Race Engine Forum UK

Guy; thanks for a superb answer and enjoyable read! I am sure so many others will benefit from this knowledge. You were correct with all of your assumptions! I will definitely do one step at a time as you suggest from now on until this problem is resolved.

Regarding my ‘soggy’ bottom: I feel it must be as you suggest an ‘exhaust gas problem’ relating to the exhaust cam. I am aware of people with 16v Integrales that use the Tipo inlet cams and are very happy with the characteristics.

In fact if any one reading this has a Dyno graph of an Integrale 16v before and after the Tipo cam modification that would really help at this stage.

Guy, on a previous post: phpBB3/viewtopic.php?f=13&t=373&p=1758#p1758 you mentioned this regarding the use of the Tipo inlet camshaft:

“The increase in lift at tdc is very modest - and remembering that my suggestion was to change the inlet cam only and retain the std turbo ex cam, this is not going to have any noticeable effect on idle - and pickup from idle. The reality is that we have not increased the overlap event to any real extent because the ex phase is unaltered… However the peak lift and lift integral (area under the cam curve) is quite a bit more - … The overall effect will be more torque everywhere and the rpm at which peak power is developed will be a bit higher to because the cylinder is filling more effectively - in other words the engine is 'breathing' better…This does presuppose that the ex valve, port and manifold can cope with the increased massflow of ex gas, without getting into a serious pumping loss or backpressure problem which I can tell you on the 8v and 16v TC units it certainly can, either in standard trim or ported/modified.”

My Tipo inlet cam timing (as requested):

Inlet opens: 1 deg BTDC
Inlet closes: 45 deg ABDC (226 duration) 10.15mm lift

My previous Thema S3 Turbo Inlet Cam (below):

Inlet opens: 0 deg BTDC
Inlet closes: 43 deg ABDC (223 duration) 8.6mm lift

As mentioned before the exhaust cam is identical (43-0), 8.6mm lift.

It seems my Tipo inlet and Thema exhaust cam is not a good formula.I now need to choose 1 of 4 possible solutions to solve this reverse flow, poor purging/ scavenging at low RPMs. I have placed them below in my order of preference:

1. To use a new Evo 1 Integrale exhaust cam (as I have one) but only if it were to achieve similar results to option 3 (below). Guy would this work? I have searched and can not find the 1992 Integrale Evo 1 exhaust camshaft data anywhere. If anyone reading has then please post it up.

2. Return to original cam setup (as suggested). This is probably best.

3. Modify current setup by advancing exhaust from 111.5 BTDC to 108 or 106 degrees, opening later and closing later (need dti, protractor etc to do this). As suggested this may improve purging and cross scavenging.

4. Return to old turbo (not an option I’d like to consider at this stage).

What I need to know is what would the likely outcomes be for each solution and best for a road car?

Thanks again!

Good report, well done!

The Integrale ex cam lift is lower, 7.5mm, timing 30/0.

I do know I'm driving a bit 'blind' without knowing the lift at tdc on your setup at all. I just don't know what would happen if the Int cam were used, after all, you don't have the Int turbocharger...! My advice is definitely: change your ex cam timing from current to the 16v Integrale setting of 105 deg FL BTDC and report what happens. I don't imagine there will be a piston to valve clearance problem but I'll have to leave that to you to check. This later opening/closing of the ex valve will give more overlap at tdc but at the same time extend the power stroke. I think we will see a noticeable change in engine behaviour - whether better or worse doesn't matter - so long as I get the feedback, then I can start filling in some of the 'blanks'. If the response gets worse, the issue may be too much overlap for that turbo rather than too little and one might perhaps try going to 112 or even 113 deg.

Be careful with you cam timing.

GC

Guy; thanks for help so far and speedy reply.

I have just found out the information I acquired for the S3 Thema cams both having a lift of ‘8.6mm’ were wrong, not by much and I don’t think it changes theory you have suggested so far, however for your reference here are the correct timings from an actual Thema S3 Turbo manual:

Original Thema S3 Cam Timings:

Inlet opens: 0 deg BTDC
Inlet closes: 43 deg ABDC (223 duration) 8.22mm lift (not 8.6mm as thought).

The exhaust cam is identical (43-0); 7.07mm lift (not 8.6mm as thought).

Because of the above error I thought both my camshafts were the same; however it does mean that because of the phase sensor mounting issue I am currently using the original S3 Thema inlet cam (8.22mm) as an exhaust cam.

So my actual current setup is:

Tipo Inlet opens: 1 deg BTDC
Tipo Inlet closes: 45 deg ABDC (226 duration) 10.15mm lift

My exhaust cam (previously inlet with the same timing but different lift) is (43-0) with 8.22mm lift.

Does this change your Theory?

You said you’ve “…done many turbocharged competition engines with fully-ported head, n/a inlet cam and std turbo ex cam and got great results.” Were these Integrale engines with the Tipo cam?

I ask because you wrote “The Integrale ex cam lift is lower, 7.5mm, timing 30/0.” By this I presume you mean the Integrale camshaft will open earlier and close at the same time, therefore not “…opening later and closing later” as suggested for the cure to the soggy bottom. So the Integrale cam is no good, right?

Once I have an answer to the above I’ll reply to let you know what I think my plan of action should be.

Thanks as always!

OK, some more info, well done..

