[dgblkbelt]

How much additional HP is there likely to be gained by getting a full streetport and oversized valves to go along with cams/cam gears, versus just putting the cams/gears into a stock head? Its a Gen 3 head if that makes any difference.

Planned setup is to be GT28RS or GT2871R based, so I am going for decent (over 300rwhp) but not crazy power. I am more interested in getting the most out of the motor without going to a huge turbo, in order to keep the spool and response good.

 

[MRQturbo]

u will definitely see some gains with aftermarket cams.....

 

[dgblkbelt]

u will definitely see some gains with aftermarket cams.....

I know... question is stock head + HKS cams vs ported head and OS valves + same HKS cams. Obviously the second is better, but is the power and response to be gained $2k better?

 

[99_GS-T]

Hum, doesn't Bruce always get on here and say how great of a match the GT28RS is to the stock VE?

I think you would be wasting your time with head/cam work on the GT28RS. Just turn up the boost.

Now if you had a bigger turbo...

 

[dgblkbelt]

Well I said "or GT2871R"... but lets not start that again. RickyB predicted high 300s are possible on the GT28RS with headwork etc... so its at least a reasonable guess to make well over 300. GT2871R is more likely candidate though if I were to get serious headwork done as the porting will help spool.

 

[99_GS-T]

You can potentially pick up some power at lower boost levels. But from my experience, head work and cams will do VERY LITTLE to make more power once you hit the choke flow of the comrpessor wheel.

 

[dgblkbelt]

You can potentially pick up some power at lower boost levels. But from my experience, head work and cams will do VERY LITTLE to make more power once you hit the choke flow of the comrpessor wheel.

Correct. But that won't happen on a GT2871R, and it might not happen easily on the 28RS either, no one really knows yet.

For now the question assumes it won't. I just want to know what kind of gains ~2k in work will get me.

 

[Bruce H.]

Try picking your desired boost level first. If you feel that with your available octane that you are comfortable driving at 17 psi to keep everything safe, and you don't plan to rev past 7200-7500 rpm, then the RS will already be flowing about its maximum rating of 35 lbs/min. If you up the boost you will be asking it to flow more at each rpm and will max. it out just a little earlier. Because your Gen 3 has slightly higher VE with it's larger intake cam and intake manifold it will already consume more airflow than my Gen 2 at the exact same 17 psi.

Extra boost will however benefit you with extra torque everwhere above ~3250 rpm...that's where I hit 17 psi and 250 ft-lbs on my Gen 2. You might like the idea of more midrange torque even if it means not being able to wind it out to high rpm...it will do it just like the CT26, but you know it's exceeding its limits and there's always a cost when you do that.

So you can see that even at a safe 17 psi you are already going to max. out the RS by using your full rpm range. You will also be putting the most power under the torque curve because of the strong bottom end power. !7 psi is safe and there's no real need to improve VE to lower it a pound or two.

Now if you want a stronger top end that's strong to redline at the same boost level (over 300 whp), and don't mind giving up some low end power, than you will need a larger turbo, and if you want to get past maybe ~320 whp you will also need to poor money into improving the VE...or run higher boost.

While the RS will undoubtedly produce some high power on race gas with all the best supporting mods, that won't be the reality for many. I think it's a great daily 300 whp solution because it uniquely makes large low rpm power, has a very strong midrange, and gives up very little at the top, but I've never felt it was a good choice for much more than a daily 300 whp.

If you want to go any larger in a BB GT then I would only consider the GT3076R for up 400 whp capability with the next spool to the RS.
The GT2871R will spool slower for the increase in power it will provide.

Bruce

 

[dgblkbelt]

If you want to go any larger in a BB GT then I would only consider the GT3076R for up 400 whp capability with the next spool to the RS.
The GT2871R will spool slower for the increase in power it will provide.

Bruce

Thanks as always for an intelligent and intelligible post Bruce. Won't the 2871R outspool the 3076R though? I am just don't see wanting a turbo as big as a 3076R, spool will be too slow and overkill for my goals. As you know I want something like the GT28RS, just a bit bigger...

 

[Bruce H.]

As you know I want something like the GT28RS, just a bit bigger...

Don't we all I've wrestled for two years with this question and haven't found the solution yet. I wish Garrett would make a turbo half way between the 28RS and 3076R. But until they do you will be forced to sacrifice a chunk of low end for a little more on top on a stock or near stock VE engine with other choices. If your priority was racing you might gladly swap the entire bottom below 4000 rpm for the top in a heartbeat. On the other hand I race my 28RS and absolutely love it.

We might debate whether a 2871R would spool faster or slower than a 3076R (and you can see a dyno of one on the ATS site, Warren's GT30R), but unless you are capable of really upping the boost and controlling detonation I think it's not a good choice for a 3S-GTE...and Ricky'B experience with one would support that claim.

