It seems to me that most of people here do .20 overbore, just curious, any specific reason why most of you guys end up with this specific number? why not go larger (other than it would req bigger piston)?

 

A .020 overbore is just to roundout the cylinder and remove any imperfections. Removing more material obviously thins and weakens the cylinder wall. I have seen as much as .100 cut from the walls. As an open deck block the less material you remove the better.

JET

 

ic... Thanks

 

True as Jet said ---- Also if you push it much farther, because of Core Shift, you can get Hot Spots in the walls that can ignite fuel at out of time intervals. In other words a thin area that gets hotter than the surrounding areas and acts as an igniter

 

It also leaves room, for boring again, if something should happen to your block!

 

^^^What they said^^^
There is no way to insure consistent and correct piston to wall clearance, without doing a slight overbore, and matching each cylinder to each piston.

FYI, if you use Darton sleeves, you can overbore to 100mm, and achieve roughly 3.8L. I am running this setup on my car. I was a little worried about head gasket sealing, but so far, with over 20K on the engine, and plenty of track time and abuse, its holding up very well. It's a poor man's stroker kit.

 

technically, that isn't a stroker as the stroke hasn't changed.

what would you really call it.....a "boring kit"?

just messin' with you Sharif!

 

haha..you got me.

 

Have there been any reports of built engine failures due to the cylinder walls? Bored .020, 96mm, or otherwise? I know that the "best" bet is to sleeve, but I haven't heard of a built motor failing due to this issue. Maybe I haven't searched enough...

Before this turns into a huge debate, I'm not stating that with our open deck blocks you're not better off sleeving. BUT - is this a known issue that has caused people to lose their engines? I'm under the impression that most guys running "average" power levels on built setups (500-600), that sleeving doesn't really do much for you. Overkill maybe? Kinda like 1/2in. headstuds vs. L19's IMO.

Again, just looking for cases where we've seen a built VQ go due to the above mentioned concerns. TIA.

 

To my knowledge noone has lost a motor resulting from the cylinder walls failing. APS was running their R&D car into the 800's without sleeves. IMHO, sleeves are more trouble than they are worth - especially when I have yet to see them be a weak point on a build.

.020 overbore is the way to go

I don't know if the 1/2" studs are overkill though. With the open deck, I would think any little bit of extra clamping force would help. That said, I am running the the regular ARP head studs with oem head gaskets and running over 16 psi.....knock on wood, my car is holding up. I will be honest; the discussions have me nervious about headlift, so if I decide on cams for this winter, I might just pull the heads and run the L19s with the HKS gaskets and port the heads a little. Until then I guess I am running on borrowed time

 

Like Ziv mentioned..I havent seen one cracked or distorted cylinder wall yet...unless something else in the engine let go...causing the damage.

I have a feeling, the stock cylinders will take much more than people think. but until a bunch of people are in the 650whp+ level without sleeves, we are still suggesting sleeving for people shooting for 600whp+. Darton sleeves have no reported cases of leaking or sinking on the VQ35, that I can recall. The only drawback, is it adds costs to the buildup.

In regards to going more than .020 or .040 over on stock sleeves, I wouldnt suggest it. Darton designed their sleeves to allow overbore of 4.5mm (100mm bore)....the stock sleeves were not engineered for this purpose.

 

Thanks for the answer guys
Kinda OT since somebody mentioned it, how important is actually head gasket for FI application?

 

Above 10% or so -- Very, as are the studs, Its what keeps that boost where it belongs--In the cylinders.

 

At what boost/whp do you think it would be necessary to replace to gasket?

 

WHP isnt a factor. There are those better suited to answer that, But if I was going to push hard at 10 PSI or higher, I would go through the top end, but if you are going to do the top, you might as well do the bottom too

 

Do you have any idea which head gaskets are good (other than HKS)?

 

Right now HKS is the deal. Nothing approaches it's performance so far. MRC is experimenting with new copper head gaskets. The copper gaskets need to be tried and tested first.

If your going to build a motor then go with the HKS. There would be no point in putting Cometic or Cosworth head gaskets in there as they have no real advantages over OEM. The HKS have a stopper ring which gives them an advantage over the others.

JET

 

Thanks jet. I ws actually gonna ask about cosworth head gasket but you answered it first

 

+1... HKS is the way to go unless you're looking at a bored 3.8 like Sharif mentioned. Then you've got no choice but to use the cometic/cosworth 100mm HG's. HKS HG's are 97mm ONLY. Fine for stock-96mm bores, but that's it. You "could" sleeve, bore to 97mm, and still use a HKS unit with custom pistons, but it probably wouldn't be worth the hassle...