flatter torque curve

[95lstegman]

i've been looking at dyno sheets from various modifications and setups, but except in very built engines or on engines with pretty large turbos running 20psi or more, the torque just seems to fall flat on its face around 5000rpm. and even on those engines with very large turbos the torque often falls off sharply after 5000rpm.

so i was wondering, is this an issue with the very long intake manifold runners or an issue with smallish stock cams? i only want to make ~300whp with as fast spool-up/response as possible, but i'd really like to know which part would help the torque's death after 5000rpm. any and all input is welcome other than telling me to run 20psi+ as i'm in the game for very quick-spooling power.

EDIT: of course i realize there are other possible weak points in the stock setup, such as small turbine housing and awkward exhaust manifold, although i don't image the T25/28 turbine housing to be that big of a restriction here for 300whp. the exhaust manifold is probably one. but basically i'm just wondering what part or parts are mainly responsible for the fall-off up high.
Modified by 95lstegman at 11:34 AM 12/8/2005

[Dori Dori]

Its definitely a combo of the two. I'd get a new intake manifold or design your own custom plenum before you mess with cams. With a Greddy plenum, stock motor, power fc, and z32 maf; we had the torque curve flat after 5k on a stock t25 @ 12.5psi. It's the only stock t25 dyno I've seen where the hp numbers keep rising somewhat rapidly after 5ish.

I've been doing some research and according to many of the Aussie boards and tuners who have tested the Greddy plenum, cyl 3&4 would get more air than 1&2 thus possibly causing lean conditions. The plenum is larger and the runners are shorter so additional top end hp can easily be attained...but at what cost? This is why I've been designing my own mani. Really I'd like to do a cylindrical (even though they don't look anywhere near as nice as a tapered plenum) and have the TB enter in the center on the bottom. That would ensure even flow but hood clearance becomes a bit of an issue

[95lstegman]

sorry, you said a combination of the two piece, do you mean the intake and exhaust manifolds?

i wouldn't figure GReddy/TRUST to make such a rookie mistake as tapering the plenum poorly such that the runners don't get equal flow. at least for $450 and from such a good name as TRUST i would expect better than that. i surely wouldn't trade any amount of power for a sacrifice in reliability of the motor intself. BTW, would you be so kind as to post up this dyno you mentioned?

i'm not so worried about having the intake manifold/runners resonate at a higher engine speed because 1) the stocker is designed to resonate at some awful engine speed like 3500rpm, and 2) with a fast-spooling turbo, i'll have extra boost to down low to make up for the losses, so it shouldn't really be noticeable.

how did you come to the conclusion that runner 4 was outflowing runner 1, and by how much? and how much do you consider detrimental? i would think that within +/- 2% would be optimal, although i don't have data on the stock piece and the difference would probably rise as pressure/flow rate increases.

and finally, are there any designs out there [for a reasonable price] other than GReddy/TRUST that do not exhibit such uneven flow between runners? or perhaps having the intake manifold Extrude Honed and then port-matched to the head would help just a little, since the main problem is the runner length, not the finish or the diameter.

EDIT: or at great cost, what about buying the GReddy intake manifold and then having that Extrude Honed? the Extrude Hone process it known for equalizing flow across runners and ports because it is basically a high-flowing abrasive. when it meets obstruction to flow, it removes it until flow is darn near perfectly equal. kinda hard to describe other than just saying it's a high flowing abrasive putty, but that will have to do i guess. still, $450 for the manifold + $450 for the service is kinda rich for my blood. just wondering.
Modified by 95lstegman at 3:18 PM 12/8/2005

[95lstegman]

actually dori, i think you should try to make one with the throttle body in the standard location and just work on getting the exact right taper to acheive even flow rates across the runners. you can adjust the taper and you can adjust it so that cylinder 1 meets the plenum at 90* angle, 2 meets at 85* angle, and so on to improve runner 4's flow or go the other way around to increase #1's flow. just make sure they all have the same resonance values so you don't get differentials between runners based on engine speed as well. also you might work on the shape of the inlet from plenum to runner to help make adjustments.

just trying to lend a hand in your quest, not trying to call you stupid or anything. if you need any help in designed let me know. i'm a mechanical engineering major, so i 'm sure i am able to help you on that kind of stuff.

