825 replies to this topic

[Kyle Freiheit]

Pretty funny. I downloaded the SCCA CR spreadsheet awhile back to compare against one that I made for my engines and when I compared them it took me awhile to figure the - and +  out too. I was definitely surprised that they weren't taking into account the volume above the ring land too as albeit small its worth about .05 CR or more depending on cylinder to bore clearance(on a 1.6L if I remember right).

 

Kyle

[Jim Drago]

All this has been done and the area above the rings was in the calculation. Not sure what he is talking about?
I really dont care what/which one we use as long as all of us use the same sheet and tech does as well. We came up with piston dome volumes for each of the engines. This was all that needed to be measured in tech was how far down in the hole the piston was, thickness of head gasket and cc the head. The rest was already in the formula. You could overwrite any of the std other dimensions ( bore, stroke etc) but was not needed. This simplifies the process in tech as the hardest part is CC-ing the block. Just about anyone can cc the head IMO, not so much on block.

Dans sheet is really neat. If any info is entered outside the norm or spec the square would pop up red.

[speedengineer]

Dan's sheet sounds nice.  Certainly adding that functionality would be really easy.  I guess the question is will SCCA adopt a special spreadsheet just for SM?  That would be ideal.  Obviously they also need a generic one for all of the other classes.

 

I'm with you, don't care what sheet is used.  But it will be nice when the process is known and used by all.

[38bfast]

Been doing some studying of the official scca CR calculation spreadsheet.  Ugh, it's got issues...wrong in a whole bunch of ways. 
https://www.scca.com...orms-procedures
 
First, if you follow the detailed instructions, you'll end up with an incorrect piston CC - it's missing a negative sign.  So, vvt motors will have a calculated CR that is way lower than actual, by like a whole CR point.  99 engines will read just a couple tenths low.  1.8NA engines will have CR measurements that come out about a half point high.  The only way to get around this error is to disobey the directions, and enter two different measurements as negative numbers. 
 
Also, the formula for calculating the piston land crevice volume is completely wrong.  Way off.  Just not a huge contributor to CR error as it's a small volume.
 
I've informed the correct person at scca and he will be working with the CRB to establish a new calculator that is simple, accurate, and used by everyone.
 
 
No wonder everybody's been shaving those VVT heads down so much...    hehe

The SMAC has been working on updating the spread sheet.

[Steve Scheifler]

It's one thing to make a mistake creating an important spreadsheet to be trusted by members. Really bad and hard to excuse, but a mistake. The fact that they've known that it is wrong, for how long now, and yet it remains on the site?? Speechless.

There could easily be a pick-list for engines with known parameters plus an "other" choice. No need for a dedicated SM version. As for the gap above the top ring, it should not be ignored completely but with a couple very simple physical measurements it can be calculated more than sufficiently close for our purposes.

[speedengineer]

The SMAC has been working on updating the spread sheet.

You're late to the party 

[Jim Drago]

For the record.. the area above the top ring is accounted for in both Dans sheet and the new SCCA sheet.

[Todd Lamb]

Jim you haven't seen the new(proposed) SCCA spreadsheet. It is not Dan's as he would not unlock it for SCCA use.

[Ron Alan]

Is it just me or do the wheels at SCCA seem to barely roll??? 1.5 years after compression gate(incorrect method of using whistler)and STR gate and it suddenly becomes public that the written method of CR used by SCCA is incorrect?? The transparency is blinding....

[Jim Drago]

Jim you haven't seen the new(proposed) SCCA spreadsheet. It is not Dan's as he would not unlock it for SCCA use.

want to bet , I have been using the last two months or so. John asked me beta test it.

[Jim Drago]

Is it just me or do the wheels at SCCA seem to barely roll??? 1.5 years after compression gate(incorrect method of using whistler)and STR gate and it suddenly becomes public that the written method of CR used by SCCA is incorrect?? The transparency is blinding....

ohh the drama...

