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Check camshaft type
- Thread starter NIB
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The stock BJ8 cam's are actually a 3/4 race profile(I've read this several times), and will not be as smooth as a stock 100-6 or early 3000's idle.NIB said:
Patrick
Superwrench
Jedi Trainee
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Yes Just put a indicator on the push rod side of rocker and turn engine over with a wrench. It should have .368 inch lift.
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The only way to tell if the cam in your BJ8 is stock, or not, is to pull it and take it to a cam grinder and have them do a profile.
Secondly, the BJ8 camshaft is far from a 3/4 race grind. It idles just as smooth as any earlier 6 cylinder engine.
Thirdly, there is no way that any Healey camshaft could have a .368 lobe lift. I have measured many cams, 100-6s, early 3000s and a BJ7. They range from .230 to .264 in lobe lift. An Iskenderian grind, the T-3-6, is truly a 3/4 race cam and it's lobe lift is .289 - .290.
It is not the lobe lift but the overlap that determines how racey the cam actually is.
And if you start to check valve lift with a dial indicator, remember, the stock rocker ratio is 1.43:1, not 1.5:1, as generally advertised by the cam grinders.
Secondly, the BJ8 camshaft is far from a 3/4 race grind. It idles just as smooth as any earlier 6 cylinder engine.
Thirdly, there is no way that any Healey camshaft could have a .368 lobe lift. I have measured many cams, 100-6s, early 3000s and a BJ7. They range from .230 to .264 in lobe lift. An Iskenderian grind, the T-3-6, is truly a 3/4 race cam and it's lobe lift is .289 - .290.
It is not the lobe lift but the overlap that determines how racey the cam actually is.
And if you start to check valve lift with a dial indicator, remember, the stock rocker ratio is 1.43:1, not 1.5:1, as generally advertised by the cam grinders.
Superwrench
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I stand corrected The .368 lift is on the valve side of the rocker. 1.43 x lift. :hammer:
Randy Forbes
Yoda
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Kind of easy to tell if it's an Isky cam, if you happen to have the transmission, clutch/flywheel and backplate out...GregW said:
The T-3-6 is a totally streetable, if higher output cam grind; it's what I have in my car, plus 3 X 45 DCOEs, headers and high output ignition.
Thanks for the answers.
I probably should have told why I want to check which it is. I noticed the engine block dont appear to be stock, it has the short oil stick. The other engine parts seem to be BJ8, so I want to see if the camshaft is the stock BJ8 or perhaps from an older 3000 engine.
I probably should have told why I want to check which it is. I noticed the engine block dont appear to be stock, it has the short oil stick. The other engine parts seem to be BJ8, so I want to see if the camshaft is the stock BJ8 or perhaps from an older 3000 engine.
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Not only is the Isky T-3-6 cam totally streetable, it is one Big Stick for our size of motor. I have used the Isky T-3-6 in a street car and in my race car in the past. I use a different grind right now, but still in the 260-270 degree duration. I make 230 Hp at 5900 RPM and have over 200 ft lbs of torque from 3000 RPM to over 6000 RPM.
If you use a "bigger" cam, that is, one with longer duration (like the Isky T-4-6), you will kill the engine. Which means, loss of torque and it will push your peak power band into the stratosphere (7000 RPM).
The simple truth is cubic inches will kill a cam. We have small engines (3000 cc) or approximately 165 cubic inches. A cam with 268 degrees overlap is HUGE with our engine. If you put the same duration cam in a Chevy, or Ford, or Chrysler V8 351 or 360ci, the cam is an absolute wimp. A cam with BIG duration works in BIG motors, not vice versa.
If you use a "bigger" cam, that is, one with longer duration (like the Isky T-4-6), you will kill the engine. Which means, loss of torque and it will push your peak power band into the stratosphere (7000 RPM).
The simple truth is cubic inches will kill a cam. We have small engines (3000 cc) or approximately 165 cubic inches. A cam with 268 degrees overlap is HUGE with our engine. If you put the same duration cam in a Chevy, or Ford, or Chrysler V8 351 or 360ci, the cam is an absolute wimp. A cam with BIG duration works in BIG motors, not vice versa.
