Forged pistons and rods questions

[trq-str]

Hi guys, I’m currently in the process of rebuilding a 6 bolt vr4 rs engine. It will be my first forged build so I have a few questions to ask. Help / advice would be much appreciated.

What compression ratio should I go for if I’m looking at running around 20psi with a 16g turbo? Would 9:1 be too high?

Can forged pistons and rods at standard size be used with factory crank and balance shafts? Or, will I need to remove the balance shafts and have the rotating assembly balanced?

Should I buy JE, Wiseco or CP pistons? Which is the better or more common brand?

And for rods should I get Manley or Eagle both being h beam design.

In advanced thanks.

Koray

 

[bazeng]

If you are going forged pistons, I'd get 20thou over to be safe. Get the block bored/honed to suit the clearance.

The last thing you want is to get the block cleaned up (bored and honed) and find out that your pistons will be too loose in the motor..

Comp, I say anything from 8:1 to 9:1 is ok. It is up to you really.
8:1 will give you more ability to boost it whereas 9:1 will give you more torque down low with lower boost capability. The rules change with race fuel though....

As for brands, I've used wiseco with success. Wiseco have a higher silicone content which means less expansion therefor are not as noisy as others at cold start (piston slap). Once again it depends on what piston to bore you decide to build your motor at depending on specs / requirements of the motor.

Rods, Eagle have proven themselves. Manley are one of the strongests on your can get (i beam type). The h beam type seem ok also.
I'd try manley over eagle if you are going H beam simply because I have heard that Eagle have now dropped a little in quality??? Previously made in China and machined in USA? but now fully made and machined in China??

Anybody purchased a set of Eagles lately and measured the bore in them???

 

[trq-str]

Thanks for the info Baz

After some further inspection of the cylinder bores, I will diffidently be going 20thou over. I won’t send the block off to be machined until I get the pistons. This way I can give them to the machinist along with the block to be honed, then I shouldn’t have any dramas.

How do I go about the balance shafts? Can they stay or must they go?
I would have thought that they where designed to work with the weight of the standard pistons and rods. If this is the case wouldn’t the lighter forgies throw the balance out of wack?

Dont evo123 engines run 9:1 comp ratio?

 

[mattrat]

evo i thought 8.5 comp

 

[Jonson]

I ran Wiesco 8.3:1 forged pistons and Eagle Rods, never had a problem, only had very slight piston slap in the morning for the first 2 minutes. Had the block machined to suit the pistons and was fine.

 

[trq-str]

For clearances did you go by the spec sheet which comes in the box with the pistons?

 

[EVO-00X]

Id go Wiseco 8.3 or JE 8.5's. As Baz said, they have a higher silicate content so less expansion rate plus they are more forgiving under knock as well. Stock VR4 ratio is 7.8 and a bit too low in my opinion. Somewhere around the 8.5 is best all round and provides you with some further scope if you decide to do some more engine work later.

The JE's and Wiseco's I have installed in a couple of 20thou overbore motors dont have piston slap as I requested the blocks be honed as per the clearances on the manufacturer spec sheets for high performance street/strip motors. The spec sheets will advise the recommended clearances to suit your engine's intended purpose. i.e. If you are going to use something like NOS that will heat up and expand your pistons more then you'll need to run a bigger piston to bore clearance and piston knock will almost certainly be evident on cold start ups.

Rods wise I'd go either Eagles or Manley as suggested. Im not sure what the latest quality control is like on the Eagles but if Baz reckons they've dropped a bit then go with the Manley's.

Yes, forged pistons and rods can be used with stock crank and balance shafts. You'll need to submit the pistons, rods, crank, flywheel, clutch, flywheel bolts, crank pulley, crank pulley bolt, to the machine shop to do a full bottom end balance. You dont need to submit the balance shafts. If it were me, Id ditch the balance shafts altogether.

The'll remove the oil plugs from the crank, clean it up, crack test it, micropolish and balance it. They'll also machine and balance the flywheel and clutch assemblies with the bolts in place.

