ledslinger29
Well-known member
Thanks bill, funny you should that weep, bats where this project started...
Yet another static compression ratio question
- Thread starter ledslinger29
- Start date
Just remember if you do run into detonation a too lean fuel mixture will aggravate the condition.
Just keep your WOT between 12.5-13.1 to be on the safe side.
I go by cranking compression. My previous had engine 195# & with 93 octane i had no problems.
My current engine with dished pistons, but with a milder camshaft has 175#. I can run 91 or 89 with no problems. But my ignition curve is spot on & the same with the A/F ratio.
Just keep your WOT between 12.5-13.1 to be on the safe side.
I go by cranking compression. My previous had engine 195# & with 93 octane i had no problems.
My current engine with dished pistons, but with a milder camshaft has 175#. I can run 91 or 89 with no problems. But my ignition curve is spot on & the same with the A/F ratio.
The easiest thing to do looks like leave the bottom end as is and have the head disassembled and milled to at least 48cc's and find an oem shim gasket from green sales, a member or wherever you can get one. Decking the block at this point would be a nightmare imo. Finding pistons with more comp height would fix everything. But that's a slim proposition for a new finished bore.
ledslinger29":3vxuuyw5 said:
As the info comes togeather and also all the great advice from the other forum members it should help you in making your choice on how to finish your 170 build. To review you mentioned in your above post that the block was bored out to .060 by the previous owner so that is also a factor that accounts for some of the difference in deck height. The replacement pistions will typically measure with less than the stock piston compression height, so now we know why the deck height measurements very so much from the stock "approximate .025" deck height plus with the stock steel shim head gasket of .025 where we would have had a quench area of from .044 to 050 that is close to the ideal range. So the replacement Pistons Together with the reground cranks being .016 less than a stock 170 stroke crank accounts for the increased deck height being at.052.
I know this is is a tuff call to make considering all the work you have in it right now. So as it stands now you have a quench area of .097 Ie .052 inch piston to block deck height plus .045 gasket thickness this is quite far from the ideal of a .035 to .045 quench. This is also the reason of why the bigger 250 sixes don't do well when going to higher than stock compression ratios i.e. Some years have even more quench area (.130 to .150) this extra quench can aggravate detonation when trying to raise the Compression Ratio to optimize the performance of our six'es.
With the old stock steel shim head gaskets the block and head decks need to be nice and flat in order not to get a good gasket seal. You mentioned that you had leakage with your 170 before. Your head looks real good so it should be good to go, but is the blocks deck nice and straight? With the new style gaskets it usally isn't as much of a problem in getting a good seal even if the block deck is a little out of spec. So personally I would use a FelPro or the Victor head gasket if you leave the block deck as it is. I have personally used the FelPro PermaTorque type head gaskets for many years with very good results.
So if you want to leave the block as it is and try to be able to use Regular fuel (87) I would probally not cut down the head too much so that the chambers are around 48 to 50 CC and would shoot for about a 8.5 - 8.6 to 1 static compression ratio. If you cut the deck then you could go to a 8.7 to 9.0 to 1 ratio plus you get a nice flat surface again for a better head gasket seal then you could even try to use one of the steel shim type gaskets or a better copper one (they can be reused too) if you could find one or have one made. Good luck that should be a nice driver once it's all back togeather.
ledslinger29
Well-known member
Well I got some help making my decision yesterday. People across the street had a bunch of trees taken out this weekend, and the crew made a huge mess, they had a bobcat and all kinds of stuff out there. There was about a pickup truck load of dirt in the street. I walked past the kitchen window and looked outside and couldn't see my driveway. I ran outside and the !##$% was using a leaf blower to blow all the dirt out of the road, and it looked like an Iraqi dust storm outside. I had just washed my truck and the wifes car. I darn near came unglued. I went over there and wallered out the guy doing it, and I literally couldn't see my own house when I was standing in the road. My garage, and my motor, are completely covered in dirt. Inside and out. Looks like I'll be taking it apart.
WoW,
some don't care, some don't think, and some R a$$hose. Don't matter which, same bottom line &
gotta "keep relations". Glad U hadda talk & didn't explode/get irrational.
I hate it when others make decisions 4 us.
Keep us informed!
i6 bronks have longer cranks
some don't care, some don't think, and some R a$$hose. Don't matter which, same bottom line &
gotta "keep relations". Glad U hadda talk & didn't explode/get irrational.
I hate it when others make decisions 4 us.
Keep us informed!
i6 bronks have longer cranks
:wow: yeah that's a rotten thing to have done to your place and that new 170 engine. Sorry
ledslinger29
Well-known member
I got .052, so I think I'm gonna deck it .050, and maybe go with the felpro or victor gasket to keep from limiting myself on timing. The neighbor who hired the tree company wasn't home at the time, and everyone on the street is pretty ticked, everything here is covered with dirt. There were four tree guys and one of me, so fortunately strong words were all that it came to. He hosed the rest of it to the curb and shoveled it up.
ledslinger29":2s25hrca said:
Good plan! As a side note I have been using a heavy duty trash bag to wrap up all my engines (for many decades) when not working on them to keep out the dust and dirt. Best of luck
ledslinger29
Well-known member
I had it in a bag for months, got lazy and didn't cover it back up when i was done checking my deck heights. Lesson learned!
ledslinger29
Well-known member
Decked .050
Sorry for all the rookie questions here, but what's the best way to clean this thing up now? Compressed air? Pressure washer? Take it back and have it hot tanked?
Sorry for all the rookie questions here, but what's the best way to clean this thing up now? Compressed air? Pressure washer? Take it back and have it hot tanked?
Just pressure wash it & dry it with compressed air. Then oil down the cylinder wall to prevent rust.
The machine shop should have chamfered the head bolt holes with a 45 degree light touch to remove the sharp edge after decking. Would not hurt to chase the threads with a bottom tap to remove crud.
Otherwise looks great. I like the Victor-Rentz headgasket seems to allow less seeping of coolant on the drivers side of the block.
The machine shop should have chamfered the head bolt holes with a 45 degree light touch to remove the sharp edge after decking. Would not hurt to chase the threads with a bottom tap to remove crud.
Otherwise looks great. I like the Victor-Rentz headgasket seems to allow less seeping of coolant on the drivers side of the block.
Tanking it will kill the cam bearings and they would need replaced again. Soap and water, pressure washer would be good, be quick about drying it with compressed air ect and then oil the shit out of it with WD40, don't forget the oil/lifter galley area.
ledslinger29
Well-known member
Okay fellas, I got my block decked .050, reassembled, and my deck height is essentially .000, plus or minus a few thousandths here or there. This should put me at 9.04 SCR, by my calculations. I'm pretty excited....
Congrats on getting it back togeather! You might want to chase the head bolt holes with a bottoming tap. Good idea to get a set of the hardened flat washers if you will be using the stock type head bolts too. Good luck 
