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MG MGB GT V8 Factory Originals Technical - Milder street cam
|Now that I've had some help from Curtis in identifying my '62 215 Buick engine with a 4 bbl Holley, I'd like to get some ideas about a milder street cam than is in the engine right now. My steed is a '70 mgb roadster, future T-5 trans and a stock rear end, so far. |
I'm going to be stupid right now and say that I don't know what cam is actually in the motor at present- I bought it this way and have not taken the motor apart yet but I know I can't live with this cam for street use- it's way too lumpy at idle.
I don't have functional mufflers yet and the car is not ready for driving in other areas either but I'd like to get some ideas from other h/o 215 users about a more suitable cam for this lump. Street driving is my game and I need a little better idle. Any suggestions on a milder cam with some rpm/hp/torque numbers will be welcome.
They have 3 different cams for the Rover/Buick 215
You probably already know this, but don't forget to use new tappets with the new camshaft. Old tappets will wipe out your new lobes faster than anything you'll ever experience!
|Steve, I always wondered why that is. I mean, although 100.00% of all car people certainly agree with you, and it says in the book that came with my Erson, essentially "-->HEY, SLOW ONE, CHANGE THE DAMNED LIFTERS -- THIS MEANS YOU!!!<---", with hydraulic lifters I never really understood the reason. |
Anthony, are you sure it's the cam that's giving you a lumpy idle? Not that many 215s that I've seen have really long-duration cams -- of course, that doesn't mean yours didn't. Further, one characteristic of this motor is that in order to suffer a lumpy idle, you'd need a truly monster cam in there. It's really not _that_ hard to get some ballpark measurements if you just take the valley gasket off. You can do that when you have taken off the Holley before you put on an Edelbrock or what have you so that the car will (i) not require so much fiddling, (ii) not catch on fire, and (iii) have a little more hood clearance.
no, not sure at all that the rough idle is a cam problem.. this car came to me as an incomplete project and I really don't know what I've got here since I bought the car from a 3rd party- not the person(s) who did the conversion. There is a n/f exhaust system on the car and the engine has not been run on a regular basis since the installation several years ago so there could be other reasons for a rough idle, not just the cam spec.
I haven't done much digging in the engine since getting the car recently but by taking off the rocker covers, I know that the valves have new spings and retainers and the engine is spotless inside but as to the condition of the rest of the supposedly rebuilt engine, I have no idea of the extent of the claimed rebuild. I'll be finding out more when I've removed the driveline to do some welding in the tunnel area.
As you suggest, I'll check the lift on the cam before I take the engine out. I hope the correct break-in method was used for the cam and lifters if they were new.
Is there a difference in the height to the air-horns between the Holley and Edlebrock carbs?
|Yeah, the Edelbrock/Carter/Weber units sit a little lower. I think it's only about 1/4".|
I wouldn't worry about the lift per se; pretty much only the overlap would really affect the idle.
|Harry,lifters are not flat but convex and the cam lobes are machined with a minimum of .001"-.0015" taper across the face to induce the lifter to rotate.If you ever see a cam with low miles on it you can see that the contact patch is not in the center but off to one side.Cams that do not have this taper ground correctly on them are often the reason for early failure.So if you put a used lifter on a new cam it will point-load the lobe and wipe out both.If your liters are low mileage you could possibly reuse them but why take that chance?|
I am using an Isky 262 grind. It idles at 700-800 rpm with a slight "lump" to it. Base ingition timing is set at 10 degrees, this seems to give me a strong vacuum signal, thus a nice streetable idle. I'm not sure about horse power but it pulls strong past 5000 rpm. I could probably go with a 272 grind now that I have more compression (10.25 to 1) but I have been using this cam for years and I know how to tune the engine to it.
Several factors affect idle quality for a cam. Engine size, the bigger the engine the more duration you can get away with and have an acceptable idle.
Compression ratio, a high compression engine will tolerate more valve timing than a low compression one.
Ingition timing, less base timing = a lumper idle, more base timing generally smoothes the idle out.But you can only go so far on the base timing before you have hard start,and detonation problems. If you add 5 degrees to your base timing you will need to recurve the dist advance to take away that 5 degrees so you don't have to much total timing.
Mismatched engine parts, ie. low comp., big cam, small port heads, big carb, and a restrictive exhaust system.
HTH Bill email@example.com
|Gentlemen, thank you for your insights and advice on my idle problems- once again, I've learned something.|
This thread was discussed between 03/07/2001 and 12/07/2001
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