MP 292H cam too big?

-
WA71swinger

WA71swinger

Well-Known Member
Joined
Jul 11, 2011
Messages
96
Reaction score
0
Location
Eastern Washington
Passed on a camaro driven to the track every weekend running 12s for 2K. Bought a 71 scamp w/318 and a built (by who nobody knows) 360 on a stand for 3800. Happy with the choice even If the car I bought has been setting on the side of a garage for years and turns out to be a swinger.

Ran the car with 318 at the local strip 7 or 8 times since. Started in 17s. Put 3.55 ring/pinion and sure grip carrier in the 8 1/4 rear, test and tune street driving, and finished the season@ 15.17 best et. on street tires (traction limited for sure).

Decided to take the 360 apart and verify the build before installing it. It was supposed to be 10.1, bla, bla, bla, 350-400hp build. What I found was not what was advertised. Decided to build it. Wish I had known more before getting started (first build). Machine shop prepped stock crank, resized rods, ARP rod bolts w/ other work, turned/posished crank, pistons worked to same weight, entire rotating assembly externally balanced (with damper and TCI external balance flex plate). Had given machine shop block/head numbers and purchased (shop's) recommended pistons (KB 190s).
Problems:
Have MP 292H cam (.508/.508 lift), No cam card
 
Cam with cam in motor (was supposed to be crane 292 cam but does not meet the specs. Only cam specs it matches (measured) is MP 292H (and it is painted purple on the ends.

Problem 2) My compression works out to be too high for pump gas. This is a street/strip car with full interior, etc. Static CR almost 10, Dynamic CR around 9.2.

Problem 3) have 2400 B&M stall (brand new), don't want to spend another 500+ on a new converter. Cam calls for 3500 stall (so I've read). anyone running smaller stall with a cam this big on the streets, how does it run?

Problem 4) Quinch. (bench racing, have not assembled yet). If piston to deck height is .048-.050 (based on other posts by members using these pistons), dome is .050, then height =about 0 deck. Combustion chamber depth measures .105, plus .040 head gasket = what quench? If I mill heads as suggested for optimum quinch (.035-.045 according to kb pistons) then I will really have too much compression.

Advice, inlightenment, your experienced/suggestions please. Considering going kb 107 flat tops, rebalancing, milling to greater compression, going with oob edelbrock heads. Which means I will be rodding the 318 again next season because that's a lot of cabbage ($). Would like to drive to the track and run a 13. Is that unrealistic?
 
What kind of heads do you have now? Also what cam were you getting specs from when you came up with your dynamic compression? To get 9.2 dynamic from only 10 or so static means you must have a really mild cam with early intake valve closing. I'm building a 360 Magnum and with around 10.5:1 static comp. I get 8.75 dynamic running the smallest Lunati Voodoo hydraulic cam (#60401, 256/262 dur.). Try looking up the detailed specs for the MP 292 cam, I think it should give you WAY less dynamic compression than you calculated.

About the quench you will have .145" clearance if the pistons are really at zero deck, as simple as chamber depth + gasket thickness +/- distance pistons below/above deck. This much quench will do nothing to improve combustion efficiency... You want about .045-.050" MAX for there to be any effect.
 
Yeah. It's pretty big. 248.5* @.050 on a 108 LSA. It's a cylinder pressure bleeder for sure.....but they are good cams if you have a matching build. I'd say 10-10.5 compression with iron heads would be fine on pump gas.

Also....a dynamic CR of 9.2....I think you're figuring something wrong somewhere. That's REAL high. I would double and triple check those numbers.
 
A, yea, Dynamic seems a bit sky high. Regardless. the actual measuring ratio is 10-1? That is OK for pump gas and a cam that size. Been there done that. BUT, I have done it with the KB-107's (@ 030 overbore) with J heads w/a slight mill for 70 cc and a 040 gasket, it all equals 10-1. I had the Purple 292 cam in there. 93 octane was just fine.

IMO, I'd shy away from domes and iron heads intended for 93 pump gas.

I also had the above build later on with Edelbrock heads. That combo, weight dependent, car set up etc....and it's all in the set up..... can have you anywhere from the high 12's to the real low 12's.

While the stall converter is low, what is the gear ratio, tire size and weight of the car?

Is this going to be a drag car only or mostly?

The reason I ask is that if the car is lightened, has a high gear ratio like 4.10's and a 26 inch tire, the converter will be , well OK, not great, but OK for use.
 