[95lstegman]

i talked to XAT and Enjuku today about the GReddy intake manifold. i got pretty differing opinions that make me question the credibility of both.XAT: perfectly even cylinder filling on stock manifold, and the GReddy manifold also has no problems with too much flow to runner #4/leaning out in cylinder #4. also GReddy makes a good product.Enjuku: the stock one leans out #4 a lot, but the GReddy solves this problem and is a good piece.

so both seem to agree that it's fine, but the guys down at Enjuku seem to think the stock manifold has a problem leaning out cylinder #4? hrmmmmm . . .

i'm kinda tempted to buy a GReddy and have it flow bench tested, but i don't know where to get such a procedure done locally. i'm not that comfortable sending out a $450 part to someone i can't meet in person and who has a solid address i can visit. and besides, what do i do if i just spent $450 on a manifold and another ~$100 or whatever testing and it turns out it will kill my motor? that would be just flipping great.

dori, i'm still hoping you'll shed some more light on this. i'd kill to have a sports car's powerband. the stock SR seems to still have sort of a truck's powerband.

[codyace]

I'm pretty sure the manifold wouldn't be as popular or on many cars if it was known to blow engines, ya know what I mean??

Your math and philosophy are pretty well thought out though, and it's still probably, but maybe not to the extreme??

As far as extrude hone, the inside of the greddy manifolds are already pretty smooth, so the benifits may outway the costs. I am in no way doubting the E/H process, as I am getting it done to my OEM manifold and turbine housing to increase spool GT2871r. 64 with the parts above, Greddy o2 housing and a 3" exhaust should be pretty fun

[95lstegman]

OMG CODY. let me know how that turbo spools with that process on those parts. i wondered the same thing. if you could get more like S15-R response out of that thing you would be a living GOD.

well what i'm going to try to do is contact a couple places that may actually have one on the shelf (i live ~40 miles from Enjuku and ~70 miles from XAT ) and put a deposit on the manifold and go out and have it flow bench tested. if it's no good, i'll return it, totally unused and unmarked. if it's good, i'll buy it (or wait until i can really afford not to get back that $450). then, when i get it in there, i'll take my stock one out and have it flow bench tested. then i'll have real numbers to compare. not only that, but if/when i do get a GReddy IM, it will be my first mod since the swap, which only included Koyo rad, SPAL fan, and 3" DP + exhaust no cat. i'll have a before and after dyno sheet. it made 188whp after the swap, and i'm expecting more like ~220whp after just the IM b/c the top end torque won't suck any more. this should put down the naysayers that say the GReddy IM is only for built engines.

EDIT: BTW, when i mentioned Extrude Honing the manifold, i was referring to the way the E/H process makes all runners flow the same. in a runner that flows less, the pressure is greater, causing more normal force, hence more frictional force, and therefore causing more material to be abraded. this continues until it no longer flows less. when it's done, they generally flow almost EXACTLY the same.
Modified by 95lstegman at 3:08 PM 12/11/2005

[dareo]

Your concerns have been addressed by nissan with the S14 SR20DET. VTC helps the preboost low end a bit, the T28 ball bearing turbo helps response a bit. The peak horsepower moves up a bit. With my lightly modded engine i have a huge powerband that seems to peak around 6000rpms. For example, blasting up this freeway onramp in 4th i had grip untill 6000, and then the tires broke free and started to spin. On a dry road going straight, but open diff. i was doing about 80mph and had to lift off the throttle to keep it going straight. I chuckled and feathered back onto the gas.

Story aside, you'll want efficiency mods to hit your goals. Intake manifold, new or ported stock turbo manifold, 3" elbow downpipe and catback is a great start. Get an S14/15 T28 or better yet a smaller trimmed GT2871r if you can spend that much. More driveability and power can be had with a custom ECU tune. A small and efficient front mount with a good piping setup will also help lag and response.

If you do those mods and tune it well, you should be able to hit 300whp with only a T28 and have great spooling. GT2871r would be great also, and you could get closer to 350whp efficiently. I'm quite happy with my swap at just 9psi. I turned it down from 12-13 cause its plenty fast for me.

[dareo]

Also, you can upgrade your cooling system. Get a big alumanum oil pan or an external oil cooler and a koyo radiator. I chose these parts to not only keep my water and oil from getting too hot but so i could run mobil 1 5w30 oil. M1 5w30 compared to a castrol syntec 10w40 i ran prior was quite a nice difference in responsiveness. the S14 FSM calls for a 5w30 in the S14 blacktop, i'd double check on the redtop engine's recommendation before using a thinner oil like M1 5w30. Larger MAF and throttle body can get you a few free hp if you can tune well.

