the 2.0 crankshaft. Improved oiling mods and rod journals cut down to 1.99" for Clevite/Mahle rod bearings and lightweight Pauter rods.











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Looking good Mark!

My dream motor! Love a 66mm crank. especially one with high rpm oiling mods.

Keep going Mark. I am watching with interest.

More details on the build please.

Are those rods titanium?

The crank is super tasty!
cheers,
dug

Very nice Mark... that's going to be a great engine for the 72 ;)

Beautiful start Mark
It looks like your plan is to spin that puppy so make the piston and pin package as light as possible. We chose a lightened JE FSR piston for our 3.1 spinner.

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Rods are 4340 Chrome-moly weighing in at 523 grams. Pistons are from JE and are the later FSR design. Did some trading and ended up with a very good deal on a GT-3 oil pump. 930 pump would have been fine. I have to do a little grinding on the case to fit the GT-3 pump. Photo with toothpick shows what I had to remove.

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Nice build. I used R&R rods. Super lite and still forged 4340. Rods were 480g each for my 3.6 build. Who did your crank work? My first go around was this sort of build but never could find the turbo case so I went the 993 3.6 route. Good luck.

Looks like a well thought out build.
Congrats and looking forward to seeing the future updates.

Forgive me for the silly question, but how much smaller is the 1.99" bearing compared to stock? If I remember correctly the 70.4mm stroke crank got its extra stroke from making the rod bearings smaller and offset grinding them. We know the 70.4mm cranks had rigidity problems, so does making the rod bearings smaller on a 66mm crank reduce one of its inherent advantages?

Hi Max, journal diameter was reduced by about 6.2mm from the original 2.0 liter. It is 1.8 mm smaller than a 2.4. The journal width is still 22mm, not the 24 of the 2.4 crank. Which I believe is the problem with those particular cranks.

Does the journal diameter reduce the advantage? To some degree, yes. But we run 53 journals on 2.0 liter cranks with no harmonic issues that are quantifiable.

Reciprocating weight as well as counterweight mass are a real factor in where the harmonics will show up.

Wow..... this is the deep end of the pool for sure. Beautiful parts and work.

Aaron gave a great answer to the journal question. The main reason I had the rod journals cut down was so I could use the Clevite/Mahle rod bearings. Very good bearings.

Nice Wilton vise Mark! I have the same one and it is a brute.

Brian & Co. at Pauter went to town on those counterweights! I had my crank knifed a bit by Marine and David only took a slight amount off. I see they also grooved #4 main and certainly must have cross drilled it. NICE.

Shuffle-pinned main supports on the case too!

I'm surprised you didn't choose to use a straight cut I-shaft gear set? Pauter makes a nice pair of gears.

Thanks Kevin. Yes I thought about the stright-cut gears but put that $ toward Pauter's rocker arms instead. Moving along, main bearing are Glyco std/std and coated with Calico's CT-1. Cranks ready, I.S. cleaned inside & out. Replaced I.S. gear and flipped timing chain gears. Checked oil pump drive shaft fore & aft play. Test fit I.S. and checked backlash. Checked crank rotation clearance. New chains installed, lubed all bearings and sealed everything up, case together and torqued down. The case had shuffle pins installed so the last 1/4" of closing up the case I needed to use the help of a rubber mallet. Worried thought's went thru my head about if any of the oil pump seals got moved around or misaligned while I was tapping the case together??


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Those new Pauter rocker arms are the cat's a$$ They really turned out a beautiful product with those.

Thanks for sharing and don't fret over those pump seals.

Installed a set of Henry's studs. Was thinking about the 993TT studs which I have used before and think they are great, but for the price of Henry's kit with washers & nuts you can't beat it. Pistons are JE's newer 932P FSR with coated skirts and are in the 509g range. Piston rings all filed to correct gap. Setting up #1 & #4 for some deck height calculations.

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Beautiful werk Mark.....It's a pleasure to watch.

Mark,

What's the proposed comp. ratio & pins for those pistons, if you don't mind sharing?

Thanks,
Kevin

Piston pins came with the JE's and are 98g. So with the 509g pistons and 98g pins I'm @ 607 grams. Add the 523g rods and were @ 1130 grams. I weighted a Mahle 92mm RSR piston and pin and it came in @ 579 grams. With my 100mm pistons and .670" dome it's easy to see the 28 grams of extra weight. I'm calculating a comp. ratio somewhere between 10.5 up to 11.0. I needed the large dome volume to make up for the low sweep volume of the 66mm stroke.

Thanks for sharing the pin weight. Reason I asked is because I was considering a lightweight pin for a 95mm FSR 3.0L application. The pins I received with a rather off-the-shelf set of SC 95mm 10.5:1 pistons are the 22mm size and they weigh 109g. I assume your pins are shorter & that's the 11g difference.

Mark you might want to break that sharp edge between the valve reliefs, my JEs had the same thing.

Good idea John, Thanks. I'll get to that after I finish the deck & compression calculations which I'm in the middle of.

