2088cc Mi Bottom End

[PumaRacing 2]

How about oversquare engines can make more power than the same sized undersquare engine becuase you can get bigger valves in an oversquare engine than under?

We have a winner

 

If the bore/stroke ratio is altered (for a given capacity) but the head stays the same then the power curve will hardly change. The engine won't rev higher or lower just because the stroke changes. It's still the same swept volume breathing through the same head and it will rev until it becomes strangled for lack of airflow.

 

Engines don't make lots of power because they rev high. They rev high because they are making lots of power and that's determined by airflow. If a head can flow 5000 litres/min it will supply a 1 litre engine for 5000 power strokes a minute (10000 rpm). It will supply a 2 litre engine for 2500 power strokes a minute (5000 rpm). The 2 litre engine can't be forced to do 10,000 rpm with that head and even if the components inside were very light or didn't break it still couldn't breathe at those rpm.

 

Attaining high rpm isn't a goal, it's a natural result of improving flow.

[miamistu 1]

So whats the downside? More expensive?

[PumaRacing 2]

Yeah thats right, that why I asked if anyone had heard of the NR750.

 

Honda developed this bike that was a V4 engine. It had 8 valves per cylinder. Oval pistons and twin conrods.

 

http://www.sportbikez.net/picture/324

Honda first looked at oval pistons a long time ago. Maybe the 70s or 80s. I recall a 500cc race engine which I think might have been a V4 or V8. I'm sure there'll be something on the web about it. When I was studying engine theory in Brunel uni library some of the best info was in papers from the Japanese SAE. I'm sure one of those covered the oval piston engine.

 

It's a shape that lends itself very nicely to maximising valve area but it has a poor chamber shape for fast combustion. I suspect it requires twin, or multiple, sparkplugs. The bore sealing problems are not dissimilar to that faced with the Wankel engine and I imagine the long straight section of piston ring was prone to flutter. Must be fascinating working on that kind of project though and trying to find the technical solutions to making it all work.

[KRISKARRERA 2 1 Cars]

So does that mean that when a standard Mi16 gets to 6500 -7000 rpm and the power drops off it's reached the limit of it's airflow?

[huckleberry 0]

So does that mean that when a standard Mi16 gets to 6500 -7000 rpm and the power drops off it's reached the limit of it's airflow?

I can't imagine it being that simple. I mean the caracteristics of an engine also have to do with things like a camshaft. I don't think it's that easy to get to the max of a standard MI head. So when all is done like TBs, camshafts etc and the you reach the max you could say it is because of the flow of the head.

 

Come to think of it, the flow is also determined by those things. That would mean flow = everything.

[PumaRacing 2]

Surely if Peugeot had made a 3 litre V6 engine with exactly the same head flow and valve size as a 1.9 or 2 litre Mi16 the increase in capacity would have been worth it?

Isn't it a case of increasing cubic capacity will give an engine an increase in torque and power without needing lightened/stronger conrods etc ?

Increasing capacity without increasing head flow makes very little difference to power. All that happens is the rpm at which everything happens comes down in similar proportion to engine size. If engine size goes up by 10% then very roughly peak power rpm and peak torque rpm will fall by 10%. Torque will of course go up which feels faster on the same gearing but gearing really needs to then be raised by 10% so that peak power rpm comes at the same road speed as before. Once that is done the wheel torque and acceleration stay the same.

 

Yes you gain a small amount of power but not in proportion to increase in engine size. A rough rule of thumb for small increases in capacity is you gain 3% extra power for every 10% increase in capacity if head flow stays the same.

 

The ONLY point of making engines bigger is bigger engines have more room for bigger valves - that's where the extra power comes from - not the engine capacity itself.

[huckleberry 0]

Can I please ask one question about this subject? What about forced induction like a turbocharger. Does also flow have a thing to say or is it just head-capacity that means max power?

 

Tim

[PumaRacing 2]

So does that mean that when a standard Mi16 gets to 6500 -7000 rpm and the power drops off it's reached the limit of it's airflow?

Exactly. Every engine sets its own rev limit automatically when it becomes unable to breathe. That's what peak power rpm is. There is no way of "forcing" an engine to rev higher other than supplying it with more air. Bigger valves, longer duration cam, better induction and exhaust systems etc.

[KRISKARRERA 2 1 Cars]

I think you said that an otherwise standard Mi16 engine with your big valve head can make 190bhp. Does that mean the standard inlet and exhaust is good for that increased level of air intake?

[Hilgie 16 2 Cars]

Dave can we take classes?? LOL

 

No really...I think we all start to understand now.

 

From you website I understood that max bhp for a standard Mi head is around 200bhp? Which can be increased through forced induction, or on a N/A engine by fitting bigger valves or different cams (longer duration, higher lift).

[Jay 1]

Attaining high rpm isn't a goal, it's a natural result of improving flow.

 

But I would assume that if you took a mass-produced engine, even a particularly good one like the MI16, and managed to work the head to a point where it could flow enough to breath properly at say 10k rpm, you would still need to balance, replace or strengthen various parts on it not to have some kind of failure associated with sustained use at that sort of rpm?

