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 Post subject:
PostPosted: Sat Sep 17, 2016 8:36 am 
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EFI Slant 6

Joined: Mon Aug 08, 2016 11:38 am
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Location: Pittsburgh, PA
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Wow.....this is all pretty coinfusing to me.....

We, too, (redBaron and I) are having our slanty redone as we speak.

Just got off the phone with the builder --- he says he has the compression up to 8.8......he took .010 off the head and .020 off the block, but he also went to an overbore so I guess thats part of it.....

Some of the numbers I am seeing here are much more than than the deck/head cuts we had done........I am relying on the shop (very reputable) to know what they are doing....the big numbers here though have me wondering?


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PostPosted: Sat Sep 17, 2016 9:45 am 
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Location: Sonoma, Calif.
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Quote:
So now, if we plug the 44.75 in...that would lower the SCR to about 8.7955:1 and DCR of 7.95

But if we roll the cam phasing to 100 instead.... the DCR becomes 8.06:1...

So no problems there... the thing to really watch-out for on heavily advancing the cam is it limits the top end of the engine... so you may get all the torque lower, but you may have an issue if you go out of town and need to run the tach up to 3500 to pass a stubborn truck.... just sayin'...
Great work DI...
And yes, the DCR calculation is somewhat complex but today's on-line calculators makes it easier.

The DCR calculation and setting up the DCR to 8.0 to 1 for the cam you select, is the key to getting any engine to run well, on today's pump gas.

And the most "complicated" part of the DRC calculation... knowing the intake valve's closing point. (all the other variables are pretty easy to get)

Truth is, I usually mock-up the engine first, with the cam I intend to use and find the exact intake valve closing point, on the cam's installed center-line and at the recommended lash setting, then calculate DCR for the needed deck & head milling.

It's a lot of extra work but you get a great running engine out of the effort.
DD


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 Post subject: Has he?
PostPosted: Sat Sep 17, 2016 9:49 am 
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Location: Salem, OR
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he took .010 off the head and .020 off the block, but he also went to an overbore so I guess that's part of it.....
I am hoping your "reputable" shop had actually CC'd the head, and mounted the crank and assembled at least one piston/rod to make sure that he has the deck height correct.... and also, hoping that he has taken into account that going from the OEM shim head gasket (.020 compressed thickness +/-)to a composite Fel-pro or Victor Reinz gasket (.039 +/-) will take away some of the static CR. You don't get much from an overbore on a slant... going to a .020 overbore on a "stocker" 225 rebuild makes it a whole whopping 227... The only other scenario I could think that would have your engine get loads more compression on such a slight mill, would be the engine had been milled or modded before you got the car, and the previous owner took a good sized scrape off the block/head...

2 cents...


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 Post subject: Re: Has he?
PostPosted: Sat Sep 17, 2016 12:19 pm 
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EFI Slant 6

Joined: Mon Aug 08, 2016 11:38 am
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Location: Pittsburgh, PA
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Quote:
he took .010 off the head and .020 off the block, but he also went to an overbore so I guess that's part of it.....
I am hoping your "reputable" shop had actually CC'd the head, and mounted the crank and assembled at least one piston/rod to make sure that he has the deck height correct.... and also, hoping that he has taken into account that going from the OEM shim head gasket (.020 compressed thickness +/-)to a composite Fel-pro or Victor Reinz gasket (.039 +/-) will take away some of the static CR. You don't get much from an overbore on a slant... going to a .020 overbore on a "stocker" 225 rebuild makes it a whole whopping 227... The only other scenario I could think that would have your engine get loads more compression on such a slight mill, would be the engine had been milled or modded before you got the car, and the previous owner took a good sized scrape off the block/head...

2 cents...
Yeah that is what I am thinking...the engine had been apart before.....new mains......so it is very possible that it has been cut before.

I asked if his calculations included the new head gasket and he confirmed that.

He had held off doing the calculations until the cam and timing set was in to see where we were clearance wise etcbefore taking any more off....

The same shop has been in business over 40 years and the guy building my engine has been there since the beginning I am told....and came highly recommended...I cant see this guy cutting corners.

Not really any way for me to know for sure I guess except take him on his word.