 

[trq-str]

Thanks for the info guys, been very helpfull.

I haven’t yet made up my mind on wether I will ditch the balance shafts or not, but if I decide to use balance shafts, can I get away without a balance? Or is it necessary either way?

 

[VR-4Squid]

Thanks for the info guys, been very helpfull.

I havent yet made up my mind on wether I will ditch the balance shafts or not, but if I decide to use balance shafts, can I get away without a balance? Or is it necessary either way?

Common myth: Mitsi fitted balance shafts instead of balancing the crank/etc...

They are actually fitted to counter the inherent vibrations from an inline four - making the engine 'smoother', that is all.

Whether you decide to keep the balance shafts or not, you need to have the bottom end rebalanced after replacing the rods & pistons.

 

[bazeng]

The'll remove the oil plugs from the crank, clean it up, crack test it, micropolish and balance it. They'll also machine and balance the flywheel and clutch assemblies with the bolts in place.

Only if you request it. Not all shops will do this as a basic service.

Without the removal of the oil plugs, you'll most likely still have crap in the crank which is pretty much un cleanable unless the plugs are drilled out (ballbearings), and tapped to fit grub screws to block off. It does cost a bit to do actually, as the crank will probably kill some drill bits and taps... Just clarify with the machine shop if you want this done.

Also if you want, get the machine shop to measure everything and order the bearings for you.

Tell the shop what clearances you want or if you don't know, ask what they reccommend, then all you need to do is put it together. I'd measure everything again BUT if you don't have the tools to do so, maybe invest in some or take the shops word for it and put it together.

Another option is to use the plastigauge stuff..

 

[trq-str]

Thanks for the advice guys. I decided to go with the Wiseco/Manley combo and after about a month of waiting for them, they finally arrived!

I have been measuring all the clearances on all the internals for blueprinting purposes mainly to ensure everything is within spec before I have the block sent out to suite the new .020 over pistons. But before I do so, I wanted to ask for members opinions on piston to wall.

Wiseco calls for a .0025 piston to wall clearance, but since the coating on the lower piston skit wears after some use I will probably be left with about .0035. Im sure Wiseco know their pistons well. However, I have heard horror stories of pistons locking up in bores, crowns coming apart and cylinder walls hairline cracking all due to the tight clearance they recommend.

According to the boys on DSMtuner and DSMtalk wisecos recommendations are damn tight. Most of the boys on these US forums recommend a piston to bore of .0045.

What clearance should I go with? My aim is approx 230-250kw ATW.

 

[EVO-00X]

Alloy technology in pistons these days can make them run very tight piston to wall clearances without issues, especially those with the special ceramic coating. It also depends on what intended purpose the engine is going to be used for. I know 0.0025" can be considered tight for some and for these pistons under normal road use with 98 octane fuel and relatively low boost its fine. Its when you start playing with high boost and race fuels and NOS that gets the temperatures up and people into trouble.

I personally consider manufacturer specs in their tech sheet as the 'minimum' clearance. Therefore always err on the side of caution and go up to the next level or two usually listed in their table as high performance street/strip etc. It makes sense because lets say you or whomever else buys the car in future decides to give the car some high boost, NOS etc. I always add up an extra 0.0005" to be safe. Not only that, but its also good insurance in case the block wasnt bored out to 0.0025" as a minimum!!! Dont go as far as the US boys are talking about.

 

[trq-str]

It also depends on what intended purpose the engine is going to be used for. I know 0.0025" can be considered tight for some and for these pistons under normal road use with 98 octane fuel and relatively low boost its fine. Its when you start playing with high boost and race fuels and NOS that gets the temperatures up and people into trouble.

So how dose .003 sound? Or should I make it .0035? If I go with one of these I should be left with about an extra thou once the coating has worn off.
Will this be OK for a car that gets driven quite hard? I ALWAYS use 98 and plan to run 20psi with a 20g or 60-1 and 272's in the near future (currently 16g at 20psi with stock cams). Ohh yea and lets not forget the occasional track days.

