I finally decided on a GT2876r to go on my restricted FJ20 IPRA Datsun Sunny. Now we just have to build a new restrictor and airbox.

Pic #2 - The new turbo in place


Pic #3 - A shot from above.

That should frighten them Mark, a bit lumpier than the GT28RS. Dyno soon?

Yeah..... should create a bit more panic in the field. The guy who won the 3L-6L calss in NSW IPRA last year was only 0.8 of a second quicker than me at Eastern Creek. he was running an older style corolla (KE25?) with a 3SG Turbo. He told me he was making 270rwhp, I was only making 209rwhp! Add to that, we discovered my struts only had one inch of bump travel, so every time I hit the brakes, changed direction or hit a ripple strip the front end hit bottom.....the struts are off being completely rebuilt as we speak..... so with all these changes we should be considerably quicker this year, and able to challenge for a class win in the championship.

With the Dyno.... we plan to be on the dyno by mid to late february. We still need to build a new restrictor plus a new airbox to house it properly with a cold air intake. Plus, I can't go anywhere until the front struts come back.....mid Feb is the aim at this stage.

Mark.

Nice looking setup. Love it.

Just one question though, if you need to run a restrictor, why did you go for a 76mm compressor?

The reason why I ask is becasue the GT2540 is a bit of a mismatched turbo already ie 53mm turbine vs 76mm compressor, the turbine is going to have trouble spinning that compressor properly and then a restrictor is only going to make it harder. A basic rule of thumb american racers set themselves a while ago was that the compressor should not exceed 15 percent larger the turbine which seems excessive but worked for them (DP03, can you confirm this 15 percent rule please). It seems that simply a GT28RS or GT2871R would have done the trick for you application. But when adding a restrictor, it changes everything I know about turbos...this is where you can explain things to me

Is that an NA engine with a turbo?

Cheers

After speaking to a bunch of guys running in our category, I realised all of them were running the .70 compressor housing. I was also told by my tuner to run this set-up and the guys at Dynatorque and GCG also said the same thing.

The reason I was given for this was that the bigger compressor housing will move more air at slower turbine speeds than the smaller comp housings. We need to get as much air in to the engine at low revs as possible, as we have an effective rev range of about 6,100 rpm with the restrictor. We want to build as much torque as possible in the low end of the rev range, effectively, we are building a tractor engine!

The National champion this year was driving an SR20 powered Datsun 1200 with the same configuration, so we know that it will work. As Paul from Dynatorque said to me..... once you bolt the restrictor on, everything you ever knew about turbo's goes out the window!

We will soon find out when we get to the dyno.

Mark.

You have been doing your turbo homework Mark, what you say makes sense.

Never had a close look at a Sunny but it and the Corolla seem to make a good platform for IP. The rules as they stand seem to favour smaller lighter cars with a fairly rigid body, something with a relatively wide track and suitable track/wheelbase ratio too.

Yeah... the Sunny has the advantage of a slightly wider track than say a datsun 1200, and doesn't suffer from the IRS (squat) problems of the 1600. Plus it's lighter than a 1600, but we are a bit heavier than the 1200's. the other big advantage is the coil spring rear end....I don't have to battle with leaves, we can adjust height easily, and change springs rates in less than 5 mins.

A Sunny won the under 2L championship 2 years ago with an L20B running twin webbers, so we know they can be made to handle well also....it's just a matter of time and development.

Mark.

Intersting to see it goes with restrictor in place on the dyno. Keep us posted. What management are you running and what fuel? Are you boost limited?

Your engine has a small rocket cover...is it from a gazelle or is it NA to begin with?

Out of interest, does anyone know what the WRC cars run in terms of turbos and that compares to your GT2540? I was under the impression they ran like small things...

Post some more pics of your car :p Would be nice to see it in its entirity including rear end, suspension etc.

Nice work

Cheers

Hey French,

I'm not sure what the WRC guys run, but I do know they use lots of boost down low, I have heard upwards of 30psi. Theya are now building so much torque some teams have moved awayfrom the 7 speed gearboxes and gone back to 5 or 6 speed boxes. They found they were losing time from topo many gearchanges, when the engines had enough torque to pull taller gears.

