Big Valves For Mi16/1.9gti

[stefan 4]

A response to various cylinder head experts/shops and so on, who are selling various big/race/special/and so on valves for all the money in the world :

 

Mi 16 big inlet valves (36.5mm): from a Peugeot/Citroen TU 1.4 engine

1.9 gti big inlet valves (43.5mm) : DATSUN-NISSAN 2.7 TD

 

The valve stems need to be shortened and regrooved, using your old valves as a sample, which can be done anywhere for almost nothing.

 

 

So there you go people, let's all go BIG(and not poor)!

Edited June 24, 2010 by stefan

[unariciflocos 49 1 Cars]

There's a pinned topic in this section called "Big Valves". You should read it. The general consensus is that big valves, especially on the 16v engines, don't help.

 

I've achieved 97lbft/litre and 133bhp/litre from XU 16v engines I've built and set up so far, on standard valve sizes;

 

So if you really don't want to go poor as you said, don't go spending your money on bigger valves.

[stefan 4]

I beg to differ.

And I'm not the one doing the spending.

Installed quite a few, and the cost is really not that big.

Need not say again, you could get ripped off if you buy them from someone who sells these OEM valves as some misterious/special/race/or whatever valves.

If someone decides to go for the big valve option, they are available at any store either as OEM or aftermarket,for example AE, osvat and so on.

[stefan 4]

There's a pinned topic in this section called "Big Valves". You should read it. The general consensus is that big valves, especially on the 16v engines, don't help.

 

 

 

So if you really don't want to go poor as you said, don't go spending your money on bigger valves.

 

 

 

Regarding the whole 10 page debate mentioned above (in which I didn't want to be included),

here as follows:

 

1. buy the bigger valves

2. take your head to a local machine shop/engine reconditioner, and tell them the following:

make me a vertical cut through the valve seats 2mm wider and 3 mm into the port throat

3. then take your head home and gradually grind out the edge(extra material) that appeared after the machining took

place.

Don't remove any more material then you have to, that is till you blend the new cut through the throat smoothly into

the port. When you get into the main part of port ( that is the manifold side) it's time to stop grinding. The port is wide

enough and needs no enlarging. The point is to get a smooth transition from the 'old and new' while removing as less

material as possible. I recommend using a sand paper grinder because you wont make a mistake so easily because it

takes the material off slowly and gradually. You will also get a really nice and even shape because of the large

diameter that these grinders are made in, cca. 30mm. When done with the porting, take the head back to the

machine shop/engine reconditioner, and order the following:

4. recut my inlet seats like this: 20 deg upper cut, 45 middle cut, 70 deg lower cut, with of course changing the guides

5. shorten and regroove my valves (the ones mentioned above);

6. additionally cut them in the original 45 deg angle ( just to remove some of the excess material ) and a 30 deg back cut

till the cut mates with the surface below.

7. lap the valves in, install them and you're set to go.

 

The process is for the mi 16. For the 8v you need new wider seats pressed in to accomodate the 43.5 mm valves.

You can also use 43 mm ones from the 2.0 pug engine, they don't need shortening.

BV heads work either on the 8v or 16v, admiting that in my opinion it works a tad better on the 8v.

The porting itself is a matter of experience, but even your first head can make you smile when you put the pedal to the metal. It’s been done and proven many times. Now that's the whole science.

 

The initial idea of my topic was to share knowledge on where to get the parts you need for the least amount of money, instead of getting ripped of, as opposed to the suggested post which debates the pros and cons for BV.

 

Even maybe to try and do the work yourself, if you make a mistake you'll be richer in the end because of the extra experience and know-how.

 

Now again as to the whole 10 page novel mentioned above I sure would like to hear what the people who designed the maxi’s, stw and such 300-330 HP engines would have to say to some of those 'smart scientific tales'.

I bet they would be in a wonder!

I rather leave that kind of talk to them, the ones that actually know what they are talking about, and have been extensively trained to do it, have M.A. degrees in physics and so on.

