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MG Midget and Sprite Technical - Fast road cylinder head on standard engine

Good afternoon, sorry to follow Les's earlier thread with one so similar, but I didn't want to hijack the other thread with a slightly different question!

I missed the recent rolling road session at Aldon (was being patched up in hospital!) so missed the opportunity to canvass opinion across a group there so: I have a 1275 Sprite, and have spent the last couple of years getting it reliable and sorting the body/interior (I know, I know, but I have three small children!!) so now have a base from which to look at improving the performance. I thought I would start with a fast road cylinder head, and thought I would use Peter Burgess (having heard nothing but good reviews and he's only just up the road!) and then move on to a faster cam later (probably a Swiftune). But will I notice much performance increase in the meantime, running just the fast road head on an otherwise standard 1275 engine with standard 1¼" SUs? I have no idea what to expect and would appreciate any views on here? Or is it not worth doing the head without doing the camshaft at the same time, so would I be better off saving up a while longer (I don't have the pennies to have a new cam put in at the moment as I imagine that will be much pricier than changing the head?) Very sorry if this goes over old ground, I have as I say been out of commission for a few months so feel a bit out of touch. As I plan to do this in January I thought I would ask you guys!

Thank you in advance,

Piers
Piers Colver

Piers. My daughter's car has a Burgess Econo-Tune cylinder head on an otherwise stock engine. Yes, it made a difference in performance and, perhaps, economy. (Hard to tell when you are driving it in spirited fashion.) My opinion is that the cylinder head is basic modification that allows you to take advantage of all of the other modifications you may wish to make. A performance cam, without a modified cylinder head and some carb tuning is mostly wasted. Larger carbs without a performance cam and modified cylinder head may produce a decrease in engine performance over the stock carbs.

Assuming that the existing engine is in good condition, the modified cylinder head would be the first "performance modification" I would make to the engine. But, the exact specification for the cylinder head would be best discussed between you and Peter.

Les
Les Bengtson

Yes, definitely worth while first step. Easy to do and good performance gain. Second step (if not already like this) should be a 3-2-1 exhaust manifold as the standard manifold promotes interference between cylinders resulting in backwash exhuast gas which displaces incoming fresh charge. Certainly this must be done before upgrading the camshaft which would otherwise make this effect even worse.

The only time to contemplate a camshaft change as a first step is if the engine happens to be out for some other reason as it then saves a lot of repeat work. A fast road spec camshaft with no other modifications will be drivable and provide useful gains if the exhaust manifold is changed at the same time.

As for retaining the std 1-1/4" SU's, obviously it is better to upgrade eventually, however the engine will still respond reasonably well to other modifications while retaining them. One of our midgets runs a 286 cam with a 3-2-1 manifold, well worked head and 1.5 rockers, all inherited along with a 45 Weber from the previous owner. However it has fitted at present the std SU's for insurance reasons as it belongs to my youngest son who is 19. Despite this, it goes very respectably, certainly much better than standard, and gives 40mpg. We are wondering if a change from twin to a single SU could be acceptable .... :-)
Paul Walbran

I remember my first car. It was a mini 850. I read Vizards first book, and on his advice found myself a 12G295 head in a breakers. I had it skimmed 90 thou, and bolted it on with no other mods. It felt like a rocketship compared to standard (I was 17 remember!). It was supposed to add 12hp at the wheels just doing that mod, and when you only have 28 to begin with, that goes a long way. The comp ratio would have been raised with that head, as well as the superior porting, but that would be the case with you too. You won't be dissapointed.
Shawn

Hi Piers

Might I recommend the Fast Road spec, we fit the 1.401" inlet valve used in the MG Metro or Cooper S. On alike for like basis the head with the bigger valve makes 10 more at the wheels than the smaller inlet valve ( as used in some classes of racing!)that 10 is on top of the already impressive gains from modding the head!

As you are local why not pop up for a before power run and if you buy a head from us an after run?

Peter
peter burgess

Piers.

I can't really add to any of the above, all of which offer good advice.

I would take up Peter's offer and pop in to see him.

He'll do you some Rolling Road work with a Power run before you change the head, the once you have done that (and fitted a 3-2-1 exhaust manifold, preferably a Maniflow one as sold by Peter May), he'll give you a back to back test so you can compare figures.

It's most important when using a Rolling Road, to use the same one with the same operator for consistency.

Perhaps you may post the results of both RR tests and your thoughts after you have carried out the work.

As a side note, the Midget cam in its standard form is NOT a bad cam, its just we all seem to want to replace it with something seemingly better. Once you are at this stage, may I recommend the Swiftune SW5-07.