I really need to know if you have read the GC cam timing info in GC V/W see:
phpBB3/viewtopic.php?f=3&t=213

and also whether you actually have:

1. Large diameter protractor, long-fingered DTi 0-12mm lift scale, magnetic holder for, steel plate to bolt it to the head (to ascertain full lift ) and similarly an adaptor to go down the plug hole to determine crank true tdc.
2. Adjustable cam wheels.

If you don't have all those things you simply cannot do what I need you to.

I want to dwell on some technical aspects of cam timing before we go any further.

I have put up a cam timing diagram which shows your current cam timing setup and also put a downloadbale version on the post too, so you can put in your other figures to see where full list will be.

1/43 inlet timing? Well what does it tell you? Not much! It tells you that at Fiat, when the engine spec was being published for EU approvals, and during checking the camshaft timing using (note carefully ..) an 'industry adopted standard' wide running clearance of 0.8mm (not the 0.4mm we shim up at) the cam timing was, well, 1/43. So the duration of the cam with that wide clearance was 1+43+180 deg of crank rotation ie: 224 deg. But - in the actual built engine the true duration is much longer, because the cam base circle is not miles away from the bucket. So you cannot read much into the 1/43 figure except that, yes if you sum them up like this:

[(1+43+180)/2] - 1 = hey presto ... 111 deg, which is where a cam of that timing will produce full lift - 111 crank deg after tdc.

Or will it?

Not quite. A cam will produce full lift where the cam_pulley_tells_it_to! The only thing 1/43 tells you is that if you set inlet valve opening at 1 deg before tdc, it will, well close at 43 deg abdc. I certainly doesn't assure that the FL will be 11 deg, unless you kept the same pulley on the same engine.. You can set FL anywhere you want on any cam. This is where adjustable pulleys come in and I implore you to read my V/W article!

Take a look at the Integrale pulley. The dowel hole is alway in line with no 1 cam lobe, but the timing notch could_be_anywhere according to what engine the pulley came off. So you could change either cam to one with different 'timing' and think you've changed the FL position and thus critical overlap characteristic - but unless you've changed the pulley - you haven't, all you've done is altered the position of open and shut!

What I am trying to do with you is determine what effect the overlap is having on your motor. I mean this in the most professional way - there is no point comparing to anything I have ever done because nothing I've ever done is like your motor! (remember I said copy someone else's setup - you can't really copy me because, whilst my exp of successful - cam swaps on turbo Fiat/Lancias is more than most - I have no idea what your turbo characterisitics are..) So let's forget other peoples' setups and concentrate on yours. If you move the ex cam timing so that FL is closer to tdc it will increase the overlap event. I think the engine will either get worse or better and depending on what you report we can make some decisions based on that. It may not change at all. Whatever happens it will mean something to me.

You will need to be 100% accurate with your determination of the FL posns of inlet and ex. Inaccurate measurement will at not help, and at worst activively hinder the search for 'true cause'. And as I said above, if you don't have the right equipment, you cannot do it at all and there will then be little I can add by way of guidance. Don't forget I have remarked on the possibility of other causes of the problem, so I'm 'feeling my way on this' to a great extent going one-step at a time, easiest things first, and depending on you to follow-thru - if that is indeed how you want to tackle this.

GC

Guy… thanks for the link regarding the cam timing diagram and especially for the Excel file (which can be modified)! I am impressed.

I have some more information for you. I have been in contact with ‘BoazG’ on this forum (the other Thema Turbo S3 owner with the similar 'soggy' bottom problem) and can confirm his setup (below) is very similar to mine, except he runs the standard .36 A/R turbo (mine is a .62 A/R). My compressor map here: http://www.atpturbo.com/root/maps/gt28rs.htm):

BoazG’s setup:

Fiat coupe turbo head
34.5mm inlet valves (standard coupe valves)
29.5mm exhaust valves (S3 Thema turbo valves)
N/A S3 Thema inlet cam (similar to Tipo n/a inlet cam)
S3 Thema Turbo standard exhaust cam (7.07 lift)

BoazG's setup suggests the N/A inlet cam may be the reason for the soggy bottom (as he has standard exhaust cam and turbo) – it is either this or the new larger inlet valve size (we both have).

The only difference between the N/A inlet cam (we both use) and the standard cam seems to be the lift, the timing is not far out. This is worrying at it also suggests to me that going back to standard setup may not help which in turn points to the new inlet valve size! Either way we can rule out turbo and exhaust cam, right?

What are your thoughts?

Guy… I have experience in fitting but unfortunately I do not have the tools or the familiarity to do what you need me to do to rule this experiment methodical.

Is there another way to tackle this, perhaps going back to the standard setup (if the above is wrong and it will actually help?). After this experienced specialists (such as yourself) will be required, unless you can think of a possible cam choice solution that may fix the issue?

Thanks so much again!

No, I simply cannot offer any other way of dealing with this other than resort to the good old 'Institute of Applied Guesswork', which - whilst it is widely employed here and there- isn't my way, sorry!

This being a race engine website it is beholden on members to uphold the ethic of 'doing it properly', which is why I write long and (laborious?) posts about, er, the most professional method. The most professional method I can think of anyhow, or the method I'd use, which amounts to same thing..

Naturally, if you happen to hit on a 'robust' solution by any other method, good for you!

Best get those tools and go back to basics, you'll be the better off for it.

GC