Engine tune-up? Where to start? So many questions... (long)

Post by **KirstMin** » Wed Aug 23, 2006 4:21 pm

Peetee wrote: On a 1300 the best £/bhp/character retention improvements go along the lines of:
alloy inlet+carb
flowed/large valve cylinder head
cam

I'm not sure i completely agree! You'll be strangling the hell out of this lot if you dont change the exhaust and manifold. That's why a stage 1 tuned kit always includes a wider bore exhaust system. Addressing the head and cam is moving towards stage 3 tuning and that is a waste of time if you cant get the gasses out. With a 948 maybe its ok but not a 1275.

Post by **JimK** » Wed Aug 23, 2006 4:23 pm

OK, noob here. What's LCB?

Post by **paulk** » Wed Aug 23, 2006 4:33 pm

Long Centre Branch

Post by **bmcecosse** » Wed Aug 23, 2006 4:42 pm

Using a separate inlet manifold with NO exhaust (or water) heating IS worth several extra HP on the 1275 engine - Mr V ran tests to show this. In fact - most of the extra power a 1098 Midget has over a 1098 Minor comes from the inlet gas NOT being exhaust heated - the actual twin carbs are worth very little, it's the lack of inlet heating that gives almost all the benefit. I would bet that the air filter casing is the main power loser on your engine - and then the inlet manifold. Try a run without the casing - take it all off including the mounting plate - it could even be blocking the little holes on the front face of the carb - and this seriously compromises the operation of the carb.
LCB = Long centre Branch. It IS worth extra horsepower over the standard Minor/Mini exhaust manifold - the V comment about little extra power is by comparison with the Mini Cooper 3 branch exhaust which is quite good as standard - but not easy to squeeze into a Minor . The Mini standard exhaust manifold is exactly the same as that fitted to later 1098 Minors- it is of course far better than the earlier manifold fitted to 948 Minors - the one where the inlet bolted on the top with 4 bolts and a 'hot spot'.

Post by **JimK** » Wed Aug 23, 2006 4:42 pm

OK, I googled for pictures.What does this actually do?

I've seen performance manifolds that have one pipe per cyclinder carefully matched in length to make sure pulses of gas from each cylinder are time-domain multiplexed* into the exhaust pipe. How does the LCB help? It's still got fewer pipes than cylinders.

* I'm such an engineer...

Post by **Packedup** » Wed Aug 23, 2006 4:46 pm

I'd agree that there's a point where getting gasses in is going to acheive next to nothing if they can't get back out. Plus the pumping losses of forcing the gasses down the normal system are going to be pretty large too.

In fact, a change of exhaust is probably one of the first things to be doing, coupled with (but not necessary in this case) a change of inlet tract. Give the air as easy a time as possible in, and as easy a time as possible out, whilst still keeping the velocity up to improve cylinder filling/ extraction. So a 1.5" carb on a reasonable inlet (I reckon the cast one isn't all that bad), and a slightly larger exhaust with free flowing boxes should help give a bit more go without ruining the character of the car, IMO

Post by **chickenjohn** » Wed Aug 23, 2006 5:41 pm

Has anyone tried the trick in the club manual of (carefully) hacksawing a small gap between the inlet and exhaust parts of the manifold- thus making the induction gasses slightly cooler and therefore denser, therefore more power? Does this actually work??

Post by **JimK** » Wed Aug 23, 2006 8:58 pm

So, I took the airbox off just now to see what was underneath:
http://www.flickr.com/photos/25441688@N00/223104501/
This shows that the hole in the plate has been enlarged to match the carb opening. Approximately.

This photo shows the quality of the work:
http://www.flickr.com/photos/25441688@N00/223104545/
It also shows that the entrance to the carb is well grubby. Is that dirty surface the one that lets in the air? The dirt can't be helping...

Another question - what's the lump on the intake manifold in this pic:
http://www.flickr.com/photos/25441688@N00/223104562/

Chickenjohn: I wondered about doing that. Kevin mentioned cutting off the intake and using a new intake manifold, but it looks like they could be separated.

EDIT for many typos...

Post by **Peetee** » Wed Aug 23, 2006 9:41 pm

I'm not sure i completely agree! You'll be strangling the hell out of this lot if you dont change the exhaust and manifold.

Yes i agree but Jim wanted to keep the minor exhaust rasp. Thats why I mentioned the stainless standard bore system which flows better.

The Mini standard exhaust manifold is exactly the same as that fitted to later 1098 Minors

I think what is being referred to is the MIni `1000 manifold. The exhaust outlet matches the minor's downpipe but the inlet is sized for a 1.5 carb.

Another question - what's the lump on the intake manifold

It's a casting to allow a threaded hole for a brake servo pipe take off.

I'd agree that there's a point where getting gasses in is going to acheive next to nothing if they can't get back out

This is another good reason for a rolling road set up. when you achieve ideal tuning you reduce the exhaust gasses (and waste fuel) to a minimum. less waste needs a smaller bore.

Post by **Packedup** » Thu Aug 24, 2006 12:47 am

Peetee wrote:
Another question - what's the lump on the intake manifold
It's a casting to allow a threaded hole for a brake servo pipe take off.

