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I seem to remember something about 4 into 1 manifolds (many derivitives including stock) give better low rpm torque. 4 into 2 into 1 make for better breathing at higher rpms, hence more power.
Smaller dia primary pipes will help with mid-range, and larger diameter (41-44mm) with longer runs will help with high rpm power, particularly if the all primaries are of the same length.
If you have a carby 3.5, you can get a definite and cheap benefit by fitting 3.5-3.9 injection manifolds and a free flow muffler..
They are designed to increase torque by having very long secondaries. The standard 3.5 carby manifolds are not very free flowing.
I took extractors off my old carby 3.5 and fitted injection manifolds and got a definite increase below 3K revs, and no leaks, and less noise inside.And they fit perfectly, and are not close to the starter or floor.
Regards Philip A
Reading back. I did forget to mention that I reduced the pipe size back to 2 1\4 behind the rear axle. And, it did have a pair of modified Harley Davidson baffles fitted into the mid and rear pipe sections to give the little bit of back pressure needed to reflect the return pulse back up the extractors to begin valve seal. And of course, to placate Mr. Plod.Quote:
Originally Posted by shorty943
I remember reading some thing about exhaust theory, in a borrowed copy of "Tuning for Speed", by either Ted Turner of Triumph fame, or was it Phil Vincent. And again when I had to build up a new system for my racer. Slightly too tech for a steam ship driver.
A nice free flowing exhaust does not have to be raucously loud.
Apparently, we are not allowed to scare the neighbhours, with loud engine noise.
As far as I know, a turbo engine automatically gives back pressure because the system has to work against the compressor turbine, so the valve side of the exhaust manifold must be slightly back pressured.
With a top fueler, an engine that can drink almost 200 litres of fuel in a few seconds needs to get rid of waste. The best place for a drag engine exhaust gas is out. Doesn't matter where or how, just get rid of it, there is some more coming right behind.:twisted:
have spent many hours two up in a buggy with a racing 1200 Datsun,,,
ah,, memories:p
https://www.aulro.com/afvb/images/im...007/08/151.jpg
dig the drivers side front wheel track-----
Strangely capable little car weren't they. The little coupe I had would out run any thing except a good V8. I honestly have no idea just how fast it was, because it ran out of speedo 1,000 RPM before red line in THIRD gear.:twisted: But it ate any six that came up against it.Quote:
Originally Posted by Pedro_The_Swift
Yep, happy memories.
OK, I got that the wrong way around... 4 into 2 into 1 have better mid range torque. 4 into 1 better top end power. The reason is that you get an acoustic reflection at each change in the orifice. With a 4 into 1 you only get one (bigger) reflection and you must try to set the lengths up so the reflection rebounds off the exhaust port as it opens to get the scavaging effect. This is hard to tune and generally only works over a limited rev range. 4 into 2 into 1 gives two reflections and two oppertunities for scavanging rebounds and therefore they tend to have a positive effect over a greater rev range. e.g. V8 supercars have many stepped diameter changes in their primaries - causing even more reflections.
Oh and the reason a 4stroke needs some back pressure is to to increase the mass of the inlet charge. eg if the exhuast port was connected to a vacuum, yes you will get good volumetric efficiency however the whole charge in the cylinder will also be very low pressure and density. So it's a compromise situation. Perhaps the best arrangement is to have lower than atmospheric pressure when the exhaust port opens and then increase the back pressure as it closes.
HPC will coat anything you send them walker..Quote:
Originally Posted by walker
They're in your corner of the nation!
So if 2 1/2 to 2 5/8 is good for a single system, what size for a duel system.
Or is that totally out of the question?;)
Get extractors (pacemakers if you have the $$$, or contact Triumph Rover spares)
2.5" straight thru exhaust with medium sized hi flow muffler.
Expel the system just shy of the rear of the vehicle tucked up in one corner facing downwards (to the road)
No cats, no secondary muffler/resonator.
This gave me about 10% better fuel economy and my 3.5 turned the 37" maxxis creepys with standard gearing no worries.
And being tucked up well it never got damaged!