Voyager 03 Manifold improvement
  There maybe a simple modification for the Voyager (and Quasar) that appears to release more power - and doesn't cost a fortune...or take long to do!

I was perusing the web and came across this site. Bob's Bug site Here was an interesting site about Reliant tuning and mods by someone who appears to think - check out the engine build page! 850cc Engine build

While looking through the site I found this nugget of information...

"This modification to the inlet manifold has been developed by Rebels Racing I have done this for a number of Bug owners (including myself) and can report that it makes a significant difference better starting, quicker warm-up, better pull throughout the rev range" and there was this image...

I wrote to the chap to ask more about the manifold modification - this is his reply.

The manifold modification was "discovered" by the chap at Rebels Racing who used to work for Reliant towards the end of their manufacturing days. He prepares and seals all engines used in the Rebels class of oval racing so that their spec/output is the same for all competitors. He had a newly built engine on his dyno fitted with a brand new 4-branch exhaust manifold, and noticed something unusual about the "blueing" of the down-tubes as the engine warmed up. He expected, as you or I would, that cylinders 1 & 4 would heat up quicker because of the tendancy to run weak owing to the extra distance gases have to travel from the carb. However, I believe that he observed cylinders 1 & 3 to be making the pipes go blue first. He wondered if this might be caused by the incoming charge vortexing down the carb and first part of the inlet manifold. (A bit like water going down the plug-hole!!) So, he machined out the material as shown on the photo you've seen and tried it again on the dyno - to his amazement, the engine produced 23% more power at the top end than any engine he'd done before. That was all he was interested in - more power for the race boys. This info was passed to me by the owner of a Liege kit car which also runs the 850 Reliant engine who had spent the day at Rebels Racing. Since then, I have modified a number of these for people who have reported back the same things that I found. The most recent feedback I got was from a chap who's been running one for 3 months - exactly the same feedback - quicker warm-up (3/4 a mile instead of 3 miles) better pull throughout the rev range AND 11% better fuel consumption!!! As he said - "It's not often you can have your cake and eat it!!"

His 'photo' is here -

So armed with this information I got myself a spare manifold and got it machined..... (only £32, all done!)

I have had @35mm of material machined away.

Looks like I'm not the only one to do this as Mark Crowson as wrote to me recently:

"I've been checking out a company called 'Rebels Racing' who build miniature race cars styled like something out of a ZZ-Top video. The company sells the cars for just £6,500 and they're fitted with an 850 Reliant engine and gearbox. All the engines are built at the factory, dynoe'd to give a standard power output, then sealed to prevent further modification. They're more or less standard except for a piper cam, better valve springs and a Weber carb. Unfortunately they're rather secretive about the power output. This is the same company that discovered that, if you use a standard Reliant inlet manifold, it's possible to get power increases of up to 27% by carving away the bridging material between adjacent ports at the cylinder head end of the manifold."


"I'm sending you a copy of the original article in the Bond Bug mag dealing with the manifold mod, along with a couple of pictures of my own manifold. As you can see, I first milled out the bridge between adjacent ports, then blended them with a rotary burr in a die grinder."


"I talked to Dick Harvey a couple of years ago about whether you could remove all the material between the 2 manifold ports. He reckoned this was a bad idea. The firing sequence is 1:3:4:2, or 3:4 2:1, ie there's a small interval between 3&4 drawing fuel through the manifold, but a long interval between 4 and 3. Because of this he reckoned that using a common feed for both cylinders would cause charge depletion for No. 4 cylinder.

I think that the reason that this mod works at all, (cos logically it shouldn't!), is that the ports through the manifold are smaller and more restrictive than the ports in the head. Even though connecting them together must slow down the speed of the charge hitting the inlet valve dramatically the increased flow seems to outweigh the disadvantages. I'd guess that the real solution would to be to have a manifold with one port per cylinder but it being equal in flow rate to the inlet ports in the head.

I've fitted my modded manifold but, the way the new Quasar's running at present it's impossible to gauge how much of an improvement it is. I guess you can always put your Voyager back on the Dyno and find out for sure."



But does it work....?

13 December 2003
After fitting the carb back to the machined manifold I thought it was running 'a bit weak'. But I found (with the aid of a Gunson Colortune) it was running massively weak - I must have wound the mixture screw in (or was it out? I needed to make it richer anyway!) about 5 full turns!I had to readjust the tick-over several times while doing it as well! Once I got it rich I turned it back to a 'bunson burner' blue and it was fine - ticks over smoothly - so no air leaks or anything to worry about.

Only had a relatively brief blat about on it (in the rain...) and it does seem quite better a bit better. Seems like there is rather a lot more power 'low down'. Obviously it needs a dyno test to be sure - but it picks up very well and does seem much smoother.

Time will tell - I'll keep an eye on the fuel consumption, which was currently @65mpg - if it improves to 70mpg (the promised 11% increase) and warms up quicker (which I think it does) I'll assume the power claim is also possible....!



Updated 14/12/03