Intake port opinions.

[Truckedup]

This was done by an Australian bike tuner I know...The head is a 60 'S BSA 650. These engines stock made about 1 hp per cubic inch....His poert design is based on the XR750 Harley falt track engines that make about 90 hp@8500 on gas from 45 cubes...
His claims are 200 cfm at .410 lift using 28 inches on his flow equiment....His other claims are about 100 HP ( i believe he means crankshaft power) from 888 cc, which if true is quite high for a two valve push rod engine...
I have my doubts on the HP claims but who knows? What do you think ?

[swampbuggy]

Are you meaning the 888cc's is the BSA engine Mark H.

[pcnsd]

I have read some of the articles from those days and IF I remember correctly, the parallel twins were topping out in the low 80;s RWHP against the XR7500 in the low 90's RWHP. Both Ron Woods (Norton) and Shell Thuet (XS650) said they had issues keeping the motors together at those HP levels but both were eventually able to build semi competitive machines for that time by which I mean they were able to drive HP a fraction higher than typical. I don't recall either claiming to match the XR750 in output. Shell Thuet had to have Yamaha build a different head to get there. (OW73?)
Time moves on and technology and understanding advances. Those are very pretty ports and 888cc is bigger than 750cc. 100HP...??? that is a stretch IMO. Certainly not with the stock cases or crank or rods, or just about anything from the stock machine.

Thanks for sharing.

[mk e]

I used to roadrace an XR860...it easily made 100 crank hp, 9200rpm redline but peak hp at like 8600.

[Truckedup]

Are you meaning the 888cc's is the BSA engine Mark H.

A 650 BSA originally, now 888 cc's....I believe this is commonly done for side car racers. I have no idea what is done internally but I believe it bored at the minimum...
The best 750 Triumphs in current vintage road racing make about 78-82 RWHP using drastic intake port modifications....The Triumphs has a 90 degree angle between the vavles, Norton and BSA havr a more shallow hemi with less valve angle and in theory a better head to work with...
Some BSA crankcases can take 90 HP for a short period of time, but some will fly apart at 70 HP.It's a street bike so he may not beat on but briefly..He used a Dynojet chassis dyno and they are known to be optomistic and readings are affected by how fast the engine spools up.And it's possible he had added 10 percent to call it crankshaft power...
But it does look like a nice port

[mk e]

The best 750 Triumphs in current vintage road racing make about 78-82 RWHP using drastic intake port modifications....

82rwhp has to be pretty close it 100 crank, maybe a few short but right in the ballpark and there it they got 888 instead of 750 I'd think.

[Truckedup]

The best 750 Triumphs in current vintage road racing make about 78-82 RWHP using drastic intake port modifications....

82rwhp has to be pretty close it 100 crank, maybe a few short but right in the ballpark and there it they got 888 instead of 750 I'd think.

Well, it might be then damn Dynojet dynos...Inertia dynos are ok for tuning but not for the most accurate power readouts...So it's hard to really compare any numbers..

[mk e]

Well, it might be then damn Dynojet dynos...Inertia dynos are ok for tuning but not for the most accurate power readouts...So it's hard to really compare any numbers..

My XR numbers were all measured on a dynojet. It was ...86rwhp at the dyno shootout at Daytona bikeweek back in '96 iirc, then some changes later and it was 93-94, both dynojet rwhp numbers. One dynojet to another seemed to compare very well, but how to compare to any other type/brand dyno don't know other than for sure there are losses crank to wheel of at least 10% and I''d guess more like 15%-18% about like a car but that's just a guess.

When you say crank are you talking side cover off and grab the crank directly so its true crank hp or do you mean trans output so it includes the primary and trans losses but not tire losses like are also in a dynojet?

[Truckedup]

Well, it might be then damn Dynojet dynos...Inertia dynos are ok for tuning but not for the most accurate power readouts...So it's hard to really compare any numbers..

