Which To Buy First Plenum Or Exhaust Manifold?

[Edge]

Which should I buy first - a high mount GCG 300rwkw optimised exhaust manifold or a greddy plenum?

Is the 274rwkw figure that seems to come up so much, due to restriction of the standard exhaust manifold or the standard plenum?

As far as I can tell the GT30R turbo with a .63 exhaust A/R is going to top out at 6500rpm?

I want around 300rwkw and a turbo that will give me power to 7000rpm on R33 series 2

What happens if I go .80 A/R compression side?

Does bigger A/R on the compression side mean more boost at lower rpm? Or is this a function of the wheel size on the compression side? (I do mean the intake to the plenum)

Can someone give me turbo trim specs and A/R for something that makes same or better power curve in the low rpm ie below 3800rpm range as well as around 300rwkw up to 7000rpm. What else do I need to consider to get this low rpm power (torque) along with the power above 6500rpm - header mods?

edit - did some more reading, seems to be the exhaust manifold would be the more restrictive, but is it around the 274rwkw point?

ECR33 series 2

will use an adjustable exhaust cam wheel

Edited December 26, 2006 by Edge

[BHDave]

There's a bit of debate as to whether the stock exhaust manifold is getting restrictive at that point.

That said, there are a few people with the larger garrett turbos in I/W housings as well as the HKS variants that are making better than 300rwkw using the stock inlet and exhaust manifolds.

For a compromise between ultimate power and response I think the garrett 3076 (GT30R) in a .63 IW housing on the stock manifold would be very close to what you are after. The .63 will limit top end power some what but the the improved response is worth the trade off IMHO. The compressor housing A/R only really plays a small part in the equation. 3076 comes with a port shrouded .6 cover. Older style turbos of the same size (T04s wheels) usually came with a .7 cover.

You will see more gain with a better flowing exhaust and cams than a manifold in the mid to high 200's.

At the end of the day, if you are happy with the power and response of the above setup (and you will be) but want to trade off some bottom end for top end then an upgrade to a .8x non gated exhaust housing and better manifold would be worth considering.

The trouble is that your goal is smack in the middle of what a 3071 will offer response wise and a 3076 (in larger A/R exhaust housing) will offer power wise. Small housing 3076 is probably the best compromise.

I'm sure other will disagree

[discopotato03]

I put up a string recently about the GT3076R/GT3037S 52T turbo which is suppsed to be available in March 07 . Its basically a HKS GT3037S 52T but with a Garrett GT30 IW exhaust housing and minus the bell mouthed inlet insert that port shrouded HKS turbos usually have . The ported shroud compressor housing should deal with any surge issues caused by using smaller than ideal exhaust housing AR sizes . The slightly smaller compressor trim (52T vs 56T and 55mm vs 57mm inducer diametre) costs about 30-40Hp according to HKS but still could easily top 400Hp , 450Ps according to HKS figures .

Speaking purely turbocharger wise three things about this unit could potentially pull down its boost threshold . I have to assume that most things engine wise are optomised at this point .

Firstly you should have the option to use the smallest Garrett GT30 IW turbine housing which is .63 A/R . HKS also produce a .68 A/R T3 flanged turbine housing which many think have a better nozzle and passage form . Extrude honing any turbine housing helps clean up the volute passage because the abrasive goop flows like a fluid so optimises things for the also fliud like gas flow .

Secondly the slightly smaller 52T or mid trim GT37 compressor will have a little less bite into the atmosphere so for the available turbine power would get a wriggle on slightly earlier .

Thirdly the port shrouded compressor housing . If you look closely at a properly designed housing with this feature you'll notice that the leading edge of the compressor wheels lower or spliter blades line up just below the radial slot . Logically there will be times when the airs pressure is higher or lower in the area between the heights of the upper and lower blades . Obviously if is higher the least path of resistance will be out through the slot and returned to the area in front of the boss . If its lower it would pass through the housing and on to the engine . Everyone who's tried the plain and then shrouded compressor housings says that the shrouded ones want to pull up into boost revs earlier . My guess is that the air bled off means the compressor workload the turbine see's is less so more energy to accelerate it to positive pressure type revs . I know I sound like a broken record but I still think the ported shroud is way to go . HKS uses it often and even goes to the trouble and expense of custom compressor housings that have it for surge prone small capacity sixes like RB20's .

Just incase you missed it I'm told the unit will retail for ~ 2G .

I have been asking in the States for a comparison of the real GT3071R and this 52T GT3037 but no one seems to have tried them back to back . I have not seen a compressor map of the GT3071R with the optional .60 A/R port shrouded compressor housing so its difficult to compare maps with the 71mm and 76mm (GT35 and GT37) compressor families . So untill we see the results of similar engines with these two turbos all we can do is speculate . I believe Mafia is in the process of fitting a 56T version of the GT3076R/GT3037 (.82 A/R IW housing I think) and I'm keen to see the results of that one . Based on how it goes we will get an idea of its power characteristics and be able to judge if its just right or want a bit more downstairs .

Cheers A .

[Edge]

thanks BHDave and discopotato03

Have to wonder whether the drop off top end above 6500rpm is due to hitting the max flow on the turbine side with the .63 A/R exhaust. ie. supersonic or just too restrictive?

If I was to get one of those HKS exhaust manifolds would this give better exhaust flow (have 3" exhaust straight through) to get boost on earlier.

What about the cams, I gather changing these is to help top end, would this be enough to enable rpm to go to 7000 with the .63 A/R turbine or will I need to get a bigger A/R turbine side.

I'd surely like to see the results of that Mafia setup.

[wilch]

Cams will give you a meatier midrange.

From what I've seen with my car, and friend's cars the top end power will be limited by the size of the exhaust housing. That said, the bigger the exhaust housing the later it will come onto boost.

[Edge]

thanks wilch,

I'm going to look at some more graphs to see what .82 A/R exhaust gives down low.

If I put cams in would they still be adjustable like the standard ones?

Also I think I'll take a closer look at that HKS produced .68 A/R T3 flanged turbine housing

[discopotato03]

Its the one intended for their GT3037 Pro S turbocharger . I think The Overboost Store (US) shows a listing of HKS housings or some of them anyway , possibly Nengun as well . I have seen a few HKS housings at GCG in Sydney but have not asked Brett specifically about the Pro S ones . I will when I get the chance because I'm interested in them as well .

Cheers A .

[Edge]

Spoke to GCG

They make a .70 A/R HKS exhaust replica

in either 84T or 90T (which is something like 55mm vs 58mm wheels)

GCG recommended gt3076 (76mm wheel comp side) 90T turbine side

comes in either internal or external wastegate

iw good for 450hp flywheel

for above that they recommended using manifold with ext wastegate

I asked and they said - if go 84T then go smaller compressor wheel.

How do you think this replica would compare to the true HKS exhaust housing

what does the size of the Trim in the exhaust do to the ability to bring on boost early? Is it that the bigger the exhaust wheel (not A/R) the more boost comes on early? Would choosing the smaller 71mm compressor wheel to go with the 90T exhaust wheel get boost on earlier?