G30 770 turbo

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G30 770 turbo #1679627 15/06/2026 19:20 15/06/2026 19:20
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	Hey everyone I'm back! after 13 years of not having my coupe. It got offered back to me and I couldn't refuse. The nostalgia hit hard and already looking for an upgrade, being away from the scene a long time now I was wondering if a g30 770 turbo would fit easily to replace the gt3076r on my current setup. I want to aim for 550-600bhp (only by changing the turbo and mapping) not sure if I'll get those sort of gains whilst also getting the turbo to spool quicker. Any coupes used this turbo since I been gone? It's good to be back Thanks Nick

Re: G30 770 turbo [Re: TurboNick] #1679628 15/06/2026 20:01 15/06/2026 20:01
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	The G25 series would be a better size for the 2.0L engine. The G30 is better suited for 3.0L engines. I have a G25-550 fitted to my 20v turbo and it makes 480hp and 438Tq. I plotted my dyno results on Garrett's compressor map and it fits pretty well Garrett actually overstate the power rating on their turbos - their compressor maps show that a 550 can only flow enough for 500hp and the 660 can only flow 600Hp. TBH 480Hp with the G25-550 is scary quick - it makes 300 lbft at 3500rpm I suspect that the G25-660 may produce too much power for the Coupe chassis. Attached Files Dyno Plotted on G25-550 Compressor Map.jpg (129 downloads) Simon

Re: G30 770 turbo [Re: TurboNick] #1679629 15/06/2026 20:11 15/06/2026 20:11
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	A g25 660 might actually be the better option I will definitely look into that. I would love to see my old Dyno graph. The car is currently off-road until it gets a full check as it's been off road for a long time now. My car was 483bhp on a gt3076r .86 @ 1.95bar ?after all these years. I would definitely like the power on sooner and more power whilst also running cooler on less boost maybe the g25 660 is the better option Thanks for the advice. Did you need any modifications to fit the g25 would my gt3076r be a straight swap?

Re: G30 770 turbo [Re: TurboNick] #1679630 15/06/2026 20:35 15/06/2026 20:35
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	Ok so after a discussion with chatgpt (never had this technology when building my car ?) it seems to think the best option for what I want would be the g30 660. What I want: Faster spool Lower tempts Better mid range daily at base boost 0.8 bar And higher top end for any race events. Idealy breaking the 550+ bhp So if I can find one at a reasonable price I might have to go for it I just don't want to pay full price for one at the moment

Re: G30 770 turbo [Re: TurboNick] #1679631 15/06/2026 20:49 15/06/2026 20:49
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	I'm pretty sure that you can get it with the 5 bolt GT28 turbine housing which should be a direct fit replacement. I welded a new V band flange onto my downpipe because I wanted to go with the V band turbine housing - it allows the turbo to be rotated slightly to acheive the best fit in the tight space. I went with a Pulsar turbo rather than an official Garrett unit. Their build quality is excellent and they are half the cost They are pretty much identical and their turn-around time and service is much better than Garrett. Simon

Re: G30 770 turbo [Re: TurboNick] #1679632 15/06/2026 21:59 15/06/2026 21:59
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	Interesting I will have a look at pulsar turbo's and do a comparison in price and performance. Thanks Nick

Re: G30 770 turbo [Re: TurboNick] #1679637 16/06/2026 11:53 16/06/2026 11:53
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	Originally Posted by TurboNick Ok so after a discussion with chatgpt (never had this technology when building my car ?) it seems to think the best option for what I want would be the g30 660. What I want: Faster spool Lower tempts Better mid range daily at base boost 0.8 bar And higher top end for any race events. Idealy breaking the 550+ bhp So if I can find one at a reasonable price I might have to go for it I just don't want to pay full price for one at the moment The G25-660 and G30-660 have identical compressor wheels so will flow the same amount of air. They both can flow enough air for 500+Hp at your desired 0.8 bar and can flow circa 580Hp at 1.5 bar. So the real decision is which turbine housing to go for? The G30-660 has the same size turbine wheel as your old GT3076 (60mm inducer and 55mm exducer), but it's 67mm compressor wheel is two sizes smaller than the 76mm on your old turbo- so I would expect this turbo to boost quicker than your old turbo. The G25-660 has an even smaller turbine wheel (54mm inducer and 49mm exducer) - so this would boost even quicker. So in summary - both the G25-660 and G30-660 will acheive your Hp targets (both flow the same amount of air as each other) and will spool quicker than your old GT3071. The G25 will boost quicker and harder than the G30 which will be a bit more progressive. Last edited by Golfpro; 16/06/2026 11:56. Simon

