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Camshaft specification, what have I got?

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bob hughes

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Ok, here is one for the experts and those who are in the know.

Just finished stripping the BJ7 engine, and assuming that I had a stock camshaft, I have started looking for a slightly warmer cam - BJ8 to fast road.


I had one of those special moments today, you know, when the light comes on! :smug: so had a look at the end of the camshaft that I had just removed.

It would appear that we may not have a stock cam at all. A certain cam profiler - Racer Brown, has engraved his name at the end along with the following - 17-A 163 - 35. I have found some evidence in an old book on tuning that an RB 17-A is a fast road spec but this was applied to an MGA :wall:

Now to be fair, I have just e-mailed the above to try and find the spec for the cam, but I have had bad experiences with other suppliers - members of the Commonwealth, on your side of the pond, so I thought that I would cover all bases and ask the collective assembled at the same time. Can anyone please heeeeelllpp

:cheers:

Bob
 
I've got spec.s on the Racer Brown 16-A, SS6, and ST15 cams. You should be able to bring it to a reputable cam grind and have it measured.

FYI - The 16-A has duration of 270 and is described for competition. It sacrifices low end for good mid and top range, 6500 rpm attainable with HD springs and super tuned engine.
 
Thanks Dougie, it's a start.

THE SPORTS CAR ENGINE its tuning and modification by Colin Cambell has a reference for the the 16-A as you describe it, the book also has a reference for 17-A on the MGA as having a duration of 270 and is described for Competition and some street use good at above 6000 and a modified engine is necessary. I am having the moving parts balanced, and the flywheel lightened, but keeping the head as is, not sure if it is modified as such, will have to check with my local Healey specialist, I am seeing him tomorrow. Do you think that this same spec would apply to the AH3000 version?

Reading other forums, it would appear that after all this time, the records may be unavailable. Other people have been hunting out information on older cam grinds and it would appear that Racer Brown have been unable to come up with the details.:nopity:

:cheers:

Bob
 
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Bob - I do think the Spec on the 17-A cam for the MGA would be similar for the AH 3000.
 
Thanks Dougie.

I have now had some imore information from Don Gould of FBO Systems. The cam has a 272 Adv duration with a 385 lobe lift. I am pressing him for a little more information as I do not understand what this all means.
I am going over to see my local Healey man today and he may be able to interpret the results. In the meantime if any of the gathered ensemble can throw any light on it, I would be obliged.

:cheers:

Bob
 
Good News

I have an update, apparently it will work between 3000 and 6500 revs and with balancing and a lightened flywheel, it will give me what i want - a slightly hotter cam.

:cheers:

Bob
 
Bob,
Unless you are going to race this car 100% and live in the 4000 to 6500 rpm world, do not use this cam. At 270 degrees this is a big cam even for a 3000 cc. Healey 6 cyl. For a smaller MGA 4 cyl motor 270 degrees is a monster cam and you will have no torque.. Remember......no torque....no grunt... no fun. But I have had this conversation many times over the years with many others who think that bigger is better. It's your choice.. just remember.....you have been warned. If you use the big cam....we (I) will all say...I TOLD SO SO. Some things that are bigger are better.....cams are not one of those.
Cheers, Richard
 
Side topic (related to similar thread on idle problems): Are duration, etc., always spec'd at 0.50" lift at the tappets? For example, is a 270deg duration cam assumed to be measured at 0.50, or is that 'advertised' duration (gotta believe that it's 'advertised')?
 
To the best of my understanding- 50 thou is the lifter rise at which one method of measurement is done and 16 thou is the clearance to which the tappets are set in order to get readings for the "advertised duration" but this varies by manufacturer. I don't think the two measuring methods are able to be correlated as it would be dependent on the individual profiles.

Original BMC cams are quoted at 16 thou tappet clearance- I checked a BN4 cam and it came out spot on to the book specs.

Andy.
 
I think I made a mistake in my previous post in assuming you were using this cam in an MG. More about this later in this post.
Advertised duration is measured when the tappets just start to move. Usually measured at .006" lift. That 270 cam is advertised duration. I'm guessing, but it probably has around 200 to 225 duration at .050 lift.
The best way to compare cams is by using the duration at .050 lift but the cam grinders never use that number when advertising the cam. It seems you only get that info when you buy the cam and get the cam card.
And, valve lash has nothing to do with cam duration. You can loosen or tighten the lash to effect the way your engine "sees" the cam duration, but the duration is built into the cam and valve lash will not change it.
If I remember correctly, the 100-6 and early 3000 cams have 230 degrees of duration. A BJ8 cam has 252 degrees of duration. Again, this is advertised duration.
A 270 degree cam on an MGA would be horrible but on a 3000 it could really wake things up if you bump the compression a bit, use two HD8 carbs, and headers. But more importantly, you need to advance the cam. My experience is that with any reground Healey cam it will end up being retarded. If anyone can prove me wrong I would be happy to hear from them. If you install it "straight up" you will loose a lot of low end torque because the 270 grind (or any other performance regrind) is meant to increase Hp and that only happens at higher RPMs. You cannot compensate by moving the timing chain one tooth because that will advance the cam almost 7.8 degrees and that's twice the amount of advance you need to compensate for the performance cam.
So, here is some shameless promotion. I am working on two engines right now and I have to get some more offset cam bushings made. They ain't cheap, so if I get some interest from you guys, I can double or triple my order and get the per unit cost down and we can all save some money. Send me a PM if interested.
Richard
 
Bob, I imagine you will be using Bill Rawles so Im sure he'll put you on the right track. I just removed the DWR8 fast road cam from my car. It has a 278 degree duration, 0.293 cam lift and 0.401 valve lift. Please note that this cam needs valve pockets in the block to clear the exhaust valves. I was running it with 2 HD8s and a 10:1 compression ratio. It produced a nice flat torque curve from 140 ft/lb at 1500 revs then a flat 155 ft/lb from 3000 to 5000 revs. Very driveable. I now have the DWR rally cam with 300 degree duration, triple Webers and an 11:1 compression ratio. The max torque is now 232 ft/lb at 4500 revs, max power 213 bhp at 5500 revs, but not much happens under 2500.
 
Thanks guys for all this information, you must remember that I have been driving this car for 11 years without much of a problem except that it consumed oil as if it was going out of fashion ( found that I needed to go up two rebore sizes) and we found that the timing was out which was resolved by adjusting the dizzy.
It may be that I can squeeze something more out of the engine by putting a DW vernier cam sprocket on, but it was quite tractable with the standard settings. When I dismantled the engine, the cam timing was standard but as Bill Rawles is envolved I will be discussing it with him prior to putting it back together again.

:cheers:

Bob
 
Yes I have, and we have two events there this year. That is Shelsley Walsh and it is the oldest motor sport venue in the world that has been in continuous use. It is right in the middle of very beautiful, rural, Worcestershire countryside. Over the years the club facilities, which include an old water mill, have been beautifully upgraded. It has old, wooden paddock shelters which are very narrow. Ask me how I know!!!!
 
Dougie,I should add that the track is very narrow, with high sides and can be quite intimidating. Search for it on youtube and you'll see there have been quite a few hairy accidents, particularly in the wet.
 
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