VN1700 pistons to raise 1600 comp ratio

[andyvh1959]

Sure the 1500 Mean Streak pistons are the easy choice. But I've not seen any data that confirms the 1500 Mean Streak had higher compression ratio numbers than the 1600 Classic engine. Looking at the pistons there is an obvious visual difference but is there an actual comp ratio difference? The rated comp ratio for the 1700 is 9.5:1.

For both the VN1500 Mean Streak and the VN1600 Classic the rated comp ratio is 9.0:1.

[andyvh1959]

WAY too many other projects around the house (major kitchen remodel) that has kept me from tearing into the 1600 engine. But this winter it will happen. Like said earlier I have a pair of VN1700 pistons which I'll fit into the 1600. The standard comp ratio on the 1700 is 9.5:1. Perhaps with some shaving as DL detailed I can bump that up closer to 10:1. My 1600 already has the usual mods done (smog crap gone, intake/exhaust/Power Commander) so I'll be able to dial in more juice as needed. But the 1700 pistons and 1600 pistons likely have different compression height numbers, aside from the difference in stroke and con-rod length.

Was thinking of a way to confirm the if valves do or don't interfere with the 1700 pistons in the 1600 bores, when that time comes. I'd take the heads off, and measure the TDC piston position in the barrels, lets assume they are down from the deck 0.015" at TDC. Then take the barrels off, 1600 piston/con-rods out, then put the barrels back on and slide the 1700 pistons (no con-rods) into the bores, flush to the stock 1600 deck height. Then head gaskets and reinstall the heads, torqued down. Then hand crank the engine over four times. Remove the heads and see if rotating the engine over by hand caused the valves to push the pistons down slightly into the bores.

Just for discussion, lets assume the pistons get pushed down 0.015" from flush deck height. So now I'd have an indication that the 1700 pistons with custom con-rods made to position the 1700 pistons at 0.030" down from the deck height will insure the valves cannot hit the 1700 pistons. So if I have lighter con-rods made by Carillo to fit the 1700 small end dimensions, and the 1600 big end dimensions, I can then run 1700 full-floating pistons for the improved piston design and higher compression.

Also, the 1700 pistons are much lighter than the stock 1600 pistons. With lighter Carillo rods, and the lighter Mean Streak rotor (which I already have) it should make for a much quicker revving engine. The Mean Streak rotor is still pretty heavy, but much lighter than the stock 1600 rotor. Hmm, would i need to get everything balanced and have the MS rotor weight adjusted?

[DragonLady58]

Well andyvh1958, its like this....when I was putting together my stroked 1500....I enlisted the help of several co's, telling them my plans....
they will work with you.
I had 1 piston co. that machined out 2 sets of pistons, 1 aftermarket rod mfg'er for some rods, and a co. that balanced everything. I got all the pieces parts close to the weights needed, then sent things off to get balanced. 1st time around I left the balancer shaft in as to add more enertia to the rotating mass.
As for compression, I'd cut the heads some, sent the heads to a co that cnc ported them, then resized the combustion chamber. Had some meat machined outta the head, allowing for a slight dome, with machined valve reliefs.
With all this done, we had established I was close to 10.8 to 1 on compression. Then, had to notch the bottom of the jugs and cases to clear the big end of the rods....
Cams were machined, lift wasn't all that high, but since you have 4 valves per cylinder, super high lift wasn't needed. slightly oversized valves were used, too.
Intake manifold was cnc ported, slightly larger bosch injectors were used....
All that time and money, added a little over 175 cc's, engine made about 120 horses....with the nomads gearing, I could romp with the 117's easily.
The bigger motors, just too much torque and ponys to keep up.

[andyvh1959]

I'm no engine builder, though I have an ok grasp of engine building. I'm just looking for easy ways to do most of it myself. I have a compete set of 1500 Mean Streak heads, and I'll set them on the bench and rotate the cams to see how much, or if, the valves at full lift actually extend down below the level of the deck. That would at least tell me how much I may need to plan for the 1700 pistons with the flat dish profile.

I thought using the 1700 pistons at deck flush in the 1600 barrels with the 1500 MS heads torqued down, then turn the cams through four rotations to see if the valves push the pistons down. Doing that I should have an indication of the needed con-rod length change. Then its a matter of making sure the entire spinning mass is balanced to work the 1600 crank and MS roto.

[DragonLady58]

Yes andy if your wristpin to deck height is correct, the skirt profile has adequate clearance, and the weights can be equalized....which your not changing rods like I did, so If the piston measures out correctly, I don't see why you couldn't do it.
When I had my heads mod'ed, with a slight dome on the pistons, (0.065), which were modified SBC pistons from Manley, heads were lightly cut, then I took some off the base of the cylinders, to avoid cutting too thin up on the decks.
Then was able to get the cams ground with slightly more centerline, and lobe seperation, only using .46 of valve lift.
Even thought the pistons had to be cut very lightly for valve clearance, it was only about .040 deep trench to clear the 4 valves, picking up a little more by trimming the cylinder base....
My piston to valve clearance was .090....I wanted to make sure I had plenty of clearance there....
My rods are slightly shorter, (.030), you can kinda see how I was jiggling clearances here and there to make everything play nice together....
With that piston, and a slightly shorter rod, that engine rev's so hard, it's really hard to ride when its wet....
These 1500/1600's love to rev....

[DragonLady58]

If I get the Haltech efi working correctly, I'm gonna plop on a turbo, pipe it all up, that way the 1500/1600 platform can get some more performance and tunability....

[andyvh1959]

I suspect the 1700 pistons have a different compression height (wrist pin to top of piston) than the 1600 pistons. Also, the 1600 fixed wrist pin is larger diameter than the smaller wrist pin in the 1700 full floating style. And the 1600 journals are larger diameter than on the 1700. So that all means I have to get custom rods made to make the 1700 pistons work in the 1600.