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 Post subject: Re: Has he?
PostPosted: Sat Sep 17, 2016 12:43 pm 
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Turbo Slant 6
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Joined: Sat Sep 13, 2014 8:25 am
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Location: Rio Rancho, NM
Car Model: Highly Modified Chevy S10 Race Truck
Quote:
Not really any way for me to know for sure I guess except take him on his word.
No, but you can always ask what the head CC'd at. It could be useful information later on down the road.

And of course if he's got that number handy it's a good bet he was thorough.

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 Post subject: Re: Has he?
PostPosted: Mon Sep 19, 2016 11:25 am 
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EFI Slant 6

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Location: Pittsburgh, PA
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Quote:
Not really any way for me to know for sure I guess except take him on his word.
No, but you can always ask what the head CC'd at. It could be useful information later on down the road.

And of course if he's got that number handy it's a good bet he was thorough.
He just got back to me and said that he "filled the combustion chamber with fluid and measured 80 cubic centimeters." He clarified and said that was the head bolted to the blocks with the head gasket, with piston at TDC. I asked if he measured just the head chamber......waiting to hear back.

He goes on to say " I measured head thickness and came up 3.525 thick compared to 3.265 new head thickness"....... I dont understand that part....I think maybe he has the numbers reversed? 3.525 for new and 3.265 for mine?

He goes on to say that the head we have may already have been milled somewhere along the way.


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 Post subject:
PostPosted: Mon Sep 19, 2016 12:54 pm 
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Turbo Slant 6
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Location: Rio Rancho, NM
Car Model: Highly Modified Chevy S10 Race Truck
None of those numbers makes any sense.

If it were mine I'd have him stop right were he is and I would make my own measurements to ensure I was getting the result I was after.

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 Post subject:
PostPosted: Mon Sep 19, 2016 1:18 pm 
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Quote:
He clarified and said that was the head bolted to the blocks with the head gasket,
Sounds like he check total volume through the spark plug hole with everything bolted together? Don't know if there is a calculator to figure CR. it that way? Might be.


Is it possible that he is measuring the distance from the head surface to the valve cover rail? That distance is usually @ 3.600 give or take a little(.010 or so). If he measured 3.525 that would indicate that it had been milled approx. .075

I am not sure what his other number may be? :shock: Unless he swapped the 2 and the 6 in the 3.265 and it should have been 3.625? If using that measurement he would be saying that the head was milled .100.

Just thinking out loud and trying to help.

Rick

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 Post subject:
PostPosted: Mon Sep 19, 2016 1:26 pm 
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Turbo Slant 6
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Joined: Sat Sep 13, 2014 8:25 am
Posts: 797
Location: Rio Rancho, NM
Car Model: Highly Modified Chevy S10 Race Truck
OK, I misread or misunderstood. 80cc would give close to 8.7:1 static CR which sounds like right in the sweet spot for a street motor.

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 Post subject:
PostPosted: Mon Sep 19, 2016 1:51 pm 
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EFI Slant 6

Joined: Mon Aug 08, 2016 11:38 am
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Location: Pittsburgh, PA
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He emailed back...the head alone is 47cc...... says the cr is 8.8. .....

Sound like I am good!!!!!


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 Post subject: Pretty close...
PostPosted: Mon Sep 19, 2016 4:15 pm 
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Location: Salem, OR
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Quote:
the head alone is 47cc...... says the cr is 8.8. .....
I reverse engineered this math calc... although I can't see being 100% accurate CC'ing the assembly with it all bolted together (when you CC the head you have to do it with the sparkplugs installed in the chamber....)

If you truly have 80cc at TDC, and 47cc chamber... taking out a felpro gasket volume... puts the deck height close to .153-"ish"... so it puts the SCR at 8.7-8.8:1, ad a DCR in the 7.9:1 range assuming he clocked the RV10 cam at 103 centerline.... if this all is somewhat accurate then you're are in good shape...


As you can see one good reason to double check the work, and even follow up, and learn to do some of the work yourself...if the machinist was off, it could get "messy". (I got worried when you said the machinist said 80cc... heads from 1973-1987 are typically around 54cc untouched...the worst one I've seen from the early 60's and the valves were sunk was 72cc...80 after being milled would mean the machinist didn't know what he was doing, or he gave you some V-8 guys measurements...