Re: G30 770 turbo [Re: TurboNick] #1679638 16/06/2026 13:31 16/06/2026 13:31
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	Looking at compressor map for my current turbo it seems to be exactly as estimated for that turbo. My car ran 483bhp at 1.95 bar at that pressure the turbo is rated at around 48lbs of air, if we say as a rule of thumb 10hp per lb we would be almost exactly at my power figures. At this pressure the turbo is only at around 70% efficiency and some possible restriction Obviously going bigger with turbo there will be other factors/restrictions to the build but let's imagine the only restriction is the turbo just for argument sake. The g25 660 compressor map shows at 2 bar we are around 50 lbs of pressure which would suggest around 500bhp whilst also making it spool quicker. At 1.5bar this turbo should produce around 410-430bhp The g30 660 again 500bhp at 2 bar with it spooling quicker than my gt3070r at this rate it will be at 77% efficiency again at 1.5bar around 410-430bhp Interestingly the g30 770 which will still likely out spool my gt3076 we are almost at 55lb @ 2bar so around 550bhp. Once again obviously there are other limiting factors but one of my main concerns is keeping heat temps as low as possible and this turbo is bang on the middle of it's efficiency pretty much at the prefect level to make 550bhp. I don't see much difference between the g25 and g30 660 although these would likely be the best for what I want currently I cant help but think future if I end up wanting to go 600+ I doubt it but if I do this would be the turbo of choice. Now I'm not professional regarding turbos or mechanically! I could be completely wrong from what I'm saying above but this is how I understand it lol. I think it makes sense if someone could confirm or correct if I'm right or wrong in my thinking I would appreciate Thanks

Re: G30 770 turbo [Re: TurboNick] #1679639 16/06/2026 14:05 16/06/2026 14:05
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	Originally Posted by TurboNick Looking at compressor map for my current turbo it seems to be exactly as estimated for that turbo. My car ran 483bhp at 1.95 bar at that pressure the turbo is rated at around 48lbs of air, if we say as a rule of thumb 10hp per lb we would be almost exactly at my power figures. At this pressure the turbo is only at around 70% efficiency and some possible restriction Obviously going bigger with turbo there will be other factors/restrictions to the build but let's imagine the only restriction is the turbo just for argument sake. The g25 660 compressor map shows at 2 bar we are around 50 lbs of pressure which would suggest around 500bhp whilst also making it spool quicker. At 1.5bar this turbo should produce around 410-430bhp The g30 660 again 500bhp at 2 bar with it spooling quicker than my gt3070r at this rate it will be at 77% efficiency again at 1.5bar around 410-430bhp Interestingly the g30 770 which will still likely out spool my gt3076 we are almost at 55lb @ 2bar so around 550bhp. Once again obviously there are other limiting factors but one of my main concerns is keeping heat temps as low as possible and this turbo is bang on the middle of it's efficiency pretty much at the prefect level to make 550bhp. I don't see much difference between the g25 and g30 660 although these would likely be the best for what I want currently I cant help but think future if I end up wanting to go 600+ I doubt it but if I do this would be the turbo of choice. Now I'm not professional regarding turbos or mechanically! I could be completely wrong from what I'm saying above but this is how I understand it lol. I think it makes sense if someone could confirm or correct if I'm right or wrong in my thinking I would appreciate Thanks Normal atmospheric pressure is1 bar, so 2.0 pressure ratio on the compressor map is actually only 1.0 bar turbo pressure. On both the G25-660 and G30-660 1.0 bar turbo pressure produces a maximum 55 lbs of air flow (550 Hp) Last edited by Golfpro; 16/06/2026 14:18. Simon

