Red hot manifold only on middle cylinders...

[debaron]

What causes red hot manifolds?


Cylinders 3 & 5 and 4 & 6 and are running red hot when car is driven anything more than mildly urgent.

Lambda is fine (nothing above 14.3)

Precats long gone, as are plug extenders. Main cat is still in

I'd expect it to be on all cylinders if it was lean or timing. Car drives fine until the heat burns a HT lead....

Any ideas anyone?

[Zener]

Choked/duff inj ? air leak on that intake runner only 2 things can create this condition too lean AFR or retarded ign timing

[debaron]

Zener said:

Choked/duff inj ? air leak on that intake runner only 2 things can create this condition too lean AFR or retarded ign timing

Good call on the air leak on intake. It's possible - my inlet manifold isn't a *perfect* match to the heads (skimming/decking etc) but it should only be perhaps 10 thou out plus I'd expect to see leaking coolant if it were that bad. Worth a check though

[Steve_D]

The coolant passages are at the ends of the line of ports. An air leak on the middle cylinders would point towards a bowing of the mating faces.

Steve

[spitfire4v8]

what do you mean by red hot ? do you mean that after a run you open the bonnet and the manifolds are actually glowing red ?

[Pink_Floyd]

Check your timing, I had a similar issue and the timing was out. adjusted the distributor and no more red headers.

[debaron]

spitfire4v8 said:

what do you mean by red hot ? do you mean that after a run you open the bonnet and the manifolds are actually glowing red ?

Yes exactly this, but only the middle 2 cylinders on each bank.

[Pupp]

If you're still on a mechanical dizzy, check the adv/retard mechanism is working. If insufficient advance occurring, combustion could be taking place in the ex ports or headers... that only visible on middle pipes may just be down to wall thicknesses or hardness after bending etc.

[spitfire4v8]

^ yes checking the advance is the easiest first thing to do. You might still have a blocked main cat though too.

For the timing- you want to get it right, so make sure your crank pulley TDC line is in the correct place - check it first before checking the timing.

[QBee]

Pink_Floyd said:

Check your timing, I had a similar issue and the timing was out. adjusted the distributor and no more red headers.

You aren't a member of the Royal Family by any chance?
They had a bit of an adjustment the other week and got rid of a red header

[debaron]

QBee said:

You aren't a member of the Royal Family by any chance?
They had a bit of an adjustment the other week and got rid of a red header

Hahaaaaaaaa very good QBee