AVY/ARC PISTON

Chat about your MKV (6N2) Polo GTi
Post Reply
damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

AVY/ARC PISTON

Post by damunk99 » Wed Sep 06, 2017 10:15 pm

Anyone had part no for pistons AVY ARC or where I could buy some from , cheers

damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

Re: AVY/ARC PISTON

Post by damunk99 » Sun Sep 24, 2017 9:12 am

I cannot get the part number for this piston. Infact looked at Yenmak and KS catafalque.
The two alternative pistons that are available pistons for BCB Golf that are interchangeable but I do not want to upset the compression ratio as there are two types.

KS (BCB) pIston:
Recess depth: 2,7mm
Bowel diameter: 64mm


Yenman (BCB) piston:
Recess depth: 2,35mm
Bowel diameter: 64.60mm

Can someone kindly please measure the AVY/ARC PISTON bowl depth please as this would tell me which one I require to keep the same compression ration of 11.5:1

Also why have they stopped selling the AVY pistons? Was this engine design scrapped. You hardly see many of these on the roads and plenty of ones breaking up lol

User avatar
937carrera
Bronze Member
Posts: 231
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: AVY/ARC PISTON

Post by 937carrera » Sun Sep 24, 2017 5:20 pm

I've just looked on ETKA. Piston part numbers are not listed separately , but ARC / AVY engines have the same part number for the complete piston 036 107 065 AG

Not sure if that helps - I haven't got access to a piston

damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

Re: AVY/ARC PISTON

Post by damunk99 » Mon Sep 25, 2017 8:56 am

That's confused things even more:

That part number you gave is the part number the VW dealers gave today but according to www.ksmotorshop.com that Recess Depth is [mm]: 2,46 mm.

036107065AH - Can you check this. I am pretty sure these would fit too. The recess depth is abit bigger which would hopefully bring the compression down a tad from 11.5:1

Cylinder diameter (Ø) 76.51 mm
Compression height (KH) 29.27 mm
Bowl depth (MT) 2.7 mm
Bowl diameter (MØ) 64.0 mm
Total length (GL) 50.27 mm
Pin diameter (BoØ) 17.0 mm
Pin length 54.0 mm
Casting number 076 157
Piston rings 1, 2, 3
1 × R 1.2 mm PC ST
1 × M 1.5 mm

User avatar
937carrera
Bronze Member
Posts: 231
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: AVY/ARC PISTON

Post by 937carrera » Mon Sep 25, 2017 11:31 am

What are you looking to do ?

Rebuild existing engine with new parts, just for freshness
Assemble a running engine where parts are missing
Build an engine for a race project

The options vary with the answre

damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

Re: AVY/ARC PISTON

Post by damunk99 » Mon Sep 25, 2017 10:34 pm

937carrera wrote:
Mon Sep 25, 2017 11:31 am
What are you looking to do ?

Rebuild existing engine with new parts, just for freshness
Assemble a running engine where parts are missing
Build an engine for a race project

The options vary with the answre
thanks for the reply
I am looking to Rebuild a AFH engine with new parts, for freshness & race spec.

It's a conversion from 1.4 to 1.6 which has been done by many peeps 5-10 years ago.
You basically use the rods, pistons and crank from a AVY/ARC Polo 1.6 16V which then increases the stroke.
There have been a few that have also used the internals from BCB Golf 1.6 16V.

I have used the AVY crank, purchased some h-beams and now need to choose the piston wisely due to the compression ratio.

The AFH was 10.5:1 as standard
By using the AVY or BCB internals you end up with a CR of 11.5:1 which is optimum for carburetor application.

I have been offered three versions of this piston.


VW dealers have offered:
KOLBENSCHMIDT Piston
Number of article: 94845600
Recess Depth 1 [mm]:2,46
Compression Height [mm]:29,27
Bore Ø [mm]:76,51
Length [mm]:58,77
Bowel diameter; VW don't have this information

From autodoc
KOLBENSCHMIDT Piston (BCB)
Cylinder diameter (Ø) 76.51 mm
Compression height (KH) 29.27 mm
Bowl depth (MT) 2.7 mm
Bowl diameter (MØ) 64.0 mm
Total length (GL) 50.27 mm
Price: £340.00

From Ebay
Yenmak (BCB) piston:
Cylinder diameter (Ø) 76.51 mm
Compression height (KH) 29.27 mm
Recess depth: 2,35mm
Bowel diameter: 64.60mm:
Total length (GL) 50.27 mm
Price: £200.00

The issue is recess depth and bowel diameter;

I will now try and calculate volume; 3.142 x radius x radius x depth. Can somebody please check my answer.

KS piston (AVY):
3.142 x ??? x ??? x 2.46 = ??????

KS piston (BCB):
3.142 x 32 x 32 x 2.7 = 8687

YENMAK(BCB) piston:
3.142 x 32.3 x 32.3x2.35 = 7703

User avatar
937carrera
Bronze Member
Posts: 231
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: AVY/ARC PISTON

Post by 937carrera » Tue Sep 26, 2017 8:37 am

OK, some further thoughts for you:

What you actually need to know is the volume of the dish in the piston. Normally this is done by filling the dish with a liquid and then carefully measuring the volume when it is poured off. Maths can be used for simple piston designs, but simple maths will not get to the right answer, especially when the piston design includes valve recesses, very common on interference engines.

