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engine build question
https://slantsix.org/forum/viewtopic.php?t=48151		 Page 1 of 2
Author:  akbmotorsports [ Sat Mar 10, 2012 2:17 pm ]
Post subject:  engine build question
hello. went to the shop this afternoon to obtain some more accurate measurements on the 67 long rod build and have questions.

first question, piston popup (all above deck) measurements are 1 to 6 - .006, .019, .016, .016, .017, .016. should i get the (wiseco) pistons shaved to zero deck?

i have an Oregon grind 346, 234/226 @ .050, .476/.479 lift per card installed at 100*.

next, using the KB-Silvolite calculator, i entered 60cc chamber, 6cc piston recess, 3.484 bore, zero deck, .035 gasket, 4.125 stroke, 7.005 rod length, intake closing (mocked up head so ACTUAL) 56* gives SCR 10.013, DCR 8.490 so i need to lose some compression. if i can add 4cc to the chamber that gets me SCR 9.536, DCR 8.094. (at .019 piston height SCR 10.403, DCR 8.814 wooaaah)

question, could i get the chambers machined to match the gasket bore? how many cc's do you think i would gain from removing the material around the perimiter of the chambers?

Image


thanks, andy :D
Author:  DadTruck [ Sat Mar 10, 2012 2:51 pm ]
Post subject: 
Andy

I can see some clearance cuts along the combustion chamber next to the valve, have you de shrouded that area to the limit?
may not get you all you need, but would be a step in the right direction.

see this article..
http://www.eurospares.com/graphics/engi ... 0Time!.pdf

what head gasket are you using that gets you a .035?

regards
John
Author:  akbmotorsports [ Sat Mar 10, 2012 3:06 pm ]
Post subject: 
hello DT. the unshrouding is right up to the edge of the gasket, felpro 7918PT-1, i have seen some posts saying they are .043 to .035 and used the latter to be on the high side in the calculator.

andy.
Author:  1974duster kev [ Sat Mar 10, 2012 3:17 pm ]
Post subject: 
Just curious why do you want to lose some compression? My na motor was 10:1 compression with a slightly larger cam and i drove that as a daily driver with no problems.
The thicker head gasket you mentioned wouldn't that bleed off the compression you were looking to get rid of?

Kev
Author:  akbmotorsports [ Sat Mar 10, 2012 3:41 pm ]
Post subject: 
hello kev. my understanding is that DCR of 8.5:1 is on the edge for street gas premium. i had considered going ahead and trying it there and see if it pinged. when i was degreeing the cam with only #1 piston installed it measured .006 height, so i thought the rest would be close, but not so. the highest being .019 #2, lowest .006 #1, seems that one rod is probably a bit short. (using OEM 198 rods)

these are the kinds of things that make this stuff a fun learning experience!!!

andy.
Author:  DadTruck [ Sun Mar 11, 2012 5:01 am ]
Post subject: 
Andy

going back to your original question, opening the chambers to the diameter of the fire ring..

would be ok,, as long as the stack up of the gasket to the dowel pins to the case is minded,, basically be careful that the fire ring is always fully supported on both the head and case sides.,

to see how much volume that you will gain by working the diameter of the combustion chamber, maybe .050 larger,, get a strip of metal, .050 thick,
3.484 long, as wide as your combustion chamber is deep,, then use the syringe that you have for cc chambers as a graduated cylinder and determine the volume change when you submerge the metal strip in the cylinder..

regards
DT
Author:  Dart270 [ Sun Mar 11, 2012 8:12 am ]
Post subject: 
Sounds like the build is progressing along very well. I had my wisecos cut for 0.005" out of the hole (about 0.020" off in my cast crank app), and will use a 0.046" gasket. My measurements of about 10 Felpros come in around 0.033-0.035" compressed. The Aussie permaseal is 0.044-0.046" compressed.

10:1 with that cam should be OK on premium with a good ign curve. 8.5:1 is probably a big bore V8 number, and the Slant should be OK to run higher on premium. I have run higher.

Lou
Author:  akbmotorsports [ Sun Mar 11, 2012 8:33 am ]
Post subject: 
DT, good idea. i wish i had thought of that.

