K04 or gt28r

[jmyfkr]

Hey guys, im in the procedure of turning my s4 b5 -99 in to a time attack/track day car. Or atleast trying .:D

Its nothing brutal.. more then
Forged pistons & conrods
Rs4 intercoolers
2 deutchwerks 350 fuelpumps
Aftermarket fuel injection mapped on ethanol

And... the big question the turbos - the plan is to run gt28r, but shots are being fired and im being called stupid to run these over stock k04s.


What do you guys think?

[DxC]

It's always a grass is greener on the otherside situation - do you want quick spool and midrange, or do you want lag and a monster top end

[gmdiluca]

If your doing time attack I'd suggest K04s because you want low end coming out of corners and they have enough up top for straights.


Sent from my iPhone using Tapatalk

[Monty23]

Your stock pistons are already forged...

[Bordom]

K04 for time attack. If you were dragging or highway pulling then gt28r

Everything graciously mispelled by Android

[FCPEuro]

These guys hit it right on the head, if you are doing any kind of racing I would be sticking with the K04. Although GT28 are awesome in their own right, the K04 will likely be better suited for the task.

[NOTORIOUS VR]

These guys hit it right on the head, if you are doing any kind of racing I would be sticking with the K04. Although GT28 are awesome in their own right, the K04 will likely be better suited for the task.

Any kind of racing seems to be a stretch... Unless you're doing parking lot time attacks or some similar shenanigans, I don't see why you wouldn't want to have a bigger turbo. K04's run out of breath pretty quickly in the top rev band.

If you're doing laps on a proper road course bigger for sure.

[slowrideBC]

K04 race car lol

[MikeyB3]

GT28s probably arent going to be the route you're looking for when creating a time attack. I'll agree that K04s are going to run out of breath up top but are better suited to smaller, tighter courses than anything larger. The other option is F21/RS6 turbos which are a little more friendly up top, and can handle tighter courses and wider opens. Anything bigger than that, you'll lag out a bit, or a lot depending on how big you go.

Example, 770s, while total monsters in most situations, suffer hard on a track that requires anything less than 40mph. But if you have a slightly wider track, and the ability to wind them ou, they more than make up for it. However, the completely wrong setup for a parking lot attack, or a tighter technical course that might require some low end grunt. Oil gets mega hot, and 2nd gear is too high, and 3rd is too low. Do let us know what you decide though, I am always interested in hearing the route people choose.

[FCPEuro]

You are correct, any kind of racing is a stretch, beginner track days and light duty racing is better said. Thank you for the correction.

Any kind of racing seems to be a stretch... Unless you're doing parking lot time attacks or some similar shenanigans, I don't see why you wouldn't want to have a bigger turbo. K04's run out of breath pretty quickly in the top rev band.

If you're doing laps on a proper road course bigger for sure.

[bigern45]

RS6's or an RS6 variant, SRM or TiAL 605 would be a great in between option. they both have great midrange and pull like a beast up top.

[FlyboyS4]

What do you guys think?

I like K04's. Run them at an appropriate PR and they will not 'fall on their face'.

TTE550's are a nice, larger, option. I like TTE's emphasis on quality components, which I would put more weight on having with your intent to push the car.

[james 408]

go for it if you want. Increased turbo lag for increased power -- it's as simple as that.

Just be aware in the twisties you will have more turbo lag. On most road courses even, as stated above, the larger turbos will still be faster. Once you introduce traffic and/or a more complex road, the turbo lag will have a greater impact on reducing your dynamic handling and likely be slower than k04s; where I drive I almost never WOT for longer than a gear before having to brake, so there really just isn't any advantage to the power, and it would hurt the mid-corner shuffle.

[NOTORIOUS VR]

go for it if you want. Increased turbo lag for increased power -- it's as simple as that.

Just be aware in the twisties you will have more turbo lag. On most road courses even, as stated above, the larger turbos will still be faster. Once you introduce traffic and/or a more complex road, the turbo lag will have a greater impact on reducing your dynamic handling and likely be slower than k04s; where I drive I almost never WOT for longer than a gear before having to brake, so there really just isn't any advantage to the power, and it would hurt the mid-corner shuffle.

