what pistons for rebuild? v4 looper

[looper power]

I really dont know what I should put in my 120-140 rebuild. any input would help me. stock cast or hypereutectic? forged needs too much piston to wall clearance for my stock 3.50 bore and is kinda noisy. it wont be turning up past 6000. thanks

 

[walleyehed]

Re: what pistons for rebuild? v4 looper

This is a Dhadley question, maybe he'll take a look and give you an answer...He's top-dog on the loopers for sure.<br />In "my" opinion, passing on the forged pistons is barking in the wrong direction, and if you are needing pistons, I would guess you haven't been turning that 6000+ that it should be...

 

[Dhadley]

Re: what pistons for rebuild? v4 looper

The forged Wiseco pistons dont need any more clearance than the OE cast pistons. If you ever hear a forged piston thats noisy it will be way wore out. The forged pistons are always quieter than stock.<br /><br />Regardless of which piston you use, there are a couple of things to keep in mind.<br /><br />Always have a marine machine shop bore the block. Not an automotive shop. If you cant find one, we'll get you hooked up.<br /><br />The small bore 120-140 can easily be bored out to the 3.685 of the big bores (1988 & newer). All you need are the big bore V4 heads. Since youre rebuilding the motor it's probably safe to assume you'll need one head anyway. And the bb heads are easier to find anyway.<br /><br />If you do bore it out to the bb specs, you can use the 1993 & newer V6 pistons. And rods. They are much lighter and you wont believe how well the motor will idle.<br /><br />No matter what you decide to do, make sure you find and correct the cause of the damaged piston. A damaged piston is a result -- not the cause.

 

[R.Johnson]

Re: what pistons for rebuild? v4 looper

Dhadley: I recall reading in one of the publication's, I believe it was Bass&Walleye Boats about BRP coming out with a new alloy piston that will reduce the possibility of scuffing. Have you heard anything about this? Has anyone else?

 

[jy118lfd]

Re: what pistons for rebuild? v4 looper

Dhadley if he bores it out to the big bore won't he need a different crank. I thought the counterweights are different. Or is the big bore piston and small bore pistons the same weight?

 

[Dhadley]

Re: what pistons for rebuild? v4 looper

RJ, yes its a new alloy used at NASA. It lends itself very well to the casting process but is very expensive -- as you can imagine. Wiseco is experimenting with another new alloy that is (supposedly) even more resistant but is also very expensive. It forges very well.<br /><br />Jon, the cranks are the same on the V4 loopers. To be honest I've never weighed the bb and sb piston to see the difference. Since we dont mix them I never thought about it. The 1993 V6 pistons are much lighter. The light pistons and light rods in a V4 make for an extremely smooth idling motor.

 

[looper power]

Re: what pistons for rebuild? v4 looper

I need pistons cause im building an engine from scratch. the block is pristine and doesnt need to be bored. I have both types of heads, small bore and big.i just have heard things about pistons that have high silicon content in them for low expantion rate,hypereutetic.as far as the 93 and newer pistons, I thought they had extra ports in the piston that matched extra ports in the block.

 

[Dhadley]

Re: what pistons for rebuild? v4 looper

Be careful about what you hear about pistons. A lot is based on rumors and hearsay. Just take it with a grain of salt and let common sense be your guide.<br /><br />Yes, the 93 & newer V6 pistons have finger port holes. You can run that piston in a sleeve without the finger ports. It wont matter at all as long as you run all 4. However if you run a non finger ported piston in a finger ported sleeve, the finger ports wont do you much good.

 

[looper power]

Re: what pistons for rebuild? v4 looper

as far as my engine rpm's,I can get 6000 with my setup 15-17 and the v6 gearcase. the pistons i do have are stock and came from an engine I never ran. they are really crudded up and slightly scuffed.as nice as this block is I would really like new pistons. is forged lighter than cast? and who makes a light piston for my app?

 

[Dhadley]

Re: what pistons for rebuild? v4 looper

The shelf stock Wiseco forged are the same weight as the OE cast. Thats so you can mix & match them. The only light piston is for the bb V6 closed deck looper. Either OE or Wiseco. It will work fine but youll have to bore the block to 3.685". (Actually the exact size is 3.6855")<br /><br />That gearcase is the size of the V6 but its different. It has a different gear ratio and the pinion nut is very small. Never heard a good explaniation as to why they used that small nut.