Bruce

 

[Tomg]

Isnt the GT3071 (R) inbetween the 28 and the 76?

I know the turbine efficiency, on paper at least, arent that stellar, but I heard good stuff about them on actual cars..

T

 

[IPS Ryan]

Reading the primer, it says basically, you shouldnt do headwork till the stock head is restriction and youll gain power, if i mreading it right.

 

[Tomg]

True, the head is fine for a while, however if you plan on doing more than 350whp, doing a good head will make sure that whtever you throw at it, it's ability to flow is taken out of the equation.

T

 

[Bruce H.]

Isnt the GT3071 (R) inbetween the 28 and the 76?

...as are the GT2876R/HKS GT2540R/E.B. GT25R.

I know the turbine efficiency, on paper at least, arent that stellar, but I heard good stuff about them on actual cars..

...as have we about the GT2876R/HKS GT2540R/E.B. GT25R.

Turbine efficiency is the key to predicting performance once you've found a compressor that looks able. If it isn't stellar on paper it won't be stellar on the car, unless you have the mods and tuning to mask it. The GT3071R and GT3076R maps are really very close, but the dramatically superior turbine efficiency of the GT3076R will make it a better overall choice, and a much stronger spooler IMO.

Bruce

 

[Tomg]

So the gt30 definition is the housing, and the 71, 76 etc is the tubine/comp combo?

Or how is that working again?
Ohh, Hell I just going to test both of the turbos, and see what they do.

T

 

[mr2turbored]

...as are the GT2876R/HKS GT2540R/E.B. GT25R.

please correct me here but aren't theses all the same turbo as garrett recently renamed all its turbo and went from the gt25r to the gt2876r.

What about the GT3071r with the t25 footprints, this would allow a direct replacement for the gt28rs as the footprints are the same? would that give a better top end and similar low down spool and allow a higher boost level, higher rpm with the ability to increase the VE's without the turbo tailing off at top end like you've described.

I'm in the same boat here as well, i'm running a gt28rs at the moment but am currently building a mid power engine build at the moment with poring and 264 cams and i know from what you've said before the gt28rs will run out of puff at the higher rpms, So i was thinking of the GT3071r like mentioned above to give similar spool and pull characterists low down but the ability to wind the boost up and let it stretch its legs to the higher RPM's without turning asmatic .lol

 

[Tomg]

..or anemic

 

[mr2turbored]

lol

 

[bugalu]

to fully benifit, especially on such a small turbo wouldn't he also want a larger tb/ intake mai? or is my thinking backwards and since it is a small turbo he would not want to go any bigger on those? also how much more will it flow with the stock intake componets in place arent they still more of a restriction than the head(besides cams)?

 

[dgblkbelt]

to fully benifit, especially on such a small turbo wouldn't he also want a larger tb/ intake mai? or is my thinking backwards and since it is a small turbo he would not want to go any bigger on those? also how much more will it flow with the stock intake componets in place arent they still more of a restriction than the head(besides cams)?

VERY true. I plan this for later but its not in the budget now. I'll get one over the summer or fall. Everything else I talk about below I already have or will get now though.

The point of my post is to determine whether headwork is worth the money, based on the gains made in power AND spool. If a built head would help a 2871R or 3076R spool significantly better, AND make much better power, it would be worth it to me. Or if headwork was not wasted on the GT28RS but gave 50rwhp or something, that would be worthwhile too.

Basically I am sitting on two options:

1) I have an Extremeboost based 2540R kit coming, which can take another GT series turbo instead of the 2540R. So I plan to switch to another turbo, but I don't know which one, and I can cater it to a built head if necessary...

2) I will definitely have 272/264 cams in my Gen 3 head, that is a low cost upgrade which is definitely worth the hp/$$$ to me. However, futher headwork is PRICEY, and so I need to know that I would stand to gain ballpark Xrwhp or Xspool with X turbo. I know there isn't hard data for this, which is why I am asking more generally.

Make sense? I am basically building a motor from the ground up, I can mix and match turbo and headwork to make the best combo for spool and power and price. Rest of the engine mods I will have, since they have become relevant, are:

-Gen 3 head with 272/264 cams, cam gears (OS valves and porting is a ???)
-Stock Gen 3 bottom end
-Extremeboost based GT turbo kit with GT___turbo: exhaust mani, external Tial, SS lines, etc...
-3" downpipe and exhaust
-Power FC (which I have, or some other standalone if I decide its better)
-720cc HKS injectors in HKS rail, SS lines, walbro pump etc...
-Berk Tech intercooler kit
-MBC (might go EBC)
-Etc... probably some other stuff

I have all this stuff now. The only question is further headwork, which turbo, any other additional mods, and tuning. The goal is a compromise of spool and power, with a definite bias toward spool. 300rwhp on pump is fine (GT28RS) BUT if spool trade off is not that much (with or without headwork) a bigger turbo may be preferrable too.