I personally consider manufacturer specs in their tech sheet as the 'minimum' clearance.

That is what I thought, glad someone agrees.

Therefore always err on the side of caution and go up to the next level or two usually listed in their table as high performance street/strip etc. I always add up an extra 0.0005" to be safe.

When Wiseco list the high performance street/strip in the table, they are talking about the piston ring end gap. i will most probably gap to these specs. But I'm not to phased about this as they provide a table with clearances to suite different applications.

But for piston to wall they only provide one clearance, there should be a table with different clearances for different applications IMO. But there isn't and this is the reason as to why I have been searching on forums and annoying you guys with my questions lol.


Thanks to all who are putting up with my questions.

 

[D3bb4]

specify gaps instead of wall clearance as they indend for the piston to fit snug and the rings to take up the gap. I'd imagine larger gaps for higher performance motors? so that the piston and bore remain constant sizes, and allow the rings to expand more in higher temps.

 

[EVO-00X]

The hardest thing to trust are the bloody machine shops. If they cant bore squarely to the exact size requirements then thats where you can come undone and the slightly extra bore diameter makes for good insurance when your pistons expand.

I think I have a Wiseco piston tech sheet in the garage left over from Godfather's engine build I'll look for tonight. Im pretty sure its still there as I remember it was pink paper! lol...

FYI JE piston tech sheets show a recommended piston to wall clearance table as well as piston ring end gap table. The JE's minimum clearance is 0.0030" but you always add a little bit more to play with.

Edit: Just checked photos on my computer and the Wiseco paper I had in the garage and realised that Adrian [Godfather] delivered his block to me already machined by his chosen machine shop. I know the bores werent at 0.0025" though and were either 0.0030" or 0.0035".

In your case I'd still add an extra 0.0005" and go to 0.0030" to be on the safe side.

 

[trq-str]

Did Godfather's engine have cold start slap at .0035?

So lets say I decided to use a clearance of .0030" and my #1 piston measured In with a 3.3661" diameter. My final bore diameter for the #1 piston should be set to 3.3691" Am I correct?

And once the coating on the piston skirt has worn out I will be left with even more clearance, probably an extra thou. So the final piston to wall clearance will be around .004"

 

[EVO-00X]

Nope it doesnt have piston slap from what I heard.
You've mentioned the coating wearing off on the Wisecos? Are you entirely sure that's true?

 

[trq-str]

Did the wiseco's you used have the coating?

Nope it doesnt have piston slap from what I heard.
You've mentioned the coating wearing off on the Wisecos? Are you entirely sure that's true?

Not from personal experience, but I've read this on a few forums and Bazang (Barry) mentioned this also when i called him last.


The way I see it, if I decided to use a clearance of .0030" and my #1 piston measured In with a 3.3661" diameter. My final bore diameter for the #1 piston should be set to 3.3691" am I correct? Can someone please confirm this.

When I was researching on some other forums, there were questions popping up about about the specified piston to wall clearance being for each side of the cylinder bore rather than the total diameter. This would result in double the gap!!! For example, a clearance of .0030 from each side of the piston to the bore would lead to a total clearance of .006 isn't this excessive? Sounds false to me, can any1 agree?

 

[bazeng]

Keep in mind, pistons are measured from the lower part of the skirt which in most manufacturers case use a tapered piston design to allow for stability when rocking at the bottom of the cylinder. Most of the expansion will occur at the top of the piston where majority of the meat is. I'd honestly go with manufacturer specs. I've done the 4-5 thou piston to bore which lead to a noisy motor even when up at temp and with thick oil. I also had fractured skirts which I believe would have been caused by the excessive clearance.

The coating on the wiseco pistons are only for run in purposes. They rub off. Wiseco measure the pistons before the coating so go by the documentation, not by actual measurement of the piston.

 

[JC evo1]

im running wiseco's at .0030, no problems yet at 360kw, touch wood. If i was building the motor now i would run them a bit looser to be safe when i decide to turn the power up and use race fuel. Theres no piston slap cold and stuff all oil consumption.