I sure as heck hope that's not true now.
Commando 273 cam specs
- Thread starter Miranthis
- Start date
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We put an original 67 Commando cam with 50,000 miles on the odometer on a cam doctor at Racer Brown and got the .050 duration numbers. I'm satisfied those are correct minus .010 lift from wear. Next, what lobe masters are available? Racer Brown came pretty close. The Isky E-4 is close with .425 lift but has 216 duration @ .050. A 340 cam has how much duration@ .050? 210? 212?
73Charger318
Member Rt 66 Mopar Club
I put the Isky E-4 mentioned above in my 65 with all original commando engine. That cam was recommended by several here. Isky 390144.
Good to know for the 340 cam.
Back in the day (1971) I overhauled the high mileage Commando 273 in my 65 Barracuda (really cheaply, rings, bearings, valve job, didn't even hone the cylinders) and put in a TRW cam, 284 advertised duration, only .426/.422 lift. It woke that little 273 up. After I windowed the block a year and a half later trying to drive 200 miles home in second gear after breaking the 3-4 shift fork, I put that cam in the 340 that replaced the 273 and it worked well there. Not sure if it was stronger than the stock 340 cam, but it was at least as strong, and the lifters didn't pump up if I held it in low gear too long.
I don't know if I'm "hiding behind a keyboard," and I'm certainly no cam expert, but I do think the MP instructions to multiply its advertised duration by .85 to get the duration at .050 is not very accurate for at least some of its cams. Using that formula gives me 231 duration at .050 for my MP 761 cam with advertised 270/272 duration and .450/.455 lift. I don't remember where I got this chart from, but the big block MP 272 degree cam has (according to this) 224 duration at .050.
Good to know. I thought Oregon ground your 340 cams but I guess not. Let me change my post above. No reason for me to post misinformation.
No Mike, there may be a misunderstanding...
Delta Cams ground both of my cams (68 340 auto and 4 speed) from factory specs but were slightly off, but not enough to make a difference... I bought them unused off of another FABO member...
I sent them to Oregon to be measured and he is able to map them and make replicas or bump the lobes forward or back, but he cannot add a little lift to a lobe... Oregon copies the lobe profiles...
So Delta cams cam make a lobe profile from scratch (give them the specs), Oregon can copy the lobes or bump them forward or back a few degrees...
Sorry guys, I had to go to a doc appt...
Here's info from a spreadsheet I made 20 years ago... The numbers in bold black are given specs from the manufacturers, the numbers in regular black print are what I calculated from the given information... Then I added the perecnt duration comparing .050" to advertised duration... Notice how all of the MP cams are .85 (85%) +/- 1%...
Here I did the average for the MP cams...
Some of the other manufacturers had more of a spread for their .050" vs adv duration numbers, but the MP cams were pretty consistent of 85% +/- 1%...
Here are the other manufacturers... The cams with the gray backgrounds had incorrect/conflicting data from the manufacturer, that I corrected to the best fit from the other data... I did the calculations forward and backward to check the information and correct it... I did find a few errors and was able to correct them with the forward and backward calculations to find which spec was wrong and corrected it in my charts...
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It may depend on the vintage of the MP cam you have...
Your chart shows the 'revised' cams with the AB at the end of the part numbers...
I did my spread sheet before the part number update and they list different specs... My data is right out of the MP catalogs for the early 2000's before the new part number system... They may have changed some of the profiles when they changed to the new part number system...
The two letter designation at the end of the part number was to help engineers and production control people to track changes to the part number...
they also changed the .484"/248° cam to the 114 centerline to make it more street friendly than the 108° .484/284 cam, but made both grinds available...
You don't happen to have any Camcraft numbers for the slant 6, do you?
I would like to see someone have Powell grind or regrind a cam. I sure like what he does on his videos.
It does... My spread sheet shows that the MP cams are between .849 - .851 of the @.050" duration compared to the advertised duration very consistent average to .850 or 85%.... Which is less than 1% variation...
I'm very good with numbers and calculations...
No. I don't even remember where I ran across that chart. Just luck, really.
Small Racer Brown 273 solid cam specs same lobe, int and exhaust.
200 degrees duration @ .050
.405 lift @1.5 rocker ratio
Larger cam is:
210 degrees @.050
.430 lift @ 1.5 rocker ratio
200 degrees duration @ .050
.405 lift @1.5 rocker ratio
Larger cam is:
210 degrees @.050
.430 lift @ 1.5 rocker ratio
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Sorry to go on the tangent, but here's what you are looking for...
The 66 Commando 273 cam had 248° duration...
From similar MP cams with 248° duration, you can see that the duration @.050" is 211°
Now, adding the 66 273 4 bbl to my spread sheet, we come out with...
