Changing The Mi16 Engine Characterists.

[jonD6B 0]

Following another thread on here very recently about peoples opinions on the 8V lump compared to the 16V lump and how the 16V gives you a higher power output but feels like it doesn't come alive until it starts to hit 4K revs. where as the 8V lump gives a more constant delivery throughout the whole rev. range I was curious as to whether it was possible and what would be involved in keeping the max. output at around the 160 bhp mark on the 16V but increasing the low down shove to create a flatter power curve. Thus giving the higher output of the 16V with more of the characterists of the 8V engine. Is it possible by reducing the exhaust bore size and altering the inlet cams? Is it possible at all?

Don't go down the lines of why would you want to, the question is posed as I'm personally curious whether it can be done as I feel it could be a strong engine for my needs.

[DrSeuss 0]

buy a 2ltr mi and keep the acav system.

[simonb 0]

I would have thought that advancing the cam timing would move the power further down the rev range, however this would require a vernier setup and a bit of RR time to get it right, and you would loose top end power if you move away from the std settings.

 

Try searching on google from cam timing as there are hundreds of articles on the subject.

[mfield 20]

If you read loads into PR's post you'll find that the mi makes it power due to the head at a certain rev's due to flow. You can achieve the power through the flow at lower rev's by increasing capacity like drSuess suggest's with the 2.0 mi . From what ive read you can make the power lower down by using the mi head with let's say a 2.1 bottom end and make the power band shift about 800 rpm, thus simular to the 8v but with more power

[M3Evo 0]

Fit a positive displacement supercharger

[alternative 0]

I havent seen much discussion lately on the advantages of the 8v but I entirely share your desire for power lower down. When mounted firmly enough to stop it banging in a 205 the 16v seems a flat and far from ideal unit. The 16v is more powerful but who wants to drive at a buzzing 7000 rpm all day in a small car? I have long wondered whether the 8v is not more suitable in a light car like the 205. One doesn't actually need so much power due to the light weight and the low-down power is enough to propel the car well using high gear ratios which makes it all a lot less stressfull (for engine and driver!). Peugeot presumably knew this. The higher frequencies of the 16v are better absorbed by a bigger car (eg 405).

 

I am thinking of fitting a 16v in a CTi with a much reduced compression ratio to make it more flexible and able to pull a higher final drive. I am also considering moving the servo so one can use much more flexible engine mountings all round so as to isolate the effect of high revs and enjoy smoother running. I would personally not fiddle with the valve timing if flexibility is the aim. Could I suppose, try a heavier flywheel! Interested to hear what everyone thinks!

[mfield 20]

I havent seen much discussion lately on the advantages of the 8v but I entirely share your desire for power lower down. When mounted firmly enough to stop it banging in a 205 the 16v seems a flat and far from ideal unit. The 16v is more powerful but who wants to drive at a buzzing 7000 rpm all day in a small car? I have long wondered whether the 8v is not more suitable in a light car like the 205. One doesn't actually need so much power due to the light weight and the low-down power is enough to propel the car well using high gear ratios which makes it all a lot less stressfull (for engine and driver!). Peugeot presumably knew this. The higher frequencies of the 16v are better absorbed by a bigger car (eg 405).

 

I am thinking of fitting a 16v in a CTi with a much reduced compression ratio to make it more flexible and able to pull a higher final drive. I am also considering moving the servo so one can use much more flexible engine mountings all round so as to isolate the effect of high revs and enjoy smoother running. I would personally not fiddle with the valve timing if flexibility is the aim. Could I suppose, try a heavier flywheel! Interested to hear what everyone thinks!