Cam with cam in motor (was supposed to be crane 292 cam but does not meet the specs. Only cam specs it matches (measured) is MP 292H (and it is painted purple on the ends.
What spec? just the lobe lift? Purple Shafts (MP cams) should have the entire non-machined surface of the cam blank coated purple. (unless they changed that). Is it solid or hydraulic?

Problem 2) My compression works out to be too high for pump gas. This is a street/strip car with full interior, etc. Static CR almost 10, Dynamic CR around 9.2.
What intake valve closing event are you using for the dynamic calculation? I think you're off if that is indeed an MP hydraulic .509.

Problem 3) have 2400 B&M stall (brand new), don't want to spend another 500+ on a new converter. Cam calls for 3500 stall (so I've read). anyone running smaller stall with a cam this big on the streets, how does it run?
What you have will work. If you had higher, it would work better. If you have more gear, it will work better. If not, it won't.

Problem 4) Quinch. (bench racing, have not assembled yet). If piston to deck height is .048-.050 (based on other posts by members using these pistons), dome is .050, then height =about 0 deck. Combustion chamber depth measures .105, plus .040 head gasket = what quench? If I mill heads as suggested for optimum quinch (.035-.045 according to kb pistons) then I will really have too much compression.
If you are working on a set of open chamber iron heads, I would completely ignore teh quench issue. I've built with open chamber heads and quench domes. To get any benefit, you have to get thigns tight. If you have to get things tight, it's a lot of work with open chamber heads. Here's what you need to do:
Establish your block's deck height. If you cant measure it, mock up the crank and 4 rods and piston 1 in each corner. Measure the distances, and use the tallest.
Establish which chamber is deepest of all 8, and then make the others all match it. Smooth out the casting features while doing this.
Mill the heads to establish the correct chamber depth in relation to the tallest piston. Clay the top surface of the piston edge nearest the valley of the block. That will be your quench distance, and if it's wider than .040" when measured in the right spot you aren't getting much benefit. So be precise with your measurements and machine work. What I did was have the main bores align honed and the block square decked to blue print height. The crank was indexed, stroke corrected, and turned and polished. Rods (factory) were all resized and lengths matched. Then I had the valve job done and I did the porting. Then I mocked up a piston and rod, and clayed all eight holes. Mine had depth variations of .015". I matched the chamber depth and made it flat using a depth mic and hand grinding/polishing. Then I had the heads cut to eastablish .035" quench distance. It's a lot of work if it's not being done by you, and that's assuming you did have the rods, crank, and block blueprinted, which most don't do. So really, I'd say ignore the quench deal. Make the static around 9.8:1, kep the dynamic (properly calculated) to below 8.25, and you're good to go.

Advice, inlightenment, your experienced/suggestions please. Considering going kb 107 flat tops, rebalancing, milling to greater compression, going with oob edelbrock heads. Which means I will be rodding the 318 again next season because that's a lot of cabbage ($). Would like to drive to the track and run a 13. Is that unrealistic?
A 318 could run that with the right parts and setup. A 360 needs less to do it.
 
Also....a dynamic CR of 9.2....I think you're figuring something wrong somewhere. That's REAL high. I would double and triple check those numbers.


Yes I meant around 11:0 static CR (miss typed). According to Victory library, the intake closes at 74 degrees ABDC for 292H (hydraulic) cam. Other sourced give other figures ranging as low as 37.5 degrees ABDC. Using the Victory info CR is fine for highest octane pump gas. CR is way higher using the lower value. When I look up comp cams, lunati cams, etc. They all seem to have intakes closing around 40 ABDC or so. This translates into a dymamic CR of greater than 9. Why would MP ABDC intake closing be so drastically different than everybody else's cam? anybody know?

Also car is driven (either direction) around 85 miles to the track (more than 1 track) and then ran and driven home. Trusing my mechanical skills (and yes it sat in an orchard one night). 3:55 rear end, 727 trans, 235/60/15 (26.1" tires), 2400 B&m stall.
 
