Picked up 2 mph on Octane boost

[dbv8]

I would be interested on peoples thoughts as to why and maybe where i can improve my tune.

I was racing at York last weekend. The TVR was quite consistant despite the weather and was running terminal speeds of 114.5 mph.
On the Monday a friend offered me half aa bottle of Royal Purple octane boost so i dumped itt in my tank which had about 15 litrres of Vpower in.
First run i ran 114.8, then 116.2

My engine is a 5.0 with a solid cam and fairly high CR of 11:1
Do we think its crying out for higher octane?
Maybe i could add a couple degrees advance but its set at 34 degrees already.

What do we think?

[SuperV8]

Was it windy?

Unless your ecu/engine can take advantage of the additional knock protection I can't see it helping much.

[dbv8]

The weather was consistent both days, cool with a tailwind.

When I had the car initially mapped after the rebuild my first terminal was only 109 then went 111, 113 at York.
2 weeks later at Shakey it rose to 114.5 and levelled out.

I put this down to the engine still bedding itself in.

The engine gave 330 bhp on Bailey Performance rollers before running that 109 mph. I reckon it's got to be a fair bit more now it's hitting 114+ regular.
I want to get it onto another rolling road soon. I think it will top 350 easy enough maybe more

[sidecar]

I would be interested on peoples thoughts as to why and maybe where i can improve my tune.

OK I have couple of theories off the top of my head!

1. Maybe your engine is suffering from trace detonation and losing power, the octane booster got rid of the detonation so the engine made more BHP.

2. Maybe your ignition is over advanced. Any engine will produce peak torque for any given RPM when the peak cylinder pressure occurs at a crank angle of 14-20 degrees ATDC. If the peak cylinder pressure occurs later or sooner in the power stroke then power is lost. The octane booster probably slowed down the flame speed which means that the peak cylinder pressure is occurring nearer the ideal crank angle and that could be why the power went up.

I know that this goes against what lots of people think which is to always push the ignition timing up and up but really this is not the right thing to do, you can end up running way more advance than is required. Your engine may still not detonate in this state but power is lost due to the 'negative' work that the engine is doing.

Another 'fly in the octane booster' is that in your case the 34 degrees 'all in' may be right for your engine but the over advance state might be lower down in the RPM range, the octane booster would still help here and this would still have an affect on your 1/4 mile times. In other words it could be the timing curve that is wrong and not the all in figure. This all ends up being a bit of a 'mind blow' which is why I think about this sort of stuff but I have done very little to test it out on my car!

People boast about how much advance they are running, this just indicates how poor the combustions chambers are, or that they have just over advance the engine. The better the engine is in terms of flame speed and overall design the less ignition advance that it needs. (Unless it has been built with to high a CR, in which case the advance has to be 'pegged back' just to stop the engine running into detonation)


EDIT... Just done some googling on octane rating and flame speed, it seems very hit and miss whether the flame speed depends on the octane rating which blows my second theory out of the water (possibly!)....

http://www.2strokeheads.com/tech-octane-detonation.htm

[mgbv8]

2mph is a good improvment if its doing that everytime for a few days out in various weather conditons. But 2mph could also equate to a few degree's lower air temp or a few mph difference in wind or a slight difference in track temp / tyre temp etc etc....
Without proper weather data such as windspeed and direction + temp and humidity its just one of those things Del.

Also engine data logs between these two sets of runs may tell a tale?

The MGB hovers around 9.6 to 9.7 seconds at around 137 to 140 mph. But one day back in 2014 she ran her usual 9.6 as she had been doing for several passes that day. But on one pass she still ran 9.6 but with 145mph ?? I have no idea why this happened because she never did it again.

[stevieturbo]

Not sure it's a valid enough test really.

how many runs were there at 114mph prior to adding the stuff ?

Maybe runs through the day were just getting better anyway ? Maybe weather played a part ?

Have you datalogged all runs, to see if gearchange points etc were the same, took same length of time etc ?

[dbv8]

Here are all my runs from last weekend.
Maybe the 116 was a it of a fluke or just a good run.
It has to be said that it rained after that 116 run and the track never came back

Sunday 1/5/16
Run Time Category Reaction 60 Foot 1/8 ET 1/8 MPH 1/4 ET 1/4 MPH
10:00:20 RWYB - CAR 1.0300 2.1870 8.3010 89.8200 12.6432 111.8800
10:41:48 NSCC 0.8789 1.8321 7.8500 89.8200 12.1671 114.2500
14:03:57 HOT ROD 0.8728 1.8163 7.7222 91.0800 11.9991 114.5500
15:04:28 NSCC 0.9049 1.8520 7.9182 89.7800 12.2592 112.1800
15:48:44 NSCC 0.6810 1.8639 7.8719 90.5700 12.1621 113.0400
16:04:43 NSCC 0.6190 1.9002 7.9061 91.2700 12.1959 113.3900

Monday 2/5/16
Run Time Category Reaction 60 Foot 1/8 ET 1/8 MPH 1/4 ET 1/4 MPH
10:33:52 NSCC 0.9201 1.8147 7.7877 90.1800 12.0787 114.8400
11:02:09 HOT ROD 0.8232 1.7826 7.7188 91.6200 11.9538 116.2700
15:37:17 HOT ROD 1.0388 1.8481 8.0682 87.3700 12.6031 110.0000
15:50:17 NSCC 1.5880 1.9599 8.0309 89.0900 12.3840 113.0400
16:48:36 NSCC 0.8929 1.8521 7.9849 88.9600 12.3511 111.6700
17:51:14 NSCC 0.6139 1.8679 7.8301 90.7300 12.1081 114.7600