Shoptalkforums.com

Hi guys !

Have been lurking here and in the type 4 parts of this wonderful forum. I have decided to go turboed WBX in my 1303 super.
As i do this on a TIGHT budget i was thinking of letting my neighbor who has a fully equipped machine workshop lathe of maybe 1.5 mm on the top of the original pistons . i haven´t read about anyone else doing it this way . people tend to go MV pistons instead.

Any big downfalls to this approach ? thinking of using a cb 2253 camshaft and megasquirt by the way.

regards
Dann / Sweden

You wouldn't want to adjust CR that way, not with these style pistons. With most of the piston top being a big dish, the only part of the piston crown you could cut down is the rim around the perimeter, which would increase the TDC volume only by increasing the squish clearance. With more than .040" (1mm) clearance, effective squish dynamics diminish and the engine will be more prone to detonation, and the upper cylinder will run hotter which will makes things harder on the top rings.

The only sensible way to address this is to increase the dish volume, head chamber volume, or some of both. You could carve out the bottom of the DJ piston dish but then you're decreasing the crown thickness when if anything you want that thicker to handle boosted combustion. So probably not a good approach.

And that's why you guys on that side of the pond go to MV pistons for boosted apps, if you can get them. They'll make a static 8.7:1 CR on a 76mm crank and stock 5.4" rods. The center of the crown is plenty thick, over 6mm.

You may have an easier time finding 1.9 DH pistons but to run them on a 2.1 76mm crank you would have to decrease rod length ~3.5mm to get them to zero cyl deck so the combustion sealing ring sets the squish at 1mm. You could use a 5.3" rod and take the extra ~1mm off the top rim of the piston. You would have to run the numbers to figure the static CR with that combo, with the longer stroke it might be almost as high as the DJ pistons make (the DH dish is also broad and flat-bottomed much like the DJ).

I think the best wbx for boosting is a 1.9 DH, with 8.3:1 static CR it's just begging for boost. My thinking on boosting is since you can double the power on demand why not use a smaller engine so it can be more efficient under cruise.

So any other ideas anyone ?

i have looked at the head chambers and i am a little afraid of hogging them out as i really dont know where to take away material.

It is starting to look like the good ol gal isnt going to get a glorified fan on her back

I used MV pistons and sunk the valves on my '80s rallycross motors, this gave 8.2 c/r and ran well over 300 hp. alternatively you could use the AA Chinese pistons, not sure about the c/r on them tho, I'm told the deck height is lower on them which may help with that.

There are a few options that have been discussed...

The AA/COFAP piston stupid deck height is just a good excuse to ditch the head gaskets and trim 1mm or so off the deck at the sealing surface for a cleanup... will require shimming the rockers or new pushrods, IIRC the valvetrain geometry on mine benefited from both.
This is a reasonable plan with stock length rods.

Note: The AA deck height issue may have been fixed since I bought mine, at least Rocky said so.

...Or better, copy Tencentlifes use the AAs or Cofaps w/5.4 or 5.5" SCAT I-beam rods repinned for 24mm (much stronger than stock, great choice for ANY motor, but particularly a turbo motor) he then shaves some off the piston top to set deck exactly.
IIRC Even with the correct deck the dish is a touch larger than std MV.

The better rod design/material also reduces>eliminates the high mileage big end ovaling 76+mm stroke motors get with the stock rods (Consensus is this is the root cause of most low pressure issues and ventilated 2.1 blocks)

Gowesty also has Wiseco make them some lovely pistons, with the exchange rate the way it is that might be practical, and forged is good. As Wiseco obviously has the dome shape down, you could likely have some made to your spec.

I believe Marco used custom Ross Pistons, so they are another forged option.

Even with the correct deck the dish is a touch larger than std MV.

I use the QSC's, they have the same volume as OEM MV slugs (47cc). As far as I know the Cofap and AA's do too, if there is any difference it's not more than a cc which won't make the difference you need for boost.

QSC and Cofap are still about 1mm low in the bore, AA did fix that problem on theirs. That's an asset to me since I use a longer rod and shave them to reduce dish volume and up the CR. But I would never run them below deck on stock rods, there's no squish and thats the thing that's gonna save your bacon when it wants to detonate under boost, especially with no proven knock sensing system for this engine. Call me a squish believer, I've even been cutting them to be a bit above deck for ages.

thank you for all your input. i will look into getting me a set of qsc´s then. hard to find here in sweden. will have to go fleabay i guess

there is a 96mm "bigbore" kit available from qsc ? i guess they only made the liners thinner and this is something i dont want in my type of engine right ?

regards
dann

Thanks for the clarification.

IIRC you had figured a sane ring package for the QSCs as well?
Are you having the rods rebushed locally or dud SCAT come to its senses?

The free standing WBX liner is still pretty thick and very uniform compared to the vast majority of factory engines.
...depends on cylinder quality and boost level I suppose.

