Project: Xu12J4

[Tguedes98 0]

On 6/18/2024 at 3:15 AM, petert said:

Zero squish means the top of the piston is level with the top of block. You want that, regardless of the CR. Here are the calcs for 12:1 in 87 x 92 with a K20 piston.

Bore 87mm

Stroke 92mm

Deck Height 234mm

Compression Height 30mm

Rod Length 158mm

Dish & Valve Pockets -1cc

 

Are you hung up on 12:1? Why not use the SC70457 flat top piston which has -3.3cc pockets and would give 11.5:1.

 

Also, I am not exactly sure about this website, but I take it that they're making the correct math

https://blackartdynamics.com/Compression/EngineCompression.php

Trusting their calculations, with the values you gave me, it would come out at 13.28 CR... Which I'd say is a bit high...

Even with -3.3cc piston dish, it would come out at 12.68 CR, which is still very high! Are their calculations wrong?

[welshpug 1,644]

have you forgotten the gasket CC?

 

10-1 isn't especially high for forced induction, a modern ecu and good knock detection can cope with that,   add direct injection of more modern engines and you'll often see 11+  and a fair amount of air forced in as a standard road engine.

 

the days of old turbo engines running dizzys and carbs at 8-1 are well behind us!

[Tguedes98 0]

2 hours ago, petert said:

These are the K20 pistons I'm using for SC and turbo builds. They have a 9cc dish and a Ø22 pin. These end up at approx. 10:1. Note that they still have a squish band.

Also, what pistons do you usually use for NA builds where compression can be higher? Do you usually use those SC70457 that you talked about?

[Tguedes98 0]

11 minutes ago, welshpug said:

have you forgotten the gasket CC?

 

10-1 isn't especially high for forced induction, a modern ecu and good knock detection can cope with that,   add direct injection of more modern engines and you'll often see 11+  and a fair amount of air forced in as a standard road engine.

 

the days of old turbo engines running dizzys and carbs at 8-1 are well behind us!

No, I didnt't forget it Welsh! I introduced all the values, with the HG height as well, beeing 1.1mm (stock head gasket) 

With these values:

Bore 87mm

Stroke 92mm

Deck Height 235mm

Compression Height 30mm

Rod Length 158mm

Dish & Valve Pockets -1cc/-3.3cc

 

One of the calculations is wrong i guess

[welshpug 1,644]

you don't mention the combustion chamber which is 37.5cc from memory, the gasket is 1.2mmx86.5.

[Tguedes98 0]

2 minutes ago, welshpug said:

you don't mention the combustion chamber which is 37.5cc from memory, the gasket is 1.2mmx86.5.

 

2 minutes ago, welshpug said:

you don't mention the combustion chamber which is 37.5cc from memory, the gasket is 1.2mmx86.5.

Yeah, I took it into consideration tho, 37cc combustion chamber! even with these values

Bore (mm):    86.0
Stroke (mm):    92
Rod Length (mm):    159
Deck Height (mm):    235
Combustion Chamber (cc):    37.5
Compression Height (mm):    30.00
Piston Volume (cc):    -3.3 / -1
Head Gasket Thickness (mm) :    1.2

 

I get 12.19 and 12.75

 

Something is still not right with the math

[petert 577]

I used 41cc for chamber and 1.3mm for gasket. 

[welshpug 1,644]

Mi16 is 40cc, standard, I guess you open them out a little Peter?

[petert 577]

I thought they were 41? I guess he should cc what he has anyway.

[Tguedes98 0]

2 hours ago, petert said:

I used 41cc for chamber and 1.3mm for gasket. 

Hey Petert! I take it that a s16/mi16 head you're talking about! Mine's an RFS head... which i take it it has a slightly smaller combustion chamber in the head! Do you open the heads peter? in order to make the combustion chamber bigger?

 

Many thanks

[Tguedes98 0]

32 minutes ago, petert said:

I thought they were 41? I guess he should cc what he has anyway.

Yeah, I'll be CC'ing the head I have anyway, so there are no surprises!

 

I made a little excel for calculating CR! Can you guys review it and check if my calculations are sound?

 

Many thanks

 

 

Taxa compressao.xlsx

[petert 577]

RFS head is only approx. 38cc, thus the significant difference.

No, I don’t open chambers significantly, only for cleaning up, unshrouding inlet valves, etc.

 

If it's a street car, I'd use the -7.7cc pistons and be happy with 11.2:1.

Edited June 20 by petert

[Tguedes98 0]

6 hours ago, petert said:

RFS head is only approx. 38cc, thus the significant difference.

No, I don’t open chambers significantly, only for cleaning up, unshrouding inlet valves, etc.

 

If it's a street car, I'd use the -7.7cc pistons and be happy with 11.2:1.

Hey Peter! What are those 7.7cc pistons from? also for a k20 turbo application i'd imagine

 

I would like to use a thinner gasket so I can get better squish! Thinking of going cometic, 1.01 by 88mm for example! 

 

It is a street car, but when it comes out of the garage imma give it the beans!

