Cylinder distortion
Cylinder distortion
(OP)
What would the specs. be for out of round and taper of the cylinder bores of a small block Chevy. It is a regular production 400 engine out of a 1976 car. It has been bored .030 over and honed with a torque plate, and will be used for racing.





RE: Cylinder distortion
RE: Cylinder distortion
RE: Cylinder distortion
looks like Torque-Plates might not have been used
or used with bolts ...also its possible they did use the Plates but not knowing how to hone ?..there should be ZERO out of round with plates and main caps torqued, and theres a lot more to Honing like Hone rpm, stone load/pressure, grit, grit stages used, cross-hatch pattern, hot/cold honing, intake manifold bolted in place (with 2 torque plates), ring materials, cleaning bores after hone,ring gaps,piston groove quality, etc.
i have a Sunnen dial-bore gauge that reads in Ten-Thousandths....when Hone is finished w/Torque Plates, the Sunnen gauge reads "Zero" anywhere in the Bore...if you remove the Torque Plates and undo the main caps the Bores will not be round , especially on a SBC 400 OEM block that has half the bolt threads cut into the back of the cylinder walls.
becareful using Studs in a 400 OEM block
as they will distort the bores more during full-load acceleration, especially inbetween the 2 Intake port pair headbolt location...in that area a stud can cause the block to form a crack to the steam hole if its not previously cast-iron tappered plugged up ?
its better to use atleast 2 Bolts in those locations instead of studs...the Bolts have looser fit in headbolt holes due to their reduced diameter as it might pass thru a "sleeve" there in a highly modified intake port, or just interfere with headbolt hole in the casting if heads were angle-milled a lot but the hole was never corrected back to the old angle or even the spot-face at the nut location was not corrected back flat can all these things cause bore distortion
using a 12-point ARP bolt instead of studs would be better ring seal and less deck distortion than studs
studs need 10 to 15 more LBS. Torque to clamp the headgasket the same as a Bolt
the stud can act as a "Lever" thru distance with any tiny movement of top of stud distorting the block..as cylinder head is under full load acceleration with Combustion heat, pressure,intake, exhaust, compression strokes, coolant temperatures , differences between Aluminum Heads vs cast-iron block in expansion rate, spring pressures open/closed, etc.
you could also checkout these Posts on Rings
http://speedtalk.com/forum/viewtopic.php?t=152
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
http://www.maxracesoftware.com/
RE: Cylinder distortion
RE: Cylinder distortion
RE: Cylinder distortion
RE: Cylinder distortion
When I first read your question I thought you said the leakdown was more at BDC and had the following thought:
I expect the JE pistons have short skirts and when cold at BDC probably are not square in the bore due to being half out of the bore and .005 inch clearance. If the piston is rocked out of square I would expect the leakdown to increase. This is conjecture on my part, not experience.
Then I reread your question and the greater leakdown was at TDC and discredits that theory. Or does it?
RE: Cylinder distortion
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but what's your "ring seal" when the Engine is under full-load in an acceleration rate Dyno test or down the DragStrip ????? i've seen a lot of SuperStock engines , especially when the same Block is used for years, and gradually piston-to-wall clearances grow larger thru rebuilds,and with a Dykes top ring, have terrible leakdown numbers like as much as 30 % percent...but only 2 to 4 CFM on a Blowby Meter under full load going down the DragStrip or on the Dyno .
leakdown numbers are not the "final word" in ring seal quality !! Leakdown=Static Blowby Meter = Dynamic
what counts is when the engines running .
in the end..what counts is the Torque/HP losses or gains
during when the Engine is running down the DragStrip
http://www.maxracesoftware.com/bbc.jpg
http://www.maxracesoftware.com/BBC_OrangeDSC00028....
http://www.maxracesoftware.com/Chevy_II_Headers_Dy...
suppose you let 1 CFM BlowBy equal = 2 HP
if you get 10 CFM Blowby on a 600 HP engine you would loose 20 HP ...and 10 CFM on my BlowBy Meter would be pegged-out... 2 to 6 CFM would be a typical Race Engine
so 10 CFM = 20 HP loss
and 4 CFM = 8 HP loss ...a difference of 12 HP
its possible to see more Toque and HP loss than those above figures "if" the engine is Hi-Compression Ratio and oiling starts to affect combustion rate
the lower the RPM band..the more time for BlowBy
the higher the RPM band..the less time for BlowBy
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
http://www.maxracesoftware.com/
RE: Cylinder distortion
http://www.maxracesoftware.com/Vac_Pump.jpg
would help out more and more as Engine has greater BlowBy , bad rod ratios, and large crank stroke
on engines with exceptional ring seal with 3 stroke ,very large oil pan, not a lot of gain with Vac-Pump ..
but Engines like BBC 632 cid can gain 25+ HP from a vac-pump or 4-Stage dry sump pump
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
http://www.maxracesoftware.com/
RE: Cylinder distortion
Even torque plates do not truly replicate cylinder pressures, but at least they apply most of the final force to the same spot.
