Hello all,

After a blinding day at Thruxton 19th July, I'm wondering if there is any great advantage of going big turbo over my current hybrid setup for a track day car? Thanks

I'd go for a quicker spooling turbo every day of the week; just about every track in the UK will have at least 2-3 corners where you only lift off for a fraction, the smaller turbo will give positive boost far more quickly.

 

I'd go for a quicker spooling turbo every day of the week; just about every track in the UK will have at least 2-3 corners where you only lift off for a fraction, the smaller turbo will give positive boost far more quickly.

Yea,

That's what I'm thinking, just after someone with experience of both.

 

Look at G25-550 quick spooling but expensive!! That's what I'm aiming for ultimately.

 

Not a tt but check out team prawn racing on you tube/Audi-sport.net he built an A3 track car and now competes so there could be some useful information regarding engine setups for track use.

 

I've seen some of those video's, he's gone full Stroka Mota now.

 

As above probably the best you can get in terms of low down response and 450 reliable bhp is a G25-550. The issue with any K04 size turbo is the hot side is just too small. Back pressure is high so regardless of the boost the turbo is making you don't have the flow. Water meth is a sticking plaster that hides some of the issues with small frame turbos, the compressor wheels are inefficient at high boost levels which means they heat the air a lot resulting in high IAT's.
If you are just comparing the boost response of a k04 against a big turbo it doesn't really tell the story. A big turbo will make a lot of power with smaller amounts of boost than a K04 because there is more flow.
I did the stage 2 275bhp and it was good, I considered a hybrid but looking at the advantages of a larger frame turbo I went for that. If you pick the right turbo boost response on track is not an issue at all, If you were doing something like an autotest where you are stopping and starting and accelerating short distances a big turbo wouldn't be better.
I run a G25-660 and don't have issues with lag.

 

Think I'll go with the water - meth until the speed lust gets me some more.

As it is my talent is running out compared to the cars performance at the moment.

 

I'm no expert but you might find decent brakes make a bigger difference. I have had loads of cars and every single one apart from the Golf 2009 TDI my daughter and Son In Law gave me have not been able to manage the Buckingham to M1 South string of Milton Keynes round-abouts without brake fade (obviously as fast as you can within the law). That's about 10 in a row, even new cars struggle a big new Mercedes was overtaking going to 60-80 then braking and 7 roundabouts in, stopped trusting their brakes.

What MAF g/s through-put are you currently getting? I have opened the chinafold up to 45.5mm to just about match the AET Hybrid. To try and get more than the brick wall of ~260-265g/s and taken a 5 psi spring from actuator and am just about ready to put the gearbox etc back on after changing the clutch to a Sachs DMF and paddle friction disc. Still need to drill a hole through the passenger footwell into engine bay

At least if you change to a big turbo after your brakes and probably a clutch if you're still 370 ft/lb torque (I can't imagine that lasting much longer) they'll still be good.

 

Think I'll go with the water - meth until the speed lust gets me some more.

As it is my talent is running out compared to the cars performance at the moment.

I don't agree with Karl's 'sticky plaster' comment regarding water meth, it adds octane which combats pre-ignition so the ECU doesn't pull any timing. I would say it added 10% extra bhp and more torque. Where I was trying to keep the ignition retard to 3 on a couple of cylinders and did good runs on early frosty mornings, if I tweaked it a tiny bit it would go over the edge with higher figures as soon as I added water meth all that went away and I got as far as this 260gs wall.. hopefully now the CF is opened I will get closer to the 295g/s turbo design throughput

I suppose it is equivalent to using shell v-power instead of 95 unleaded.

 

Stuart,

I've got Mtec discs front & back with EBC blue pads on the front and the Mtec pads on the back with castrol react fluid. This holds up well for 4 laps of Thruxton and then starts to fade on the 5th (didn't do any more than 5 in a stint and it was very hot over 30c 19th July).

With the ambient temp above 10c & below mid-teens MAF is topping out just over 240, and the timing is about 20 bdtc (I've adjusted the timing map and the timing knock pull map), when the temp is over the mid 20's it gets the double whammy of less O2 and timing pull due to high IAT's so doesn't even get to the point of knock leading to the MAF dropping down to about 230 or below depending on the actual temp. The timing does make a lot of difference to the power and I found that adding methanol to the petrol (Esso 99 Supreme) 1:10 holds off knock a few degrees of timing (when the temp is over about 20c it doesn't make any difference as the high IAT's pull the timing anyway).

Also I think the spring in the turbo actuator is a little on the weak side as I went down 2 stages as before it was way way to strong, so there should be a little more left in it but it will require map adjustment.

At Thruxton on Monday I managed to fry the EGT sensor (think it was on the way out already sometimes it was reading 1150c at idle) & I think the plugs will need changing as well as the DV. I didn't get an engine warning light on the day but when I scanned it yesterday there were a few codes EGT, DV, lambda, etc.

As for the water - meth, it should increase the performance widow to higher ambient temps. I'm planning to install either later this year or early next, things dependant namely time, money & Mrs.

All in all really pleased with it at the moment, the double rebuilt engine held up even with the scorching temps at Thruxton. I was fully expecting some sort of failure as we did give it a really good thrashing, so to come away with minimal failures which should be resolved relatively easily is a good result and it lives to fight another day.

Big turbo will probably come at some point but not in the immediate plan.