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Piston matched to a specific bore?


turbogrill

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Hi,

 

I just realized that the machine shop screwed up the piston order. What they have marked as piston 1 can not go into bore 1, the valve pockets will be upside down...

 

Can I just put that piston into bore 2 instead? I have measured the pistons and I can't see any differences in diameter what so ever.  

(I would have to disassemble it from the rod since these are marked, but luckily the pistons are floating and not pressed).

 

What about piston rings? He gapped the rings for me, but shouldn't matter either right?

 

 

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 @mender

 

I know it's a thing, but not a common thing. One of our vintage racing setups has a pretty agressive overbore and a couple cylinders needed an extra thou or 2 to clean up fully. Since they were already spinning up a set of pistons they went ahead and made them bore-specific to account for the minor sizing difference. Most sets however aren't bore-matched.

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It used to be a big deal because the piston tolerances could be out by as much as a thou, not a good thing for a precision build. The thing is to make sure you don't end up with one cylinder that is tighter than your minimum piston to wall clearance. 

 

The rings need to stay with the cylinder they were fitted to, 0.001" difference in the bore diameter will make 3.14159 times that difference in the ring end gap. :)

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2 minutes ago, mender said:

It used to be a big deal because the piston tolerances could be out by as much as a thou, not a good thing for a precision build. The thing is to make sure you don't end up with one cylinder that is tighter than your minimum piston to wall clearance. 

 

The rings need to stay with the cylinder they were fitted to, 0.001" difference in the bore diameter will make 3.14159 times that difference in the ring end gap. :)

 

ok thanks. That is easy enough!

Pistons are nice wiseco pistons so they are probably very close in tolerance.   

 

 

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33 minutes ago, turbogrill said:

Hi,

 

I just realized that the machine shop screwed up the piston order. What they have marked as piston 1 can not go into bore 1, the valve pockets will be upside down...

 

Can I just put that piston into bore 2 instead? I have measured the pistons and I can't see any differences in diameter what so ever.  

(I would have to disassemble it from the rod since these are marked, but luckily the pistons are floating and not pressed).

 

What about piston rings? He gapped the rings for me, but shouldn't matter either right?

 

 

I thought you were building a straight 6?

Sounds like a V8?

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3 minutes ago, mcoppola said:

I thought you were building a straight 6?

Sounds like a V8?

 

Nope straight six. The intake/exhaust valve are different sizes and sometimes to the left and sometimes to the right.

This is not for the focus but another car.

Edited by turbogrill
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3 minutes ago, turbogrill said:

 

Nope straight six. The intake/exhaust valve are different sizes and sometimes to the left and sometimes to the right.

This is not for the focus but another car.

 

OK, makes sense now, I didn't realize the valves were IE-EI in different cylinders.

Speaking of the Focus, did you ever get a set of hubs?

I'm placing an order for a batch tomorrow.

Let me know if you need any.

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1 minute ago, Wittenauer Racing said:

Oh weird, it's reverse flow but everything still has it's own port. I'm used to the brits with their 5 port heads on a 4 bangers or jumping straight to crossflow...

 

Maybe it's weird all I know is that the heads are not great compared to modern heads.

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1 minute ago, turbogrill said:

Yes but with bigger and more turbos obviously.

I have a couple of RB26DETT turbos that should work well.;)

 

1 minute ago, turbogrill said:

Maybe it's weird all I know is that the heads are not great compared to modern heads.

I raced the 4 cylinder and it took a lot of work to get decent flow. I moved the spark plugs, seats, and guides a bit and bumped up the flow by about 35%. Way too much work though. 

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1 minute ago, mender said:

I have a couple of RB26DETT turbos that should work well.;)

 

I raced the 4 cylinder and it took a lot of work to get decent flow. I moved the spark plugs, seats, and guides a bit and bumped up the flow by about 35%. Way too much work though. 

Yeah, especially if you have to do all that with Harbor Freight hand tools..... Oh wait, that was soooo yesterday....

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18 minutes ago, turbogrill said:

This is not for the focus but another car.

 

12 minutes ago, mcoppola said:

Speaking of the Focus, did you ever get a set of hubs?

I'm placing an order for a batch tomorrow.

Let me know if you need any.

 

Do you need hubs?

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3 minutes ago, mender said:

I have a couple of RB26DETT turbos that should work well.;)

 

I raced the 4 cylinder and it took a lot of work to get decent flow. I moved the spark plugs, seats, and guides a bit and bumped up the flow by about 35%. Way too much work though. 

 

Wow, that is ambitous. Getting decent power from these engines are pretty easy but the 100hp/L seems to get very expensive due the head limitations.

 

 

It's almost a kick in the nuts, you can spend a lot of money and it's not even close to a freaking honda factory head...

1 minute ago, mcoppola said:

 

 

Do you need hubs?

Hi,

 

Now we have them. Another team member got them.

 

Thanks

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2 minutes ago, turbogrill said:

Yes! He is doing all the work :)

 

AWESOME! Pete and I have exchanged a whole lot of emails. He sounds very sharp, with a lot of focus experience and knowledge!

Great to hear you're working with him - small world.....

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52 minutes ago, mender said:

Like this:

Image result for l28 engine

 

I like this picture, I had a thought about going this direction. I could make the argument that 2 small turbos will perform similar to a larger twin scroll turbo, we go through these kind of decisions all the time with the OEM customers when we are just starting out on a program and have a lot of data to help make the decisions, but I doubt that the powers that be in ChampCar would see it that way. Two of the turbos for the Ford Nano 2.7L would fit perfectly and be a very close thermodynamic match, they are super compact turbos, and probably the last large program that will have pneumatic wastegate actuators. We build tens of thousands of these a week so it would be easy to snag a handful for “testing”

 

With two turbos the headers would be very easy to build but every other thing would be much harder.

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18 minutes ago, Wittenauer Racing said:

I mean intake is 50 and exhaust is another 25, so it's really only another 25 pts. The real trick is fueling, throttle and timing. Can be made to work on a dizzy with a carb, but would be much easier with fuel injection and modern spark control (more points to spend....)

 

No points needed, ECU is free.

I ran the numbers on this combination and my problem with building it is that I don’t see how I could slow it down enough to stay competitive. The exact word I got from Mike about building a turbo car is that yes if it fits the letter of the rules you are OK, but if you bring it out and stink up the show expect to be slapped down.

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7 minutes ago, mhr650 said:

The exact word I got from Mike about building a turbo car is that yes if it fits the letter of the rules you are OK, but if you bring it out and stink up the show expect to be slapped down.

When was this “rule” relayed to you? Asking for a friend... :)

Edited by enginerd
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