Your making more out of this than there is..
First the new sheet was the engine builders idea as none of us believe the tech guys can accurately CC the blocks in tech. We all wanted a standardized sheet we all used that did not require CC'ing the bottom end. Just use established piston dome volumes and how far down in the hole the piston was. That way we would all be building and inspected the same way.. If that meant we were all building to 9.36 or 9.49 it really didn't matter, as long as it was the same for all.
The only reason I found the SCCA sheet ( not a SM specific sheet btw) was wrong is I filled it out before the Runoffs so I knew I would have the correct answers to the test before SCCA inspected and gave me the wrong ones.

A standardized sheet for SM is a very good idea. the easier and more accurate we ( smac, engine builders, class in general) can make this process the better. I think all just want a clear sheet that is accurate and easy to get to the same numbers, which is what we now have IMO.

[Todd Lamb]

Yep - you don't have the final version

want to bet , I have been using the last two months or so. John asked me beta test it.

[Bench Racer]

Kind of like Windows 8, kept revising until they admitted they blew it big time and out came Windows 10.

[Jim Drago]

I just put "final version" on mine and called it a day

[Ron Alan]

ohh the drama...

Your making more out of this than there is..

The only reason I found the SCCA sheet ( not a SM specific sheet btw) was wrong is I filled it out before the Runoffs so I knew I would have the correct answers to the test before SCCA inspected and gave me the wrong ones.

 

Of course! It is SM remember

 

Maybe...following Steve's "speechless" lead

 

So not only is the published CR worksheet wrong...but know one who represents SCCA knows how to use it apparently? 

 

Makes sense though that this was never worried much about(or brought up) since the end result could only help the competitor. Glad to see it being fixed...and like Jim's approach of simple!

 

Anything else out there on the horizon?? My guess is the new Mid Ohio Majors date just announced will be well attended!

[FTodaro]

 

Anything else out there on the horizon?? My guess is the new Mid Ohio Majors date just announced will be well attended!

I think the date remained the same it just added a joint event with the Northeast conference but I agree if you plan to go you better sign up early. In fact our region and the regional events we are hosting, are planning on sellouts, for the obvious reasons.  

[speedengineer]

I think the date remained the same it just added a joint event with the Northeast conference but I agree if you plan to go you better sign up early. In fact our region and the regional vents we are hosting, are planning on sellouts, for the obvious reasons.  

Even the regional event at MO last October had a huge turnout.  Can't imagine how it's going to be this year...!

[speedengineer]

So, axles wouldn't come out with the air hammer.  But, they popped out effortlessly on the hydraulic press 

 

Decided to go ahead and drop the subframe so I can throw some paint on it.  Might as well make the car look fast just in case it isn't fast 

 

 

 

 

Lot's of undercoating on the car.  Figured I'd try to estimate how much mass there was of it.  First, I estimated the total area of seam sealer with a tape measure and notepad to be in the ballpark of 3500 square inches.  Next, I scraped a small section of 3" x 1.25" seam sealer off the car, from an area that had 'average' coat thickness.  Weighed it on the scale, 3 grams.  That suggests that there is ~6 lbs of seam sealer in total.  I've decided it's not worth removing.  It would look nice to remove it all and paint.  Just not worth the effort to me.

 

[dstevens]

When I removed my undercoating IIRC it was about 8 lbs or so but was pretty heavily soaked in oil residue.  It's an easy 6-8 lbs.  Once you start getting the car to weight it's tough to find that much weight that will come off that easy.  With a lift and either a Crud Thug or coating removal discs it's pretty easy.  And I did it on my back with the tub on rolling stands, no lift.  If you don't get it now it's going to be more of a pain if you want to get at it later.

[Jim Drago]

I have swept up and weighed all that was on the floor when finished as I had heard the claim that there was 15-20 lbs there. I was never able to gather more than 5 lbs. so I would guess your estimates of 6-8 is ver close. I can't afford to leave 6 lbs on the car as I am often too close on weight. It is absolutely not worth the effort unless weight is an issue.
Jim