Which heads are applicable to this build?

Kevin, The heads are big port 3.0 SC heads. Steve Weiner & Jeff Gamroth did the heads about 2 years ago. Intake valves have 8mm (7.96mm) stems and the valve size is 51mm, 2mm over stock. Exhausts are also 8mm stems and stock 41.5 valve size. Idea was to have less weight. CC'ing the heads and also getting a theoretical cylinder volume.

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This simple modification to the dome of a 2.8 JE pistons results in a less than a tenth of a compression point yet yields 5-7 hp.


Some times the nuance makes a project memorable..

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Thank you Henry and John for the valuable information on the piston valve pocket edges.

Now to figure the compression ratio. First step is the Sweep Volume (in centimeters) Bore x Bore X Stroke x (constant) .7854, I came up with 518.364cc (V1)
The case cylinder base surface was milled .020" or .508mm so I started with a .50mm shim & a .25mm shim. I tried several different methods to get a consistent deck height reading and ended up using the Jo-Block method. So with a .670" piston dome height plus the TDC dome height of .869" using the Jo-Blocks gets 1.539" minus the 1.498" (jo-blocks) I ended up with .041" = 1.0414mm. Change that to centimeters and calculate the Deck Height Volume. bore x bore x .10414 x .7854 = 8.179cc (V2)
Measured all the cylinder head volumes and came up with an average of 89.9cc (V3)
Piston Dome Volume (V4) is two math steps. First install a piston into a cylinder on the bench, with the piston dome below the top of the cylinder edge measure the distance from top of cylinder to top of the piston dome. I recorded .171", add this to the known piston dome of .670" = .841". Convert this to CM = 2.136cm. So bore x bore x 2.136 x .7854 = 167.76cc. Step 2 is to calculate the Piston Dome Volume by cc'ing the cylinder with the piston installed as above in the first step. With the lab burette filled I opened the valve and recorded 121cc.
So if I take step 1 measurement of 167.76cc and subtract the 2nd step of 121cc I get 46.76cc (V4)
So 518.364 (V1) + 8.179 (V2) + 89.9 (V3) - 46.76 (V4) = 569.683
over 8.179 (V2) + 89.9 (V3) - 46.76 (V4) = 51.319
Equals 11.1:1 compression. If I did the math right that sum is too high for a street/some track use engine.

I removed the .50mm and .25mm cylinder base shims and installed a 1.00mm shim and did the math again. I now get a TDC dome height of .879".
So .670" + .879" - 1.498" = .051" in CM = .12954 cm. 1.29mm deck height.
Bore x bore x .12954 x .7854 = 10.174 cc (V2)

518.364 + 10.174 + 89.9 - 46.76 = 571.678
over 10.174 + 89.9 - 46.76 = 53.314
Equals 10.72:1 compression ratio.

That's more like it. I could get the deck height down by removing some piston dome volume and go less that 1.00mm cylinder shim but I think this will be fine.

Heads are all on and torqued down. Cooling tins around cylinders installed.

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Cam towers and oil return tubes were next.


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RSR Sprint Cams installed and adjusting the chain sprocket alignments.


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Very cool build. Thanks for sharing

Engine is looking great Mark!

Henry,
Was the mod to the piston domes done by hand with a die grinder? How closely do try you match the dome volumes, or do you do it by weight?
thanks,
dug

Also, what is the reason for grinding away the edge?

I believe it's to allow the incoming mixture to flow more easily into the entire chamber and promote even propagation of the flame front. With the very tall peak in between the valves, the piston bifurcates the chamber. The sharp edges also create hot spots that can promote detonation. Please someone correct me if I'm wrong. Totally arm-chairing this one:)

thanks,
dug

Dug, I think your right on that. Fuel flow rushing in around the sharp edges must cause some flow disturbance compared to a softer flowing smoother edge.

I'm using the RSR Sprint Cams for the engine. They are the 4 bearing, 49mm journal bolt style. Cam specs. are 278/267 degree duration @ 1mm lift and .470"/.450" valve lift with a 101 degree lobe separation angle. Lift @ overlap spec is 6.2mm + - 1.5mm.
I have been using the Stomski Racing cam timing tool with very accurate results. Interesting to find some of the stock pulley's with the TDC mark off as much as 1.5 degrees.

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Henry's pulley right on the mark!


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Ok, so the gain mentioned is mainly seen in single-plug engines?

Wow... I'm just in awe of this kind of stuff. The knowledge and craftsmanship (actually, artistry) of you top-tier engine builders is amazing. Thanks for posting these projects!

Rob

Now I'm ready to install the rocker arms.

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I bought a set of Pauter Rocker Arms for this engine. They are a machined from billet steel and heat treated. They come DLC coated for less friction. They have a longer follower pad and that helps increase the usable wear surface which is great for an aggressive cam profile so they say! We will see. The rockers weight 85 grams each and that's a big weight savings compared to the stock 128 gram weights. The rocker ratio is stock. I will be installing the RSR seals also.


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