The Doris Dilema

[RussellT]

OK just for the glory, a challenge for the RTOC.
Doris used to have 204 bhp in race trim. At the end of 2012 she dropped an inlet valve. It was repaired and she had 180 bhp (all on the same RR at Scoff's) she then dropped another inlet valve we changed all the remaining old inlet valves. I had the head skimmed to raise the compression ratio back to standard. We ran her again and the result was the exactly the same.
The timing is checked but tends to wander when it shouldnt, tthe fueling is solid as is the boost pressure attached is the graph of the power run.

The challenge, she is booked into Scoff at EFI on 14th Feb for work, state the root cause of her problem with a tie breaker of nominating the final at the fly wheel bhp.

https://www.rtoc.org/files/Technical%...lots%20001.jpg

[Woznaldo]

Russell, you say you had to have the head skimmed to restore the compression ratio. Why would it have changed? Did you machine the pistons? Are you running low comp pistons and skimmed the head to bring back to std comp ratio?

Is the question why you are dropping valves or why the motor isn't making 204bhp anymore?

[Matt Cole]

Is it on stock AEI? I would look at the timing.

[Matt Cole]

Also the gear box. Drive train losses could be up.

[Matty]

Have you done a leak down test to see if it's holding pressure? Cylinder pressure could be passing by the rings?

Ignition timing will also effect the AFRs you could have the optimum AFR for power then if the timing were to advance you could end up with it running lean, or if it retards could run rich, even a few degrees in timing can make a massive difference in AFRs and power.

How much by and when is the timing changing?

Is the cam timing still the same as before? If you're running a vernier pulley, could it have moved slightly when you dropped a valve...worth checking? May also be worth checking lift on each valve, to check none of the lobes on the cams are worn.

Check colour of plugs... The lambda is only taking an average of all cylinders, so you may have one cylinder running worse than the others.

[Trevhib]

Weak spark through ignition probs? Is the dizzy drive adjustment nut loose?

[RussellT]

OK
Forged pistons gave a lower CR than standard.
Running Adaptronic ECU trigger wheel on crank pully bolted to it apparently crank pully is rigid on crank. (so no diff) New coil wasted spark set up. New timing chain last year No vernier pully.
All cylinders compression tested and the same (159 psi) boost circuit leak tested
here is a plot of the fueling and boost
https://www.rtoc.org/files/Technical%...lots%20002.jpg
The engine sounds OK revs well fuel pressure is solid all the bent pushrods were replaced after the last valve went.
The idea you have to predict what Scoff will find (if anything)

[RussellT]

OH and yes the question is what has taken my missing bhp?

[LiamR]

My amateur mechanic guess........knackered head.

185bhp is my guess but doubt it will be needed

[RussellT]

[Matty]

Graphs look nice and consistent.

I'm going for cam timing or a touch of clutch slip at peak torque.

[RussellT]

Bump any more answers predicted max BHP torque before I reveal all?

[Slammed 66]

191bhp and 207lb/ft

Reason for power loss: nipped piston ring.


Hopefully she gets a clean bill of health though

[RussellT]

Slammed very close on the power and torque but not the underlying problem. Some one has mentioned it though.

[Rob1980]

Mouse running the opposite way inside the rollers... Now dead from exhaustion due to high speed running....

[Matt Cole]

Come on Russel put us out of our misery!

[Alex]

I would say something head related like a gasket for possibly something a miss with regards to the work that's been done on it when the dropped valves/skimming was done. Spill the beans Russ!

[rabbitstew]

Mouse running the opposite way inside the rollers... Now dead from exhaustion due to high speed running....

[RussellT]

OK
The cam timing was way retarded at 121 deg, it had 8.4mm lift. The new one is timed at 112 deg with 9.4mm lift. Power now 193.3 with 209.6 lb/ft torque.

And the brakes seem to work better

[Alex]

Any idea how it became retarted Russ?

[B18ftMOJO5]

Good read didnt even consider the timing. lol.

[Matt Cole]

Aha. So who gets the prize Russel?

Now I guess the brakes are better because your pulling more vac?

[RussellT]

Well as for who "won" as it was just for the honour I will let the forum decide.

Re how it became retarded, I bought the cam off Ian Nixon years ago and as the timing marks were aligned (no vernier cam wheel) I suspect that whatever the cam was had to be installed with the timing adjusted. When the engine was rebuilt my team naturally aligned the timing marks. Just a theory but would explain why she was down on power straight after the rebuild. I suppose Ian could answer that one.

[RussellT]

The final power run graph with the "before new cam" plot in red.

https://www.rtoc.org/files/Technical%...IMG_1323sm.jpg

[Trevhib]

Wow, what an improvement, and all for the sake of cam timing. Shows how important it is.

Really glad this issue is fixed as I want to see what the new Doris can do against the class leaders on track this year