115 replies to this topic

[siztenboots]

okay, pistons, the dish profile has a much pronounced square edge on the LEH, on the LET it is rounded. pistons, the centre dome outer diameter on the LEH appears to be larger, but the dome peak inner diameter appears to be the same. taken from the Mahle thread about c20let, z20let, z20leh differences "The forging tool used for both parts is the same (86P47), however the alloy used for the C20LET piston is M124 and the alloy used for the Z20LEH is M142 - you should also see these numbers inside the piston. I can't give the complete compostition of these alloys, but the properties of M142 make it stronger and more resistant to detonation damage than M124. The Z20LET piston is a cast, solid skirt piston (086L061) alloy used is M145. The bowl is approximately 0.5cm3 greater volume than the Z20LEH, and a larger diameter. Ring sizes are the same as the Z20LEH, 1.2mm, 1.5mm, 2.5mm "

[Nev]

My honest opinion is that for mid powered cars (300 to 400 BHP), it makes little difference what the crowns are like and you shouldn't worry about it really. The key is to have a squish band on the perimiter and make sure the valves clear the crowns (obviously). Secondly, all you need to do is lower the CR a bit if you can for increased boost. My CR in Nipper is 8.3:1 for running 21 PSI of boost, which is about right. Give me a ring some time Steve if you like

[Nev]

Owing to unforseen circumstances, Steve is bringing his engine round to mine this weekend for a re-build over the next couple of months. I owe Steve a big favour for helping me 2 years ago to strip Nipper, so this is my way of paying my favour back

We intend to strip it and make it semi forged so it be a sturdy unit for his hopeful entry into Time Attack. Having talked to Steve at length about this, I dont think he intends to do anything dramatic to the engine as he intends to run an almost normal KKK turbo on it. However, by stripping the engine apart and inspecting/rebuilding it, it should be a really sturdy and reliable unit. I think the aim is:

• Forged rods
• New crank shells
• New big end shells
• ARP rod bolts
• Head stud kit
• Mild cam regrind
• Bespoke inlet manifold
• Balancer shaft delete

That lot should make somthing between 310 and 330 BHP hopefully and around 375 ft/lb of torque.

Steve is deliberating about installing Mahle squeeze cast (semi forged) pistons in it as well, but we will make a decission on this once he have inspected the bores and piston crowns. BTW, all this is based on a 70k mileage engine. I have heard the OEM pistons are ok to 350 BHP once before, though I have to confirm this yet with someone I know.

Edited by Nev, 14 January 2012 - 08:46 AM.

[Dave E]

Given the intended use of this engine I'm supprised you haven't mentioned under piston cooling from an Leh.

[Nev]

Hmmm, it's hard to know if that is justified. Maybe. The main reason the Z20LEH had piston jets installed was for emissions reasons (particularily at idle) apparently, not specifically for cooling at high revs.

[coople]

Surely if it is all apart, now is the time to go fully forged and save the hassle in the future of stripping it again.

[siztenboots]

There are quite a lot of issues with going fully forged, the different thermal expansion of the alloy and the wider tolerances to the bore. Realistically the standard pistons have been happy at 360 ft.lb of torque for a huge amount of mileage and years of track use , just how much more do you really need. I have a picture of the head to put up to show 70000miles of use, when I can get it uploaded. Plus some dimensional information for the inlet manifold and engine bay.

[siztenboots]

[siztenboots]

[siztenboots]

[siztenboots]

nevs hand, plus detail of the cambelt routing and tensioner*

[siztenboots]

[siztenboots]

[steveboyslim]

Owing to unforseen circumstances, Steve is bringing his engine round to mine this weekend for a re-build over the next couple of months. I owe Steve a big favour for helping me 2 years ago to strip Nipper, so this is my way of paying my favour back

We intend to strip it and make it semi forged so it be a sturdy unit for his hopeful entry into Time Attack. Having talked to Steve at length about this, I dont think he intends to do anything dramatic to the engine as he intends to run an almost normal KKK turbo on it. However, by stripping the engine apart and inspecting/rebuilding it, it should be a really sturdy and reliable unit. I think the aim is:

• Forged rods
• New crank shells
• New big end shells
• ARP rod bolts
• Head stud kit
• Mild cam regrind
• Bespoke inlet manifold
• Balancer shaft delete

That lot should make somthing between 310 and 330 BHP hopefully and around 375 ft/lb of torque.