I didn't do the original engine build, but I believe it is Turbo engine to start with. The NA cover was probably used originally for bonnet clearance...not 100% sure, but I like the slim line look anyway.

If you want more details on the car, we have a website dedicated to it

http://www.full-throttle.com.au/Race%20Team/Race%20Team%20Intro.htm

The above link is our new site, the one below is the diary I kept while building the car.

http://www.angelfire.com/retro/mpamotorsports/sunnydiary

Cheers,

Mark.

I'm not going to be popular here but I can confirm that those GT2876R turbos are good at nothing - no thing . As I would have said many a time too much compressor for the turbine or not enough turbine for the compressor - means the same thing .

Couple of theories to smash here :

Small restrictor in front of large compressor is pointless , what happens is the restrictor reaches maximum flow and forms a depression or area of lower pressure between itself and the compressor inlet . So the comp pulls some air , pressure ahead drops and the wheel unloads and speeds up , pressure rises after restrictor wheel loads up and so on . This is the woofing noise you hear when a compressor surges , if you continue to push it the woofing becomes a banging or hammering and the wheel will desintegrate under the hammer blows of massive pressure fluctuations .

Small 53.8mm turbine cannot develop the shaft torque to drive the 76mm compressor . Slow (for turbo) turning compressor also means slow turning turbine which is going to create restriction to flow in the small turbine housing so choke the exhaust . You can look at small turbines in a similar fashon to small capacity engines , need to rev piss and pick handles out of them to make any worthwhile torque - the work demand of the large compressor wont let it rev and at low speed theres no grunt . I'm afraid the 2876 will lag to a point in the rev range and be strangled by the restrictor not too far beyond that point - ie narrow usable rev range .

The people who work with Grp A and WRC rally engines have the smarts with what you are looking for . Ford found out the hard way that big compressors ie Sierra RS500 style dont work with small restrictors when they went rallying with the Cosworth YBB powered RS Escort .
What worked with Grp A Rally was ALS to excite the smaller turbo at low revs and a progressive reduction in boost pressure once the restrictors maximum flow was reached . By smart electronic boost control they could reduce boost (meaning airflow demand) while increasing full load timing so that the engine would not go flat and have an insufficient rev range to be competitive . WRC regs are even tighter - some of these cars are being upchanged at 5500 rpm and still making 650 Nm of torque .

I'm not sure what your class is or what size restrictor you have to use though would it be 32-34mm ? Also I don't know what kind of power is a realistic expectation but if the comp inlet is bigger than the restrictor bore I'd say its too big .

If the class allowed it the Mitsubishi 4G63 engine is better suited to this type of work because it evolved with the Lancer from the original Evo to the present Evo 10 and stayed competitive . Many of the bits they use - particularly the Evo 6 and later intercoolers - are brilliant and available to anyone through Ralliart , much better than any truck core fab job .

Lastly there must be figures for the restrictors maximum flow rate , when choosing a turbo to park behind it look at its compressor map . Anything beyond that flow rate on the map has ceased to exist . If you really get that GT28RS working properly I reckon it can do better than the 2876R .

If I really wanted a small light car to race in turbo form it would be an MX5 , they can easily out handle any early Nissan or Toyota 2WD 4 and its Mazda PB18 loves to be turbocharged and was in factory Lasers and Familias . There is a T28 flanged cast manifold out there as well . A genuine sportscar and a real roadster .

Thanks Anon for your input.

Our restrictor size is 36mm, so slightly bigger than the rally guys. We are aiming for 250-260 RWHP. Our peak horsepower is reached at approx 6,100rpm with the old restrictor/turbo set-up.

We can't race MX5's as our class is based on a touring car platform, therefore no sports cars.

I understand your reasoning behind the smaller compressor housing, and it was a toss up. We even looked at some very small turbo's. I spoke to many many people about this set-up, includng people who race in our category, and people running Rally cars. The majority of those people all recommended the larger compressor. One of the guys running a similar set-up just won the National Championships this year - so it can't be too far wrong.

I guess the proof will be in the pudding - and we should have some results by mid-late february when we get back on the dyno.

Tell me Anon....do you have information on restrictor designs? We are about to build a new one - any help would be appreciated.

Mark.

