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TR5 & TR250 Forum

tr250 cam

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YankeeTR5 Dan M
Seattle, washington, USA   USA
Scott....welcome to the rabbit hole. When you say the carbs were rebuilt, who did the work? You or were they done by a shop? If it was you (which is fine, its pretty easy to go thru these carbs) you may want to pull the rich running carb and redo the process. You might find that something was reassembled wonky.

If you are interested in tuneability (which I would be) I stand by my earlier recommendation of getting a set of pistons with the adjustable needles. Replacement needles are cheap so you don't need to source "correct" TR stuff, just make sure they're for a 1.75 ZS. If you had them in your carbs now it would be as simple as turning a long handled allen screw to adjust the single carb that's out of whack (ok, maybe not that easy as you're into balancing both carbs....but you get my point I hope....)

Best of luck. 250's are a great car to cruise.....

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Rick in Miami Avatar
Rick in Miami Rick Z
Miami, Florida, USA   USA
1973 Triumph GT6 MkIII "Spit 6"
1974 Jensen Healey
In answer to the original question, the 307689 was the 150 HP cam used in the TR5 & early TR6 PI's while 311399 was the later 125 HP cam. 311399 is probably the easiest to find factory performance cam as it was also used in many of the late model detuned TR6’s. 307621 was probably the weakest of the factory offerings.

https://www.chriswitor.com/cw_technical/camshaft_applications.pdf

Rick

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
In reply to # 1493522 by YankeeTR5 Scott....welcome to the rabbit hole. When you say the carbs were rebuilt, who did the work? You or were they done by a shop? If it was you (which is fine, its pretty easy to go thru these carbs) you may want to pull the rich running carb and redo the process. You might find that something was reassembled wonky.

If you are interested in tuneability (which I would be) I stand by my earlier recommendation of getting a set of pistons with the adjustable needles. Replacement needles are cheap so you don't need to source "correct" TR stuff, just make sure they're for a 1.75 ZS. If you had them in your carbs now it would be as simple as turning a long handled allen screw to adjust the single carb that's out of whack (ok, maybe not that easy as you're into balancing both carbs....but you get my point I hope....)

Best of luck. 250's are a great car to cruise.....

Thanks Alice... I mean Dan. Yes I rebuilt the carbs myself. The only thing I din't change from the kit was the butterfly bushing. They seemed to not have any play in them but you may be right about the reassembly.
The tune-ability is important for sure. And I'd like to be able to adjust that. Saw the needles on Moss.

Sorry for hi jacking the thread Chris. Seemed like a natural place to chat as I'm pulling the engine and doing the same work you are this winter. And those carbs have been on my mind of late and what would be the best plan moving forward.
I might just go to the Patton throttle body conversion and be done with it.

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oregon250 Chris P
Salem, Oregon, USA   USA
Berry......It seems like I talked to Moss and also Joe Curto and I was told that the TR4 adjustable jet wouldn't work in the 250....that it was similar, but a little different. I never did try it though. I agree with your reasons for the richness.

oregon250 Chris P
Salem, Oregon, USA   USA
No biggy Scott....hi jack all you want. I'm pretty easy. just ask wyoming250. speaking of him, he bought a set of the adjustable jets from Joe Curto and is in the process of getting them in now. we'll see how they turn out.

I went with the HR270 cam that BPNW offers. middle of the road cam. I talked to Layton over there and he thought it would be just a step up from the cam put in the tr5's and early fueled injected tr6's, but not as big a step as the 290 they offer.

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
What were the comments from BPNW about the idle on the 270? Not that i'm all that worried about smooth idle. I'll gladly give that up for some extra giddy up.

Being new to this car I can't help but think there is some un tapped potential in this engine that is reasonably accessible without to much wallet strain.

YankeeTR5 Dan M
Seattle, washington, USA   USA
A note on cams and the 2.5L Triumph engine: There are lots of choices in cams these days, although many of the old school, knowledgeable guys in the UK claim the TR5/early TR6 PI cam is hard to beat. That said, most cams out for the TR's are symetrical - that is both the exhaust and intake lob profile is the same. That's old school and doesn't really take advantage of, oh, 40 years worth of research in camshaft design maximizing engine performance and economy that's gone on. There are a couple of asymmetrical designs that have come to market in the last 5 years (so pretty recent) that offer very good low end torque (very good for our engine), a smooth consistent torque curve and decent top end power while delivering good economy. They do this by having different cam lob profiles for the exhaust and intake valves that results in intake/ exhaust valves with different durations. If I were looking at a new cam, I go either the old school way (TR5...but hey, I own one so I'm biased) as its been benchmarked to be very good, but I most probably would go asymmetrical (will require some searching for a vendor btw)

One thing I would not do: do not get a cam that movs the power up in the rev band (above 5500)!! The long stroke nature of the 2.5L means that pushing the engine to 6K rpm on a regular basis will guarantee a relatively short life - irrespective of balancing, beefed up internals etc. Its physics....So a good cam will give very good low end torque (which is what one wants) and have a power band that starts low and runs thru 5500. The higher revving cams are fun, until they're not...which usually happens when things disintegrate (pistons, rods, etc)...Long stroke motors do not like and can not handle high revs. For comparisons... the GT6 2.0L engine is "square" and can be made to run reliably up to 8000 rpm. Same basic components (mostly anyway) but the long stroke nature of the 2.5L limits its rev potential (although gives much better low end torque).

Ok...enough of the soapbox. Best of luck with your decision on cam!!

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oregon250 Chris P
Salem, Oregon, USA   USA
They said the idle was smooth, but better to bump it up to a 1000 rpm idle which isn't a big deal. I usually idle about 750 to 800. The 290 he said was a bit lopey. The 270 is an asymmetrical design like Yankee was talking about. Short duration opening with long duration closing on the inlet and long duration opening and short duration closing on the exhaust. When i asked about loosing anything on the low end, he said no.....so I guess time will tell that tale. And he did mention a steady pull. I think the 290 would be too much at least for what I'm looking for, and put the range too high. I like the low end torque. Our old pickup is the same way....long legged. (old J10 Jeep with the 258). eye popping smiley

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
Thanks Chris. I think it's time to call BPNW.
And as I type my buddy is texting me to be at the shop on Saturday to pull the engine

And thanks Dan that is some good info you have imparted there.

Enjoy the PNW sunshine while it lasts

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