For the static compression ratio, you need to then know the head volume (again, generally done by measuring, especially if the head has been planed away from spec), deck height, head gasket thickness when compressed and piston volume to get the volume at TDC, to which the volume of the stroke is added ( 1/4 of 1588cc in this case ) and the ratio calculated.

You need a few more data points to establish which piston design gives the right answer (and don't forget to convert the dish volume from cubic mm to cubic cc, so 8.687cc is the right answer for the KS BCB piston).

In terms of quality I would probably prefer Kolben Schmidt. But there are other alternatives, especially if you are going for a race engine. If you can get hold of an original arc/avy pistons you can get custom pistons made. Go to the right people and they will 3D scan the existing piston and be able to reproduce new pistons to higher spec, probably forged rather than cast.

How do I know this stuff ? I had to do this once because an engine builder planed a block against my specific instructions meaning I needed a piston design to work with a non standard block. (blocks of this design being hard to come by). I had to change compression height and ensure that the piston clearance to the head was still satisfactory and get to the compression ratio I wanted, it being a turbo engine. In case you are wondering I personally use JE Pistons. Lead time is probably about 4 weeks and cost around £100 per piston. not a lot more than you are currently looking at. In my case custom pistons are cheaper than OE, so a win win.

If you look of ebay right now there's a complete engine available for £50

One point of caution on the rods. Are you sure they are stronger than OE. I have seen aftermarket rods which claim / appear to be stronger than OE, but in practice despite the H beam design are not as strong as OE. Not only were they weaker, but when measured they were also heavier, which would tend to slow down piston velocity = slower acceleration.

In terms of track use, the 6N2 handles very well on track (unplanned excursion at Croft one day), but just so you know the 1600cc engines from Peugeot / Citroen give over 200HP, as do the Ford Zetec, all on injection

Hope that helps. :)

damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

Re: AVY/ARC PISTON

Post by damunk99 » Tue Sep 26, 2017 9:27 pm

Thank you for that detailed answer.

1) £100 per piston. Would this be forged?
2) The AFH rods are prone to bending, The AVY rods are abit thicker. The H beams are more or less the same weight, so all in all there is not too much difference in them apart from the VW rods having an oil feed right through the rods. Where H-beam have two holes either side of the small wrist.

3) I have been told that 036 107 065 AG which is the genuine piston that VW are offering me would give 11.5:1 compression ratio because it is a OEM part. I can get these for £320-340

You would think it would be logical to use those.

4) Does a CR of 11'5:1 shorten the life of an engine?

5) The valve cut outs are interesting. Have a set of mild schrick cams. only an extra 1.5mm lift

p.s im a VW guy so no fords or Peugeot's lol

User avatar
937carrera
Bronze Member
Posts: 231
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: AVY/ARC PISTON

Post by 937carrera » Tue Sep 26, 2017 10:33 pm

Responses to your points:

1. I'm pretty sure that the JE pistons would be forged...... my work was done on a 944 engine which has forged pistons as standard, I doubt I would have bought the replacements if they were inferior.......... but it's a few years ago and I don't have access to the specs at the moment.

2. See if you can get past the marketing blurb........ my aftermarket rods in another engine turned out no be not only heavier, but weaker than OE rods, evidenced by a partial piston / rod assembly popping out of the crankcase. :(

3. It's a reasonable assumption that the OE pistons would give the same the right CR, everything else being equal. Question is do you actually want standard CR and standard strength in a race engine if you have a choice.

4. I think 11:5 CR is standard for the GTi, so it would seem to be a reliable specification. You end up with short life problems if you use poor oil, the engine overheats or the mixture goes weak. As you said you intend to use carbs (on the other forum) you are already giving away half of the benefits of using an ECU as it will now only manage ignition. Not impossible, but it wouldn't be a route I would go down unless forced. By all means use throttle bodies.

5. Yep, you don't want them to kiss the piston tops, 1.5mm is a lot if there's only 1.4mm clearance. Measure, take a view and then make an allowance / speak to someone about what you need so that the gap is still there at high rpm / temps. More valve cut out allows for higher lift cams and more power. Are you using standard size valves of moving to larger valves - that's another consideration for you that could affect piston choice as well.

I'm definitely a German car guy, but I thought you should be aware of what the 106 / Clio / Fiesta guys will have available to them. I'd love to see a quick 6N2 on track, but received wisdom is that they cannot be tuned to any great extent, but I am yet to understand why.......

damunk99
New
Posts: 14
Joined: Wed Jan 28, 2015 11:16 pm
Drives: polo

Re: AVY/ARC PISTON

Post by damunk99 » Tue Sep 26, 2017 11:21 pm

The valves are standard size because the AFH head does not really have the space to be cutting out any bigger holes.
The reason why is maybe because on an air bench flow the head flows for 200bhp so the head is designed the best it can be.

I already have a cbr600 carb setup on the 1.4 16v with megajolt and i must say contrary to the opinion it's doing me fine.
I am impressed.Obviously not as good at throttle body but my set up was alot cheaper doing it this way and being a noob it was the best first step to take.

Hopefully if i can get this next project going i'll then just swap over the carbs to throttle body and swap the ecu so megasquirt or something.

User avatar
937carrera
Bronze Member
Posts: 231
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: AVY/ARC PISTON

Post by 937carrera » Tue Sep 26, 2017 11:54 pm

OK, sounds good, I hope I've given you some useful suggestions & ideas. It would be great if give some updates as you go through your project, I would be interested to hear more. Money, time & technical knowledge always seem to be the key constraints :)

All the best

Post Reply