Edited June 24, 2010 by stefan

[blessed6383 0]

I've got to say that after having my 1900 16v rebuild with bigger valves fitted and cam'd along with a few other bits it was a lot more responsive, But i am unsure of the real difference the valves would of made on there own as i had a full rebuild new piston/liners ported n polished etc.

 

but as far as im concern for the extra cost of getting the valves and having them fitted i would do it again as it wasn't silly money.

 

really would like to drive another mi16 with same spec but not had valves so could see the difference.

[Sandy 189]

A good pointer Stefan and useful info for anyone going down this road.

 

But on the subject of bigger valves and physics degrees etc. There are very few people who are genuinely getting near 300bhp (at practical/reliable revs) with good driveability from these engines and those who are will know that big valves make it harder to achieve. A few issues basically... ones is valve to valve proximity limits the cam profiles and timing that can be used, which is made worse with bigger valves; bigger valves exacerbate the dynamic compression issues with serious cam profiles; valve inertia is more of a problem; and to make best use of the flow characteristics you get with big valves, you need rapid valve opening and closing, which causes a great deal more valvetrain stress and wear, again exacerbated by the increased weight of the valves.

 

Finding more power through tuning components to work together better, rather than simply making stuff bigger, I find tends to give better overall results.

[edbar 6]

I can see why big valves in a 16v would limit overall progress due to limited space and valve clipping at high lift, but these arent an issue with an 8v yet most people still shun the idea yet the likes of longman and skip brown do enlarge valves on the 8v heads. Also appreciate weight is not good in the valve train. Just find it confusing as with 8v tuning in most marques bv heads are the route most take?

[welshpug 1,627]

I can see why big valves in a 16v would limit overall progress due to limited space and valve clipping at high lift, but these arent an issue with an 8v yet most people still shun the idea yet the likes of longman and skip brown do enlarge valves on the 8v heads. Also appreciate weight is not good in the valve train. Just find it confusing as with 8v tuning in most marques bv heads are the route most take?

 

 

As Sandy said above, if you are chasing numbers then big valves will work fine, but is very difficult you get decent driveability.

 

Those that shun the big valves realise that driveability on the whole is far more important than the big power numbers, especially as most you talk to will be used in road and track cars, not out and out race cars.

 

That said Sandy does build race engines using the same approach I believe, as making a car more drivable makes for a quicker car than something so peaky that someone can nip past if you're caught off cam.

 

Now again as to the whole 10 page novel mentioned above I sure would like to hear what the people who designed the maxi’s, stw and such 300-330 HP engines would have to say to some of those 'smart scientific tales'.

 

They wont tell you, but they'd gladly sell you an engine for £XX.XXX because they know they are the best engines (for the purpose) and produce the power.

 

 

I'd love to see you try and drive down to the shops with one of those engines, it would be the most expensive and uncomfortable pint of milk you've ever seen.

[stefan 4]

Finding more power through tuning components to work together better, rather than simply making stuff bigger, I find tends to give better overall results.

 

Yes, I couldn’t agree more.

I find engine building a matter of a complex compromise between a lot of factors, so I would never state that BV or any other mod is ALWAYS the way to go. The factors can vary, from the predicted use of the car, the driver’s wishes, the engine itself, and of course the budget.

Based on my experience so far, I can say that I was rarely disappointed in the gain that BV’s made on the ROAD, off course with the seat cutting and porting done properly.

That isn’t to say that I don’t believe otherwise is possible.

 

There are very nice engines out there, often being built without the use of BV.

A recent example that springs to mind, that a friend of mine built, a small (standard) valved 1.6 16v TU in a 106gti with just the ECU reprogrammed, cam timing changed, and the 1.3 rally gearbox fitted. I can state with a certainty that this car would show a nice clean pair of heels to a lot of the 205mi16(with its 34.6mm or 36.4mm valves) out there, BV or not.

