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[DmC]

Yeah when vitaras come new in the box they look horrible. They have really sharp edges that could cause some preigniton. Preignition is Detonations bad ass older brother that you don't want to fuck with because he doesn't warn you he just punchs a hole in your block.

But anywho here's a pic of before and after sanding with some 400grit.


Discuss.

[DreaMeR]

did not know about sharp edges creating pre ignition. oh well, anywho I got my vitara running...its sounds good

[DmC]

Yeah sharp edges can become hot spots. This is just one of those tricks to use on your way to a 400hp Dseries.
But according to slow crx he already knew how to do that years ago.

[Corey]

sharp edges create a hot spot, hot spots will ignite fuel prematurely ala preignition.

on a side note ive never seen vitaras with the outer edges of the piston turned down like those, mine we just cast with no finish machining on top.

[DmC]

Their the FJ distributors brand. I'm not in love with these pistons as they come in the box I'm getting them media blasted and coated Before they get installed

[DmC]

I resized the pic that thing was way to big.

[DreaMeR]

ah, well good thing Im not shooting for super high numbers then

[DmC]

ah, well good thing Im not shooting for super high numbers then

Don't sweat it man about a half hour with some 400grit and they'll look like I have mine I'd say they'll hold up fine without the coating but hey I'm doing it just to see if it really makes a big differance.
Seems to be working great in fowee's car. The guys running 11's on turbo edit. the coating has got to be saving his ass imo.

[drunkinmaster1]

mine are stock and dd and havent been sanded worth a tapeworm stringing out of hotrexes ass.
a cast piston that has proven to hold over 400 hp. wht the fuck would you want to mess with a proven formula is beyond me.

[DmC]

mine are stock and dd and havent been sanded worth a tapeworm stringing out of hotrexes ass.
a cast piston that has proven to hold over 400 hp. wht the fuck would you want to mess with a proven formula is beyond me.

Not messing with a proven formula I'm refining it to perfection. Success is in the details man. I'm going for longevity.

[Blacksi]

good tech never seen this prep for vitara's

[Urban Indian]

good tech never seen this prep for vitara's

+1

[junkyard racer]

This is some good info, if it is something people are doing to prep there pistons, like for real. I dont know why you would post some shitty info...but...

id move it to another section, and sticky it. or maybe make 1 sticky with "good links" or something.


 

[TTC]

When you do it im assuming you just do the face? Like the top of the piston.  What im wondering is do you smooth th edge around the outside piston? 

[92CXyD]

I'm doing the same thing but using this link for a reference : http://theoldone.com/articles/engine_tips/enginebuildingtippistons1.html

[DmC]

When you do it im assuming you just do the face? Like the top of the piston.  What im wondering is do you smooth th edge around the outside piston? 

Just the top of the piston only you don't want to sand down the outside edge. on these I did the outside edge only slightly in the valve reliefs ,I had to it came to such a sharp edge that you could cut a rope with it.

[chris]

what are you using for coating?

[Joseph Davis]

You can develop hotspots in a 7.5:1 CR engine?

[Robb]

You can develop hotspots in a 7.5:1 CR engine?

To this I submit the six-bolt 4g63.   

[onlyflash944]

You can develop hotspots in a 7.5:1 CR engine?

think effective CR

[Joseph Davis]

Think power levels you can get traction.

[onlyflash944]

You can develop hotspots in a 7.5:1 CR engine?

Think power levels you can get traction.

i don't see the connection between hotspots on pistons installed in low compression engines and traction

[widebody93]

They are can happen in harmony 

[Joseph Davis]

You can develop hotspots in a 7.5:1 CR engine?

Think power levels you can get traction.

i don't see the connection between hotspots on pistons installed in low compression engines and traction

How much power do you generate by revving your engine out of gear?  Do you have to worry about what octane you use to free rev your 7.5:1 CR engine, or what octane you use to make 450 whp with your 7.5:1 CR engine?

[HiProfile]

IMO all you really need to do is go over the piston with a scotch brite pad. Sandpaper is a bit overkill. If you had crap like the old CP pistons, which have uncut releif edges which are prone to getting red-hot, you'll want to grind material.

Hot spots are projections that have lots of surface area but a small contact patch with the base metal. When it can't wick the heat away fast enough, it keeps getting hotter. And by hot we're talking well over 536F, autoignition for gasoline. The piston is dumping heat into the cylinder walls & oil, which are cooled with 200-240F fluids. The arrow & bumples wouldn't get very hot, since it has almost as much contact with the piston as it does with the air.

[Joseph Davis]

If you had crap like the old CP pistons, which have uncut releif edges which are prone to getting red-hot, you'll want to grind material.

All the old pistons were like that, some still are.  Although it was a weak spot on all brands of pistons there was a problem with CP's design/materials/etc.  But every machinist I've met freaks out about them since they are machined to spec w/ clearance built in so they only have to bore/hone to an exact 81.5, 84, 84.5, etc figure and the piston drops right in.  The only reason people like those pistons is because they confuse convenience for quality.

[That Guy]

oh dammit i just got some CP's shit now im fucked or something? i gotta do more prep work?

[Joseph Davis]

Cut the side of the valve reliefs out of them, you'll be right as rain.

[patsmx5]

Polishing the tops of the pistons will cut down on heat transfer in and out of the piston. Reduces the effective surface area of the top of the piston. IE-if you zoomed in with a magnifying glass, you'd see the top isn't flat, but more like /\/\/\/\/\/\/\/\. Peaks and valleys.

[TTC]

JD you mean shave down the Valve relief part that is on the high side of the machine, for isntnace the Round part of the C. Like the old one does.