Lou, i guess i will be pulling the pistons out to get a shave. #1 is at .006 so maybe just pull 2-5 and get them cut to that? then i can adjust compression if necessary.

would there be any advantage to opening the chamber to match the fire ring?

thanks for the input. andy.
Author:  Doctor Dodge [ Sun Mar 11, 2012 9:51 am ]
Post subject: 
What happens when you swap the #2 piston / rod combo into the #1 cylinder, does the deck reading go up to .019?

You may have a slightly bent con rod or poorly machined piston... or both, that should be reviewed and addressed first.
I would not selectively machine the piston compression heights to different levels to "fix" this issue, unless a piston is incorrectly machined to begin with.

Once the deck reading are all grouped within a few thousands, I woulds cc & sweep-out the head chambers... one more time.
Was the head "matched" to the cylinder bores... are the chamber openings well centered? If so, a heavy edge break on the head chamber's sharp outer edge should be done... to "blend" the edge out to the large bore size.

Also think about giving the piston valve reliefs a little edge break work... we know the relief's outer edge is a little close to the valve, on the Wiseco pistons.
Do all that and remeasure, then find the thickest head gasket available and run it.
DD
Author:  akbmotorsports [ Sun Mar 11, 2012 10:48 am ]
Post subject: 
very good. will do that swap tomorrow. if .019 follows along that will eliminate the crank as being offset and identify either the rod or piston as being off. the pistons all weigh the same if that may be used as one indicator for bad piston tolerance.

i would tend to be more suspect of a bad rod (they are used parts) before a mistake by wiseco. the measurements will tell all i suppose.

the chambers are aligned well with the cylinders. should the edge break be ground at such an angle to meet the "corner" of the upper portion of the chamber?

will post results.

thanks again for all the replies, andy. 8)
Author:  Dart270 [ Sun Mar 11, 2012 10:54 am ]
Post subject: 
I guess I would think the crank would be the culprit rather than these relatively simple to make and modern tolerance pistons/rods. Doc's idea of swapping is great.
Seems like a lot of trouble to get the head chambers cut out to piston diameter, but that could work.
I think my engines have been w/in 0.005-0.008" of each other on deck ht.

Lou
Author:  akbmotorsports [ Sun Mar 11, 2012 11:19 am ]
Post subject: 
lou, i had the machine shop scrutinize the crank (napa reman) so hopefully they would have found that. we will see.

its great how something that is puzzling you can be, in very few words, totally simplified. :bow: :bow: :bow: :bow:

andy
Author:  1974duster kev [ Sun Mar 11, 2012 2:15 pm ]
Post subject: 
I can't offer much support about the problems with the uneven measurements, but i can say the same as lou i ran penty of compression on the street and never had a problem with either cam first cam with 10:1 compression was the erson 270 220/220 @.050 on a 108lsa 464lift
second cam worked even better 238/240@ .050 on a 108lsa 510lift.

Both worked fine didnt have any pinging the second cam did the help the top end a bit more though.

Kev
Author:  CNC-Dude [ Sun Mar 11, 2012 8:42 pm ]
Post subject: 
Usually, you let the cylinder bore dictate the boundary to open the chambers up to. Since the gasket is quite often a lot larger than the bore size, you actually create an over hanging ledge of the chamber to the deck surface and introduce as much or more shrouding than your trying to eliminate if you go all the way to the gasket ID. You take the cylinder head and run just a couple of head bolts in it to snug it to the deck surface. Use machinist dye on the entire circumference of the chambers before placing it onto the block, then flip the block upside down and from the bottom of the cylinders, reach in with a scribe and mark all the chambers around 360°. One of many advantages to using this method, other than the overhanging issue, is you are marking each chamber to its specific cylinder bore reference location, so whether you have any cylinder bore shift, or chamber shifting from the casting process, each chamber and each bore are going to be aligned correctly to each other.
Author:  Dart270 [ Mon Mar 12, 2012 6:18 am ]
Post subject: 
Echo that! I do that for matching bore notches and side valve reliefs in the chamber too...

Lou
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