[petert 577]

On 6/20/2024 at 5:25 PM, Tguedes98 said:

Hey Peter! What are those 7.7cc pistons from? also for a k20 turbo application i'd imagine

The -7.7cc pistons are CP-Carrillo. This is an outdated parts list. There may be more options now.

 

https://www.spoolimports.com/sc70402

[Tguedes98 0]

On 6/21/2024 at 11:15 AM, petert said:

The -7.7cc pistons are CP-Carrillo. This is an outdated parts list. There may be more options now.

 

https://www.spoolimports.com/sc70402

Hey Peter... You probably already guessed what bothers me... K20 pistons on a XU10... That tickles ALL my bearings! Will it actually work? squish band in the head will be correct? won't it explode? these are some of the questions that easily come to mind... 

 

Do you have a lot of experience using these pistons on XU10's?

 

Many thanks for all your help mate!

[welshpug 1,644]

Why would it not work?   I have vauxhall/opel pistons in my XU..

[petert 577]

Close enough. Obviously with any custom build, you'd verify valve to piston clearance in both directions.

Edited June 24 by petert

[Tguedes98 0]

11 hours ago, welshpug said:

Why would it not work?   I have vauxhall/opel pistons in my XU..

Hey Welsh,

I know they should work! However, I think you can understand me wanting to be very certain of things, before spending close to 2k on forged custom internals... right? 

 

11 hours ago, petert said:

Close enough. Obviously with any custom build, you'd verify valve to piston clearance in both directions.

Yeah, I'll be having the head taken of to the machine shop! There's one in my country that already has a set CNC program for these heads, for a good price too!

I'll be using SINUS Performance +1mm intake valves and stock exhaust valves

I also have an RSX flywheel  (3,9kg) to have it balanced with the crank and the rest of rotating assembly!

Solid lifters and cams are still in the picture (maybe in the future), but will probably stay with a milder cam set and hydraulic lifters, in order to have a better all rounder.

And of course, I'll be making a dry build!

Tonight, alongside some pizza and seven up, I'll be measuring the stock pistons and rods on the 92mm crank, just to make sure of everything and check how much it actually sticks out from the block! Also to check that the head/block has not been skimmed.

When the head comes from the machine shop, I'll measure it as well, just to confirm everything, but for now, I'll use the stock 37/37.5cc for calculations

 

I wonder about rev limit... I think I'll stay in the 7500 range! probably won't need anything more than that with a set of mild cams and hydraulics, I guess...

 

What do you guys think of my "malefic plan"?

Thanks for all your help

[petert 577]

If high compression and mild cams, you need to put it all through a dynamic compression calculator.

[Tguedes98 0]

57 minutes ago, petert said:

If high compression and mild cams, you need to put it all through a dynamic compression calculator.

What is "high compression"? 

I'm aiming for maximum 12:1, maybe a little less, since, as you said, it's a "street car" ! I was thinking somewhere in the range of the 109's, or maybe the 108's from catcams!

Will put through a dynamic calculator yes! Aiming for maybe 9.0 for dynamic compression!

 

I do have a big question regarding one if your previous builds!

 

This a photo taken from your thread!

Is it a 2.1 td crank? A 92mm one? Or what is it? I see it only has 4 balancing weights, but the rod journals are different than my 92mm crank! Mine have a radius on the side of the journals!

 

Thanks

 

[petert 577]

Yes, forged 88mm from XUD9TE.

[Tguedes98 0]

12 hours ago, petert said:

Yes, forged 88mm from XUD9TE.

Ohhhh, ok, that makes sense, since it's a 24.xx mm wide rod right? The jounals are the slimmer ones!

I'm in contact with Robson conrods already to try and get a quote for custom 159mm rods delivered to Portugal! Thinking of using the K20 pistons! Probably the -7.7cc CP Carillo ones, or even the Wiseco -9cc ones!

The head will most probably have to be skimmed to flatness, so maybe the 9cc ones! But I'll only know for sure when I measure everything and after sending everything of to the machine shop for measurement and machining!

Crossing my  fingers and praying I can get the engine running before summer end!!! But we'll see....

 

Tiago

[Tguedes98 0]

On 6/25/2024 at 10:28 PM, petert said:

Yes, forged 88mm from XUD9TE.

Hey Peter, question here,

What did you you do regarding thrust washers? In the 92mm crank I can't use the 4 original ones because they hit the sides of the crank and don't allow it to spin!

 

On 6/24/2024 at 10:13 PM, welshpug said:

Why would it not work?   I have vauxhall/opel pistons in my XU..

The previous question also applies to you mate!  How did you do it?

[welshpug 1,644]

I didn't do it, but sandy brown machined the valve cutouts to suit, I believe only the exhaust need a little tickle as the valve centres are slightly different.

[welshpug 1,644]

Also I think I used standard 118f4 thrust bearings,  that's what I ordered from peugeot 6 years ago

 

This picture is in my build album for mine

 

https://flic.kr/p/G9yxuh

Edited July 1 by welshpug