Garrett Turbos

[S2central.net]

I'll look at the GT35R properly but I think its better suited to 2.5L and will have a natural bias to the top end of the scale - don't forget the compromises you'll be making for low range torque on such big turbos.


Paul

[Albert]

So is the gt35r out of the question?
If I used one of these, what would the characterisics of the engine be?

What power are U looking for ?

If 400-450HP than go for Gt30R

if for 500-550HP go for GT35R

I have a GT35R and I'm very happy with it ... it starts coming to live at arount 3800 rpm giving me .8 bar at 4k ... from 4.5k I can have full power ... do to calculations I have set it to 1.2 ... than at 5k for 1.4 bar ... the ride starts at 5.5k where I open it up to 1.8 bar ... till 7500 ... the car is like a rocket ... I'm still on stock setup but I have Pauters just to be put in ... than i will pump the air to 2.0 bar ... that shold with other mods give me 500HP+

I would recoment that turbo for a car that is driven on weenends ... and also I'm having a 2 map program ... the first one for street 1.4 bar ... that is ~ 400HP ... I have made a dyno on RS2 and it came out that on 1.2 we had 380HP ... we don't want to dirve on the race map all the time shoping ...

For 2.5L aplication I wold go with GR42R ...

[diesel des]

Albert, are you running 1.8 bar at 7500 rpm on a stock bottom end???? What power does that make? Who did the mapping? What else is done to the engine, eg cams, intercooler etc? What manifold do you use? I dont understand why people are saying to back the boost back at high RPM with the big turbos. Surely its in the mid range/ peak torque that you will bend rods etc, so boost should be keeped lower there. Boost only needs to be pulled back at high rpm if the turbo runs out of puff and starts to go into the Choke zone.

[diesel des]

Des, sounds like you combo will be putting out somewhere in the region of 370bhp @flywheel. With the bottom end stock it wont take it. Boost will be limited to 1.7-1.8 and will have to tail off to about 1.2 at redline. Shimming the head is one way, but that wont last. Either skim pistons or buy custom ones. and replace the rods. Its the only way. I have bent a rod at 1.8bar. And thats with boost low at top end!

Why did you run so much (1.8 BAR) mid range boost though? Surely thats what bent the rod, not the low 1.2 bar at High rpm? If the boost is held at say 1.5 bar from 3-4K through to 7K rpm surely that would be safer on a stock bottom end and big turbo. Where am i going wrong?

Cant Mineha chip RS2's with turbos and stuff, but stock bottoms to 400-450BHP? I thought i read that some where?

[Albert]

I'm doing my tuning on my own ... based on books and other technical manuals. There is a lot of crap in the internet.

As for the rods they are killed by torque ... that is why I keep it down to 1.2 and 1.4 on lower rpm. From 5.5 i give full power to have drag racing capabilities, when I go form 1-2-3-4-5 gears i have full boost all the time. Yes I have 1.8 bar on stock end till 7500rmp. But i have 3B roods that are suppose to be stronger than the ones form ABY.

Cams 7A ext, IC ... big front one (see pic), S4 modified in manifold, special ext manifold for Garrett, mapping done with AFR wideband probe on 99+ V shell vpower with Perfect Power SMT6.

As for power I'm still waiting for my head to be returned form porting and polishing. I will have my car dynoed than. The ET12.17 is not too good becouse last comp was uphill and there was a problem with my gear box.

[Jamo]

Are you sure about the rods more? I'm sure Audiman wouldn't agree with you over the rods!!
The ADU engine is based on the ABY which happily runs 315 bhp and with the amount of 3B engine rebuilds going on at present doesn't quite add up!

[diesel des]

I take it then you ae useing a stand alone ECU not the Mototronic? Sounds great!!!! Yes torque is what i beleve does the damage, not BHP. What EGT do you have and what air/fuel through the range? Do you measure post or pre turbo?

[Albert]

I take it then you ae useing a stand alone ECU not the Mototronic? Have you any power graphs? Sounds great!!!!

No, SMT6 is a piggy back. I have a chip form Hohenster + the signal is modyfied by SMT6.

[S2central.net]

Its an odd one Jamo - the rods on the 3B are alleged to be stronger than AAN/ABY/ADU ones but the 3B engines have weaker big-end bearings than the other engines.

BUT I agree these claimed numbers are very scarey for the longevity of any stock bottom end from 3B or ABY.

Torque is proportional to engine speed and boost pressure, so I don't really understand the statement about reduced boot at low revs conserving the rods. Such reduction is necessary to prevent surging on a large turbo like the GT35R though.