You can do wonders with a little headwork like port and polish, stiffer valvesprings, carefully chosen camshafts, and possibly a raised RPM limit if you do the required mods.

Think getting more power out of the boost and injectors you have, instead of putting in the largest CC injectors and forcing huge boost from a big turbo and you'll really love your car.

[95lstegman]

ultimate power is not my goal, and i will not rip out my swap in favor of an S14 swap. thanks for the effort, but i'm after a real solution to the problem, not someone telling me to get cams, IM, t/b, turbo, FMIC, and then it will be good. i know it would be fine if i buy every bolt-on there is. it's proven. what i want is to take a step back and figure out which part it is that is repsonsible for the truck-like torque curve of the stock S13 SR20DET.

in my recent research, i've pretty much found that the intake manifold is 90% responsible for the intense drop-off of torque on the top end. GReddy's intake manifold seems to be too short for an engine running either <1.5bar or running a stock redline. it seems to be optimized for about 7000rpm, causing losses below 5500rpm. i'm not convinced i will actually buy one, but it is satisfying having done significant research and found that the IM is almost single-handedly responsible. BTW, i will hopefully have flow bench numbers from the GReddy S13 SR20DET IM later on this week. this should disspell the rumors that it doesn't provide even flow. i am expecting flow will be nearly dead even, considering the good name of the manufacturer.

EDIT: BTW, i am planning on stuffing a 20" intercooler into the fender of my car to stay sleepy but support the 300whp i want. that will probably be my next mod unless i find a really good deal on something else i need to push the T25G to 12psi. after that will be VLSD i think and then on to fuel upgrades, clutch, and flywheel in anticipation of a GT28R/S15 Spec-R turbo and even more boost.

[dareo]

The point of my posts was obviously not conducted or received. Of course you wouldnt reswap to an S14. I was just letting you know things Nissan changed on that engine to improve those things. Intake manifold is one. I know you don't need/want ultimate power but if you maximize your efficiency you can get good power out of a smaller turbo and get the best lag/response. All around efficiency and a turbo no bigger than what you need should be just what you want.

[95lstegman]

right. i just wish there was a intake manifold out there designed for just basic mods. GReddy's and the like seem to be made for high-revving and super-boosted engines, shifting major resonance frequencies from ~3500rpm to ~7000rpm. i just wish there was something on the market that was aimed at ~5500-6000rpm, like a sports car with 7500rpm redline should have. unfortunately i'll have to live with the stock piece for a while i think. once i increase the boost level, which will increase the low end a lot, i'll be more willing to sacrifice some low end with a GReddy intake manifold.

[codyace]

OMG CODY. let me know how that turbo spools with that process on those parts. i wondered the same thing. if you could get more like S15-R response out of that thing you would be a living GOD.Modified by 95lstegman at 3:08 PM 12/11/2005

Trust me, I am a HUGE fan of response vs power

While not a complete list of everything, this is my engine setup:

Stock EngineApexi H/GJWT ECUJWT Fuel RailMototron 60lb InjectorsCobra MAFJWT S3 CamsExtrude Honed OEM ManifoldGT2871r .64Extrude Honed Turbine3" Downpipe3" ExhaustGreddy I/mStock Throt. BodyGreddy RSPL I/C Kit

I'm fairly confident that it will have at least 1 bar of boost before 3500 rpm, and pull ALL the way to redline

One of my good buddies has a FWD SR that is putting down 316 whp (16psi!0With stock engine and IM, S3 Cams, 3" exhaust, JWT ECU, 50lb Injectors, Cobra MAF and the extrude honed GTiR Manifold, J Pipe and Turbine housing. It starts building small boost around 2500 RPM and has 14 pounds around 3300/3400 rpm on a Custom HUGE t28 (not ball bearing though). The only downfall is that around 6200 RPM it falls off, leaving us to think the Intake Manifold keeps us from making the upper power I'll be honest on a track it's MUCH faster than vette and cobras and the sort due to response, and on the highway it's so quick that most races are quickly over This thing INSTANTLY builds boost at a roll

[95lstegman]

mmm i'm thinking of going with a GT28R instead of the GT2871R w/ .64 a/r turbine b/c i don't think i want to wait until 3500rpm for full boost, and b/c i don't want to feel like i need to tear the head off and put in a new HG and head studs, but mostly b/c i want a turbo that can be a nice daily driver at low boost like 7-10psi when i want good gas mileage. i think the GT2871R is pretty much a dog below about 17psi, where the GT28R should be good at just about anything i want 7-17psi.

