Another big bore thread

Hey guys been a lurker a long time and appreciate all the useful posts you guys make. I am freshening up my dinasaur yz 400 with a 426 barrel and 97mm piston along with the 426 rod and fresh bearings etc etc. My questions are about piston(s) and replating. I am looking at wisecos piston and the prox...I get the differences between cast vs forged etc and hope to get real world feedback from you guys. I am an ex racer who now so. cal desert and trail rides w occasional hillsclimbs fast sandwashes etc. and want reliability.

Can I get away with 13.5 compression on pump gas

Is the 97mm wiseco piston lighter than or equal to the stock 400 piston

Does the wiseco high comp. piston weigh more than the stock comp. piston or did wiseco just move the wristpin hole down to get the higher comp.

Will I have to have bottom end balanced to keep it from being a boneshaker

Does LA sleeve have good results w/ plating ( I am considering them or US Chrome)

Thanks in advance for any feedback you guys can give.

Jim

There was an interesting thread about compression ratios and pump gas, I'm pretty sure that I read that if you use an aggressive cam for the intake it can actually lower your compression ratio slightly. Elevation I believe can have an impact on whether you can run pump gas on a given compression ratio for a particular engine as the air density changes....

This is why people with 13.5:1 compression ratios for 450's can run pump gas while others who just use a 13.5 piston cannot....

Not to sure, but hopefully someone will remember the thread cause I can't seem to find those particular comments.

Someone will correct me if I'm wrong, but I'm still learning this stuff too :thumbsup:

  1. I am an ex racer who now so. cal desert and trail rides w occasional hillsclimbs fast sandwashes etc. and want reliability.
  2. Can I get away with 13.5 compression on pump gas
  3. Is the 97mm wiseco piston lighter than or equal to the stock 400 piston
  4. Does the wiseco high comp. piston weigh more than the stock comp. piston or did wiseco just move the wristpin hole down to get the higher comp.
  5. Will I have to have bottom end balanced to keep it from being a boneshaker
  6. Does LA sleeve have good results w/ plating ( I am considering them or US Chrome)

  1. t may be reliable, but your plan is going to stretch things quite a way.
  2. It will be tougher in the desert because of the very low altitudes (below sea level here and there). If you avoid lugging it and use a fairly aggressive cam, you might, but it wouldn't surprise me if you run into pinging trouble.
  3. The 97mm piston will obviously be heavier than the 95mm piston, which is going to be more than just a little heavier than the 92 the 400 came with.
  4. Piston manufacturers usually try to come as close as practicable to the weight of the OEM so as not to impact the engine balance. Increases in compression are never done by relocating the wrist pin bore downward, since to do so would cause the edges of the piston to stand above the cylinder deck in most cases, and possibly hit the head. Compression gains are achieved through reshaping the crown.
  5. I'll almost guaranty that you'll need to have it balanced, yes
  6. Don't know

I just got my 97mm wiseco piston and cannot believe how heavy it felt so I ran down to a fedex store to check the weight and cannot believe the piston alone is 11 ounces (313.4 grams) and the wristpin is another 3.4 ounces (96.7 grams). This seems rediculessly heavy does anyone have any piston weights I can compare to? If JE's site is correct their piston is supposed to weigh 272 grams. If anyone has access to a scale and can weigh a stock 426 piston and or a big bore piston I would really appreciate it. I have built many Race Car Motors in the past and this piston seems really really heavy. Also this piston is not coated and I was under the impression wiseco was coating the skirts...any info would be greatly appreciated.

Thanks

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