Here is a 34mm restrictor that a friend of mine just had made for his Evo III...

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The restrictor really needs to be designed on a flowbench, and should be looked at in conjuction with the inlet piping. PVC piping and Play-Dough are your friends! Also, it should slide as far as possible into the turbo in order to minimise the low pressure zone that was mentioned earlier by Anon.

I can put you in touch with the maker of this restrictor if you would like.

Cheers,

Matt

Thanks Matt.... that looks very similar to what we are toying with making.

When you say Slide in to the the turbo, do you mean the restrictor itself should finish as close to the compressor as possible? That is what we plan to do. The diverging side of the restrictor is extremely important from what I understand.

On the front of the restrictor we will be mounting a bellmouth also. The whole unit will be housed within an airbox to allow maximum flow in to the restrictor.

Anon refers to a depression behind the restrictor after it hit's maximum flow (sonic velocity). Our plan is to use the Motec to tune the boost map in such a way that we can keep the airflow at a level just under Sonic Velocity for the widest possible rev range. This means running higher boost at lower revs and tailing the boost off as revs increase. With the larger compressor we can move more air through the restrictor with slower shaft speeds which will hopefully get us to Sonic Velocity earlier.

To do this we are planning on running the car p on the dyno with the wastegate not connected. This will give us a boost map of maximum airflow through the restrictor. From there we can map the boost curve with the Motec to sit just under the boost curve to help with the lifespan of the turbo.

The big question mark I hae at the moment is over restrictor designs (there's a couple of theories out there) and also teh current exhaust Manifold. I hope to have anew Manifold constructed my Round 3 (June) which shouls also free up some more HP and reduce lag further also.

I'll Keep Ya'll updated.

Mark.

Yep, it should finish as near as possible to the compressor.

If you are going to mount the restrictor in an airbox, then I would look at a design similar to a carburettor trumpet.

You may find that this analysis will get you thinking: http://www.gt40s.com/ubbthreads/showflat.php?Cat=0&Board=UBB6&Number=29735&page=9&fpart=all

Cheers,

Matt

Thanks Matt for the link....very interesting read, in that I have been told by numerouis sources that an open velocity stack pulls most of it's air from around the sides, not from straight in front of the opening.

I wonder if the fact that he has modeled it in 2D has an effect on the result? Perhaps if it was modeled in 3D you would find that most of the air does in fact come froma round the sides of the velocity stack. It makes you think about when people are building custom inlet plenum chambers, why would they put trumpets inside the plenum? Interestingly, my plenum has been built in the fashion that the author of that thread suggests. Each inlet runner is radiused, but finishes flush with the side wall of the plenum chamber - does not protrude into open air space.

Very interesting read, and something else to research before we design and build the airbox.

Thanks.

Mark.

Mark what you'll find is that the 54mm turbine will struggle to drive the 76mm compressor so the lag component may be an issue . For the 250-260 whp the GT28RS is probably a smidge large on the comp wheel trim . I think I once mentioned the HKS GT-SS which is basically a GT28RS with a smaller trim 60mm compressor . No one wants to accept this but truthfully going down on comp trim size is a good way to reduce lag - less for the turbine to power so the rotating group gets up to speed faster read sooner .

Honestly brave would be the person who told the manufactures eg Mitsubishi/Subaru etc that their WRC cars used poor thinking in their turbocharging . They have the financial resources that us mortals can only dream of and none of their cars are slouches . WRC cars are leading the world along with F1 for automotive technology .

If I was trying to be competitive I would be aiming at as much torque as I could get in the lower mid range - sort of 2500 to 5500 . Torque is god , Hp or KW is just torque x engine speed .

I will get back on the compressor spec of the GT-SS , I cant remember but hope you used the .86 a/r turbine housing on your GT28RS . Whoever makes the manifold needs to make it out of 1.25 bore pipe , 1.5 is too big and will cost all important gas speed to the turbine - particularly in a rpm limited class such as yours .

HKS GT-SS specs , same as GT28RS but 60 trim compressor instead of 62 and with .64 a/r turbine housing ie 46.6mm inducer instead of 47.3mm . If I get time I'll search to see if there is a smaller comp trim version with the all important 76T NS111 turbine .

Cheers A .