[codyace]

The GT28r will be a good choice if you're stying at the lower boost IMO. Again, my buddies Sentra basically has a GT28r without the B/B chra, and it's got 1bar by 3300 rpm...

His car is sickly quick and really 'puts ya in the seat'. The downer of his car (and he admits) is how it dies off top end...

I think for what you want, you'll be set. The GT28RS however may even be better than that, as my same friend now runs the spud and says it spools a tad sooner yet!!!

GT2871r is certainly a turbo capable of 300+ whp at 15 pounds....

[spider_slayer]

right. i just wish there was a intake manifold out there designed for just basic mods. GReddy's and the like seem to be made for high-revving and super-boosted engines, shifting major resonance frequencies from ~3500rpm to ~7000rpm. i just wish there was something on the market that was aimed at ~5500-6000rpm, like a sports car with 7500rpm redline should have. unfortunately i'll have to live with the stock piece for a while i think. once i increase the boost level, which will increase the low end a lot, i'll be more willing to sacrifice some low end with a GReddy intake manifold.

understood.....but there just isn't a market for it. most people eathier swap in their motor add a few upgrades and quit or focus on other things; while the latter never stop and will eventually run large turbos like the gt2871r.

[95lstegman]

understood.....but there just isn't a market for it. most people eathier swap in their motor add a few upgrades and quit or focus on other things; while the latter never stop and will eventually run large turbos like the gt2871r.

mmmm hence my dilemma. for now it will be stock, and when i upgrade the turbo and engine management i'll decide by seat-of-the-pants and by the dyno graph whether or not i want to make the sacrifice. i'm sure if i go with a larger turbo like the GT2871R i won't mind sacrificing a little more low end for even more top end charge. that is, after all, what the GT2871R is good for.

[codyace]

Dyno

S3's, 16psi HUGE T28, 3" Exhaust, JWT tune4th gear pull on a 90 degree day, hence the slight 'lag' on the dyno graph. Let me assure yo though, in lower gears this thing built boost like a monster!

[Nismo_Freak]

I don't see a drop in torque at 5000?

[codyace]

Details on the above setup though??? That thing must pull like a freight train uptop!!

[Nismo_Freak]

15 PSI - stock cams.

[codyace]

15 psi on what though??? gt35?? gt40???

[highmilehatch]

Dyno

S3's, 16psi HUGE T28, 3" Exhaust, JWT tune4th gear pull on a 90 degree day, hence the slight 'lag' on the dyno graph. Let me assure yo though, in lower gears this thing built boost like a monster!

It seems like HUGE T28 is an oxymoron. The torque is falling off because of the turbo. It's still has a T-25 exhaust housing. If you want flatter torque curve on these engines without going to very aggressive cams, your going to have to step up to at least a T3 exhaust housing. Here is a good example:

http://forums.evans-tuning.com...=2740

This setup will obviously benefit from cams, but it still held the torque flatter than most other SR graphs I've seen with T-25 based turbos and cam upgrades.

This is good thread. Lets keep it going.

[bdrifta]

15 psi on what though??? gt35?? gt40???

yea, i was thinking about running the gt30 and i was wondering how that would go. but i figured since im goin big turbo, i want it to rev hella hard. But all the setups i have seen don't have dyno's like that. That thing must mob!

I also had a friend bring up an interesting point...boreing doesn't kill revving as much as stroking, so what would a decent bore do for spool time. or general power...

[95lstegman]

well, boring won't affect its ability to rev, but it will weaken the sleeves' abilities to control the heat and pressures of combustion. basically, not a good idea on stock sleeves at high boost.

oh, and Nismo_Freak, that motor is also out of the scope of my original post. you don't make 500whp and 9500rpm on a mere mortal's turbo, stock intake manifold and stock cams. nice numbers and WOW for getting it up that high, if it is indeed an SR, but it think that's a bit off-topic here.

oh, and for cody, that turbo looks like i died in the top end. is that the Forced Performance Big28? the GT28R/S15 Spec-R turbo does much better in the top end than that. i thought about the Big28, but i think the GT28R will be my turbo of choice.