I do think that filling the block to within 1/2" of the underside of the deck stabilises things a lot. This will depend somewhat on the pre-load created by minor expansion of the fill on curing.
If you have less than half filled the block, then put a lot of passes on it, and now only the top is out, maybe that is the answer.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
A heated block obviously doesn't match the heat flux profile of a running engine - the heat is going in the wrong direction - but even if it's guaranteed to be wrong, it's got to be closer than a cold block. A warm block will at least have some amount of cylinder-cylinder smooshing (greater expansion towards outside than towards other cyls) in it, which you can correct w/honing to some extent.
Even torque plates do not truly replicate cylinder pressures, but at least they apply most of the final force to the same spot
I thought they were just intended to approximate bore distortion due to assembly, so that you could at least have a reasonably cylindrical cold bore? Distortion due to head bolt preload can be a fairly significant contributor to final (running) bore distortion, and if you can afford to take out the bumps by honing "assembled", there is usually something to be gained.
RE: Cylinder distortion
Thanks for your response.
I always considered heating the block a waste of time because I had no data to support the notion that it made things better rather than worse due to the reverse heat flux. Also, I expect that we cannot effectively put much heat in via water as we have so much fill in the block.
Do you really think I can find a gain by hot honing in a block filled to the level that there is just enough room for water circulation between the fill and the deck.
This is not a loaded question, nor an argument, as I do value your advice. I am simple stating my unsubstantiated reasons for not doing it to date.
I do use a head plate to hone bores as I think they correct for most but not all distortion, and anything that must be positive, must also help to some degree.
Also, I think that the right hone finish helps to correct for minor distortions, as the rings bed into that surface under actual running conditions.
I think this only accounts for a few % blow-by, not the extreme difference the original question asks, but that is only from intuition. I have no actual supporting data, other than we win more than our fair share of races.
I suspect the original problem is not enough fill in the block for a pre Bowtie 350 Chev block.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
RE: Cylinder distortion
The metal will be a bit warmer, even if the jacket side is hotter than the combustion side, and so distortion should move a little towards its true "hot" shape. I think you're right to suspect that a filled block won't respond as well to heating.
Now if you could only turn the block upside down, put a head plate on it with "coke cans" over the cylinders, fill the cylinders with hot oil, heat the block, and hone submerged... wonder if something like that could be done? Certainly wouldn't want to get splashed with the oil.
RE: Cylinder distortion
RE: Cylinder distortion
shows better ring seal. In the long run not much advantage. Just to comment on block fillers. I think its a negative. I don't know of any commonly used materials that have the same expansion characteristics as cast iron or aluminum. This would suggest that it may actually cause distortion when the engine is brought up to operating temp. The cooling system cavity is already on the small side for a big cu. in. small block endurance engine. Also the portion of the cylinder that would recieve any benifits from additional support is the least stressed portion of the cylinder.-------------Phil
RE: Cylinder distortion
RE: Cylinder distortion
as we are making about 1200 HP from a pre Bowtie SBC, short term durability is our main concern.
So far we only split one block, and that was from a stud hole to the bore, on the deck, so the fill had no effect there. These blocks are reputed to be very fragile at over 700 HP, so I am presuming the fill is helping as we have over 50 passes on the current block. We have no serious oil dilution. We have no serious blow by.
Measured cold, our bores have no measurable distortion nor wear after 50 passes.
Unfilled blocks can have a few thou barrel shape after just a few passes. I think what really matters is what shape things are at full power, and I have never seen where anyone can measure that to date. I guess an OEM might have the resources to insert a strain gauge on the outside of the bore (in the water jacket). Would strain gauges respond quick enough to measure the cycling strain and relaxation at say 6000 rpm? Has anyone here done this?
Are we getting off topic. It fits the heading, but is a bit past the actual original question, as it was related to static tests?