I still don't get this argument at all.

most larger framed turbos it 20 psi around or before 4000 (Tials do it as soon as 3700, etc)... no matter what you do, 20 psi on the larger turbo is more power. So even if you have 20 psi on a straight K04 by 3200, if you're talking about a hybrid K04 you're losing spool and you've got even less of a gap between a much bigger more capable turbo, so you're not giving up that much IMO. Much less if you consider have a much larger possible power band of 4000-7000+ where the TQ doesn't fall off a cliff.

Case in point, here is a 605 car on the track:

[james 408]

Ah PIR or whatever it's called outside of kent. Wide-ass smooth track (not more-so than other road courses, hence why i said on a road course you're still better off with the larger turbos.

If you really want to understand what I mean, go try drift in the rain up a windy road where you have no straightaway longer than 30 feet for 10 minutes straight. The on and off characteristics of larger turbos are just LONGER. not less predictable per say, but because they take more time, it is less dynamic. As a result, you tend to be less precise.

Hope this helps.


FYI, you might notice it more if you change your driving style as well. You take very smooth and wide lines, which is great, but on certain corners you could gain time by driving a different line. For example: the downhill braking zone into the right, left (turn 3 and 4 i think)) where you should be maximizing braking and apex becomes more of an on/off battle through the connector as you struggle for grip to setup for the wide (or exit focused) line on the exit of the linked corner. The way you take that, you make it 2 distinct apexes that are very smooth. Mine would look way different.

And to a lesser degree, you aren't really playing around with the car much in the video, frankly you're taking it pretty easy -- another condition that just improves the predictability and therefore turbo lag isn't that big-a-deal.

edit: don't take this the wrong way, it wouldn't surprise me if that was the intermediate or even advanced group. You did great. But just understand there's a huge gap between a professional driver and what you see on the average track day -- depending on who's out there.

[NOTORIOUS VR]

Ah PIR or whatever it's called outside of kent. Wide-ass smooth track (not more-so than other road courses, hence why i said on a road course you're still better off with the larger turbos.

If you really want to understand what I mean, go try drift in the rain up a windy road where you have no straightaway longer than 30 feet for 10 minutes straight. The on and off characteristics of larger turbos are just LONGER. not less predictable per say, but because they take more time, it is less dynamic. As a result, you tend to be less precise.

Hope this helps.

I understand what you mean... but if I compare the power delivery of say an F21 car to something like a 605 car.. there really isn't much between them IMO. Straight/OE K04's spool very quick 3100-3200 you can have 20 psi... but then the party is over.

I suppose I just was never impressed by K04 cars. For any spirited driving I am never below 3500 so at that point I don't see the advantage of small turbos.

FYI, you might notice it more if you change your driving style as well. You take very smooth and wide lines, which is great, but on certain corners you could gain time by driving a different line. For example: the downhill braking zone into the right, left (turn 3 and 4 i think)) where you should be maximizing braking and apex becomes more of an on/off battle through the connector as you struggle for grip to setup for the wide (or exit focused) line on the exit of the linked corner. The way you take that, you make it 2 distinct apexes that are very smooth. Mine would look way different.

And to a lesser degree, you aren't really playing around with the car much in the video, frankly you're taking it pretty easy -- another condition that just improves the predictability and therefore turbo lag isn't that big-a-deal.

That's not my video... no idea who it is actually.

[james 408]

Ah, lol. Yeah no you're not wrong that it's better in a straight line. And it may seem like the turbos get back up to boost pretty quick, but when it's the difference between continuing a drift and having to correct in those fractions of a second, it makes a big difference. Don't get me wrong, there's plenty of lag in k04s. Frankly the turbo lag is a real challenge when attempting to drift a narrow and technical road. You get used to it though and can drive around it. I'm just telling you, it's pure physics that it gets worse with larger turbos =D

The japanese touge guys have reported the same thing for decades. At some point, the additional power doesn't help. Additionally, some cars are faster on smaller turbos (even below that power threshhold for the course).

[FlyboyS4]

Straight/OE K04's spool very quick 3100-3200 you can have 20 psi... but then the party is over.

K04's will reach 20 psi by 2800 rpm and hold that to 6500 rpm.

[NOTORIOUS VR]

K04's will reach 20 psi by 2800 rpm and hold that to 6500 rpm.

And K04's @ 20 psi are really quite unimpressive.

[FlyboyS4]

And K04's @ 20 psi are really quite unimpressive.

You're changing the subject from what I said.

