[Mk2] [Turbo] Opinions on forged rev 3 with standard ct20b

[Lee H]

I have just finished rebuilding my rev 3 engine with the following parts:

Wossner 86mm pistons
ARP bolts throughout bottom end
All new gaskets, pumps etc
Fidanza flywheel with paddle clutch
ST205 chargecooler

Car is presently running a rev 2 lump with ct20b, rev 3 conversion and Power FC but only ever makes 260bhp at 1.2 bar. This is why I decided to go for a rev 3 lump (better head, inlet etc) and forged it for reliability.

I was planning on running the new build with a GT3071 purchased off here but have since discovered its a GT3076. I think this will give too much power in my little mk1 so am considering running the forged engine with the ct20b instead as I like the way the car drives with this turbo (lag etc).

Just wondering what sort of power I would likely make with the new engine and standard turbo at max boost permitted on a standard ecu (would likely be an improvement over 260bhp)?

Also would there be many gains to be made by having my Power FC remapped to the new engine as opposed to running the standard rev 3 ecu? Ie enough to justify the mapping expense?

Thoughts and opinions very welcome. I appreciate I could sell the 76 and get a 71 but wondering if its all a bit too much if I can make decent power on the ct20b.

Cheers

[Marf]

260 wheel hp or flywheel hp?

260 flywheel hp is bloody low for 1.2bar on a rev3 setup.

My Rev3 made 285hp @ 0.9bar with just a decat, exhaust and ARC airbox.

I'd be tempted to find out why your car is making such low power before doing anything else!

[Lee H]

Flywheel power.

Been put down to the rev 2 inlet not being very good as had plenty of fuelling left but couldn't get anymore power from it.

Car runs well, all timing marks line up, decent compression on all cylinders, ran a 13.2 second 1/4 mile so maybe the RR was very pessimistic.

[simpson_eh]

il have a gt28 up for sale soon gave me 340bhp with 335 ftib just upgraded to gt3071r

[greeny]

Flywheel power.

Been put down to the rev 2 inlet not being very good as had plenty of fuelling left but couldn't get anymore power from it.

Car runs well, all timing marks line up, decent compression on all cylinders, ran a 13.2 second 1/4 mile so maybe the RR was very pessimistic.

What dyno? It's hard to say whether one car made more power than another without putting them on the same dyno.

Id personally run the 20b to make sure everything's good with the new engine, then if/when you get bored consider swapping out the turbo/ecu injectors etc.

[simpson_eh]

wrong post

[Magic Beans]

I ran a hybrid 20b on my rev3 before moving to a 3076R. I found the 20b is a more day to day usable turbo and gave more than enough power for the street. The 3076R is a different league in terms of power and performance, however I feel it's at some expense of usability, in a street car at least.

As above, I'd advise running the 20b first. If you do decide you need more and the engine proves solid, then stick the 3076R etc in.

[Lee H]

Flywheel power.

Been put down to the rev 2 inlet not being very good as had plenty of fuelling left but couldn't get anymore power from it.

Car runs well, all timing marks line up, decent compression on all cylinders, ran a 13.2 second 1/4 mile so maybe the RR was very pessimistic.

What dyno? It's hard to say whether one car made more power than another without putting them on the same dyno.

Id personally run the 20b to make sure everything's good with the new engine, then if/when you get bored consider swapping out the turbo/ecu injectors etc.

The Racing Line in Halifax. Car previously made 270bhp at 0.9 bar on a very optimistic dyno but only 200bhp at the Racing Line before they remapped it with more boost.

Leaning towards running stock rev 3 ECU initially and the 20b and taking it to the 1/4 mile again to see what difference there is. If I run stock ecu at max boost (17psi iirc), it should be around 260bhp again I would have thought. Then maybe just do the power FC to eek out a bit more power.

[Lee H]

I ran a hybrid 20b on my rev3 before moving to a 3076R. I found the 20b is a more day to day usable turbo and gave more than enough power for the street. The 3076R is a different league in terms of power and performance, however I feel it's at some expense of usability, in a street car at least.

As above, I'd advise running the 20b first. If you do decide you need more and the engine proves solid, then stick the 3076R etc in.