I just wanted to say thank you to everyone who has chimed in to give me good information. It really helps when trying to decide what to do. Right now I'm thinking I want to just ignore the quinch (loosing all benefit) because I would have way too much compression if I tried to achieve optimum quinch (for the street and pump gas). I wish I would have known more before i got started.
In hind sight I would have gone with the kb 107 flat head pistons. Now that I have already had the 190s worked on and don't want to pay to have the kb107s done (the pistons were 8 grams difference from heaviest to lightest, seems like a lot, now all weight the same). And now that i have already spent $ 400 to have the rotating assembly balanced. I think I will assemble the short block and measure to figure actual compression with the intention of running what I have.
Please talk me out of it and offer better advice if I am on the wrong path. thanks, Dave
 
COMPRESSION RATIO CALCULATOR
Static and Dynamic Compression Ratio

(Considers Cam Timing and Rod Ratio)





ENTER YOUR DATA

CALCULATED DATA



Cylinder Head Volume (cc)

66 (casting #4027596, 66-72.5 cc. 80'-84' 318 HP police sedan head with port/bowl work, 3 angle grind, and stock 360 intake and exhaust valve diameters. Deck milled to true, don't know how much, combustion chamber depth is .105, another unmollested head measured the same). looking for quality singe springs that don't require grinding the seats but support .508 lift (unreasonable?)

Cylinder Head Vol (cubic in.)

4.026



Piston Head Volume (cc)
-1.2 (KB 190-30 with .050 dome)


Piston Head Vol (cubic in.)

-0.073



Gasket Thickness (in.)

0.040 (compressed thickness MP gaskets 4.060 bore)

Swept Volume (cubic in.)

45.665



Gasket Bore (in.)

4.060 (I have MP 10.5:1 max composite gasket with this bore at .040 compressed thickness. Let me know if you think I will need more. Did not want to pony up almost $200 for cometic gaskets).

T.D.C. Volume (cubic in.)

4.484



Cylinder Bore Diameter (in.)

4.030 (360 bored .030 over)

Gasket Volume (cubic in.)

0.518



Deck Clearance (in.)Note: Neg. nubmer above deck, Pos. number below deck

0.001 (using info here based on several abody users' posts about thier build experiences with KB pistons having 1.675 comp ht and un millled 360 block. (How would i figure this while bench racing? Using chrysler block deck height of 9.6", comp ht of piston and crank to deck clearance info from KB @5.999?)

Deck Volume (cubic in.)

0.013



Stroke (in.)

3.58 (Crank has been turned and polished, rotating assembly has been balanced with damper and flex plate (TCI, for externally balanced 360 with 0 balance torque converter). Have matched King main bearings.


STATIC COMPRESSION RATIO


11.184



OPTIONAL DATA



Rod Length (in.)

6.123 (Rods have been resised and fitted with ARP bolts and maching King bearings)

Adjusted Stroke (in.)

2.530



Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees


74 (Using online Victory library info for MP 292H cam)

DYNAMIC EFFECTIVE COMPRESSION RATIO


8.197


This is KB silvolite CR calculator using all available info and bench racing. If I look at lunati, comp, hughes cams; etc. the intake closing on a similar size cam (duration, LSA, and valve lift) the intake generally closes around 40 ABDC which would give a dynamic CR of 10.302, way too high for pump gas and the street. Recomended pump gas machines should not exceed 8.4 dynamic CR and it is recommended to try to achieve 8.2:1 dynamic CR on high performance streetable machines. I tried to copy and paste but only got some of the info. I filled in the rest. Correct me where I am wrong or offer info please. Dave
 
Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees.

Didn't notice the plus 15 degrees part before. A similar cam with 40 degrees ABDC +15 would be 9.520 dynamic CR. Still way too high for pump gas.
 
You have to look close at the details... The intake closing point should be 74° ABDC. The intake closing point at .050 is 37.5°. So you should be using 37.5+15= 52.5. Try that one...

Just to add... the calculated dynamic compression goes DOWN with a larger cam, not up. So if this cam was too large (I don't think it is...) then the dynamic would be low (in the 7s), not high (in the 9s).
 
moper said:
Cam with cam in motor (was supposed to be crane 292 cam but does not meet the specs. Only cam specs it matches (measured) is MP 292H (and it is painted purple on the ends.
What spec? just the lobe lift? Purple Shafts (MP cams) should have the entire non-machined surface of the cam blank coated purple. (unless they changed that). Is it solid or hydraulic?

Problem 2) My compression works out to be too high for pump gas. This is a street/strip car with full interior, etc. Static CR almost 10, Dynamic CR around 9.2.
What intake valve closing event are you using for the dynamic calculation? I think you're off if that is indeed an MP hydraulic .509.