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Richard,
Several folks over the years [on the newsgroup] have said they're using 300 degree cams in hot street cars with webers. Magnus Karlson & Chris Dimmock if I recall correctly. Would be interested if you have a reaction to this.
Not trying to be argumentative, but from your description below they sound unworkable, yet others swear by them.
Several folks over the years [on the newsgroup] have said they're using 300 degree cams in hot street cars with webers. Magnus Karlson & Chris Dimmock if I recall correctly. Would be interested if you have a reaction to this.
Not trying to be argumentative, but from your description below they sound unworkable, yet others swear by them.
BoyRacer said:
TimK
Jedi Knight
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My racing experience was with an MGB 1960cc with domed pistons (13:1 compression) and a 300 degree duration. It had no torque below 3000 rpm. It required high rpm to start up from a stop, but it had great power from 4000 to 6500 rpm. It also had an aluminum flywheel which hurt the startup capability but helped rev-ability. I did run it on the street with a muffler for a couple of days, but that was enough. Also, I used overdrive in 2nd gear as well as 3rd and 4th to keep the revs in the power band.
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Tim K told it like it is! But, I guess it's all just a matter of taste. If you want to drive a car with no torque, then put in a full race cam. It will sound cool in the parking lot as you impress your buddies with that loping idle. The Isky T-4-6 cam is the "full race" Isky grind for a Healey 6 cylinder. It has 286 degrees duration. It makes great horsepower after 3500-4000 RPM all the way up to 7000 RPM. Try driving this comfortably on the street! You will definitly need the 4.11:1 rear end to compensate for the lack of torque! (And, Webers have nothing to do with torque.)
If I correctly remember that old saying: "Torque wins races - horsepower sells cars".
The longest track I race at is Road America - Elkhart Lake, Wisconsin - 4.0 miles long. I hold the track record for an Austin Healey, and my cam is less than 270 degrees duration. So, why don't I run a "full race" cam?
Answer: All race tracks have turns (as well a city streets) and you have to slow down sometimes to get around those turns. You downshift, but you still need some grunt to get you back up to speed. You NEED torque to launch your car, either to win on the track, or just to get away from that stop sign when in town.
If I correctly remember that old saying: "Torque wins races - horsepower sells cars".
The longest track I race at is Road America - Elkhart Lake, Wisconsin - 4.0 miles long. I hold the track record for an Austin Healey, and my cam is less than 270 degrees duration. So, why don't I run a "full race" cam?
Answer: All race tracks have turns (as well a city streets) and you have to slow down sometimes to get around those turns. You downshift, but you still need some grunt to get you back up to speed. You NEED torque to launch your car, either to win on the track, or just to get away from that stop sign when in town.
Randy Forbes
Yoda
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I love torque! It's the primary reason (but not the only reason) why my daily driver is an M Rdstr, and not a Boxster!BoyRacer said:
I've always told people, that we <span style="font-style: italic">talk</span> horsepower, but we <span style="font-style: italic">drive</span> torque :wink:
5
57_BN4
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Its interesting that small bike engines make peak torque at over 10k rpm and use 260~280 duration cams. I'd never really thought that much about the big-engine big-cam idea but I can see some validity just in the fact that the large volumes of air consumed require more time to start and stop moving.
I know for sure that putting a common manifold/single throttle on a small engine means the idle speed goes from ~900 to ~3000rpm because the individual throttle butterflies and slide-bore air valves contribute a lot to the anti reversion effect. With just one throttle the air and fuel gets all messed up in the manifold between the cylinders. Perhaps this is why a set of Webers and a big cam go together ok?
Same thing happens in the exhaust, Yamaha have used their device called Exup which blocks up the exhaust pipes when off throttle to prevent inversion in the exhaust in the same way the slide valves block off the intake ports.
I know for sure that putting a common manifold/single throttle on a small engine means the idle speed goes from ~900 to ~3000rpm because the individual throttle butterflies and slide-bore air valves contribute a lot to the anti reversion effect. With just one throttle the air and fuel gets all messed up in the manifold between the cylinders. Perhaps this is why a set of Webers and a big cam go together ok?
Same thing happens in the exhaust, Yamaha have used their device called Exup which blocks up the exhaust pipes when off throttle to prevent inversion in the exhaust in the same way the slide valves block off the intake ports.