The examples for pros and cons are numerous.

 

So to conclude, my opinions are based on the road, all I care about is how fast/faster the car actually goes once the work had been done. I rather leave the scientific talk about gas dynamics and, inertia,

the forces that are being exerted, etc., to University degree holders, professors and the likes, who do the calculations for the 330HP builders.

 

I’ m not that happy that this post turned into the ‘to BV or not to BV’, once again that wasn’t the idea, but hey…che sera sera.

If no one else minds I don’t either.

[stefan 4]

And another thing that seems to crawl through these posts is the:

 

Big valves versus hot cams and cam overlapping

 

How does cam overlapping in such a manner that the valves almost catch each other make a low-midrange tractable car (if said that most people are so eager for such a car, so they can go out and buy milk with it)?!

 

I believe this to be misleading and can easily lead someone to a wrong conclusion.

Edited June 25, 2010 by stefan

[welshpug 1,627]

And another thing that seems to crawl through these posts is the:

 

Big valves versus hot cams and cam overlapping

 

How does cam overlapping in such a manner that the valves almost catch each other make a low-midrange tractable car (if said most people are so eager for such a car, so they can go out and buy milk with it)?!

 

I believe this to be misleading and can easily lead someone to a wrong conclusion.

 

 

are you trying to say that big valves are an alternative to hot cams?! because it sounds like it

[stefan 4]

are you trying to say that big valves are an alternative to hot cams?! because it sounds like it

No, please read again

[DrSarty 90 1 Cars]

Not wanting to ruin your post, as you've made it quite clear that you are merely pointing out options for buying bigger valves 'on the cheap', I would just like to say this.

 

By recommending sources - albeit a very helpful thing to do - you are advocating/supporting the use of larger/big valve engines. 'We' (and I include myself) are saying that BV heads are not necessarily a good route to follow.

 

The large debate referred to in this - completely forgetting about degrees etc that you keep talking about - pretty much concludes that after much testing, this apparently simple route/trick to increase power, i.e. simply fitting bigger valves is a myth. It is not what it's cracked up to be.

 

I would guess that the reaction you may feel you are getting, is not that you're not being helpful showing a way to buy the larger valves more cheaply, but that it's not really a recommended route, and better power with tractability (i.e. the ease of access to that power) is available through other means.

 

To put that into perspective: I have only a stage I inlet REGRIND cam on my 2.2 Mi with standard valves, and am close to 100lbft per litre displacement. This is a mild cam on mild lift with only slight longer duration.

 

Were we to use big valves and/or more lift, we would run into a whole new set of issues/problems/costs.

 

To conclude I'm really picking up on 2 things. Yes, its great you've sourced a cheap route, but I think there are many other factors involved and it's therefore not just a simple case of putting in bigger valves and expecting your world to change. I don't think it's right to give that impression. It may be better to stay with standard sized valves, and work in moderation and in several areas to get overall better results, than someone expect heaps of change from using larger valves.

 

I am more than happy to proved totally wrong on this matter.

[stefan 4]

work in moderation and in several areas to get overall better results, than someone expect heaps of change from using larger valves.

 

We agree on the above.

Well, anyway thanks for the effort and time spent writing down you observations and opinions regarding my posts, I can only wish you have read them first.

 

I am advocating/supporting the use of larger/big valve engines, but not as a mandatory option,as I don’t anything else.

The performance business is just too broad to think like that. How can anyone advocate the same principles on a hillclimb/circuit race car or some lad’s gti who just wants a shiny muffler. It’s just not possible.

Whether you or anyone else likes it or not, BV’s have been out there for a long-long time, and they are here to stay.

Simply doing just one thing and expect your world to change would be impossibly foolish.

I can drive a BV mi16 up the hill in 5th at 2000rpm any day of the week.

Proving anyone wrong is an ungrateful business, not that you were so much off

Edited June 25, 2010 by stefan