Been speaking to another mate who managed about 310bhp on his 20b at 1.3 bar with other mods similar to me and thinking an extra 50bhp or so would be enough to keep me entertained.

Wish I had waited for a GT28 to come up for sale now as it seems the best in between standard and a Gt30.

[ChrisW]

Wish I had waited for a GT28 to come up for sale now as it seems the best in between standard and a Gt30.

I've been thinking along similar lines - I've got a forged engine and want a turbo upgrade, but I'm more interested in fast spool than big power figures. GT28 series sounds ideal but I've heard they suffer from boost creep even with an external wastegate. Hopefully someone will come along and tell me that's not the case.

[Marf]

With a large enough EWG there's no reason it should creep.

[ChrisW]

You'd think so. It'd be interesting to hear from someone who's running one successfully.

[Kongaroo]

GT28 series sounds ideal but I've heard they suffer from boost creep even with an external wastegate. Hopefully someone will come along and tell me that's not the case.

Sorry but that was the case for me when I ran a GT28rs on a forged engine and 38mm external wastegate in the past. The solutions I found for this were:

1) Restrict the exhaust gas flow by using a less free flowing exhaust - eg. use an exhaust bung or go for more restrive exhaust like stock. But be prepared for the poorer turbo spool up.

2) Map the car to be able to run the boost the car creeps to (assuming it's not too high for the car to run safely).

Both of the above worked for me although I couldn't bear the thought of choking my super fast spooling GT28rs with an exhaust bung so I preferred option 2

I considered a larger wastegate also, but at the time it's seemed a lot of money and hassle to buy a larger wastegate and then convert my existing 38mm setup when I had no guarantee the new size would be large enough to stop the boost creep.

[ChrisW]

Interesting to hear your experience Kong. If you could go back and do it again but with a bigger wastegate, would you still go with a GT28RS?

[Kongaroo]

Interesting to hear your experience Kong. If you could go back and do it again but with a bigger wastegate, would you still go with a GT28RS?

It's hard to say - I now have a 2.2l stroker+GT3071r and I guess that I prefer what I am running now. IMO the GT28rs is too small for my current engine setup. Although it would make for a hilariously fast spooler with the extra displacement from the stroker build.

I think if you are running it on pump fuel alone using a forged 2L engine the GT28rs is probably the most optimal choice for 300 to 350 Flywheel - it should slightly outspool the ct20b and make more power at the same boost levels doing it.

If running with methanol injection or race fuel you could go a little higher but I doubt you will wring much more than 380 flywheel from it even on a car with the supporting mods to push the power band to the right slightly.

For comparison: my previous TD06 tune overlaying my GT28rs tune for FWHP and FWTQ - both running methanol injection on a 2L forged engine with upgraded cams on the same dyno. Same mapper (me ) :



Those pulls were both in 4th gear so if you are comparing those runs to a 3rd gear pull on a Dyno Dynamics you would expect to see spoolup to suffer by a couple of hundred RPMs but you would also see a slightly higher peak flywheel reading in 3rd gear (maybe 20BHP or so).

So yes the GT28rs is better than the CT20b. However I'm unsure that the actual amount of performance gain you would get from swapping out the CT20b for the GT28rs would be actually worth the time and money for the OP. Unless money is no object and you want a 'no compromise' setup of course.

HTH

[Kongaroo]

sorry double posted somehow when trying to edit in the correct link for picture - it took about 8 goes to get it to work, lol

PS TD06 is green and GT28rs is red in the above dyno sheet. The GT28rs was running at about 22psi while the TD06 was a hair less boost

[ChrisW]

Thanks, food for thought there.

Sorry to the OP for the thread hijack!

[Turbonoz]

Flywheel power.

Been put down to the rev 2 inlet not being very good as had plenty of fuelling left but couldn't get anymore power from it.

Car runs well, all timing marks line up, decent compression on all cylinders, ran a 13.2 second 1/4 mile so maybe the RR was very pessimistic.

The terminal speed is what gives a good indication of power on the 1/4 mile. What did you trap at?

[Lee H]

107mph

[Turbonoz]

107mph

Guesstimate you're running around 300bhp unless the car weighs 1000kg.

No chance you could run that terminal in a full-weight MR2 with 260bhp. No chance.