Mark.
M T Boldry

Thank you, all of you, for the varied and helpful advice. I have been so set on making the car reliable the last couple of years that I am a novice when it comes to making it faster (it was obviously better for me to start with reliable!) so thank you very much. I have now had a direct exchange with Peter and will hopefully be seeing him in the New Year for some rolling road time with a view to getting the head suggested by Peter in this string fitted some time in February. I would be very happy to share all the data on here, as Mark suggests, if you would find it interesting (although I will ask Peter how to translate it into terms those of you with more knowledge than I have will want!) and obviously happy to add my own view on the difference in the car's performance.

Peter: further to our separate emails, I will do exactly as you suggest in this thread: I never say no to good advice!!

Thank you all again & I will keep you posted,

Piers
Piers Colver

one smal bit of advice

if you have the head done and complemented the in and exhaust lines it might be worth while to fit ad diffrent ratio (roler)rockers befor you do the cam.

it gives a nice gain and does not require the engine to be removed (as a cam change does)
Onno Könemann

Onno, thank you for the tip, I'm pretty much a novice so all thoughts welcomed!
Piers Colver

what work do you want/can do your self?
anny thing can be learnd (complete engine rebuilds don on the kitchen table here)
it is just te question if you want to learn it.

it helps with the butget though
Onno Könemann

Onno,

I'm a beginner with the oily bits, really, but I have helped my father build a Caterham 7, many years ago, and I have the space to do work (our new house has our first ever detached double garage with power, a major selling point!), and I hear what you're saying on the budget, but I run my own businesses and my sons are five, three and seven months and I do a good chunk of the childcare, so realistically my time is pretty thinly spread for the next couple of years. My plan is to get the car reliable (just managed that touch wood!), now make it a little quicker so that I can enjoy it even more at the moment (hence this thread), and then take on more work myself in a couple of years' time. Perhaps when my youngest, Arthur, goes to pre-school in a couple of years' time I can find some half days for messing about with the car. I have helped a friend remove the engine from his old TVR, and help another friend work on his pre-war cars and mga twin cam, but I have always been the helper. When it comes to my own car, I'm the guy with the manual on his knee taking an age to do even the simple bits. I have so far limited myself to retrimming the interior, fitting carbs and fitting air filters. I'm a willing student but need to work on finding more time first! I like and agree with your sentiment, though. In terms of what I want to do, ultimately I'd happily take on anything. At the moment the car is more useful to me as a usable antiodote to small children and business pressures than it is in bits in the garage, though! I get the sense that the majority of you on here are a long way ahead of me in terms of technical know how.

Piers
Piers Colver

Hi Piers.

Enjoyable experience modifying engines and lots of ways to do it.

Getting more power is always easier when you can change the cam.

Changing the cam allows the engine to develop torque higher up the rev band and thus power equals torque multiplied by revs so alot more power is achieved easily.

However if an owner does not want to change the cam or does not want to push the engine above 4500 rpm then a cam is basically a waste of effort.

To increase power at lower revs you need to increase the torque, this can be done in 2 ways. Increase the amount of mixture in the engine, or make best use of what you get in.

The easiest way to get more in is to increase the capacity of the engine (put a bigger engine in simple ain't it!!) If you had an 1100 then changing to a 1275 achieves great results. However slightly more difficult with a 1275 as increasing to a 1380 (big rebore) can be costly.
The other way to get more in is to modify the head as Peter has described. This is not a cheap option however (as I am sure Peter would agree.)but can give a decent increase.

The 2nd way is to make best use of what you have got in and that means raising the CR. Squeeze it harder and the bang will be far bigger (simple physics).

So if you do not want to do major work on the engine (Taking it out) then putting on a modified head with a decent amount of CR will give a great result.

I didn't understand what Les said that changing a cam is a waste of time without a modiied head? very strange statement.

I increased an engine from 72BHP to 96BHP (flywheel) simply by changing the cam and raising the CR. Now I do not consider that a waste of time!! But obviously Les must have had a different set of results from his testing? What did your test results show Les?
Robert (Bob) Midget Turbo

Hi Bob

Raising CR good bhp increase everywhere, but have to pay to remove head etc etc, why not add three angle seats and fettle throats and valves and gain 12-15% on top of CR increase? Cam good but will shift power upwards, no pain no gain? Fully modded head loose slight bhp below 1200 rpm due to flow reversal then gain lots and lots everywhere.I tend to agree with Les that to take advantage of a hairy cam 276 and above Kent that more needs to be done to the engine breathing to take advantage.

