New member jump in with cam ???

[KSROADSTER]

Hello, I owned several British cars as a teenager and sold my last one, a 71 TR6, in 1976. It was a low mileage beauty with overdrive. Fast forward to early Dec 2005 and a serviceable 74 TR6 is the object of my affection once again. /ubbthreads/images/graemlins/smile.gif The first of many questions to come is about the Kent Cam the previous owner installed. The part # is TH2-6 It has quite a bit of duration 295* but not as much lift as some other aftermarket cams I have seen. I was just curious what kind of idle I should expect with this cam. I'm still working all of the bugs out of the car and have only had it running for short periods of time. It sounds Great! but doesn't want to idle right off. I haven't had it running long enough to get up to running temp, or check for vacuum leaks.

Does anybody have an opinion on the vacuum spark retard as far as the idle is concerned? I read somewhere that when you use it you get a really smooth low rpm idle, but that was with the stock cam. Well I'm getting long........ Hello everybody!

 

[Guest]

Kansas City,
If the PO installed a cam, be willing to bet he removed most or all of the pollution that came on the car. Are you using vacumn advance? Why not go over to the dark side and use centrifugal advance, setting it at 8 degrees BTDC at 1000 rpm idle speed. Just block off all the vacumn lines from the carbs that sucked off the dizzy. You may play heck getting it to idle at 1000 with that duration. Will have somewhat of a lope. You definately have to get it up to operating temp to set it up. Welcome to the forum.


Bill

 

[ALLAN]

Generally, High duration cam will have more overlap and will give you less vacume, the high duration will give you a more rough idle, high duration gives more top end power with less bottom end torque. A lower duration cam would give you better idle and more power in the mid rpm ranges. A higher lift would give you more power through out the rpm range. With this high duration cam--- Idle and less vacume will probably be an issue.

 

[Alan_Myers]

Hi,

You might do some more research on that cam. Many Kent grinds that I've seen are what I'd call "uprated street" cams and that 295 sounds pretty aggressive. I'd expect something in the 260-280 range. Is there any possibility the info you have about the cam is off a bit, perhaps the durationi and lift at the lobe figures are reversed or something like that? I just Googled to see if there is more info out there and this site https://www.aptfast.com/cam_chart/Mini_Cooper_MG_Triumph_Cam_Chart.htm shows what they call "nominal duration" as 278 degrees, while this site https://www.hottr6.com/triumph/tr6cams.html shows "advertised duration" that agrees with your figure of 295. Most regrind cams come with a spec sheet that has more info. These two sites also don't quite agree about that cam's "power range". APT Fast is a pretty well-established vendor and you might be able to get more info via email or a telephone call.

I agree with what others have said. If the cam is long duration, you can expect a lopey idle and will need to set it around 1000-1300 rpm. You might also need to set the valve lash larger than normal, .014-.018 is not uncommon with uprated cams, although that's more a factor of lift than duration and you said it's not a particularly high lift cam.

You might want to convert to centrifugal advance only, since engine vacuum is effected by that cam and will, in turn, effect the dizzy advance curve. It's usually just a matter of blocking off the vacuum takeoff at the manifold or carb and taking the dizzy to a shop to be re-curved with different weights and springs. I'm not familiar enough with TR6 to give any specifics, maybe someone else here has had this done and can give you some pointers.

Have fun with your new/old Triumph and welcome!

Happy holidays!

 

[KSROADSTER]

Hello everyone, and thanks for the input. I got the cam part # off the box it came in, and the specs from the Kent Cam web site so I am pretty sure they accurate. Kent says a power band of 2500 to 6500 and call it a Sport"R" grind. Their race grind has a duration of 300 and a ton more lift. Some of their other grinds have more lift, and less duration. Just a guess on the cam I have would be, more power with minimal head reworking for a high lift cam.

Here is where it gets strange............ I finally got the clutch repaired, and got out on the road yesterday. All the emissions stuff is still hooked up and I can see where that is going to be a problem with the decreased vacuum my cam will produce. The strange part is.... I can get a decent 1000 rpm idle with a lope.... I kind of like it..... but here is where it gets strange. At idle if I remove the oil filler cap the car immediately dies........... really! /ubbthreads/images/graemlins/confused.gif

Any takers on that one /ubbthreads/images/graemlins/england.gif

I just edited out a comment I made earlier about the distributor. I didn't read a previous post closely and thought I read that I would have to add a centrifugal advance, but re reading it I see that it said to modify the existing advance. I am in the dark as to what the "dizzy" advance curve is though. As I understand it, my car (forgot to say it is a 1974) is basically mechanical advance only with the vacuum retard coming into play only at idle for emissions. At highway speeds all advance comes from the centrifugal and there is no vacuum advance. I did notice some earlier TR6's had both vacuum advance, and retard.

 

[Bugeye58]

KS, check all of your crank vent and PCV system hoses for free flow. Ideally, the idle should come up a bit when you remove the cap.
Jeff

 

[KSROADSTER]

Jeff, I think for now I am going to block off all vacuum ports, vent the block to the atmosphere, and work on getting the car running right like that. I have no idea what kind of condition my carbs are in, and how well the mechanical advance on my distributor is working ...so until I have them both set I will do with out the other stuff. I just hate to strip it all off, and go 1960's with it because it may hurt the resale value someday.

If anyone was scratching their head about a comment I made regarding the distributor in my previous post please re read as I have seen where I got off track, and have edited it.

 

[trfourtune]

don't trust the box. get out your dial gauge and degree wheel and verify what you have, then see if it is what you think.
rob

 

[KSROADSTER]

An update for anyone who is following this.......... With all the emissions vacuum ports blocked off, crappy aftermarket dirt sucking air cleaners in the trash, Carb slides/bodies cleaned, dashpots filled with fresh oil, new air filters installed, and a little ear tuning of the idle screws I get a decent 900 rpm idle with a pleasant but noticeable lope. /ubbthreads/images/graemlins/smile.gif It pulls hard to red line and sounds great but only after reworking the throttle linkage especially the pivot between the carbs. The throttle blades weren't going full open before the fix. My anti-run on valve works fine, and I will probably try to re hook vacuum for the block breather. All the rest of it will be in a bag for the next owner if they want it.