3.1 Short Stroke Build 66 X 100

[356RS]

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.

[KTL]

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.

[304065]

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

[356RS]

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

[KTL]

Which heads are applicable to this build?

[356RS]

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.

[Henry Schmidt]

Originally Posted by 304065

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

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..

[356RS]

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

[356RS]

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.

[356RS]

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.

[356RS]

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






Cam towers and oil return tubes were next.




RSR Sprint Cams installed and adjusting the chain sprocket alignments.

[JV911SYDNEY]

Very cool build. Thanks for sharing

[rennzeit]

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

Originally Posted by Henry Schmidt

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..

[H-viken]

Originally Posted by dug@project914

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?

[rennzeit]

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

[356RS]

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.

[356RS]

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.









Henry's pulley right on the mark!

[H-viken]

Originally Posted by dug@project914

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

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

[RFP]

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

[356RS]

Now I'm ready to install the rocker arms.



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.