This is where I'll be putting all the information I have on OHC camshafts that are readily available to us. I'll be donating the raw data to Ian Rankin (IADR on here) who has that wonderful page dedicated to information on these things, and hopefully it'll be of some use to spurring on a discussion.

For the terminology:



The test method was that I bolted a cam into a head without any valve springs, and turned the head upside down. I mounted a dial indicator on the head so that it measured valve lift. I had shimmed the buckets so tight that the valves never closed, so that I could be sure I could zero the dial indicator on the base circle. I mounted a degree wheel to the camshaft and bent up a coathanger pointer. I turned the degree wheel until each valve showed 0.016" lift (the typical valve clearance you'd use) and started recording data every 2 degrees of camshaft rotation.



Being that I don't have a whole bunch of time today, I'm just going to post up the numbers for now. Again, when I say '0" valve lift' I mean just that. When I use .050" numbers I mean .050" from the base circle, which is really .034" lift. This is an effort to maintain consistency with manufacturer's advertising "standards". I will also be editing some of this info when I get more time, so some numbers might change.

M cam:
244/268 degrees at 0" valve lift
204/220 degrees at .050" lobe lift
.374"/.413" (9.50/10.49mm) lift from the lobe
112 degrees Lobe Separation Angle
32 degrees overlap at 0" lift
-12 degrees overlap at .050" lift (calculated)
-10 degrees overlap at .050" lift (actual)

T cam:
252/252 degrees at 0" valve lift
210/212 degrees at .050" lobe lift
.390"/.390" (9.90/9.90mm) lift from the lobe
110 degrees Lobe Separation Angle
32 degrees overlap at 0" lift
-9 degrees overlap at .050" lift (calculated)
-8 degrees overlap at .050" lift (actual)

V cam:
272/270 degrees at 0" valve lift
232/230 degrees at .050" lobe lift
.447"/.447" (11.35/11.35mm) lift from the lobe
111 degrees Lobe Separation Angle
49 degrees overlap at 0" lift
10 degrees overlap at .050" lift (calculated)
8 degrees overlap at .050" lift (actual)

A cam:
280/278 degrees at 0" valve lift
226/224 degrees at .050" lobe lift
.413"/.413" (10.49/10.49mm) lift from the lobe
109 degrees Lobe Separation Angle
61 degrees overlap at 0" lift
7 degrees overlap at .050" lift (calculated)
8 degrees overlap at .050" lift (actual)

B cam:
284/284 degrees at 0" valve lift
228/226 degrees at .050" lobe lift
.416"/.416" (10.57/10.57mm) lift from the lobe
108 degrees Lobe Separation Angle
68 degrees overlap at 0" lift
11 degrees overlap at .050" lift (calculated)
12 degrees overlap at .050" lift (actual)

D cam:
292/288 degrees at 0" valve lift
236/236 degrees at .050" lobe lift
.440"/.440" (11.18/11.18mm) lift from the lobe
112 degrees Lobe Separation Angle
66 degrees overlap at 0" lift
12 degrees overlap at .050" lift (calculated)
13 degrees overlap at .050" lift (actual)

K cam:
284/284 degrees at 0" valve lift
238/238 degrees at .050" lobe lift
.470"/.470" (11.94/11.94mm) lift from the lobe
112 degrees Lobe Separation Angle
60 degrees overlap at 0" lift
14 degrees overlap at .050" lift (calculated)
16 degrees overlap at .050" lift (actual)

Enem V15 Turbo:
290/286 degrees at 0" valve lift
226/224 degrees at .050" lobe lift
.468"/.467" (11.89/11.86mm) lift from the lobe
112 degrees Lobe Separation Angle
64 degrees overlap at 0" lift
1 degrees overlap at .050" lift (calculated)
2 degrees overlap at .050" lift (actual)

RSI Stage 1 Turbo:
276/296 degrees at 0" valve lift
224/254 degrees at .050" lobe lift
.410"/.462" (10.42/11.73mm) lift from the lobe
113 degrees Lobe Separation Angle
60 degrees overlap at 0" lift
13 degrees overlap at .050" lift (calculated)
14 degrees overlap at .050" lift (actual)

RSI Stage 2 Turbo:
274/296 degrees at 0" valve lift
232/254 degrees at .050" lobe lift
.446"/.462" (11.33/11.73mm) lift from the lobe
118 degrees Lobe Separation Angle
49 degrees overlap at 0" lift
7 degrees overlap at .050" lift (calculated)
8 degrees overlap at .050" lift (actual)

RSI Stage 1 NA:
298/294 degrees at 0" valve lift
252/252 degrees at .050" lobe lift
.430"/.430" (10.92/10.92mm) lift from the lobe
109 degrees Lobe Separation Angle
78 degrees overlap at 0" lift
36 degrees overlap at .050" lift (calculated)
34 degrees overlap at .050" lift (actual)

The numbers above might be used to compare with other data, except for a couple things: Most of my cams are used, so might show some slight wear. My dial indicator and degree wheel aren't as accurate as some other data collection services. I measured lift at every 2 degrees of cam rotation, which is 4 degrees of crank rotation, so the data is a little coarse and interpolation is required. The lifter buckets amplify valve lift slightly (when the valve is in motion, the lifter buckets generally open the valve slightly more than you'd expect by just measuring the cam. When the bucket is on the cam nose, there is no amplification.) Heat in the exhaust valve will close the valve clearance a bit more than on the intake valve, so the exhaust valve durations might actually be a bit greater in a running engine. Finally, people make mistakes: Enem claims 256 degrees for the V15 Turbo at .040" lobe lift (the lift number was given in an email between Jan and Ian R, but he can't find that email so we'll call it a rumour for now), but I measured 232-233 for real. RSI claims 254/270 and 238/270 durations at .050" for the two cams I measured, and you can see by the results below that I only got 224/254 and 232/254. Consider my numbers +/- 2 degrees for accuracy, please.

