Cylinder distortion

[70mc]

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.

 

[70mc]

Forgot to say the reson for this question. I performed a leakdown test with the pistons at B.D.C. and again at T.D.C., all 8 cyl. at B.D.C. were 2%, at T.D.C. 3 cyl. were 15% other 5 were 6-9%. When talking to friends they have said the motors not broken in yet, i said its not broken in at B.D.C. yet either. I'm using Totalseal rings, and i asked for a torque plate to be used when honing, but am wondering if the torque plate was used. I provided my studs to be used with the torque plate but when i got the motor back the platic bags the studs come in were not riped open, so if a torque plate was used then maybe he used his bolts? Back to the question, i'm going to check the bores with a torque plate instaled and was wondering what acceptable out of round and taper specs. were. I performed a leakdown test on my last motor before it was broken in and had 1 cyl.that was 14% and after it was broken in that cyl. never got better than 13%. Now i'm worried about this one, any other thoughts? Thanks everyone.

 

[bsfc9]

using the same fasteners(also torque value and sequence)with the torque plate as will be used in the assembled engine is important and will make a difference. cylinders should be no more than .0002 out of round(.0002 per 22 degrees of segment circle for a four inch bore prone to third and fourth orders of distortion;--chev. 400), and no more than .0005 taper(.0002 would be better). now, how much deviation from these values will make a difference? that depends on your application. a completly stock 100,000 mile motor will be more tolerant than a nascar "cup" or nhra prostock motor. as far as your leakdown concerns;how much time or miles are on the motor, as break in time will matter. the previsouly mentioned "race" motors will tend to "break in" quickly, a bone stock motor may take awhile. things that will affect ring break in are: ring compisition, ring width, cylinder surface finish, bore geometry, ring end gap, and break in "procedure". we do alot of engine dyno testing for oem car compainies and they like to see an average of 10 hours on the dyno to consider an engine broke in(cast iron, liquidcooled, V-8). also you may fine if you drive your car around the the block 10 times and do a leak down each time you may see 10 different results as the ring end gaps move around during operation and the oil film changes on the cylinder wall.

 

[MaxRaceSoftware]

your Top -to Bottom ring seal/leakage should be the same any piston position in the bore..you shouldn't let the taper get more than .001"..and the out-of-round should be ZERO even if theres some taper top to bottom

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/

 

[SMOKEY44211]

I agree with Larry as far as the mechanical reasons for bore distortion at the top of the cylinders. Another factor is thermal stress especially on a 400 small block because of siamese bores. I believe the best method for minimal bore distortion is to assemble the engine with heads, gaskets, main caps, and fasteners that you intend to use. Ciculate 200 deg F. water through the cooling system and finish hone the block from the crank side. Sunnen has stones for blind hole cylinders like the old Offy engines and some aircraft engines where the cylinder head is cast integrally with the block. Also on the small block I relieve the section just below the cylinders and above the main caps with a hand grinder. If you don't do this it has a tendancy to push the hone off to one side. A visual would be helpful here. If you look at a bare block it will make more sense. You might what to give Kevin Mears at Sunnen in St. Louis ( I'm sure about the last name, may be incorrect about first name) He has done a lot of R+D work at Sunnen developing the hot honing technique. All cylinders when they are ready to come out of the machine are round. It is almost impossible to hone a bore into an out of round condition. Before you tear your engine apart I would run it a few more hours under load and see if the leakdown #'s improve. They sould. --------------Phil

 

[Majik]

After taking some classes with sunnen and making it part of my lively hood with race engines. The loss of compression up top is a definite sign of poor work although don't be quick to blame the machine shop. If you walk in and say make this block 30 over and use a torque plate then you got your money's worth. If you didn't tell them the ring material what you were using in the build then they can't be telepathic nor will they stop what they are doing and call you to find out. I can't count the times I've seen a big hunk of aluminum or 1/2" steel with a headgasket pattern cut out be called a torque plate. Sunnen makes some nice torque plates that have been engineered to replicate the stress of the head. Using something other than a pure engineered torque plate is more than likely taking a step backwards.. Second your ring material. Using total seals because they "seal better and give more HP" is a waste. Only with the proper machining will they do what they should but more often than not the cylinder won't be finished for total seals. Consult with total seal over your application but you will find that the hole was finished to rough causing extended break in periods. I honestly would go with a plateau hone finish and about a 280 roughness dependant on ring material. there is no reason to not have a race engine broke in in 30 minutes to an hour of run time... running a race engine for 10 hours would be silly. if you are building this engine running stock rods and some speed hoe er pro hypereutectic pistons then you are introducing a large number of variables into the mix as they are not proper race parts. Odds are a longer break in period will help a little but after that then you are SOL. You really can't crack it back open and fix the issue. It will probably be something you will just have to live with as they don't fix themselves. While measuring with a dial bore gauge to get it at zero up and down the bore... doesn't mean the hole is round and true straight up and down.. more than likely if it was done with a simple 4 stone hone then it has a 4th-5th order distortion in it already

 

[70mc]

Majik my machine shop provided me with the Total Seal rings, but i took it upon myself to call Total Seal for the proper finish and gave that info to the shop. Im using JE pistons with Lunati pro mod rods. This engine is being rebuilt, it was built 7 years ago was splayed and has a half fill in it. If it was being built today i would use an after market block, and if this don't get sorted out proper, still may.

