Rally car camshaft

[Rallyace 3]

Over the winter I will be building a 1900 engine for my road rally car. I am interested in building an engine that is has good torque and would be happy with perhaps 130BHP at the wheels. The regulations in place mean that I must retain the injection and plenum chamber, however I am free to run without the standard air flow meter. As I understand it the AFM is the main limiting factor when determining the  amount of duration and lift that can be used, whilst maintaining good tractability and road manners. The guy that will be tuning the car is familiar with OMEX products, so the ECU will be an OMEX 600. I'd be interested in hearing the thoughts of those that have experience in building and tuning the XU engine to this level. I'm not after a full race screamer and don't intend revving it beyond 7000 -7500.  TIA

[DamirGTI 342]

Compression first (dynamic) .. build up at least 10.8 ideally 11.3 CR and try to reduce some squish clearance while at it , then you'll have good base for everything and anything else you plan on putting or doing on the engine performance wise (except turbo/forced induction !) .. performance/rally cams especially , waste of time and money if plan to run them on std. compression ratio .

 

AFM , really not the "limiting factor" as far as flow ... it's the pulses from the aggressive cams which makes it kinda go "bananas"/erratic signal , but can be rectified by re-adjusting the AFM spring tension .

 

D

[petert 588]

If you have an Omex, you won’t need an AFM. So no reversion issues to worry about. As said, build it 11:1 - 11.5:1 and find a PTS7048 cam, or similar. Be careful with valve spring bind if using std springs. It’s difficult to get enough seat pressure and not get spring bind with over 0.460” lift.

[Rallyace 3]

Thanks Damir and Peter, 

 

I will follow your advice and aim for the compression ratio that you suggest. I have ported a head along the lines that Damir covered some time ago and I understand that Guy Croft approved of the modifications. Most of the focus was around cleaning up and improving the flow around the short side radius and some of the more obvious seat to throat smoothing. I have removed a few rough casting marks in the ports, but have done nothing to enlarge them and certainly haven't done any polishing. It looks like the head, which came on an engine that had recently been rebuilt has had a light skim, so I'll check the volume. I'll do this in conjunction with the 1900 pistons, but I do have a set of 1600 pistons, so that's another option for the increased CR. I'm not sure about the skill level of the local machine shops, so machining liners and decking the block to match may not be an option to reduce the squish. 

I'll see if a PTS7048 is available, but will probably have to look for an alternative. Piper do the  P16B285B and P16BP300B and Kent offer similar products. It seems like the choice is between something with 285 degrees of duration up to 300. With tractability in mind, I don't think that anything over 300 degrees of duration is going to be suitable for my needs. In your experience, is there a cam that closely matches the PTS7048 that you would recommend? 

In junking the AFM I am assuming that I will have to attach a MAP sensor to the plenum chamber. I can get hold of a Mi16 flywheel from a friend, so crank position and speed input would be detected from here. I would quite like to get some weight out of the rotating parts. Is it possible to (safely) get the Mi16 flywheel down to the weight of the 1600 item?

I am running a tubular exhaust manifold. Will it be essential/beneficial to install a lambda sensor? What else will I require?

I realise that there are a lot of questions and I really appreciate your help.

 

Jeff 

[pug_ham 244 3 Cars]

Try running a search through old topics / posts on here with regards to the PTS7048 cam, I'm sure there was a catcam one that was very similar in lift & duration to it, if not then possibly a Newmans cam which will give you a decent spec cam.

 

The standard Mi16 flywheel is roughly 6.5kg's as standard so already lighter than a stock 1.9 item and you can get it down to under 5kg's without to much work.

 

I had the outer edge pockets machined out on the flywheel fitted to my Xsara VTS (GTI-6 engine) earlier this year & that dropped it from 6.1kg to 4.9kg.

 

 

g

[petert 588]

Crow Cams in Melbourne have essentially the same grind as the PTS7048 on the exhaust of grind 886 (attached). I'm just about to get on old PTS7048 reprofiled with that on both the inlet and exhaust lobes, on 106º centrelines.

 

ie

Adv duration 296º

Duration @ 0.050" 251º

Max Lift 0.454"

 

In regards to pistons, use the 1.6L version. It's much easier to get the compression above 11:1 and I think you'll find the compression height is 37.50mm, compared to 37.12mm on the 1.9L pistons, negating the need for any adjustment in squish height.

[DamirGTI 342]

18 hours ago, pug_ham said:

dropped it from 6.1kg to 4.9kg.

 

 

g

 

Is that just machined or machined and balanced ?

 

D

[pug_ham 244 3 Cars]

3 hours ago, DamirGTI said:

 

Is that just machined or machined and balanced ?

 

D

Just machined, I didn't have chance to get it balanced but looking at the factory balancing spot drill holes in the back, we removed the material from the same size pockets between the clutch cover mounts which didn't hit them so I wasn't too worried.

 

Certainly can't feel anything with it fitted to suggest it's in need of another balance.

 

g.

[Rallyace 3]

Thanks again for your help. 

[DamirGTI 342]

14 hours ago, pug_ham said:

Certainly can't feel anything with it fitted to suggest it's in need of another balance.

 

g.

Interesting

 

I've a few of them MI16 flywheel's , will get my machinist on a blower !

 

D