 

I think a lot of people are confused (myself included until today) by the fact that to get that extra power at high revs you are generally told you have to uprate, balance or strengthen this that and the other, so as to stop the engine pulling itself apart at the new higher rpm limit. So most people then see high revs limited by component strength and think because their crank, pistons and rods have been dynamically balanced, they can now hit 11k rpm all day... However, most people neglect to pass on what you're saying, in that the engine will only actually achieve that rpm level if the head can flow enough air to feed it....

 

Boy am I going to sound impressive when I recount that new gem the next time I'm down the pub!

 

Just to complete this so I fully understand, JWT in the 'States are developing a 2.4 stroker kit for the GTi-R SR20DET. The characteristics of this conversion are apparently it doesn't like to rev very much, but can make huge amounts of torque at relatively low rpm. I assume that by what you're saying, the reason it's not a 'revvy' engine is not because of the increased mass of the internal components, or the effects of the long stroke of the kit, but simply that at high rpm the head cannot flow enough to support the amount of air required to feed the new, larger capacity?

[Jay 1]

Ok, my question has pretty much already been answered (that'll teach me to take so long to wite my posts!!), but all very interesting reading!

[PumaRacing 2]

Can I please ask one question about this subject? What about forced induction like a turbocharger. Does also flow have a thing to say or is it just head-capacity that means max power?

 

Tim

When you tune a naturally aspirated engine the peak power rpm goes up automatically as the flow goes up. The engine HAS to rev higher to be able to take in the extra airflow it's been supplied with.

 

When you add forced induction you aren't really increasing the basic airflow capability, you are increasing inlet manifold pressure and density which means more weight of oxygen per cycle. What happens is the power curve stays very roughly the same shape i.e. peak torque and peak power still occur at similar rpm but the torque and power at those rpm go up in proportion to boost. You still need to improve basic flow (bigger valves, head porting, longer duration cams) if you want the shape (i.e. the rpm) of the power curve to change.

 

Improving basic flow is just as important (maybe even more important) with a turbo engine as a N/A one. If you find an extra 10% flow from the head then the engine will make an extra 10% power at the same boost level. If you just try to find power by raising the boost then you add heat which has to be taken out with intercoolers and causes detonation if you don't.

[huckleberry 0]

Improving basic flow is just as important (maybe even more important) with a turbo engine as a N/A one. If you find an extra 10% flow from the head then the engine will make an extra 10% power at the same boost level. If you just try to find power by raising the boost then you add heat which has to be taken out with intercoolers and causes detonation if you don't.

That's just what I wanted to hear. Everybody I ask is telling me a big valve 8v head for a turbo technics conversion is useless and should be money spent elsewhere like forged pistons for coping with higher boost.

 

I was just trying to figure out if power can be raised without adding boost. But a good big valve head should do as well since I'm trying to get over 200 bhp or anything like that. I just want to optimize the engine for the turbo.

 

Thanx for the answer!

 

Tim

[Jakob 1]

That's just what I wanted to hear. Everybody I ask is telling me a big valve 8v head for a turbo technics conversion is useless and should be money spent elsewhere like forged pistons for coping with higher boost.

 

Tim

With the XU10 8V turbo engine it is not the airflov of the 8V that makes the limit - it is the exaust manifold and very much the too small inlet manifold. The diameters in these two pipes are way too narrow and the gasthrottle is too small for + 200 hp.

 

I do not know the specifications of the turbo technics conversion but by increasing the airflow in the turbo (bigger than standard T25), new exaust and inlet manifolds then it should be no problem reaching 300 hp with the right setup

 

 

Jakob

[TEKNOPUG 3]

The TT conversion keeps the standard head.

[huckleberry 0]

Errrmmm I forgot one little word and that makes my entire reply different. I mean I am NOT trying to get over 200 bhp or anything like that. Just a healthy proper 1.9 8v turbo technics engine that will do very well on the 0,65 bar boost.

 

I guess I think faster than I type.....hmmmm that doesn't sound possible too.

 

Tim

[Robsbc 0 1 Cars]

I think you said that an otherwise standard Mi16 engine with your big valve head can make 190bhp. Does that mean the standard inlet and exhaust is good for that increased level of air intake?

So he says....where's the proof in the pudding?

 

Where's this magical rolling road he talks about that gives reliabale figues?

[PumaRacing 2]

That's just what I wanted to hear. Everybody I ask is telling me a big valve 8v head for a turbo technics conversion is useless and should be money spent elsewhere like forged pistons for coping with higher boost.

 

I was just trying to figure out if power can be raised without adding boost. But a good big valve head should do as well since I'm trying to get over 200 bhp or anything like that. I just want to optimize the engine for the turbo.

 

Thanx for the answer!