Peter

Peter
peter burgess

The problem is Peter that we could make the case that there is no point in fitting a modified head without doing work to other parts of the engine/ancilliaries when of course fitting it would give better performance, as would fitting a cam. The point is that all modifications give a result of some magnitude, doing lots of stuff will increase lots, doing only one item will do one items worth.
Changing the cam will increase BHP pure and simple it is not an arguement, IMO I am surprised you do not think that it would? Or have I misunderstood you?
Naturally if you also do other things then the total increase will be bigger. Do you not think 24BHP increase is a good result?

I just wondered what figures Les had got when he tested his theories?

While you are on Peter This winter I will have my clutch sorted in my turbo (Clutch won't take full power at present going to fit a PM competition) and I will then be thinking about a ported cylinder head. At present I have the standard head with no porting, reduced CR (8.4 to 1) that allows me to have high boost 23 PSI. Car goes like chuff, Even without breathing LOL (sorry had to get that in :-)) anyway what head mods would you consider doing to a turboed engine? and how long would that take? would it be mega bucks?
Thanks
Robert (Bob) Midget Turbo

Piers

sounds like you will get there just fine anny witch way you chose!

if you can spare the time you can read Vizard's book about the engine and Daniel Stapelton's (a bbs member) book about the rest of the midget.

this wil give you an idea of what it posible and what part of it you want.

the drive is better that the work but both are fun (i miss mine already after 2 months of stripping and panelwork)
Onno Könemann

Hi Bob

What I was saying was that cams, if they give big bhp improvement at top end will sacrifice lots of bhp at low end, horses for courses, whereas the head mods liberate power at ALL rpms. A race cam will not give good bhp at low revs a mild cam will not give good bhp at high revs.What I am trying to say is that if you add up the bhp increase at each rpm, the amount would be greater with a modded head than a cam and I believe the increase % with a cam when the head is modified would be greater than the % increase if just the cam is changed. Turbo heads at high psis....mod what you have got valve size wise and take ex guide bosses down for extra ex flow and mod chamber opposite plug.

Peter
peter burgess

My mods to BRB's 1275 were limited to exhuast, inlet mods as they were easy bolt on's. Then I fitted a BV/high CR head and needed a remapped dissy; after, a single HS6. Made a nice road engine.

Later, the engine came out for re-bore and at that point, inter alia, fitted 276 cam. It certainly gave the engine more mod and top torque, as you'd expect.

Doing it this way allowed me to judge exactly what I was getting for my ££, and spread the cost, rather than doing it all on one go.

A
Anthony Cutler

Hi again all

Off to Norfolk for a Christmassy weekend at my father's place in a minute, but I thought I would take a minute to thank you all for the various bits of advice, I found the discussion generated very helpful indeed, so thank you very much, all of you. And Onno: Vizard's book arrived via Ebay a little while ago and is my Christmas reading!

Thanks again everybody,

Piers
Piers Colver

In a rush at the moment peter will get back to you in the morning. :-)
Robert (Bob) Midget Turbo

Sorry Peter but have had a busy weekend what with taking Grand children on a Santa's train ride and helping a couple of MGCC members to repair their cars ready for our new years day run I have been unable to give you a constructive reply. Anyway a few moments now so thanks for you comments so far and hope you will get to read mine.

Peter we are exactly the same you have made it clear now that a cam will improve the power of the engine even without head mods, but with head porting it could be better. I totally agree but I was simply suggesting that without any other mods a change of cam will make an engine more powerful simply by itself. Sorry that Les has not posted his results it would have made for interesting discussion.

Anyway I hope I am not interfereing with Piers' question but may I continue to discuss my turbo head with him.

Peter are the mods you do to normally aspirated heads for max power the same then as you would suggest for a turbo?
Why do you think reshaping the combustion chamber would be an advantage?
Robert (Bob) Midget Turbo

the swirl pattern is different with forced induction, no?
David Smith

Bob, I've been led to believe that a forced induction engine will benifit less from porting than a normally aspirated engine, however, I'm sure some light fettling would be useful. Peter will no doubt advise better on this...

Mark.
M T Boldry

Some of the Lancia Thema turbo engines had inlet valves equal or smaller than the exhaust, the reverse from the usual. The idea being, I believe that with forced induction the inlet restriction was not such an issue but the exhaust still had to make its way out largely unaided so the overall package could work better with the larger exhaust. IIRC Lancias' tended to be tuned for torque spread rather than peak power.
David Billington

This thread was discussed between 15/12/2009 and 20/12/2009

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