Re: G30 770 turbo [Re: TurboNick] #1679641 16/06/2026 15:57 16/06/2026 15:57
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	No I was looking at the 3 on the compression graph just stating 2 bar here not including atmospheric pressure Thanks

Re: G30 770 turbo [Re: TurboNick] #1679642 16/06/2026 16:37 16/06/2026 16:37
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	Originally Posted by TurboNick No I was looking at the 3 on the compression graph just stating 2 bar here not including atmospheric pressure Thanks Ah ok. I assumed that you were saying that the G25 and G30 should make 410-430Hp at 1.5 bar turbo pressure They obviously might hypothetically make that power at 0.5 bar turbo pressure. Simon

Re: G30 770 turbo [Re: TurboNick] #1679643 16/06/2026 19:41 16/06/2026 19:41
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	Can I see you Dyno graph interested to see if you have it. Last edited by TurboNick; 16/06/2026 19:42.

Re: G30 770 turbo [Re: TurboNick] #1679644 16/06/2026 19:55 16/06/2026 19:55
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	Originally Posted by TurboNick Can I see you Dyno graph interested to see if you have it. The graph looks a bit weird as the RPM scale on the bottom is quite stretched out. Also there is a bit of a kink in the middle because I think the clutch slipped at maximum torque Attached Files IMG-20240226-WA0001.jpg (78 downloads) Simon

Re: G30 770 turbo [Re: TurboNick] #1679646 16/06/2026 20:04 16/06/2026 20:04
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	I also plotted the dyno results of the new turbo onto the dyno graph of the previous turbo (GTX2971r). As you can see the HP is a similar curve to the old turbo but comes in about 500-700 RPM sooner. But the torque comes in massively quicker and higher Attached Files Dyno Comparison.jpg (76 downloads) Simon

Re: G30 770 turbo [Re: TurboNick] #1679647 16/06/2026 20:07 16/06/2026 20:07
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	I can't access my graph on the FC performance table to compare would have been good to compare graph to a gt3071 or 76 car. Cant see data clearly what pressure was that at. The dip in the graph is likely the waste gate opening I would have thought

Re: G30 770 turbo [Re: TurboNick] #1679648 16/06/2026 20:13 16/06/2026 20:13
Joined: Aug 2006 Posts: 707 TurboNick OP Enjoying the ride
TurboNick OP Enjoying the ride Joined: Aug 2006 Posts: 707	There's a massive difference in torque isn't there

Re: G30 770 turbo [Re: TurboNick] #1679649 16/06/2026 20:29 16/06/2026 20:29
Joined: Aug 2021 Posts: 89 Belfast G Golfpro Club member 1913
Golfpro Club member 1913 Reaping the fruits G Joined: Aug 2021 Posts: 89 Belfast	Originally Posted by TurboNick There's a massive difference in torque isn't there Yes. The power of the old turbo was much more linear and the engine had to be revved out to get the best of it. But the car now just rides on a massive wave of torque from 3000rpm and is doing stupid speed before it gets anywhere near redline Simon

Re: G30 770 turbo [Re: TurboNick] #1679773 30/06/2026 11:14 30/06/2026 11:14
Joined: Apr 2026 Posts: 12 Kent UK VentiValvo Newbie
VentiValvo Newbie Joined: Apr 2026 Posts: 12 Kent UK	As far as I remember the Coupes don't like early big torque and prefer to have a linear power delivery through the rev range but I may be talking sh*te. I know most dyno graphs that I've seen of big turbo Coupes tend to keep the torque down in the 370-380ft lb region as it's better for the engine. Either way I quite like lag, it's fun haha! 2000 20VT Moonie Plus - 445bhp Barbz Build (Nazos)