They look like 11.5/1 TRW's
Final Engine Compression Ratio?
- Thread starter billsdartgt
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That's exactly what they are. restamped with an MP part number.
yellow rose
Overnight Sensation
With the piston at absolute TDC, measure how far the deck is out of the bore.
If it's .017 or less and the chambers are 65 cc's or bigger, with that much dome milled off you'll be lucky to be at 10.5:1, which ain't really a bad thing with your cam timing.
YR, the numbers I listed is how far the piston sticks out about the bore (.159 - .228)
The solid 292 was a much better match, IMO.
didn't know what I had, I have just been sucked into the wormhole now, when I got the car it was a biotch to get it running, once warm it ran fairly well, the person I bought the car from told me he thought it had a small purple cam in it that he had an empty box for, when I found out it was a solid cam I decided on the change, reading that these engines are generally low compression the Lunati made sense, now not so much.
But now you know what you got! You can match it right on up now.
Ive already bought my gears and don't want to invest in a convertor, want to try and get some miles on it first LOL
U would likely find that a converter built for ur combo will be better than a gear change. I did read the above post. Ur other cam is a way better fit for ur combo. Kim
Wyrmrider
Well-Known Member
put the piston half inch down Hint use 6mm
figure the vol of cylinder your bore in mm x 6mm (adjust for out of deck) (or other down distence)
grease the piston crevese aand put a small hole plexiglass at the top of the bore w grease
fill with seringe
subtract from vol of cyl cc adjusted for out of bore
do the calc with your gasket and head cc's as usual
(or you can work with inch measurements and convert)
about the comp- should be a good cam if right
however IDK and i can't tell ,
if the 292 is comp degrees .006 Or Mopar degrees which are closer to .008 which would make this cam a 300 degree class lobe for dynamic compression calcs
anybody ever degree wheeled this one?
Crane used to clean up the factory lobes however others use whatever lobe they have handy, some "our version of" are not even close
figure the vol of cylinder your bore in mm x 6mm (adjust for out of deck) (or other down distence)
grease the piston crevese aand put a small hole plexiglass at the top of the bore w grease
fill with seringe
subtract from vol of cyl cc adjusted for out of bore
do the calc with your gasket and head cc's as usual
(or you can work with inch measurements and convert)
about the comp- should be a good cam if right
however IDK and i can't tell ,
if the 292 is comp degrees .006 Or Mopar degrees which are closer to .008 which would make this cam a 300 degree class lobe for dynamic compression calcs
anybody ever degree wheeled this one?
Crane used to clean up the factory lobes however others use whatever lobe they have handy, some "our version of" are not even close
6mm AIN'T a half inch. A half inch is "about" 12.5mm.
Wyrmrider
Well-Known Member
comments from Comp's Q&A for cam referenced
For pushrods you will need to measure for the correct length using a pushrod length checking tool such as the Comp Cams part number
CCA-7702-1.
I call Bullshit will not get you correct geometry by itself
second question implies stock base circle- always check
For pushrods you will need to measure for the correct length using a pushrod length checking tool such as the Comp Cams part number
CCA-7702-1.
I call Bullshit will not get you correct geometry by itself
second question implies stock base circle- always check
Wyrmrider
Well-Known Member
RIGHT as usual RRR
"as usual" I don't know about "THAT". lol
nm9stheham
Well-Known Member
What YR is asking you to measure is the block's deck relative to the lower flat area on the piston top... the part above the eyebrows. You measure compression height to there, not to the top of the dome.
Clean off all the old head gasket material and scrape the deck area around a piston perfectly clean and smooth. Lay a straight edge across that upper area of the piston, just above the eyebrows. If the piston is above the deck, then use feeler gauges to measure the gap between the deck and straight edge. If the piston is below the deck, then use the feeler gauges to measure the gap from the piston to the straight edge. Let us know what you get and which way it is, and we can figure the compression height pretty closely.
And even if the block has been decked, having that relative distance of piston to deck is all you need. Then we can make a stab at the dome and eyebrow volumes and then get close to SCR. With these engines, a 1 cc error is about 0.1 point in SCR so we can easily get within a half point I'd bet.
BTW, check the depth of the head chamber to the shallow area. Unmilled open head chambers are typically around .100-.110" there.
my68barracuda
Well-Known Member
I see the problem with trying to get a flat Plexiglas plate over the piston protrusion, but there is a way.
Move the piston down into the bore a known - exact distance, lets say one inch.
Then cover the cylinder, and add the fluid and get the number of cc's it takes to fill it with the piston crown as the bottom surface and the Plexiglas plate as the top flat surface.
Then based upon your bore size calculate how many cc's of fluid would take to fill it to a height of one inch with a flat bottom and top surface.
Subtract the actual measured cc from the calculated empty bore cc and you will have the cc's of the piston head.
Obviously an inch is overkill, I did that to make the illustration easy, You just need to lower the piston enough so it does not protrude, but you need to know that exact distance to be able to calculate the flat bottom volume
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Wyrmrider
Well-Known Member
what I was trying to say
just down enough to let the plate seal
and then figure the height of the piston flat out of the hole and adjust your calc
point is you can do it in the car
just down enough to let the plate seal
and then figure the height of the piston flat out of the hole and adjust your calc
point is you can do it in the car
The 1/2" down fill is the perfect way and is covered in the MP engine manual in depth.
Wyrmrider
Well-Known Member
yep look there
unless your dome is more than .5 usually a hemi
or your piston deck comes out on the block
does the book cover that?
unless your dome is more than .5 usually a hemi
or your piston deck comes out on the block
does the book cover that?
Yup I believe it does, but he won't have to worry about that. His dome is much less than .500"
Wyrmrider
Well-Known Member
I just dug out my collection of Mopar manuals
I'll check it out RRR
be interesting to see what OP comes up with
I wonder if a catalog gives the cc of the dome
I'll check it out RRR
be interesting to see what OP comes up with
I wonder if a catalog gives the cc of the dome
yellow rose
Overnight Sensation
I think you need the Sped Pro catalog to find the CC's of the dome. I may have that here. I'll look in a bit.
I do know that if you aren't at least .020 out of the deck the dome is either zero or may even be a minus number, IIRC.
One thing on those Pistons is the damn valve notches are HUGE. Especially for the exhaust valve. Just freaking gigantic. Total waste of CR.
Wyrmrider
Well-Known Member
YR are those pistons one part number for all or left's and rights
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