02-01-2017

Update - Stockcar Exhaust Manifold

It has come to the attention of Midas Speedway New Zealand following technical inspections upon request, that competitors running V6 Holden engines have been in breach of the following rule;

T12-2-49 EXHAUST SYSTEM

(a) An OE cast iron exhaust manifold must be used.

(b) It can be fitted in any configuration, as long as the manifold and head surface is not modified.

(c) The following modifications are not permitted: -

  (i) Standard exhaust manifold may not be of two front or two rear halves.

  (ii) No extractors permitted.

  (iii) Spacers between cylinder head and exhaust manifold are not permitted.

(d) Mufflers are free, however sound levels must comply with Rule S5.

(e) Exhaust pipes must discharge towards the rear, or underneath the vehicle.

(f) All side exhaust systems extending past the A pillar must be shielded.

What was picked up?

We are now aware of cars running the right-hand exhaust manifold upside down, so that the exiting exhaust pipe is orientated towards the front of the car. Comments have been made that with the pipes exiting to the rear, there is either not enough room for the pedal box to be constructed adequately, drivers complaining of getting rather hot feet or brake lines melting/brake fluid boiling.

It has been common place in the past for V6 and V8 Stock Car engines to use a left-hand exhaust manifold on the right-hand side of the engine so as the exhaust exits to the front, the issue for VS Holden competitors is that when using a left-hand manifold on the right-hand side of the car, the exhaust manifold fouls on the oil filter.

So where is the issue in regards to the rules?...

The issue is not with which manifold is used, or even in which orientation it is used. But with the Holden V6, 2-4 of the bolt holes in the cylinder head have to be modified to use the correct manifold upside down, and the rule quite clearly states ‘as long as the manifold and head surface is not modified.’

The original intention for this rule was to stop competitors from raising the position of the ports in the head then in turn lifting the manifold or changing the angle of the head surface to gain an advantage. And this rule stood quite well at the time as these Holden V6 engines were not in circulation.

So where does this leave us?...

We have no doubt that the reason for modifying the exhaust face on the Holden V6 to run the exhaust manifold upside down is purely for the purpose of fitment, however, it does not comply with our rules.

We have spoken with several car builders as to how they would remedy this problem. The solution from most is that they would use the 2 standard bolts that do fit, and make clamps from another part of the head (not the exhaust face) and clamp the manifold to the head. This solution complies with every part of the rule.

For the extra holes that have already been modified into the heads, these must be plugged in order to comply.

If we were to deem the non-functioning extra holes as non-compliant, then we would also be forced to start deeming non-compliant any extra bracket holes, temperature sensor holes, any repairs to engine blocks, modification to water outlets etc.… and we really do not wish to go down that road.

To conclude:

-Only the standard bolt holes may be used on the exhaust face of the cylinder head.

-There is no minimum to how many bolt holes must be used.

-Any additional clamps or fasteners cannot bolt directly to the exhaust face of the head, but may come from elsewhere.

-Any previously modified holes must now be plugged and will be considered as a ‘repair’.

Midas Speedway New Zealand, want to make all racing as fair and reasonable for all competitors as possible, whilst also maintaining the highest standards of vehicle compliance.

The Midas Speedway New Zealand Board reserve the right to re-visit this position at a later date following feedback and discussion with the Technical Committee.