Lift at valve:
Int = .415"
Exh = .425"
Lift at cam: (using 1.5 rocker ratio)
Int = .277
Exh = .283
Advertised duration:
Int = 248°
Exh = 248°
Duration @.050":
Int = 211°
Exh = 211°
Open/Close Advertised:
Int Op = 14°
Int Cl = 54°
Ex Op = 56°
Ex Cl = 12°
Overlap = 26°
Int Centerline = 110°
Exh Centerline = 112°
Lobe separation = 111°
Open/Close @.050":
Int Op = 4.5° ATDC
Int Cl = 35.5° ABDC
Ex Op = 37.5° BBDC
Ex Cl = 6.5° BTDC
***********************************************************************************************************
However I see something odd with those numbers... There may be errors in the service manual numbers or rounding error...
Chrysler likes to have the intake centerline, exhaust centerline, and lobe separation "the same" number... And the intake open/close are mirrors of exhaust open/close...
So, if I correct the intake centerline, exhaust centerline, and lobe separation to all equal 111°, you end up with:
Look at the second row...
Lift at valve:
Int = .415"
Exh = .425"
Lift at cam: (using 1.5 rocker ratio)
Int = .277
Exh = .283
Advertised duration:
Int = 248°
Exh = 248°
Duration @.050":
Int = 211°
Exh = 211°
Open/Close Advertised:
Int Op = 13°
Int Cl = 55°
Ex Op = 55°
Ex Cl = 13°
Overlap = 26°
Int Centerline = 110°
Exh Centerline = 112°
Lobe separation = 111°
Open/Close @.050":
Int Op = 5.5° ATDC
Int Cl = 36.5° ABDC
Ex Op = 36.5° BBDC
Ex Cl = 5.5° BTDC
These numbers mirror each other which is what you typically see with the Chrysler grinds...
However, I just noticed an interesting thing when highlighting the above picture... Notice how all of the non-split pattern HYDRAULIC cams have mirror open/close numbers, but the non-split pattern SOLID cams are not mirror numbers, but slightly offset by a degree or two... Was this on purpose or an error (maybe roundoff error)???
It only effects the open/close numbers by 1° which won't be noticeable on a dyno or seat of the pants, but what is the intended grinds for these cams???
What do you guys think???
I bet Jim at Racer Brown could rattle off the numbers real quick. Somebody call him.
If perfacar says it, you can take it right to the bank.
I don't see the 273 HiPo on this chart.
Unfortunately your assumptions don't line up with measured numbers taken at Racer Brown. They are not comparable to the MP cams and I doubt the wear of 50,000 miles would affect duration as it only reduced lift by .010 of an inch on the intake and exhaust lobes. Jim will tell you that Chrysler liked real slow ramps to save on warranty claims.
Measured numbers of your part are good, and are good to see where a production part ran...
I don't like using numbers from used parts when you are trying to reproduce the part, you don't know how the wear affected the part and you don't know what side of the tolerance that part was made...
The only way to find the accurate geometry of the cam is to measure a new production one, to find how it was really made and to what amount of tolerances were used... Even then, there are also variations in manufacturing...
There are differences every time they set up the machine and wear as the tooling wears in production... Cam lobes are finished ground with a grinding stone, which wears with each part made... The first part of a machine run will be different than the last one because of tooling wear... Grinding stones wear so that will make the parts different from part to part... Especially from the first part made to the last one... Grinding stones wear faster than hard metal tools like a mill or drill... It's their nature...
When they set up new tools on a machine line, they take into account the wear of the tool.. They bias the setup so it will wear towards the nominal spec as the tool wears... They set up for one side of the tolerance, so it will wear towards nominal, then will pass over nominal to the other side of the tolerance... They will do check parts throughout the run to monitor the wear and variation so they can catch the part from running out of spec (tolerance) as it approaches the other side of the tolerance and shut down and do a tooling change before it runs out of tolerance specs...
My numbers were made off the published specs... Those are the nominal targets for the parts... There will be some variation because of tolerances... Every part has a nominal spec and allowable tolerances...
This is why I prefer to deal with actual nominal specs... If you try to reverse engineer a part off a production part, you don't know what side of the tolerance the part was run... Then when you apply production tolerances to your measured part, it will then be out of spec to one side of the tolerance, and the nominal is shifted... That's why it's best to deal with nominal specs because they are the Design Intent for the part and the center of the allowed tolerance...
When you remake a part it's best to use the original nominal spec for the part, not the tolerances... There is a reason for the nominal part, that is what it is designed for... Tolerances are used to allow for production variation...
You made a bunch of assumptions. Some I feel are bad. I was a Design Engineer and am well aware of production tolerances. I also know Jim at Racer Brown and basically know too much how cams are/were made. The master lobes do not wear and are scaled up 4 x the ground lobe. I will take our measurements over your assumptions.
NC Engine Builder
Grumpy Old Man
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I sent him one to regrind last year, for a customers build, he quoted "few weeks" but after the 2nd phone call after 2 months of waiting he stopped answering calls or returning emails. Finally the customer called, and powell said he thought it was "no rush" so we bought a isky instead. That guy is a JOKE
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