Glad you got the scoop and are looking good on the machine work.

:wink:


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 Post subject: Re: Pretty close...
PostPosted: Tue Sep 20, 2016 9:54 am 
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EFI Slant 6

Joined: Mon Aug 08, 2016 11:38 am
Posts: 303
Location: Pittsburgh, PA
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Quote:
assuming he clocked the RV10 cam at 103 centerline.... if this all is somewhat accurate then you're are in good shape...

:wink:
That, I do not know.

Oregon camshaft sent the cam card to him with the cam.

I emailed again to ask what he clocked it at........

He is probably getting tired of the questions...LOL


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PostPosted: Thu Sep 29, 2016 2:56 pm 
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Joined: Mon Jun 30, 2014 10:35 am
Posts: 30
Location: Sweden
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Quote:
Quote:
So now, if we plug the 44.75 in...that would lower the SCR to about 8.7955:1 and DCR of 7.95

But if we roll the cam phasing to 100 instead.... the DCR becomes 8.06:1...

So no problems there... the thing to really watch-out for on heavily advancing the cam is it limits the top end of the engine... so you may get all the torque lower, but you may have an issue if you go out of town and need to run the tach up to 3500 to pass a stubborn truck.... just sayin'...
Great work DI...
And yes, the DCR calculation is somewhat complex but today's on-line calculators makes it easier.

The DCR calculation and setting up the DCR to 8.0 to 1 for the cam you select, is the key to getting any engine to run well, on today's pump gas.

And the most "complicated" part of the DRC calculation... knowing the intake valve's closing point. (all the other variables are pretty easy to get)

Truth is, I usually mock-up the engine first, with the cam I intend to use and find the exact intake valve closing point, on the cam's installed center-line and at the recommended lash setting, then calculate DCR for the needed deck & head milling.

It's a lot of extra work but you get a great running engine out of the effort.
DD
Today I mocked up the engine to figure out what intake closing point I have. I set the valve lash at 0.020" and the cam intake centerline is 100 degrees.

The intake closing point I got after many tries were between 210 - 212 degrees after TDC. Now when I have those number how can I calculate so I know which DCR I'm going to have?


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 Post subject: Hmmm....
PostPosted: Thu Sep 29, 2016 4:57 pm 
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The intake closing point I got after many tries were between 210 - 212 degrees after TDC. Now when I have those number how can I calculate so I know which DCR I'm going to have?
If I enter that number along with the other data we have gathered to this point: The DCR would be 8.37:1... which is still streetable on pump gas with some distributor timing curve work...

The part that confuses me, is that when I punch in the numbers that the camshaft was ground to, the intake valve closing event is supposed to happen at 42 ABDC (or 222 after TDC....)...which when plugged in would give that 8.06 DCR we talked about...

If you still have the degree wheel centered up on the crank,and your dial gauge on the lifter side of the rocker...you might sweep the crank around by hand again and check the cam cards events on the intake side again just to make sure that the intake lobe is indeed centered on 100...and to see if maybe the closing ramp was ground a bit less steep giving the 210-212 instead of the 222....


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 Post subject:
PostPosted: Thu Sep 29, 2016 5:54 pm 
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Joined: Mon Jun 30, 2014 10:35 am
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I have degree the cam many times and at diffrent checking heights.

The method I use is rotate clockwise to lobe top. Then back off anti clockwise down to .100" then clockwise back to 0.050", then clockwise past top then down to 0.050". And since I'm metric I have also used millimeters and done the same method but used different checking heights and I have come to 100 degrees all the times. So I feel pretty sure that's right.

But when I checked closing point I may have done something wrong. Since my dial indicator didn't work properly when I put the indicator tip on the lifter side rocker arm. I instead used the valve spring retainer to put the dial indicator on and check when indicator returned to max. I had to put the dial indicator tip almost to the max/full reading on the retainer since it works "backwards" there. I also used a short and small spring that ran on the valve stem. The bad thing was at almost maximum lift the small spring jammed everything. So I turned the engine anti clockwise and I could then go to "other side of the jammed lift", then I turned it clockwise and I could then see were the intake closing point took place. When I checked the closing poiny I stopped it at zero lash and I quess when I think about it now there is probably why my numbers are lower?


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