 

Tim

James (PHyR) has one of my BV heads on his TT conversion. He'd be better able to tell you how it went before and after that was fitted. On Emerald's rollers it gave a lot more power on less boost than a std head engine but I don't recall the exact figures. From memory about 200 bhp and 200 ft lbs on 10 psi compared to 180 bhp on 12 psi from a std one but don't quote me on that.

 

However the turbo was faulty and the exhaust manifold gasket blowing when those figures were taken so I don't think it was anywhere near its potential. It split a liner and I did him a rebuild kit with Mi16 ones a couple of months ago but I haven't heard if that's now assembled or whether new figures have been taken yet.

[PumaRacing 2]

So he says....where's the proof in the pudding?

 

Where's this magical rolling road he talks about that gives reliabale figues?

In this business you have a number of options. You either don't care about how your work performs or whether it gives value for money or you spend your entire life proving yourself to doubting potential customers. I'm lucky enough to have a surplus of potential customers so I can pick and choose which work I do and nowadays I don't really have to prove anything anymore. I've done that on road and track for 15 years. I guess I could farm out the surplus and make a mark up on it but finding people who can do work to very specific standards is almost impossible so I don't bother.

 

I covered those power figures in a previous thread some time ago. The power figures weren't back to back on the same rollers so I won't lay claim to them being exact until they get confirmed elsewhere. I can however go to some extent on the driving feedback from both the customer and the RR operator. Another BV Mi16 head is going on an engine soon which already has my TBs fitted. Hopefully they'll supply me with reliable before and after figures.

 

The customer who fitted the BV head to a std engine is called Steve Pilcher. I haven't spoken to him for months and he doesn't know I'm writing this. Why don't you phone him and ask him yourself how it went? Then you can post how it compares to the people on here who have fitted ported heads and cams and are still only 10 bhp up on std. If he tells you it was crap then post that with my blessing and my word that I won't complain in any way.

 

edited to remove Steve Pilchers phone number, especially if he doesn't know you are writing this he might not appreciate his number being posted. e-mail if you want it.

Edited September 24, 2004 by pugtorque

[205007 12]

I have to say this is one of the most interesting threads i have read, and i freely admit i was, until about a 3 years ago, one of the people who bought into the marketing mans tuning philosophy "extra 15-20 bhp from this cam" and "unleash your cars potental with a 6" slash cut backbox"

the trouble is its all too believable on the packet.....

 

there should be warnings, like on cigarette packets, which warn you that you are unlikley to see the gains claimed and all they do is seriously harm your wallet!

 

im just glad most people on here do have a clue and can speak freely about tuning experiences good and bad, i must admit i have a few friends who dont share my views and wont take my advice on tuning and insist on wasting money on shiny s*it, which i know just wont work! i can only look on in horror but at the end of the day its their money!

[base-1 17]

oh my head hurts after reading all that so early in the morning!! bloody interesting though, who made it a sticky, well done

[huckleberry 0]

James (PHyR) has one of my BV heads on his TT conversion. He'd be better able to tell you how it went before and after that was fitted. On Emerald's rollers it gave a lot more power on less boost than a std head engine but I don't recall the exact figures. From memory about 200 bhp and 200 ft lbs on 10 psi compared to 180 bhp on 12 psi from a std one but don't quote me on that.

 

However the turbo was faulty and the exhaust manifold gasket blowing when those figures were taken so I don't think it was anywhere near its potential. It split a liner and I did him a rebuild kit with Mi16 ones a couple of months ago but I haven't heard if that's now assembled or whether new figures have been taken yet.

I have to go and talk to him. Thanks for sharing all the info with us on the board!

 

Tim

[pug_ham 244 3 Cars]

The customer who fitted the BV head to a std engine is called Steve Pilcher.

Totally off topic but;

 

Dave, I recognise that name from days of old when Max Power was a magazine talking about modified cars & not just totty sprawled over them for a cheap porn mag. One of the cars I remember was a red E reg 205.

 

Is this the same person?

 

Graham.

[PumaRacing 2]

Totally off topic but;

 

Dave, I recognise that name from days of old when Max Power was a magazine talking about modified cars & not just totty sprawled over them for a cheap porn mag. One of the cars I remember was a red E reg 205.

 

Is this the same person?

 

Graham.

It could very well be. I know he used to do work on Pugs for people as a sort of sideline, had connections to Guttmann (sp?) and to one of the Peugeot owners clubs. Maybe the Peugeot Sport Club but I don't recall the details. I know he said he had cars featured in magazines but again can't recall any details. He bought one of my first sets of TBs in 1998 which has now been sold to Kate and I did the BV Mi16 head for him a year or so ago.

 

He's very experienced in what works and what doesn't but he does tend to use different rolling roads every time so I never did quite get to grips with how definitive his feedback on power increases was. If anyone phones him they might get the full story. He used to use Emerald when they were in London so I'm sure some of my work has been seen by them but whether he's used them since they moved to Norfolk I couldn't say. It's been a while since we spoke. The last I recall is he fitted the TBs and the BV head together but I think the injectors ran out of flow capacity so they never got decent power figures. Then the TBs got sold and what happened to the BV head I have no idea.