You'd think so wouldn't you? But http://www.flickr.com/photos/25441688@N00/221963165/ (first pic in the thread) shows a tapped and bolted servo take off!

This is another good reason for a rolling road set up. when you achieve ideal tuning you reduce the exhaust gasses (and waste fuel) to a minimum. less waste needs a smaller bore.

Umm - Power = volumetric efficiency + fuel + spark (+ compression, but that's irrelevent here). So to get more power over good condition standard tuning means more air in, and so more air out! Setting everything up properly should see more power produced for a given volume, but there's still the need for more in and out to realise decent power gains!

Post by **Stig** » Thu Aug 24, 2006 8:24 am

I guess the point was that if everything's set up correctly then you get more power for the same amount of flow. Then more flow = more power too.

Large bore exhaust isn't necessarily what's needed, the main flow restriction is in the silencer. I initially fitted my larger s/s silencer with the original (narrow bore) pipe as the new s/s pipe had been squashed in transit, I didn't notice any improvement on that once I eventually fitted the larger bore pipe. It has, sadly, lost the Minor's happy-farty noise though.

Post by **Peetee** » Thu Aug 24, 2006 8:36 am

So to get more power over good condition standard tuning means more air in, and so more air out!

I don't dispute the reasoning but it's only true up to a point. Go too large and you reduce scavaging where the speed of the exiting gasses helps to empty the combustion chamber and thereby improve volumetric efficiency. Maniflow have done their sums and actually recommend two different bore systems based on the engine size.
Vizards book is very revealing about the state and quality of some of the large bore systems available. some of them looked like they had been deliberately sat on! I have fitted a stainless standard bore system and found it to be less restrictive than a stock mild steel unit.
And again we get back to the Minor rasp. my recommendations were based on Jim's requirements.

Post by **Kevin** » Thu Aug 24, 2006 1:21 pm

Has anyone tried the trick in the club manual of (carefully) hacksawing a small gap between the inlet and exhaust parts of the manifold- thus making the induction gasses slightly cooler and therefore denser, therefore more power? Does this actually work??

It does get rid of a hot spot but is usually done with other upgrades, I dont know anybody who has done this on its own but its worth while doing to remove the hotspot, and its not that easy to just put a cut in there its best if you have 2 manifolds and once seperated clean them up nicely and you can get a reasonable gap, if you get a mini 1000 one you want to retain the exhaust half of it as according to vizzard it flows better than the Moggie one, and it keeps the exhaust note

Post by **Packedup** » Thu Aug 24, 2006 3:11 pm

As someone who has spent a very hot summer afternoon trying to seperate manifolds with a hacksaw - Get two and use a grinder!

Unless you like losing more weight than a marathon runner in a desert...

Post by **chickenjohn** » Thu Aug 24, 2006 3:41 pm

Packedup wrote:-snip-
Unless you like losing more weight than a marathon runner in a desert...

I could do with that! ;) but then it would be difficult to determine whether the increase in performance was due to the cooler inlet manifold or improved power to weight ratio ;)

Post by **bmcecosse** » Thu Aug 24, 2006 3:55 pm

Cut the old inlet off and throw it away - and get an MG Metro alloy inlet manifold. It is VERY much better shape and completely eliminates inlet charge heating. You can spend a while 'improving' it a la Vizard - but to be honest I doubt it makes much difference - it's good just as it is. Last 2 I bought were £5 each on ebay. One is on the 1098 Minor with 38HIF and the other is on the 1360 Mini with 44HIF.

Post by **JimK** » Thu Aug 24, 2006 4:04 pm

bmc: Do you mean this sort of thing?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... %3AIT&rd=1

I guess I have to make sure I get one that the HS4 carb will fit on? There are some that have four studs in a square, whereas my carb has two bolts diagonally opposite eachother.

Can I simply leave the water pipes unconnected?

EDIT to add: What about this?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... %3AIT&rd=1

Post by **Stig** » Thu Aug 24, 2006 4:37 pm

The first ebay one isn't an MG Metro one, it's an aftermarket manifold. As far as I know, the MG Metro manifold only takes HIF carbs, not HS carbs. It's definitely got four studs in a square. An aftermarket one may well take either so worth asking the seller to measure stud spacing for you. FYI the HIF is an eighties carb whereas the HF is of sixties vintage.

You can leave the water pipes unconnected, mine are plumbed into the heater return. Water heating improves economy but might reduce power slightly though nothing like as much as using direct exhaust heat.

Post by **alex_holden** » Thu Aug 24, 2006 4:38 pm

JimK wrote:EDIT to add: What about this?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... %3AIT&rd=1

His capitalisation, spelling, and punctuation make my brain hurt.

Post by **JimK** » Thu Aug 24, 2006 4:58 pm

alex_holden wrote:His capitalisation, spelling, and punctuation make my brain hurt.

Indeed. Why do people feel that these things are optional? ALL CAPS IS LIKE SHOUTING and some appear to have no shift key at all and write in lower case with no punctuation like this i cant stand it

Bah.

Stig28: Thanks, more useful information. Nice to know about the different carb vintages; that will help me work out where I'm most likely to find a new manifold to fit my HS4 carb.