59 replies to this topic

[Tiny]

Chop: I've currently got a set of rims with my drag rubber on it, so that's by far the easier way to go. I'm not keen on swapping diff centres just to go racing.
It also sticks with my preferred philosophy of "street car" as the only change is the tyre!

Cheers, and the thought HAD crossed my mind.. Struggler bought my 4.11 Spooled centre to take the temptation away from me

[LhMusL]

Good work Liam them some nice numbers!!

[Struggler]

What is the difference supposed to be between the first 1/8 and the second 1/8th? My quickest time saw a first 1/8th 8.1 @ 87.72mph while the second 1/8th took 4.5 @ 24.81mph, looking at the splits the 60-330ft is also slower than the rest. I was attributing both these to lack of grip early on, would this be a fair conlcusion?

Any other observations are welcome.

Cheers,

Your eighth mile times and quarter times add up OK, but your terminal speeds should be closer. The 117mph one is obviously incorrect, and even 112 is weird.

[LXCHEV]

Yep, Heathcote's timing is known to throw some 'weird' numbers up here and there. I had a 125mph pass, but every other pass was my usual 114-115mph.

[Struggler]

I would have expected the 112 to be 110. You wont pick up 2mph that easily.
JMHO

[Struggler]

Liam, the difference between the 3rd and second run is all in the 60'. The time you have picked up in the 60' stays with you the whole track. If you subtract the faster 60' time from the slower then add this difference to the faster ET you should be really close to the slower ET. I'm sure earlier in this thread I spoke of splitting up your time slip and comparing different splits and speeds. Cars usually run the same second half of the track, its only the first half that makes a real difference to ET. As DA pointed out acceleration is greatly reduced in the second half of the track as air resistance is greater and you don't have the torque multiplication of a gear ratio less than 1:1.

As for your dyno results..... anything with a physically smaller converter will heat the transmission fluid rapidly, causing a loss of gearbox efficiency and consequently a loss in rear wheel power. Allowing the trans to cool will always give a higher reading after a few power runs. Engines usually make a bit more power when hotter, probably because the oil is thinner, creating less parasitic drag on rotating masses. Getting the engine hot then feeding it cold air will make the most power (usually).

Hope I have explained this in english and you get something from it.

[Tiny]

Hey Liam! Firstly well done mate!

Your times sound very similar to mine with my new engine combo so i'll post up mine and my ideas! I'm no expert to give advise though mate!

My increments:
60' - 1.767
330' - 4.995
660' - 7.659
1000' - .000 - fault
ET - 11.934
MPH - 114.60

i think always work opn your launch, gains made there are carried thru to the other end!
If you launch with higher rpm then you could see an RPM gain over the line too which puts you in your max power zone as well!

Best of luck!

[Struggler]

Liam, you need to fit lower diff gears to get the revs up at the finish line. Ideally you want to cross the line at about 7000rpm if your engine makes peak power at 6600. This will also lower your 60' times. Do this before thinking about changing the convertor.

What pressure are you running in those slicks ? I would recommend about 12psi.

Leave the line at idle if possible. This gives the engine the biggest pump shot possible out of your carb and hits the convertor hardest to make it work properly. If you don't have a transbrake then stalling the car at the line is a waste.

[Struggler]

Leave the line at idle if possible. This gives the engine the biggest pump shot possible out of your carb and hits the convertor hardest to make it work properly. If you don't have a transbrake then stalling the car at the line is a waste.

Hopefuly not a stupid question, but would this also apply to a stock VT V6 with small street tyres on it? (but in reverse)

The 2 times I have run my Commodore, I loaded my revs up slightly to reduce a bit of wheel spin, or did I, I cant really remember why I did it, it just felt better than dumping the accelerator from idle ...

Yes, I always load up the driveline a bit by raising the rpm to about 1200-1500 rpm but there is no point revving it any harder than this, in fact as I said earlier it is a detriment.

Liam, get a Moroso power speed calculator (its a big slide rule type thing) as it has a rpm V's speed scale on it. Alternately you can access the many calculators online. I use this one.... http://www.wallacera...Calculators.htm

At 115MPH with 26" tyres you will need about 4.56 gears assuming 4-5% convertor slip. If your convertor is looser you will need a taller gear. Yes that is a fairly low gear but thats what you will need to run the best ET.

What gear do you use now ?

Also if running 12 psi in your slicks please use a conventional or bias ply tyre on the front wheels (NO radials).

[Tiny]

I've only ever stalled up to around 12-1500 Rpm at the moment too and i feel there is a small flat spot cause my cam doesnt really get into it's power range till the 3000 mark! THat's why i'm going up to a bigger stall soon.

My mickey T ET streets like around 17Psi, and SMALL burnouts. I've found even though I prefer a big smokey skid ( cause i'm a hoon!) the tyres seem to grip better if you just give them a little one. Maybe a big skid overheats them? I dont know!

Struggler: I assume your talking about sticking with the same style tyre all round and not mixing bias ply and raidals front/rear? I've run the ET street raidals and my normal street tyres on the front down to around 14Psi at the track ( 14Psi in the rear obviously) . Am i right in saying that your recommendation is to keep the car stable?

[Struggler]

Struggler: I assume your talking about sticking with the same style tyre all round and not mixing bias ply and raidals front/rear? I've run the ET street raidals and my normal street tyres on the front down to around 14Psi at the track ( 14Psi in the rear obviously) . Am i right in saying that your recommendation is to keep the car stable?

Exactly.

Also I found similar results with the Drag Radials..... small burnout and 16psi works for me.