Discussion in 'Triumph (Classic)' started by Fast Eddie, Mar 6, 2019.
The 500s revved like a two stroke, I loved ‘em!
No commonality with the 750 heads though.
The story is with the parallel port head is higher port velocity for a faster fuel charge burn.Supposedly it's the best street head from Triumph for the B engines.Depending how you look at it, it may also have better , different or higher turbulence..However,without proof of flow tests this is all just speculation...
I wish we had a Triumph version of Jim Comstock who would flow test them and give proper data.
I’ve tried getting him interested in Triumphs. I failed miserably...!
The Triumph heads has a few faults, wide 90 degree valve angle means a deep Hemi chamber. This requires a high dome piston for higher compression that created combustion issues and can affect air flow into the cylinder.And port velocity is not the best .Raising the intake port floor and increasing piston quench helps a lot...
As bad as Triumph heads are it's never stopped them from winning against the supposed better heads of same displacement N and B model bikes...
Careful, that last sentence could get you into trouble on this site !
I’m aware of the hemi head issues of Triumphs. I’m a big fan of squish (can’t bring myself to call it quench).
In the past I’ve welded up combustion chambers and done the bathtub squish thing. It worked very well, but it’s a LOT of welding and I’ve heads go soft before due to it.
The late heads have quite a nice squish band anyway, I think a little careful measuring and perhaps barrel skimming could yield almost as good results as the bathtub squish but with none of the work / cost / agrovation!
I just rebuilt my 79 T140 D..The stock quench is around. 060, too much to be useful on the narrow circumference band. Milled the barrel .022". then using a .008" copper cylinder base gasket , .049 head gasket,got a quench of .032". This is with .020 Triumph pistons, 7.9 stock compression...The actual static compression ratio is about 9-1 but with the quench turbulence it runs on lower octane fuel and needs less spark advance and makes more torque than stock...Down side is $40 for Smith Bros custom length push rods and modifying the push rod tubes, no cost..
My experiments with quench on my record holding land speed race 650 Triumph..Using tight quench I make the same power as the competiti0n, Triumph and BSA that are using more compression, hotter cams and bigger carbs.
10.5 compression MAP "tight quench" pistons, .035 gap...
Nice pics and info Hillbilly.
I agree that squish isn’t really working well at .060”. And I’m with you that the .030-.040” range is where it’s at.
My belief (not based on any hard evidence) is that squish (quench) is actually more beneficial to street bikes, as it is less beneficial to anything running race fuel.
I still think it’s worth it though, even if it’s not showing more power, I think it gives other benefits in terms of cooler running etc.
It works with racing fuel because that's what I use in my race bikes, VP leaded 108 octane...And quench is often the subject of American drag and circle track racers that also use racing fuels..What I don't know if part of the thinking on extreme rpm engines like Formula 1
My point was only that race fuels, with high octane, will allow a high CR that gives good BHP even without a squish band and will probably therefore generate similar peak BHP to a motor running a squish band.
Whereas a bike running ‘pump gas’... especially a Triumph... would not be able to get to that same CR, as the combustion chamber design would cause pre ignition etc.
However, a Triumph running a good squish band can run a high CR on pump gas without issue.
Like you, I personally used to run squish in my race motors (where possible) but I think it gave the biggest benefit on an 850cc Triumph stroker motor with just over 11:1CR that I ran on pump gas with no issues. I’m pretty sure that wouldn’t have been possible using the old lumpy 11.:1 powermax’s !
Not exactly, the combustion chamber design has the most effect on combustion,primarily rate of burn...It's generally accepted that combustion need to be completely finished by 14 degrees ATDC for best power..It's also shown that the least total timing to achieve that can make more usable power..Tight quench has the ability to do this....
There's much more to detonation resistant gasoline than octane...You have to also consider evaporation rates at various temperatures..
What ign timing do you end up with when running a good squish?
About 36 degrees total advance.To be honest I have not experimented with timing very much on the dyno..But it all depends on the advance curve because if detonation isn't a factor, a bit more total advance can sharpen up mid range power.
This Triumph factory letter on late T140 is of interest, read #3
That’s a great letter, thanks for posting!
Very interesting comments on the head and sparks plugs.
That timing comment supports my own playing around on the dyno with various Brit bikes that a few degrees either side of ‘optimal’ seems to make no difference at all.
I am however a believer that Brit bikes in general do benefit from a BIG fat spark.
Yes, the big spark..I always find the Triumph engine runs better with the gap at .035 provided the ignition can fire it consistently. It's said a gap wider than necessary will retard timing two degrees.... I use NGK Competition plugs in my race and street Triumphs..The ground electrode is shorter, extends to about the middle of the center electrode. This supposedly adds more intensity to the initial spark kernel...but the plugs will wear more quickly...Ignition engineers claim a fine wire electrode plug will add a bit of HP...Some engine tuners see a slight loss of power on the dyno with fine plugs
My experience on the land speed racer Triumph is the bike ran a bit faster on the NGK Competition copper plugs compared to NGK G fine wire plugs.
You might find Speed Talk and interesting forum https://speedtalk.com/forum/index.php?sid=9492727b2a872095c1184fcb8eb5e671
There's many professional race engine builders and engineers on there. It's mostly about drag racing and oval track but there are a few bike guys ...