 

[strokersix]

70mc,

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?

 

[MaxRaceSoftware]

Forgot to say the reson for this question. I performed a leakdown test with the pistons at B.D.C. and again at T.D.C., all 8 cyl. at B.D.C. were 2%, at T.D.C. 3 cyl. were 15% other 5 were 6-9%. --- 70MC
----------------------------------------------------------

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.jpg

http://www.maxracesoftware.com/Chevy_II_Headers_Dyno_SS_4.jpg

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/

 

[MaxRaceSoftware]

a vacuum pump such as a Moroso 4-vane pump

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/

 

[patprimmer]

I must say I always wondered how heating the block goes anyway near replicating the temperature profiles generated in a running engine.

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.

 

[ivymike]

I must say I always wondered how heating the block goes anyway near replicating the temperature profiles generated in a running engine.

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.

 

[patprimmer]

Ivymike

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.

 

[Majik]

I have seen the effects of heat honing a block and the difference can be upto 2-3 orders of distortion and on cast iron blocks upwards of .0006" of distortion and 2-3x that on aluminum blocks. You don't use water in the process but you use oil. An inclinometer is your best measuring device as a dial bore gauge can't measure true center up and down. As for having half a fill I think part of your problem is right there. Definitly getting two different heating areas between the top and bottom of the cylinders. If you don't have much blowby then keep running it. Also if your running nitrous it might benifit you to run a little extra blowby : )

 

[ivymike]

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.
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.

 

[70mc]

I would like to thank everyone for taking the time to answer my post, it is VERY good information. I now have more info and questions. First i would like to add that when i said that this motor was not broken in, it has not been started. As soon as i bolted the heads on i could not wait to do a leakdown test because i never used Totalseal rings before. It was 2:00AM and only did a quick check by not finding T.D.C. letting the air pressure push the piston down the bore (knowing it should be done at T.D.C. and never have done leakdowns at B.D.C. before) i was surprised to find 2% with a motor that was not broken in. Next day did it right and found high leakdowns at T.D.C.. I talked to the shop that did the work and told him what i found, asking if a torque plate was used, because i asked for it to be used, and what fasteners were used (telling him that my studs where never opened).I talked to the owner every time i was there or called,the problem is that that the shop is large and the owner does not do the work, so his answer was, the torque plate should have been used and they my have used their own studs. So now from the info. in this forum it sound like bolts are the way to go, and since my shop my have used bolts and a torque plate, i tried bolts. Things got better, with the worst, and only 1 cyl. being 8% and others being 5.5%-6.5% at T.D.C. and no change at B.D.C. still 2%. Knowing that it takes the pressure of combustion to make rings seal and things could get better when this motor is run, why the differance top to bottom, it is an apples to apples test. Could it be that a torque plate and bolts was used but does not replicate a head exatly, and that regular production blocks are going to distort a little? Or could it be a torque plate was not used? And lastly is the diffreance from top to bottom thought to be acceptable, or should i be talking to my shop again. Again, my thanks to everyone.

 

[SMOKEY44211]

Many years ago I did an experiment to see if the honing method I described earlier (heads in place, circulate hot water, hone from the crank side) on the even # cylinders. The odd # I just honed cold without heads or torque plate. After 1 hr. of no load running the even # cylinders leaked 2-3%. Odd side #1 4% #3 7% 5 8% 7 5%. Raced the engine in that configuration ( circle track) about 1 hr of run time. Even #'s leaked 1-2%. Odd side #1 3% 3 4% 5 5% 7 3%. Two races later even side 0-1% odd side 2-3%. Engine ended up in a street car. 5,000 mi. later they all leaked 0-1%. I should add that the rings were total seal gapless 2nd groove rings, moly faced top ring, honed with 500 grit sunnen hand hone. Total seal has since come out with a gapless top ring. They claim 5-15 hp improvement over the old style ring package. They report a few cusomers eliminating 2nd grove and ring with good results. My conclusion, out of the box the hot heads on method
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

 

[ivymike]

one place where the block filler seems to work well is in engines with oversized (too deep) cooling jackets. If you fill the bottom of the jacket, you increase coolant velocities in the top of the jacket and improve top-of-bore cooling. This can be handy when you uprate a limited number of engines.

 

[patprimmer]

Our application is blown injected alcohol drag race, at 30# boost.

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.

 

[ivymike]

yep, off topic

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.