Problem 3) have 2400 B&M stall (brand new), don't want to spend another 500+ on a new converter. Cam calls for 3500 stall (so I've read). anyone running smaller stall with a cam this big on the streets, how does it run?
What you have will work. If you had higher, it would work better. If you have more gear, it will work better. If not, it won't.

Problem 4) Quinch. (bench racing, have not assembled yet). If piston to deck height is .048-.050 (based on other posts by members using these pistons), dome is .050, then height =about 0 deck. Combustion chamber depth measures .105, plus .040 head gasket = what quench? If I mill heads as suggested for optimum quinch (.035-.045 according to kb pistons) then I will really have too much compression.
If you are working on a set of open chamber iron heads, I would completely ignore teh quench issue. I've built with open chamber heads and quench domes. To get any benefit, you have to get thigns tight. If you have to get things tight, it's a lot of work with open chamber heads. Here's what you need to do:
Establish your block's deck height. If you cant measure it, mock up the crank and 4 rods and piston 1 in each corner. Measure the distances, and use the tallest.
Establish which chamber is deepest of all 8, and then make the others all match it. Smooth out the casting features while doing this.
Mill the heads to establish the correct chamber depth in relation to the tallest piston. Clay the top surface of the piston edge nearest the valley of the block. That will be your quench distance, and if it's wider than .040" when measured in the right spot you aren't getting much benefit. So be precise with your measurements and machine work. What I did was have the main bores align honed and the block square decked to blue print height. The crank was indexed, stroke corrected, and turned and polished. Rods (factory) were all resized and lengths matched. Then I had the valve job done and I did the porting. Then I mocked up a piston and rod, and clayed all eight holes. Mine had depth variations of .015". I matched the chamber depth and made it flat using a depth mic and hand grinding/polishing. Then I had the heads cut to eastablish .035" quench distance. It's a lot of work if it's not being done by you, and that's assuming you did have the rods, crank, and block blueprinted, which most don't do. So really, I'd say ignore the quench deal. Make the static around 9.8:1, kep the dynamic (properly calculated) to below 8.25, and you're good to go.

Advice, inlightenment, your experienced/suggestions please. Considering going kb 107 flat tops, rebalancing, milling to greater compression, going with oob edelbrock heads. Which means I will be rodding the 318 again next season because that's a lot of cabbage ($). Would like to drive to the track and run a 13. Is that unrealistic?
A 318 could run that with the right parts and setup. A 360 needs less to do it.
Click to expand...

dont mean to hijack - but moper that was so technical it took 20 minutes and reading it 7 times to comprehend - i love it , keep the info coming , this site has a wealth of info:finga:
 
Yea, Moper is really helpful and on the ball.
 
seriuosly though

you said that .015" variations in chamber depth were matched and made flat by hand grinding and polishing?

being a machinist this impresses me - you did this by die grinder? with carbide burr then polishing stone? then measuring at random locations to ensure flatness? this is cool , not being a mechanic but a marine/aviation machinist we fit and hand scape plenty diesel engine parts - I trying to overcome my novice gas mechanic skill i gotta start applying my machinist trade to autpmotive use

you fellas help - ya learn somepin' everyday
 
moper said:
You have to look close at the details... The intake closing point should be 74° ABDC. The intake closing point at .050 is 37.5°. So you should be using 37.5+15= 52.5. Try that one...

Just to add... the calculated dynamic compression goes DOWN with a larger cam, not up. So if this cam was too large (I don't think it is...) then the dynamic would be low (in the 7s), not high (in the 9s).
Click to expand...


Thank you. That part makes a lot more sense now. I understand the CR goes down with larger cam. I originally meant to ask if this cam is too big for a street/strip car or for this build with iron, open chamber heads. Plugging 52.5 into the kb silvolite calculator I come up with: Effective dynamic CR 9.668. I must still be doing something wrong, otherwise why in the H would anyone ever buy the KB 191s with taller dome? I wish I had asked advice before purchasing (macnine shop recommended) pistons and paying to have all the machine work done. when I asked the machinist about using the 292H cam, he told me my cam was probably too big, that i needed to go home and get on kb silvolite web site and figure out CR (yes this is my first build). He told me that I was probably not making 10:1 static CR and therefore the cam would be too big.
It looks like (from browsing other posts) if I had just asked advice before beginning to spend money, the flat top kb 107s would have been, more often than not, recommended.
DYNAMIC EFFECTIVE COMPRESSION RATIO
9.668
 
