2 Type A pistons, but a difference in quality

[YesImLDS]

Hi everyone I'd like to bring something to your attention that I realized a couple days ago. I was comparing two type a pistons I mistakenly ordered when I had a GT5 motor and noticed one was slightly lighter than the other. I already had a gram scale on the way and something I noticed was quite shocking to me.

Can you tell the differences between these pistons? They are the same size and dimensions.

The only REAL physical differences is that the one on the left has a 2 stamped on it, but there is something else different between the two. These are both from ebay dealers one is a BGF (right) and left I can't remember where I picked it up from. Now let's get down to what they weigh in their completely stock form.

The BGF piston weighs in at 78.8 grams. Not bad at all and I would expect all similar pistons to be around 2 grams of that.

This is where it gets a little weird to me because the piston on the left weighs a whopping 70.9 grams! That's a difference of 7.9 grams. That's basically 10% lighter than the previous piston.

I just thought I'd bring attention to this because when buying parts you may not realize it, but you could be sucking some performance out of your motor if you are just replacing parts. Going from a 70.9 gram piston to a 78.8 gram piston could throw the engine more out of balance causing your performance to suffer some. Obviously not greatly, but none the less kind of cool to know!

 

[YesImLDS]

I guess I didn't think well enough on the title. It's not really a difference in quality so much as they both would work fine, but they are quite different despite being the exact same type.

 

[Goat Herder]

Nice thanks for sharing this. Kewl to see the changes from a differant source. What do the casting cavities look like under the skirts? Figuring a fellow might be able to possibly shave up to 8 grams off the heavier piston.

 

[YesImLDS]

Believe it or not the heavier one is actually smoother cast than the lighter one

Here is a picture of the underside of the lighter one.

And a comparison picture to the heavier piston

 

[YesImLDS]

Update! Here is the lighter piston with rings weighed in. I thought I would do everything to this piston and show how much you can expect out of 1. Cutting the piston skirts, 2. drilling 12 3/16th holes in it, and 3. ramping it.

Lightweight piston with rings. Unmolested completely stock weight. Remember this one weighed in at 70.9 grams without rings!

For comparison here is the regular piston with rings and completely untouched weight

Now lets get down to loosing some weight on the already lighter piston

Exhaust side cut off excess skirt length, Marks also made while piston was in for ramps.

Intake side cut off

Ramps grinded in by hand and polished top

 

[YesImLDS]

Part 2 because I can only do 5 pictures in a post apparently

12 3/16th holes, Surprised this didn't take off more.

New weight with rings!

So say you had the stock piston weighing in at 86.1 grams with piston rings and swap over to one of these cut on, ramped, and drilled pistons weighing in at 72.5 grams you are going to have a light less vibes, a bit more rpm and more instant throttle with more power!

 

[mapbike]

Drilling the holes doesn't make a big difference, just a little.

 

[YesImLDS]

Drilling the holes doesn't make a big difference, just a little.

Better than nothing! Super smooth cruising at 35-40 now. It already had a lightened piston in it and this was meant to be for my next engine build, but the type b engine threw me off so I decided to put it in my PK80. It's about 3 grams lighter than the already lightened one I had in there and it's ramped correctly this time compared to the previous which I just took to a belt sander.

 

[mapbike]

Better than nothing! Super smooth cruising at 35-40 now. It already had a lightened piston in it and this was meant to be for my next engine build, but the type b engine threw me off so I decided to put it in my PK80. It's about 3 grams lighter than the already lightened one I had in there and it's ramped correctly this time compared to the previous which I just took to a belt sander.

Yep, every little bit can help sometime for sure.

 

[Davezilla]

I'll agree there, its amazing the difference a few grams can make at 9000 rpm....
Onenof the machine shops i used to use back in the 90's used to have a sign on the countertop stating that just 1/4 ounce off balance can exert nearly 400lb force at 4000rpm from just a fee inches off center. They used that along with another sign explaining that they balance everything within a 1/10 gram tolerance. I also experienced this first hand on my 300zx when I had a flywheel machined at the local Napa and the whole car shook violently above 3500 rpm. When I took that flywheel off to replace with a new aluminum one i measured the fkywheel to see how far off it was. It wss off by a whopping .019" from one side to the other.like maybe there may have been some dirt or shavings on the mill bed they didnt see or they just didnt clean off the mill bed before machining the flywheel. It wss unreal how badly the whole car shook at 3500 rpm and above, I thought it was gonna rip out the transmission.... all from being about 10 grams off balance about 6" away from the center. That car redlines at 7800 rpm and there was no way i would even try to rev the engine passed 3k until i replaced that flywheel.

 

[Theon]

I hate it when you pay good money to have an Apprentice do your Machining work.

 

[Davezilla]

I hate it when you pay good money to have an Apprentice do your Machining work.

Very true.. i wasn't happy in the least with that, the only good thing that came from that situation is it gave me a reason to get an aluminum flywheel for the car which made it rev way faster and accelerate a little better too, and this flywheel has a removable insert so at clutch change time all ya do is buy a new insert and hardware kit, no more taking it somewhere to get it machined and hoping they do it right...