 

 

I went in my first mi 205 the other day and all tho impressed with how it went was ultimately unipressed with the delievery, it did feel flat with no shove like i thought there would be the car i went in was good ( very good ) but felt like it had lost it's character from a tuned 8v ( might be biased ) maybe a tuned ( tb's/carbs) mi would bring back the character but untill i go in one of them im undecided

[C_W 3 1 Cars]

I'm not sure how reducing compression ratio makes it more powerful low down?? It also doesn't make sense to me to criticise the engine for its lack of low down power syaing the 8vs more suited to teh lighter 205 and the 16v engine is more suited to a heavier car

 

The best way to alter the characteristic IMO is to alter the gear ratios (eg 1.6 final drive), this really transforms the engine and it will pull low down in every gear well, but yes this does mean higher revs in 5th.

 

I always like my 1.9 8v engine for the lower down power and its lazy nature but when driving it flat out it felt flat and breathless to me after 5500rpm.

[petert 583]

we've suffered from this problem in Australia since day one of the Mi16. We only ever got the lower compression XU9J4Z engine, which has a peaky torque curve because it's missing torque in the 3000-3500 range, compared to the XU9J4. The answer is very simple. Advance the inlet cam a few degrees. The easiest method is with an offset cam key. The hardest is with a vernier pulley. Advancing the inlet cam will move the power range down a tad, giving you a lot more useable torque at the expense of some top end power. How often do you drive at 7000 anyway? I can sell you a key for $30, that will advance the inlet cam 4 degrees.

 

Reducing CR only makes it worse. Advancing the inlet cam increases the dynamic compression ratio, as the inlet valve is closing earlier, giving a longer compression stroke.

Edited March 28, 2006 by petert

[smckeown 1]

my mi16 was flat low down until I had the AFM professionally re-tracked and mixture played with. It felt like it had much more torque then. I then had an FSE boost valve fitted and got even more low down torque. Both combined made a massive difference

[Rob Thomson 6]

The 16v is more powerful but who wants to drive at a buzzing 7000 rpm all day in a small car?

Me!

 

Such a large part of enjoying driving comes from ragging the nuts off a high-revving petrol engine, and learning to change gear properly to maximise its performance. I can't stand torquey engines - they're fine for driving to the shops or for driving on the motorway - but they're hardly satisfying to drive. The Mi16's f***ing brilliant - I can't believe mine's in bits.

 

I agree with Sean, though - I had all new EFI on my Mi16 and it ran beautifully, and although it went like stink above 4,500rpm it was far more tractible than my 8V had ever been. I've driven some real bags of s*it Mi16s though, but then I've also driven some awful 8Vs....

[jackherer 543]

who wants to drive at a buzzing 7000 rpm all day in a small car?

 

you've got to remember that the 205 I took you out in was stripped with no soundproofing and had a bit of a hole in the exhaust!

 

I am thinking of fitting a 16v in a CTi with a much reduced compression ratio to make it more flexible and able to pull a higher final drive.

 

Like I said when I saw you, that wont help at all, it'll just make it flatter if anything I would have thought.

 

However, having met you and your pug I dont think an Mi16 is right for you after all, I think you'd be pleased with a nice rebuilt 8v and you'd do well to run it on some better management (either an AFM/distributor-less system from a newer peugeot or an aftermarket ECU) for reliability and smoothness.

 

Your CTI is very nice btw, and will continue to be whatever engine you go for (any chance you can post some pics? I'd like to see what people have to say about the colour cos its a new one on me...)

[madmoog 0]

Just a thought....

 

Does the 8V feel more touquey and constant compared to the 16V which is suggested is flat until it comes on cam, due to the differant power curves? Quite possibly. Neither would seem lacking compared to a 1.6 due to the extra 300cc.

 

Is this an illusion as the 8V does not come on cam like the 16V, where as in fact they may have similar power deliveries up to 4K perhaps?

 

It would be good to see some overlayed power/torque curves.

[Rob Thomson 6]

Yeah, that's pretty close to the mark. The Mi16 has slightly more torque than the 8V from idle to about 4k, but then the lines seperate as the Mi16 comes on cam and starts screaming. There have been some over-laying graphs on here before - but I can't be bothered to search for them now.

