Author Topic: Forge Mk1 Berg Cup Build  (Read 24148 times)

Offline Jamie_r32

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Re: Forge Mk1 Berg Cup Build
« Reply #100 on: 13 May 2013, 11:40 »
Apologies for the late update to this thread, it’s been very manic here at Forge and the Golf has had to take a temporary back seat whilst we get through some paying jobs
So back at the end of March the car was running and had it driving under its own power between the units we own in Gloucester. We took it up to Thor Racing in Coventry for them to map our Omex 710 on their hub dyno – we figured this was the most accurate way of mapping the car as it’s impossible to wheel spin. Also our rear mounted radiator setup means that traditional rolling roads with only a fan blowing at the front wouldn’t work, the Golf needs airflow down the side of the car, and luckily Thor has a good cooling setup that actually ended up having to be turned down as the combination of efficient fans and our Davies Craig electric water pump meant that the car was overcooling.
So now the good news and the bad news. The Golf made tremendous power, considering its only on the smallest GTX turbo in the range, the GTX2860. First run at 1 bar boost gave 325bhp AT THE WHEELS (it's a dynapack remember), 1.15 bar gave 350bhp, 1.35bar gave 390bhp, and 1.8bar 424bhp  and 365lb/ft. The turbo made positive boost (0.1bar) at just 1300rpm!! However, when Thor were then mapping to 2 bar it went bang – though it made an impressive 400lb/ft at 4500rpm just before and was on course to make ~450bhp at the wheels judging from the graph. Somehow we had a 0.5bar boost spike within a fraction of a second which was enough to melt the plugs, particles of which then got stuck under one of the exhaust valves which melted it, and parts of that valve then went out of the was a bit of a mess.
So back to Forge HQ in Gloucester where we repaired the AGU head (we are using a stock AGU head with only port matching, not ported and polished or anything) and fitted all new valve guides, and exhaust valves. Inlet valves were fine and went back in, as did everything else.
We had a track day coming up but the mapping wasn’t really finished, so we took the car up to Powerstation in Tewkesbury – this time however, we removed the boost control and wired up the wastegate direct to the turbo with a 1 bar spring to make it fairly tame (or so we thought) for our first proper outing. Bit of tapping on the keyboard from Rich, and the Golf was making 392bhp (flywheel) and 306lb/ft at 0.97 bar! What was better was the broad spread of torque, the car now making 0.1bar at a barely believable 1200rpm now (!), fully spooled by 2400rpm, with 280lb/ft at just 2900rpm and 300lb/ft from 4500-7000rpm.
So to the track, and the Golf is a complete animal – we were on road tyres, but this was for two reasons, one we couldn’t get ‘semi-slicks’ in the size we needed with the time we had, and we weren’t allowed to run our full slicks as it was a public track event. The car spins up very quickly as the throttle response is instant and torque is huge from very low RPM, but still Luke our driver managed to hustle it around the circuit pretty well. The plans for the day were of course to set the spring stiffness up to maybe reduce some of the wheel spin, set the brake bias, sort the handling, everything you would do on a proper shakedown.....but sadly we sheared the driveshaft where it had been modified to fit the Quaife gearbox.
The car is now back at Forge, replacement one piece driveshafts are here and the box will be going back in this week with the new shafts. We are just waiting on our flatshift unit to come for the gearbox, then we will be up and running again !
Yes our plans were always to run it somewhere – its not eligible for circuit work other than Time Attack, but is OK for Hillclimb. We desperately want to get it out there, but what we are essentially doing is a very public shakedown. Things go wrong, things break. Also we are being pulled in other directions with the work we have coming in the door, we are doing this in ‘spare time’ between other projects, and it doesn’t earn us any money !!  We want it out there running on track more than anyone, and we are trying our hardest, but not everything goes smoothly.

Here are the Dyno Graphs

This was just shy of 1bar boost

« Last Edit: 13 May 2013, 11:57 by Jamie_r32 »

Offline Diamond Hell

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Re: Forge Mk1 Berg Cup Build
« Reply #101 on: 13 May 2013, 17:31 »
Everyone likes a dyno graph.

No one likes a 9" grinder.

Just because you're offended doesn't make you right.

Holiday cottages on the Isle of Wight for 2-10 people? PM me.