WA71swinger said:
Thank you. That part makes a lot more sense now. I understand the CR goes down with larger cam. I originally meant to ask if this cam is too big for a street/strip car or for this build with iron, open chamber heads. Plugging 52.5 into the kb silvolite calculator I come up with: Effective dynamic CR 9.668. I must still be doing something wrong, otherwise why in the H would anyone ever buy the KB 191s with taller dome? I wish I had asked advice before purchasing (macnine shop recommended) pistons and paying to have all the machine work done. when I asked the machinist about using the 292H cam, he told me my cam was probably too big, that i needed to go home and get on kb silvolite web site and figure out CR (yes this is my first build). He told me that I was probably not making 10:1 static CR and therefore the cam would be too big.
It looks like (from browsing other posts) if I had just asked advice before beginning to spend money, the flat top kb 107s would have been, more often than not, recommended.
DYNAMIC EFFECTIVE COMPRESSION RATIO
9.668
Click to expand...


I've never been comfortable with using the intake closing @ .050"+15 but it shouldn't be that far off...

If you use the 0.006 figure the DCR comes out at a shade over 8:1.

Where did the intake closing at 37.5 degrees ABDC come from? That means the difference between the .006 closing and .050 closing is 36.5 degrees. If it's a symmetrical lobe that would give duration of 219 @ .050".
 
I hate this ****... I typed something out and got a D-base error. Here the short answer

Knew I should have saved it

248 duration at .050 on a 108LCA is IO = 16, IC = 52

If you want more low end, stab it in at 100-102 lobe center. If you have a true 11:1 that may be a bit forward. You could still advance it some is my guess.
 
lil red said:
seriuosly though

you said that .015" variations in chamber depth were matched and made flat by hand grinding and polishing?

being a machinist this impresses me - you did this by die grinder? with carbide burr then polishing stone? then measuring at random locations to ensure flatness? this is cool , not being a mechanic but a marine/aviation machinist we fit and hand scape plenty diesel engine parts - I trying to overcome my novice gas mechanic skill i gotta start applying my machinist trade to autpmotive use

you fellas help - ya learn somepin' everyday
Click to expand...

Yes, by hand. With first stones, then sanding rolls. You can only get so good by hand so "flat" is a relative thing, but most if care is taken it can be done pretty well. The depth mic was more of a "go-no-go" gage. When it was flat on the gasket surface and the marking dye was rubbed off evenly it was basically flat. It was years ago when the quench domes first came out and nope, I wouldnt ever do it again. I once heard a rumor that when they were hiring a machinist Ferrarri would give a guy a file, a mic, and a chunk of metal, and some dimensions. He had to get it perfect using the file in every dimension. Those that took the time and got it perfect, got hired. I forget where I heard that...lol.
 
MoparAnglia said:
I've never been comfortable with using the intake closing @ .050"+15 but it shouldn't be that far off...

If you use the 0.006 figure the DCR comes out at a shade over 8:1.

Where did the intake closing at 37.5 degrees ABDC come from? That means the difference between the .006 closing and .050 closing is 36.5 degrees. If it's a symmetrical lobe that would give duration of 219 @ .050".
Click to expand...


The reason for using the .050 spec is that get's you past the movement off the seat as most cam companies have varying ways to control the valve when it begins moving. It is less exact, and if you have an assymetric ramp the numbers will change, but it rules out the take up ramps.
I simply used the figure noted earlier in the post somewhere. No clue if that's right for this cam.I would expect a typical 292 type cam to have an intake closing point at .050 to be a bit later than 38. Probably closer to 55-60.
 
moper said:
The reason for using the .050 spec is that get's you past the movement off the seat as most cam companies have varying ways to control the valve when it begins moving. It is less exact, and if you have an assymetric ramp the numbers will change, but it rules out the take up ramps.
I simply used the figure noted earlier in the post somewhere. No clue if that's right for this cam.I would expect a typical 292 type cam to have an intake closing point at .050 to be a bit later than 38. Probably closer to 55-60.
Click to expand...

I hear ya. I guess its a case of plugging the numbers to get a ballpark figure (whether you use .050"+15 or .006") then 'interpreting' them, knowing whether you have an aggressive ramp profile or something real lazy.
Looks like Crackedback came up with the goods anyway, so we're looking at a DCR between 8-8.5 at which point the quench (or lack of), chamber design, and a whole bunch of other factors can make octane requirement a tricky call.
 
You must log in or register to reply here.
-

Back
Top