Morris Minor Owners Club

Hello folks.
My car is fitted with a mid-tuned 998cc engine.
Spec is
998 bottom end with flat top pistons
1098 camshaft
12G940 head
HIF38 with AAA needle
K&N filter

The exhaust is one that was fitted to the car when i got it, a homemade affair using the Ital twin downpipe, it had a 1275 in it when i got it.
My question is the exhaust diameter.
It is 1.25". If it is a straight through exhaust, will that be adequate? You get in the Mini world and they all say 1.65" is optimum. I just wondered if it will be causing it to suffer higher up in the revs due to not being able to get rid of the exhaust gasses quickly enough.

Your thoughts please.

The exhaust pipe of the Maniflow system for tuned 998cc engine is 1 1/2".
I would go no larger.
Bigger is not always best.
You can loose flow if the pipe is too big an internal diameter.
See Vizard for details of pipe size in relation to power output.

http://www.maniflow.co.uk/index.php?vie ... oduct=1496

Hi Phil,
Yeah, 1.5" is what i was thinking about really, to be honest that was what i thought mine had on it. partly as it was running a 1275. It was only when measuing that i saw it was 33mm.
I assume it won't cause too much of a restriction?
My.Vizard book is at my dads currently.

Well, the homemade exhaust had one silencer under the passenger front footwell, then a pipe to the rear. This set up was ridiculously loud. A really, truly ugly loud too. I'm not adverse to a "sporty" sounding exhaust, but it was rubbish.

So today i cut it off just after it goes over the axle and fitted an old stainless backbox from a Triumph Herald. It isn't a straight through silencer, but it is so much quieter, it makes it a joy to drive.

I will at some point purchase or make a more suitable exhaust system, but for my current needs, it doesn't appear to be restricting it so much.

Oh, the Herald exhaust is also 1.25" bore, but was fitted to a 13/60 Herald, so can't cause too much of an issue on a wee 998!

The original 1958 948 engine was modified over the years prior to the restoration in the 1990's, and ended up with +0.060" bores and flat-top pistons, 2A948 Cooper 997 cam, flowed 12G295 Cooper 998 head, H4 SU and a Howe LCB that had a 1 1/2" OD outlet. The exhaust system was 1 5/8" OD (1 1/2" ID) and had 2 straight through silencers - one just after the LCB and the second at the end, fitted between the spring and the fuel tank. This was in the 1970's, so well before the collective knowledge of Vizard et al was made available.

This engine is now fitted in a Frogeye Sprite (not mine), and I met the owner not long after it was fitted and asked him how it went. He said that after 'zipping up to 80, and frightening himself', he thought he ought to do something about the standard drum brakes and suspension - since then he has, and the engine is still running well. Still with the +0.060" pistons fitted in 1970, and the standard journal BMC exchange crankshaft fitted in ~1967/8, and balanced in 1970 by Oselli.

I tried to upload a picture showing the Frogeye alongside our Minor at a local car show 2 years ago, but it will not let me - don't know why as it is the same format (.jpg) as all the others I have uploaded - will contact the webmaster.

2 silencers are definitely the best arrangement, and it made for a very nice classic A-Series with LCB growl, but not unpleasantly noisy.

When we fitted the 1380 as part of the restoration, I bought a Maniflow large bore LCB, which turned out to have a 1.75" OD outlet. So following Vizard, who says the exhaust should be 2" for 100+ bhp, I cut off the end of the LCB after the collector and fitted a 2" OD outlet, followed by 2 x 2" OD oval Jetex silencers, one in between the crossmember and the 'over axle' section, and the second at the rear, as before. It was slightly loud, and had an unpleasant drone when cruising at ~4,000 rpm, or 80 mph in 5th, so fitted a small 3rd Jetex 'cherry bomb' silencer immediately after the LCB, which eliminated the drone, and also means that noise tests at some MG's On Track days are passed comfortably with ~90/92db at 5000 rpm.

Richard
I went down the same path except that I fitted 998cc flat top pistons fitted to fully floating small end rods & lightened flywheel. Started off with the H4 carb but then fitted a pair of HD4s. The LCB manifold was a S/H Janspeed item with a 1 1/2" outlet.
I also had to increase the outlet pipe size to 2" on the Janspeed/Maniflow LCB fitted to the 1380cc. The exhaust side exits just in front of the rear wheel and is currently fitted with a TI- (Bainbridge) AN-181-T which has reasonably good flow and has up to now passed all scrutineering noise checks. The engine below used to run without any silencing and what a lovely noise it was.
I am tempted to go for a Maniflow three into one as one of the next engine mods.