My XR numbers were all measured on a dynojet. It was ...86rwhp at the dyno shootout at Daytona bikeweek back in '96 iirc, then some changes later and it was 93-94, both dynojet rwhp numbers. One dynojet to another seemed to compare very well, but how to compare to any other type/brand dyno don't know other than for sure there are losses crank to wheel of at least 10% and I''d guess more like 15%-18% about like a car but that's just a guess.

When you say crank are you talking side cover off and grab the crank directly so its true crank hp or do you mean trans output so it includes the primary and trans losses but not tire losses like are also in a dynojet?

By crank I mean a guesstimate based on RWHP.On bikes with chain drive primary and final drives the loses are usally less than 10 %..My vintage race Triumphs were run a Superflow dyno..The readings are 8% or so less than a Dynojet...If you run a bike a Dyno jet, then use a lighter flywheel, the same engine will show more power because it can spool up the inertia wheel faster..Dynojet is still a valid tuning tool but the numbers only apply to other Dynojets...

[Momus]

That's about 115 hp per litre, which seems to be about it for the wide angle hemi bike designs using production parts. I'd say not impossible, but not easy. Some more details on the engine would be interesting.

[Truckedup]

That's about 115 hp per litre, which seems to be about it for the wide angle hemi bike designs using production parts. I'd say not impossible, but not easy. Some more details on the engine would be interesting.

115 hp/liter is very creditable from any 2 valve air cooled engines including OHC...Might be near impossible for any engine needing street manners..
There is very little to no reliable dyno info on old engines like this...In fact the only graphs I see is my own..LOL

[Momus]

The paucity of information on this and many other old engine's details and test conditions makes comparison and discussion speculative at best unfortunately.

I've been fiddling with little Honda 2 valve air cooled vertical single playbike engines- the type fitted to XR75's, 80's and 100's, for about 45 years.
As received they are typically Honda bike- somewhat over engineered bottom ends and a low state of tune top end. These have a reasonable sub 60 degree valve angle and keep their crank and case integrity when enlarged and revved up. A good representative engine at 146 cc with a Takegawa cylinder head, a valve to bore diameter percentage of 46%, around 13.5:1 compression and on Australian pump premium '98' is slightly over 22 hp at around 12500. This is a Dynojet number, I believe from the countershaft and is slightly above 150 hp per litre. I have other engines, stretched further and bigger valved that are considerably more powerful.

[Truckedup]

It's easier to get high output per cc's from a 100cc engine than it is from larger ones...

[Momus]

Perhaps has something to do with the size of the engine though the BMEP is not that good. They do rev up.

More likely though the Triumph fettlers are not trying hard enough. Triumph twins are everywhere in motorcycle sport and operated with reasonable funding yet the crucial cylinder head aspect is at least 50 years behind. If the Jap aftermarket can provide affordable high quality die cast racing cylinder heads (and cylinders, cranks, cases etc) for a relatively tiny number of play bikes surely the British aftermarket can do better and make a high BMEP, low rpm conversion.

[Truckedup]

Perhaps has something to do with the size of the engine though the BMEP is not that good. They do rev up.

More likely though the Triumph fettlers are not trying hard enough. Triumph twins are everywhere in motorcycle sport and operated with reasonable funding yet the crucial cylinder head aspect is at least 50 years behind. If the Jap aftermarket can provide affordable high quality die cast racing cylinder heads (and cylinders, cranks, cases etc) for a relatively tiny number of play bikes surely the British aftermarket can do better and make a high BMEP, low rpm conversion.

The Triumph twins I modify for land speed racing have been out of production since 1982 and even then were based on 1930's high performance technology.1.7 -1.9 hp per cube is about good as it gets. Some turn over 8000 rpm but it requires $2000 crankshafts . The Triumph I built was the fastest of it's class for 5 years and still holds a few speed records..I'm just a hillbilly mechanic but I applied stuff learned here on Speedtalk listening to guys talk about Chevys. ..The first photo in this thread is a a similar BSA that was a 1962 design with less valve angle and more shallow hemi...