Also when you look at "advertised numbers", you're not always getting the same thing - some folks measure duration off the seat (like I did) and some folks don't. Most people advertise .050" numbers from the base circle like I did, which is actually .034" valve lift once you take away my valve clearance. Also the lift numbers are almost universally taken from the base circle, so the valve is again open .016" less than this number. I've also shown overlap in a few different ways: first is overlap at the valves opening and closing points; second is the .050" (lobe lift - 0.034" valve lift) "calculated" number; third is the actual .050" number. The difference between the calculated and actual numbers is the calculated one is based on the LSA and .050" durations, and assumes that the lobe is symmetrical, while the actual one is based on ... actual numbers. Again, assume +/- 2 degrees margin of error.

I plan on graphing all these numbers and lining them up for all to see. I want to post more tabular information as well, such as opening/closing points at various lifts, duration at various lifts, etc. I also want to mirror them so that we can see if they're symmetrical or not, overlay intake and exhaust lobes to see if they're the same or not, and discuss the merits of each camshaft. Ian R. has many excellent points and data to back it up, all of which may make it's way into here.

My goal is not to reproduce data that exists elsewhere, or to come up with the definitive answer to "what is the perfect OHC camshaft", but is part of a personal quest to hold the data in my hands to see things for myself. When someone says that "this cam has such-and-such duration and lift", it doesn't tell you a quarter the story of the shape and detail of the thing.

nice work buddy!

from that data the RSI Stage 1 sure looks odd with all that overlap compared to other 'turbo' cams.

did you not have an IPD cam, or is that the same as the enem?

anyone else find 'degrees' sure starts to look like a funny word after you've read it 20 times?

Impressive work Matt

Excellent work - nice to see apples to apples for a change. I thought the RSI stage 1 was weird as well, same overlap as the K? Oh and degrees is ASCII code 248 IIRC (hold the alt key and type 248 on a PC and ° (opt/shift 8 on a Mac)

The V15 came from enem (with ideas from the volvo "sport" grind), was copied by unitek, copied by MVP, then copied by IPD. Pretty much how all "development" works at IPD these days. At the cam grinding shop in portland, there is a funny sheet I saw labeled "ph1," then that is crossed off to say "MVP PH1 +1 deg lobe seperation" and then "IPD MVP +1 deg lobe separation." Very telling. It works well in a B21FT shoving lots of boost down its throat to make power with a decently smooth idle and passing emissions pretty easy.

No idea on the RSI cams. My B21FT car with a T and automatic with minor head and exhaust work would shred on Aaron's car with the cam, no head work, stick shift half the miles B230 and small turbo from a roll and really shred on it from a stop. It also idled a lot nicer.

Until I make huge revisions to the head/manifolding, I see no need to go bigger than a V. That and I MUCH prefer the cams be OEM. I like that they have a slight slant to the lobes, the chamfer and are ductile iron. They last, give no oiling problems, and require no strange shimming, clearance specs etc. When I do a valve job I set them in a little if I can to ensure no interference with a V or H if that motor is to have that camshaft, and for other things I learned relating to flow. I then cut the valves by the same amount, all while staying within what the book allows and getting the surface finish I want...it did take me a month to rebuild the head on the cop car (I did the machine work and all assembly). Honestly, I'd buy the machines if I could right now so I knew all the work on my cars was right start to finish. I've finally found two machinists I trust...which has me waiting a bit or driving 350 miles in the other case...but I know it is right, so it is worth it.


Good work there. Nice to see people measuring following some standard procedure instead of cam specs being pulled out at various lifts, methods and god knows what else. At least we don't have push-rod junk. I really want a 220, want it to be all original looking, but I HATE B20s.

Oh, James... You reminded me of something: the V15 is ground on the same base circle as OEM, but the RSI cams are different. The stage 1 is 2 thou oversize (not a big deal) but the stage 2 is 38 thou undersize.

And no, I didn't have an IPD turbo. That was Raz. I borrowed it and put a profile gauge on it and compared it to my V15, and from what I could see with the naked eye, they were identical. On Tbrix there is a thread with a bunch of cam data and it claimed the IPD (and V15 NA) were both WAY different from what I found. I thought the three shared identical lobes, with the differences being LSA. I would like to measure them both, though.

I have an ipd turbo cam, if you really want to measure it

- R

If you've got it out of an engine, I'll measure it. Don't pull it on my account. I'd be curious to see if it's the same as the V15T, but it's not worth pulling and reinstalling.

I never shimmed this head when the ipd cam went in, I think it'd be nice to do, and I have a new pretty cam-gear and front cam seal to install

So, cam is out tomorrow, I'll drop it off soon.

That's nice work Matt, should help cut through a lot "internet knowledge". There's nothing like seeing (and measuring) for yourself.

You wouldn't have any data on B6304 cams by any chance?

Richard

All I know about them is that the early ones were supposedly hotter, and thenin (95?) they got milder.

James, if you're listening, I'll pay shipping both ways if you want to loan me the cams.

RSI Stage 1 NA numbers are up. Observations: this camshaft isn't machined for a rear distributor, nor does it have the rear bearing oil groove machined into it like all the other cams do, but at least this one has the right base circle... It appears to be much closer to what RSI advertises: 252 degrees and 110 degrees LSA, with 11.07mm lift. I got 252 and 109, with 10.92mm lift.