[Nismo_Freak]

It's an SR, it's stock cams, and it's a T67 w/ .58 T4 hotside, and that power was put down on 15 PSI.

[codyace]

It seems like HUGE T28 is an oxymoron. The torque is falling off because of the turbo. It's still has a T-25 exhaust housing. If you want flatter torque curve on these engines without going to very aggressive cams, your going to have to step up to at least a T3 exhaust housing. Here is a good example:

http://forums.evans-tuning.com...=2740

This setup will obviously benefit from cams, but it still held the torque flatter than most other SR graphs I've seen with T-25 based turbos and cam upgrades.

This is good thread. Lets keep it going.

The turbo used on the dyno I supplied was custom created by a Garrett Engineer and avid SE-R enthusiast who will remain unnamed. Special compressor housings and the whole deal...we'll call it the prototype of the disco potato Huge t28 is kind of an oxymoron when compariing it to overly sized turbos, but when compared to other t28's its gigantic.

As you can see in that thread you posted (coincidentally I posted in that thread a while back) the torque curve is flat, but talk about turbo LAG at 18 psi. YUCKY graph if you really ask me, especially when you can have equal peak power on a t28 based car, but 3x the response. It's easy to say that a properly setup FP Big T28 or a GT2871r would make damn near equal power, but make alot more power sooner. That thign doesn't make 300 ft lbs until 5500 RPM!!! Compare that to most high pressure t28 based turbos that are making it 1400-1800 RPM SOONER. IF you compare larger t28 based turbos to the one from Evans, you'll easilly see that ther are GOBS of more power available from properly matched turbos.

Cams will help that engine, but for the most part I'd rather opt for a MUCH smaller turbo. HOWEVER you do raise a good point about the housings not helping retain torque uptop, obviously I realized it didn't help, but maybe even moreso than the intake theories before.

oh, and for cody, that turbo looks like i died in the top end. is that the Forced Performance Big28? the GT28R/S15 Spec-R turbo does much better in the top end than that. i thought about the Big28, but i think the GT28R will be my turbo of choice.

As again above, it wa a specially made turbo

However I just found this online when surfing around:

(CarDomain page here: http://www.cardomain.com/ride/536500 )

FP Big t28 at 20-21 psi made 400 whp/323 footpounds. WOW!!! Nice dyno graph IMO for response and fun, and still retains 280ish ft lbs at redline.

[95lstegman]

OMG Nismo_Freak . . . a T67! wowzers!

cody, i didn't think a FP Big28 would ever get boosted that high. i wonder how long it would last that way . . . i would DEFINITELY like to get my hands on one knowing that most people say full boost is around 3000rpm, and if i could make 400whp on it! heck, i'd be happy with 350whp!

EDIT: are you sure that's a FP Big28? i've seen FP Big28's maxing out around the 325whp area at basically that much boost. now maybe with nice intake and exhaust manifolds, cams, and good tuning it's a different story, but i thought when i saw them making ~325whp they were already so decked out. also, that one appears to spool very late, like 4500rpm. or maybe i'm just not seeing it like it is. i wish every dyno sheet came with not just hp, tq, and a/f, but also boost pressure vs. rpm.

back on topic, i guess with a large enough turbine you can flatten any torque curve, but at what cost in lag? i was meaning for a small, fast-spooling turbo. i know if it takes a large T3/T4 or T67 or something to completely flatten the torque curve, the turbo is making up for other iniquities, like poop manifold or cams or something. i've seen a FEW nice, flat torque curves, or at least much better than stock, from smaller turbos with various mods.

[codyace]

Jason -

I am in total agreement with you about the FP T28's maxing out at a smaller HP, but thats what the guy has listed on his profile ya know what I mean??? Maybe I'll find an email for the guy or something

And trust me, even 300 whp in a 240 is plenty fun and fast...imagine 400!!

You also need to take into your research that most dyno pulls are done in 4th gear, and we all know how that will effect dyno plots....When people say it has full boost by 3000/3200 RPM it is probably true for a 2nd gear pull when gearing is on your side ya know???

[Dori Dori]

It's an SR, it's stock cams, and it's a T67 w/ .58 T4 hotside, and that power was put down on 15 PSI.

I'm calling bs without more details...9.5grand cutoff...there's more done to this motor.