One could probably run machined sections of high strength steel drill pipe if sufficiently motivated.

i will look into getting me a set of qsc´s then. hard to find here in sweden. will have to go fleabay i guess

I'm not sure if you got my meaning. To clarify, if you want pistons with correct original deck height on stock 5.4" rods (or other 5.4" rods modified for 24mm wrist pins) then the AA set is your only aftermarket choice. They have a 95.5mm set (~2150cc on a stock crank), and they make a 94mm set as well. No 96mm set from AA. The 95.5 sets are not in stock very often, though, I just looked at their site and they are sold out.

QSC makes both 94mm and 96mm sets. Cofap makes 94mm sets but no oversized ones as far as I know. QSC and Cofap pistons are ~1mm below the cylinder tops on 5.4" rods.

OEM 94mm cyl wall thickness is ~7mm. QSC 96mm cyls are ~6.5mm thick. So it appears QSC's cyl castings are made thicker to start with and then presumably they bore the same castings to both 94 and 96mm. The weakest part of the cylinder is the skirt but skirt thickness is limited by the crankcase cyl bore size, so if you wanted a heavier skirt cyl it would have to be custom made and the case bores enlarged.

You have to check the QSC cyls carefully for hairline cracks at the bottom skirt edge, there have been many cracked ones. I buy direct from QSC, they have been actually pretty good to deal with, and they have replaced those cracked cyls for me, and once notified of the problem I have not received any bad cyls since when buying direct from them. But there is still older stock on other dealers' shelves, and people who have bought thru dealers and warehouses and got cracked cyls have not been able to get QSC to replace them directly.

The cyls also have typically .002-.003" out-of-round, but I have found that they have no measurable out-of-round within 2k miles. That is running chrome top rings, I don't know if that would happen with a softer cast iron top ring.

IIRC you had figured a sane ring package for the QSCs as well?

Originally the included ring set was junk, very sloppy side clearances, but they now include rings that all fit properly. But it is just a plain all cast-iron set, so you can expect the top ring not to have a very long life in a hardworking wbx. Rocky and I went in on an order of custom chrome top rings for these which we both use instead of the supplied top ring. If you wanted a set including those rings, you should get in touch with him (I don't deal in parts, so please don't ask).

In fact, anyone overseas who wanted to get US-market parts like this would be smart to have someone like Rocky check everything out and pay him for his time, so that you can be sure what is shipped is all good and you won't have the trouble and expense of returning parts from abroad. It's that or take your chances that there aren't any bum parts in the box.

Rocky also makes OEM wbx rods sets with excentric small end bushings that correct the deck height with the QSC or Cofap pistons. So if you wanted to use the QSC big bore kit and have normal 8.7:1 CR then Rocky would be your one-stop shopping solution.

http://www.rockyjennings.com

Are you having the rods rebushed locally or dud SCAT come to its senses?

I had Scat do a couple sets before, then for the last few years I was having the mod done locally using the CB Unitech 5.5" rods, which were a fantastic value at $80/set. But CB tried to get them made cheaper, the new ones were a complete disaster and they pulled the product. So I went back to Scat and am having them do the wrist pin mod in-house. Their rods cost more but have better fasteners and overall design, they come pre-balanced, and their machining has been consistently excellent.

Why is everyone so scared to run a little compression with a turbo, in the honduh world most turbo their stock block K20's, static compression is 11.1:1. If you have good control of the fuel and spark then you won't have to compromise the compression. So the moral of my story is EFI and computer controlled ign allows you to boost a higher compression engine safely.

just running high comp was something i was thinking also but i am a bit hesitant as i probably would be able to rebuild if or when i botch the engine.... a modern inline-4 i would think is more of a stable design. knock restistance-wise that is.

of course you can run high comp with correct fueling and ignition... dont know if stock parts are up for the job though?

regards
Dann

The trick is to run less boost, which gives you a more drivable car out of boost, and the same or more power. It's not the design of the modern motors but more of the fact that they aren't using carbs and 009's. Power is power, low comp/high boost puts the same strain on the internals as higher comp and lower boost. Think about it this way, all a turbo does is raise the dynamic compression. If you are scared of knock/detonation then set it up to run e85, that stuff is 105 octane and will make your turbo spool faster.

agree with ninja here. it's all about control of fuel spark.

BUT with the stock rod's i do not agree that the stock rod's are weak.
rather the other way around , they are strong, very strong
i have used stock rod's in all my WBX TURBO engines (6 until now) variyng from 180hp to ¨380hp ,2 of them dynoed over 500nm of torque and rpm's from 6500-7500.
i have only replaced the rodbolts from the stretch 2,1 style to stock type1 rod bolts/1.9wbx.
and 3 of these engines has been tested round after round on circle track racing.
not one failure. these vere rods pulled out of used engines , just checked the big end out of "round" and the small en bushing.
i would use a stock one over a chinese casting anytime.

i guessed so much . only thing that would probably speak against the stock rods is the weight i guess ?

german quality IS german quallity.....

Concensus is that i could run low boost with stock compression and get away with it if im running megasquirt for example ?

rings and gaskets and a honing of the liners and then focus on external bits ?

u Swedes have acess to E-85, then u should be fine. then , teoretically u can get away with 2 more numbers in compreission leaving u with a ~8.5:1 (if u think gas)