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
I have never seen where anyone can measure that to date.
people can come pretty close in calculating it though, especially if they have good cold data and hot TC data for correlation.
RE: Cylinder distortion
It seems to me that the loose forged pistons can move when cold to a position where the piston axis is no longer parallel to the cylinder axis causing poorer ring to cylinder contact with a higher leakdown result. This could be easily tested by inserting shims to force a loose forged piston square for a comparison. Or perhaps heat the piston to expand it to it's operating size. Anyone investigated this? If this theory is correct then the leakdown test may be of questionable value for a forged piston racing engine.
RE: Cylinder distortion
RE: Cylinder distortion
to read a better Leakdown percent ...can be as much as 8 or 10+ % differences.
what counts is the Blowby meter CFM
and what counts more or more often is "if" the Engine will make more useable HP torque gains in your desired RPM range
and has proper oil control
i've seen plenty engines show great on a static leakdown test..but have more blowby CFM or run slower down the DragStrip
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
http://www.maxracesoftware.com/
RE: Cylinder distortion
RE: Cylinder distortion
Perhaps the leakdown test doesn't have enough pressure to seat the ring in it's groove or on the cylinder wall?
RE: Cylinder distortion
I considered that possibility, but decided against it because of the relatively small clearances involved. 0.4deg of piston tilt translates to 691um of axial displacement from one side of the bore to the other, which is probably 14x the axial clearance that the rings have in the grooves. The rings will be forced to tilt with the piston, mostly, although they could remain slightly misaligned within the clearance in the groove. I would expect even a slight amount of applied pressure to be enough to align the ring with the groove flank.
Perhaps the leakdown test doesn't have enough pressure to seat the ring in it's groove or on the cylinder wall?
100psi gage should be more than enough to seal a ring against a groove flank if everything is cold (and therefore relatively flat).
Sealing against the cylinder wall, I'm guessing, would not be significantly affected by rocking the crank slightly back and forth, although it may be the case that the ring finds regions of thick/thin oil film as it is moved back and forth, which would influence the size of non-conforming areas between the rings and the liner thru which gas passes.
RE: Cylinder distortion
Also, I still think that cylinder wall movement under dynamic loads might be large enough to cause a significant effect on a race engine. If the forces are great enough to leave a permanent distortion in cast iron, they must cause much greater dynamic distortion.
I really wish I had some actual data instead of relying on intuition, and drawing conclusions from semi related observations that all have other variables.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
yeah, that's basically the sort of thing I was referring to when I said "misaligned within the clearance..." I still think that it will only take a small amount of pressure in the cylinder to push the top ring to the bottom of the groove very quickly. The other rings don't see such a pressure difference, so perhaps they linger in odd positions due to friction - that actually doesn't sound all that unlikely, now that you mention it.
Cylinder wall motion under firing loads is significant to the piston behavior (tilt and wear), and very likely has a big impact on ring gap dilation too.
Dynamic cylinder wall shape can be calculated relatively easily by a skilled engine structural analyst (via FEA). If you've got a hundred grand (USD) or so to spare, I can put you in touch with one who'll do it on a consulting basis... ;)
The effects on blow-by and engine performance are a little bit harder to calculate, but not impossible. There are commercial software packages on the market for that purpose (although the ones I've seen both assume constant block geometry during the course of the simulation - you get to look at a single distorted shape, not a time varying one).
RE: Cylinder distortion
I think using static block geometry would be so far off as to be not much better than intuitive guessing from other observations.
I wonder what effect the dialation and contraction of the ring has on effective ring tension on the bores of a running engine.
Anyway, that is where I expect the fill helps, in reducing dynamic barrel shape distortion of the bore, and I suspect at our power level, and bore temperatures, the distortion from cylinder pressures could be a lot greater than those due to uneven expansion from heat.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
RE: Cylinder distortion
RE: Cylinder distortion
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion
nah, you can still tune a ring pack pretty well with the existing software, and troubleshoot problems successfully. It's hard to get blow-by within 10% if you don't have correlation information a priori, but if you do have correlation info then you can pretty well match ring pack behavior through a variety of operating conditions, and predict things like flutter, collapse, etc.
RE: Cylinder distortion
Now you have me wondering if race piston manufacturers might have the software to perform this analysis. I might ask my supplier.
I really expect that due to required budget, it might be restricted to F1 and OEM.
If I have anything more to say, I will start another thread and stop my hijacking of this thread.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cylinder distortion