Pro Stock John

iTrader: (34)

I'm glad we created this forum, seems like it is taking off.

So here is my thread...

How much taper, if any, is appropriate for a LS_ shortblock? BTW, this is just a general question, I am quite happy with my current shortblock.

Cstraub

iTrader: (1)

You want the cylinder concentric so that tolerance is held on the entire path of the piston. Now what can very is the honing finish from top to bottom.

Old SStroker

Why would you want the surface finish to vary?


My biggest concerns would be roundness and surface finish. That's what the rings see.

I want as little variation as possible in cylindricity, which is a combination of roundness and straightness including taper. Roundness under .0002 Total Indicator Reading (TIR) and size within .0002 would be nice, but you need to size to the piston going in that hole. I'd take a few more 'tenths' of straight taper because of the piston-to-wall clearance, and I'd prefer the taper to be smaller at the top.

As far as straightness or "banana" shape, the hone should remove a couple of thou if it's in there, which it usually isn't with a decent boring job. That's also hard to check.

My $.02

Pro Stock John

iTrader: (34)

So... minimal to no taper is ideal. .002 or less is acceptable...?

Old SStroker

2 thou? That's 10X more that I mentioned, but I'd take .0005 or so taper. If you were fitting pistons to .004/.005, .002 taper could get you to .002 clearance which might be scuff-city. If my block guy couldn't do better than .002 taper I'd go elsewhere...quickly.

The engine builders I know only work in 'tenths' (.0001 = a 'tenth of a thou'), not thousandths (.001) on bores, just like they do on bearing clearances. So do OEMs.

Cstraub

iTrader: (1)

OldSS,
HP. . .all in the name of HP. I gotta run, but I will elaborate tomorrow.

Chris

Ben R

.002 would be WAY too much. When machinists refer to 'tenths' of inches, they're referring to a ten-thousanth of an inch, not an actual tenth. (I.E. .0001 not .1)

Pro Stock John

iTrader: (34)

Sorry that was a typo on my part.

Old SStroker

Wish I'd said that...

Old SStroker

I'll hold my breath. I'd rather hear about the big NASCAR Cup rules change. You working with Mike on that?

Cstraub

iTrader: (1)

Oil control and HP. By layering the hone finish in the cylinder power has been found my engine builders. This layered finish puts oil on the cylinder where it is needed and where it is not, by doing so it has freed up some power in NA engines. Now is this worth doing in 400HP LS1, no. Is it worth it when 30M sponsorship is on the line, yes.

Teams are made aware of "possible" changes that may occur down the road. This allows for tooling changes and R&D to occur a year or so before the rule may or may not go into affect.

Old SStroker

Chris, are you talking about laser structuring in the top third of the cylinder bore? You still have to hone, of course, but the cost of laser structuring and honing was/is $500-$750 per block. Yeah, probably not worth doing to most engines. Cup shops can probably afford the equpment, so I wouldn't be surprised if they have been using it a while. I guess you could read the laser pattern on the bore and tell who did it.

Cstraub

iTrader: (1)

Old,
I have seen it done with Sunnen Stones and with the laser. I know some engine builders ship the blocks overseas to have the laser done. With shipping and the process I have heard it runs about $2500 per block. No not cost effective but whoever said racing is profitable!!!!

Torquemonster TT

As a guide for comparison - getting bores straight and no taper within +/- 0.0002" (point 2 of 1 thou) on a big block Mopar has been found to be worth around 50hp over a stock bore and hone job.... a small block musclecar era Chev will be proportionally less. Torqueplate bore and honing these old blocks is a must if you are even half serious

The improvement will be a lot less than that on late model blocks as casting techniques and CNC finishing have improved out of sight since the muscle car days... if I found 30hp on a late model block I'd be disgusted with the OEM... there is no excuse these days for factory blocks being that out unless they have been damaged.

I've seen high performance Nissan blocks run 3-500,000km on virtually zero bore wear. For the better Jap engines - torqueplate honing is usually a waste of time because they are straight as an arrow even after years of use. US OEM's are still no where near this standard but hopefully are closing the gap.

Old SStroker

I don't know how to vary the surface finish at the top of the bore compared to the bottom of the bore just with stones and still maintain the geometry. Bret likes a fairly high Rz and a low Ra, all done with various grit stones, for the rings he uses. It's important to measure both the Rz and the Ra.

caddycarlo

I think a lot of this depends on how much money the motor has in to it .... multi-layerd finish has me fascinated and I can see how it would help but I have made some high hp claimer motors with .002 taper when low buck is the goal ...... of course I have also been known to drill a very small hole into the runner from the rocker area to draw in a little oil and make it smoke just a touch on startup to keep higher dollar claimer motors ......

SStrokerAce

iTrader: (2)

I like that trick... as long as you run high octane gas and you aren't pushing anything.

racer7088

The infamous NASCAR bar on many Sunnen hones is one way.

Old SStroker

Tell me about it. I'm not familiar with the term.

Race-Prep

The "NASCAR BAR" is really nothing more than a lever attached to the hone head that allows the stroke to be held slower at that point to allow the user to adjust the size in that specific area to get the cylinder straight, really it is just a way to "cheat" the machine into making it hone right. Our Sunnen CV616 is able to vary the cutting pressure to open up tight spots in the bore and I prefer this method as it does not vary the cross hatch pattern. As for the bore concentricity and taper, I would NEVER run a performance engine with more than .0002" (2 tenths) out of round and taper, and we usually keep them less than that with the Torque Plate installed. The Cup teams and Pro-Stockers even go so far as to have the cylinder "Hot Honed" or honed with the block heated to operating temperature, this gets as close to real running conditions as possible. There is a lot of technology just in the honing process and many diffrent honing procedures for different rings.

-Bryan