On 15/5/2022 5:25 pm, Noddy wrote:
> On 15/05/2022 4:04 pm, John_H wrote:
>> Noddy wrote:
>
>>> You clearly have a love for Triumph cars and are happy to talk them up,
>>> but I think you guild the lily somewhat. I have zero experience with
>>> them (thankfully), but despite that I found your comments about their
>>> ""high VE" resulting in a "much higher than typical bmep" to be a cause
>>> for the engines to not run properly on 98ron fuel to be perplexing.
>>
>> Than let me take it a little bit further at the risk of confusing you
>> further.
>
> ROTFL :) Go your hardest. I'm up for it :)
>
>> As the octane rating for Super petrol dropped, as it did in
>> the 80s (you mentioned 98RON not me), the normal solution was to
>> retard the ignition timing (nowadays most EFI cars do it
>> automatically).
>
> Actually, you mentioned 98ron in a post you made on Friday when you said
> the following:
>
>> 9.5:1 static IIRC.  The Escort Mk1 twin cam, which was a very
>> successful rally car of the same era ran around the same CR and I'd
>> also doubt if it would be able to handle 98RON bowser fuel for the
>> same reason whereas relatively crude American V8's ran 12:1 or more
>> but had much lower VE..
>
> Just sayin....
>
>> What effect do you think retarding the ignition has on intake vacuum?
>>
>> I'll leave the rest for you to work out.  :)
>
> Right. So what you're saying *now* is that retarded the timing and
> *that* caused the thing to not run properly.

Answer the question Darren.
>
> Seriously? Just exactly how temperamental *were* these things?
>
>>> The reason for that is because unless I'm missing something that you
>>> haven't mentioned, there was nothing outstanding about either the VE or
>>> the BMEP rating of the injected Triumph engine. In fact, if you look at
>>> the specs you'll find that the BMEP of the 2.5 PI engine was only a
>>> poofteeth greater than that of a Red Holden 202, and regardless of how
>>> much of an improvement in VE the injection manifold made over that used
>>> with carburetors I'll happily bet my left nut that the VE was nothing
>>> like 100% which means the 9.5:1 static compression ratio was the hard
>>> upper limit.
>>>
>>> This one seems to be getting along nice, and while there's no mention of
>>> the fuel used, I would assume it's the regular 95Ron used in the UK
>>> these days.
>>>
>>>> https://www.youtube.com/watch?v=LyBL2wq-AX8
>>
>> Yes, he mentions putting a milder cam in it.  What effect do you think
>> that had on the intake vacuum?

FWIW, from 73 the MK2 used a milder profile cam, the same as the one
used in the MK3 GT6. That was done primarily to smooth out the idle. I'd
agree with that reasoning, I hate lumpy idling.
>
> A milder cam? I didn't watch the entire video, but I would imagine the
> factory cam in something like a Triumph 2500pi would be pretty tame,
> considering that it's fuel system relied on a solid manifold vacuum to
> correctly adjust itself on the fly.

Keerist you're stupid. It uses the manifold vacuum to *signal* the PI
system that load is increasing or decreasing and it is *calibrated* to
suit whatever engine, and cam, it is used on.
>
> Still, I'm happy to stand corrected. A quick look online and I find

No you're not, you'll kick up a stink, change the topic, or *run away*.