[S33GAV 0]

I went in my first mi 205 the other day and all tho impressed with how it went was ultimately unipressed with the delievery, it did feel flat with no shove like i thought there would be the car i went in was good ( very good ) but felt like it had lost it's character from a tuned 8v ( might be biased ) maybe a tuned ( tb's/carbs) mi would bring back the character but untill i go in one of them im undecided

What gearbox did it have? If I had driven a mis6 with a 1.9 box to begin with I would have been rather unimpressed too, but a mi16 gearbox makes a MASSIVE difference (to the feel) over the 1.9 imo

[Batfink 201]

Yeah, that's pretty close to the mark. The Mi16 has slightly more torque than the 8V from idle to about 4k, but then the lines seperate as the Mi16 comes on cam and starts screaming. There have been some over-laying graphs on here before - but I can't be bothered to search for them now.

 

exactly - it only feels flat because of the difference when it comes on cam!

[Ahl 4]

People keep going on about the 8v as if there was a massive difference in power delivery.

Last time I checked, it was a 1.9 litre 4 pot engine and I still had to rev it to 6000rpm to make it go fast! Its not a bloody chevy v8 or something.

[JERAM 0]

here is two graphs of a mi16 std engine with twin 45 dellorto carbs, you can gain a bit of bhp and a fair amount of torque by swinging the std cams.

 

far better delivery of bhp

 

and a good whack of low end torque

 

let the handbags comence

[mfield 20]

What gearbox did it have? If I had driven a mis6 with a 1.9 box to begin with I would have been rather unimpressed too, but a mi16 gearbox makes a MASSIVE difference (to the feel) over the 1.9 imo

 

 

It had a 1.6 box on it.

 

Don't get me wrong the car went quick and was deffinetly a good one Just was expecting more. I like engine's to be raw, noisy and have character the mi just felt modern, smooth and like most other 16v's.

 

After having a peaky 8v on carbs with NO power below 4k that screamed at the 7.5k redline the mildly tuned mi ( about 175-180 bhp iirc ) was quicker but felt less involving and civilised.

 

Maybe it was the lack of intake growl and precussion of pop's that biased my opinion, maybe an mi with carbs/tb's will give the enjoyment i desire

 

 

Edit: The graph's may now change that opinion , lol

Edited March 29, 2006 by mfield

[huxley309 0]

You will love an mi on bodies it makes them much more driveable and fun!!

 

You gain power thoughout the whole rev range but mainly in the lo-mid end where mi's seem to lack

 

If you ever see my 309 at a meet ask me for a spin i promise you won't be disapointed

[Guest pugpowa]

I love the way the power comes on with the mi!puts a smile on my face everytime that needle comes near 4k! admittedly the engine seems to pull less at lower revs,maybe compared to the surge of power.although a friend of me has got a 205gentry with a manual conversionand 306 dturbo engine fitted,absolutely murders me comin out of corners,runs out of puff quickly, but if you want loads of torque, tuned diesels!!!

[Robsbc 0 1 Cars]

Here's a graph of my current Mi16 on bodies forged pistons, Maniflow 4-2-1 manifold & BV head compared to my old 8v SBC 1.9GTI-S (cams & headwork).

 

The spikey bit at the end of the Mi16 power figure is due to noise interference.

Edited March 29, 2006 by Robsbc

[steige 1 1 Cars]

I have been in Jeram's car round knockhill and it really shifts. It has loads of grunt which is perfect for that track. Is pisses all over my standard mi and probably has roughly the same power. It just delivers it a lot better!

[Robsbc 0 1 Cars]

I've also attached my friend Revla's graph of his 2.0 S16 on Catcams, bodies, 3 angle valve seats & GTI-6 manifiold versus the old set up using the AVAC system.

S16_on_bodies___Catcams_v_S16_AVAC.pdf

[Ahl 4]

Thats a pretty impressive result Jeram, didn't realise it was that good!

Does the blue line show the same engine without the carbs, or just without the cam swing?