Steve is deliberating about installing Mahle squeeze cast (semi forged) pistons in it as well, but we will make a decission on this once he have inspected the bores and piston crowns. BTW, all this is based on a 70k mileage engine. I have heard the OEM pistons are ok to 350 BHP once before, though I have to confirm this yet with someone I know.

Standard ZLET pistons are not strong enough for modified engines, the ring lands fail.

Steve

[steveboyslim]

Hmmm, it's hard to know if that is justified. Maybe.

The main reason the Z20LEH had piston jets installed was for emissions reasons (particularily at idle) apparently, not specifically for cooling at high revs.

That is not correct, they were/are installed for under piston cooling.
I would also wedge the waterway.

Steve

Edited by steveboyslim, 15 January 2012 - 08:57 PM.

[steveboyslim]

There are quite a lot of issues with going fully forged, the different thermal expansion of the alloy and the wider tolerances to the bore. Realistically the standard pistons have been happy at 360 ft.lb of torque for a huge amount of mileage and years of track use , just how much more do you really need.

I have a picture of the head to put up to show 70000miles of use, when I can get it uploaded. Plus some dimensional information for the inlet manifold and engine bay.

If you use the correct brand of forged piston there is no problem of engine noise/bore clearance (piston slap).

Steve

[Nev]

Steve, We are only aiming to make 330 BHP and 370 ft/lb. The question we are wondering is if the existing OEM pistons will be happy with running just 10% more power than many 'stage 4' cars are... This is a 'budget' engine so we are not keen on splashing out on new pistons + rebore/hone if they are not requried for this 'humble' spec.

[cnrandall]

The LEH Piston is much lighter than the cast issue so it will be far happier revving harder. If you're running a stock turbo it won't breath too well at high RPM anyway so you may well get away with the heavier piston. What exact Turbo are you planning on using, the stock VX220 Turbo or VXR, or hybrid? If its a stock VX220 Turbo you won't clear 300bhp, best we have ever seen out of one is 240 @ the hubs and thats with a brilliant exhaust and EDS intake manifold... they just won't make the boost at the top.

[cnrandall]

Hmmm, it's hard to know if that is justified. Maybe.

The main reason the Z20LEH had piston jets installed was for emissions reasons (particularily at idle) apparently, not specifically for cooling at high revs.

That is not correct, they were/are installed for under piston cooling.
I would also wedge the waterway.

Steve

As I understand it the stock VXR had to run very lean (and hot) to hit emissions targets, so the under piston squirters were used to keep temps in check. I ran my car for 3 years without them with no detrimental effects although I am now using them. We have found these engines are quite knock limited so anything you can do to keep the combustions temps down is a good thing. Its one thing making the numbers on the dyno, quite another to keep hold of them when the car is heat soaked on the race track. Remember though, if you do use the oil squirters the cool the pistons you then need enough oil cooling capacity to shed that heat into the atmosphere...

[siztenboots]

Turbo sitting on my desk right now is a K06 hybrid , to be stripped of a few bits ready for shipping for a refurb. With the fitted K04 VXR, it will run 300bhp , 360 ft.lb , with max 40'C temps post charge cooler, with consistent ignition timing. The main reasons for swapping out the engine is a pressurisation of the coolent and gearbox problems on 2nd gear baulk ring and exhaust manifold lower set of studs gone walkabout. What I can do is datalog via a DL1, oil temps and water jacket temps if suitable places in the block exist to tap and npt thread the sensor. Previously I data logged top and bottom of the charge cooler jacket.