> these figures:
>
> 2500pi Mk.I:
>
> Inlet opens @ 18 deg BTDC
> Inlet Closes @ 58 deg ABDC
> Exhaust opens 58 deg BBDC
> Exhaust closes 18 deg ATDC.
>
> That's a pretty short, sedate cam timing in anyone's language, and it's
> difficult to imagine how a "milder" cam would have made any appreciable
> difference to anything compared to that. Especially with regards to
> manifold vacuum.
>
> Just for shits and giggles value, look at these figures here:
>
> Inlet opens @ 35 deg BTDC
> Inlet closes @ 75 degrees ABDC
> Exhaust opens 70 deg BBDC
> Exhaust closes 40 deg ATDC
>
> That's quite an aggressive timing profile compared to the much more
> sedate Triumph figures, and the casual observer could be forgiven for
> thinking they come from a performance engine. But they don't. They're
> the standard cam timing figures for a Holden 161 red motor.
>
> Now, if you're going to start in by saying differences in induction
> systems and volumetric efficiency are the key factor in determining the
> cam profile used in a given engine for a given role and this is
> highlighted here by the significant differences between these two
> profiles you'd be exactly right, but the point is that the Triumph cam
> is *extremely* soft to begin with and I can't imagine anything "milder"
> than that and the thing still being able to run and make as much power
> as a blender.

Darren, you clearly don't have a clue. The better the volumetric
efficiency, the more you can dispense with heaps of lead and lag in the
valve timings. The more you add improvements to the cylinder head's
*breathing* ability, the necessity for early intake valve opening and
late exhaust valve closing is minimised. That's why manufacturers moved
to heads with 2 inlet and two exhaust valves, lots of volumetric
efficiency gain and less need to have lots of valve overlap. That's
without taking into consideration you can get higher revs with smaller
valve so the *torque improvement* leads to *higher HP figures*. Did I
mention it makes engines run smoother if the cam can be *milder*? What
the above sets of valve timing figures are actually telling you is the
2.5 PI engine breathes very well whereas your *alternate* and, I must
say, *irrelevant example* of the Red 161 motor is a piss poor breathing
engine and needs a lot more valve overlap in order to have sufficient
*time* to get gas *flowing* into the cylinder for an adequate fill.
Another point of note here is that good air flow, and that includes air
speed, both in the manifold and in the cylinder, lends itself to a
*faster burn time*. Why is that important? Well, a faster fuel burn
gives *less time* for the *end gas in the combustion chamber* to
pre-ignite or detonate. That means you can use more ignition advance
(not always a gain) or, better, a *higher* static compression ratio*.
The higher static compression ratio is what Triumph opted for with the
2.5 PI. The TC version had 8.5:1 whilst the PI version ran 9.5:1
Does that mean the PI actually flowed air better than the TC? Well, yes
it did because it didn't have the restrictions caused by the need for a
*venturi* that carburettors must have for their operation. From 73 on,
the PI ran a static ignition advance of just *2 degrees*. That is very
telling.

You're not actually making your point, you're *proving* John's point.
You're also proving you don't know what you don't know.
>
>> Clue:  It most definitely wouldn't run properly on 95RON with the
>> standard cam.
>
> As much as you say this, I find it difficult to appreciate how anything
> that is set up as soft as the 2500 pi engine *clearly* was could be
> *that* fussy about fuel quality that it would refuse to run right on
> anything other than high octane fuel.
>
>> The other common modification in the 80s was to replace the Lucas
>> system with triple DCOE Webers for a considerble loss of performance,
>> as would also be the effect of a milder cam.
>
> Considerable over certain rpm ranges. There would likely be no
> difference in others.
>
>> I'd also be guessing that Zeno's mate either runs his on bug juice or
>> else has modified it to run on bowser fuel.
>
> Assuming his car runs the Triumph engine, and we have no idea on that
> one way or the other.
>
>> Supposedly Super petrol in the 70s was around 100RON.  Different
>> sources will give you different figures but whatever the real figure
>> it certainly dropped off when the lead content was lowered during the
>> 80's.
>
> It did. When I drove things like XU1 Toranas and GTHO's as daily drivers
> I had to buy Toluene from a local fuel merchant and give these things a
> heavy dose of it to stop them pinging their heads off. But then they
> were engines with very high compression ratios and fairly decent
> induction systems that made lots of power for their capacity.
>
> That's not what I'm seeing in the 2500pi engine. Not by a long shot.
>
>
>
>
>

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)