A nicely mapped RS2 setup will run to approx 380bhp - it does not have the oomf to safely break the 400bhp barrier (regardless of engine internals) - for that a larger hybrid is needed - or a jolly nice thing from Garrett

FWIW - I still think the GT35R is too big for the S2 engine in roadgoing form. Albert obviously likes the drag strip so he can reap the benefits up at the top end of the rev range, but from 30mph in 4th an RS2 will get away quicker (for a while) - heheh !


Paul

[S2central.net]

No, SMT6 is a piggy back. I have a chip form Hohenster + the signal is modyfied by SMT6.

You are trusting all this boost pressure to a piggyback system ? Thats pretty scarey in my opinion - effectively bypassing many failsafes in the Bosch system. But hey - its your engine

[Albert]

Its an odd one Jamo - the rods on the 3B are alleged to be stronger than AAN/ABY/ADU ones but the 3B engines have weaker big-end bearings than the other engines.

I have done a compleate engine rebuld with stronger big end bearings. Lot of new stuff in ... but kept the old pistons, rods, crankshaft and block. The rest is new (water, oil pump, bearings, piston rings, rs2 head gasket ect.).

FWIW - I still think the GT35R is too big for the S2 engine in roadgoing form. Albert obviously likes the drag strip so he can reap the benefits up at the top end of the rev range, but from 30mph in 4th an RS2 will get away quicker (for a while) - heheh !

Paul

For a while Yes ... but the car at 1.2 bar is making tons of power ... it is acelerates form 4000 rpm ... probably what I can do is to posta a video ... hope to record it soon

[diesel des]

Torque is proportional to engine speed and boost pressure, so I don't really understand the statement about reduced boot at low revs conserving the rods. Such reduction is necessary to prevent surging on a large turbo like the GT35R though.




Paul

Torque is only proportional to engine speed due to
1. the turbo not being At high boost at low engine speeds (could be deliberate to reduce surge),
2. Cam profile
3, Port profile etc


What i am trying to say is that TORQUE puts the biggest compressive force on the rods not BHP. As im sure you know torque and power are related eg at 5252 rpm you make the same BHP as Ft/lb torque. Its a maths rule. So to make big BHP all you need is some torque at high RPM. EG if you make 400FT/LB of torque at 7000 rpm then thats 533BHP. A honda v tec makes 140ft/lb torque at 7.5K giving about 200BHP. Doesent need very beefy rods for this. Strong rod studs though!

That 533BHP at 7000RPM puts NO more COMPRESSIVE loads on the rods than 400ft lb at 5K rpm making 380BHP or 400ft/lb at 4K making 308 BHP.

Torque is directly related to cylinder preasure (BMEP) and hence rod load not BHP.

The question is will the stock rods carry 400ft/lb for long, or what is considered safe?
Obviously one big PInG and bent rods...

[Jamo]

Its an odd one Jamo - the rods on the 3B are alleged to be stronger than AAN/ABY/ADU ones but the 3B engines have weaker big-end bearings than the other engines.

BUT I agree these claimed numbers are very scarey for the longevity of any stock bottom end from 3B or ABY.




Paul

This car is a maze of complexity, i would never have thought that in a month of sundays

[S2central.net]

Yep - my previous statement was a bit open-ended... It was in the context of Albert's engine pushing 1.8bar at high revs which must generate a lot more torque than 1.2bar at low revs.

If you've read my recent paper on 'turbology' then you'll know I understand the principles of torque and power.

I absolutely agree with you that it is torque which bends rods - not power - hence my confusion about Alberts boost profile. Seems to me it could bend a rod anytime soon - and at high revs too !

One question I do have for you is to share the source of your calculation which equates 400lbft of torque at 7000rpm to 533bhp ?

I must have missed that class


Cheers,

Paul

Torque is only proportional to engine speed due to
1. the turbo not being At high boost at low engine speeds (could be deliberate to reduce surge),
2. Cam profile
3, Port profile etc


What i am trying to say is that TORQUE puts the biggest compressive force on the rods not BHP. As im sure you know torque and power are related eg at 5252 rpm you make the same BHP as Ft/lb torque. Its a maths rule. So to make big BHP all you need is some torque at high RPM. EG if you make 400FT/LB of torque at 7000 rpm then thats 533BHP. A honda v tec makes 140ft/lb torque at 7.5K giving about 200BHP. Doesent need very beefy rods for this. Strong rod studs though!

That 533BHP at 7000RPM puts NO more COMPRESSIVE loads on the rods than 400ft lb at 5K rpm making 380BHP or 400ft/lb at 4K making 308 BHP.

Torque is directly related to cylinder preasure (BMEP) and hence rod load not BHP.

The question is will the stock rods carry 400ft/lb for long, or what is considered safe?
Obviously one big PInG and bent rods...

[Pisobiker]

Subject of conrod stresses was covered some time ago in this forum. Take a look here:

http://www.s2forum.com/forum/showthread.php?t=322&highlight=inertial

Marco