[audacity]

you could always improve your driving, stop thinking so brake now gas. impart other techniques such as left footed braking. look at the 80s rally drivers. tons of power huge turbos on relatively small motors that need the power when they want it.

probably a dying breed of people who use this style.

i use it even when I'm having fun on some twistys


id go for a mid level turbo, i doubt that if you really get into it that you'll stay at one track forever id want a well rounded turbo so you can have fun everywhere and eventually you'd get to know your car enough to where you could shave time off at your local track anyway.

[NOTORIOUS VR]

You're changing the subject from what I said.

No

[JVD]

No

Lol. I legit scrolled to read the rest of your post.

Nope, that's it.

[dannyn424]

ko4's at 24psi seem to really move!

[axnjaksn]

you could always improve your driving, stop thinking so brake now gas. impart other techniques such as left footed braking. look at the 80s rally drivers. tons of power huge turbos on relatively small motors that need the power when they want it.

probably a dying breed of people who use this style.

i use it even when I'm having fun on some twistys


id go for a mid level turbo, i doubt that if you really get into it that you'll stay at one track forever id want a well rounded turbo so you can have fun everywhere and eventually you'd get to know your car enough to where you could shave time off at your local track anyway.

yea...what he said...hahaha...don't formula one cars rev out to 15k....very small torq figures with much higher hp figures...and rpm... all relative...just slap a set on and enjoy driving it wherever your power band is...personally I like the linear power that keeps pulling harder till redline, happily give up low end torq for hi revving fun.... just my .02 cents...

- - - Updated - - -

Lol. I legit scrolled to read the rest of your post.

Nope, that's it.

me too hahahaha

[james 408]

you could always improve your driving, stop thinking so brake now gas. impart other techniques such as left footed braking. look at the 80s rally drivers. tons of power huge turbos on relatively small motors that need the power when they want it...

Well yeah most of the time on the track is made up by swapping to a better driver for sure.

But keep in mind, if you look at the feet on professional drivers, there's TONS of on and off (more so from higher horsepower or tighter/slippery tracks) -- from the best of the best. There's a reason they don't make turbod cars like that anymore, for any application, except maybe a drag strip car, and that probably has a sequential box anyway once they get around to it.

Although, you can certainly do things to mitigate it:



3 clutch pops and 2 left foot brakes, maybe an ebrake because of the imbalance in the braking/diff system, and the steering to match it -- and yeah, you can make the larger turbos work just the same. Good luck with that. (obviously the 80's rally car and comparing k04s to gt28s might be a bit of an exagerated comparison)

Again, you're better off with the gt28 for 99.9% of road course applications, unless you're doing a very tight/twisty/slippery track. But it might be more rewarding to be on the smaller turbo setup, especially to the less-than-professional driver. But then again, i know guys that just want to go fast, and they'd rather just have the power in the straights than worry about swindling out tenths in the corners -- so it depends on your style.

[james 408]

also, just an fyi, for most cars, left foot braking is a pretty rare thing to add any benefit -- you can't shift while left foot braking on a standard transmission (practically speaking), and therefore you're better off just using heal-toe. It's only really effective for certain corners, and typically only to cure a problem -- such as massive turbo lag, or sometimes to help point the car in. Modern rally drivers use it all the time, but they do clutchless shifts most of the time, so you're really dealing with something more like a sequential box.

http://www.audizine.com/forum/showth...-toe-technique

[audacity]

also, just an fyi, for most cars, left foot braking is a pretty rare thing to add any benefit -- you can't shift while left foot braking on a standard transmission (practically speaking), and therefore you're better off just using heal-toe. It's only really effective for certain corners, and typically only to cure a problem -- such as massive turbo lag, or sometimes to help point the car in. Modern rally drivers use it all the time, but they do clutchless shifts most of the time, so you're really dealing with something more like a sequential box.

http://www.audizine.com/forum/showth...-toe-technique

left footed braking isn't use where you would shift. it would be used where you don't need to gear down but will loose enough rpm to get out of boost...

heel toe is used for entering a corner left footed is for holding the rpms/boost up while mid corner where a downshift is not needed.

[james 408]

left footed braking isn't use where you would shift. it would be used where you don't need to gear down but will loose enough rpm to get out of boost...

heel toe is used for entering a corner left footed is for holding the rpms/boost up while mid corner where a downshift is not needed.

yeah no i hear you but i'm telling you it's more a style difference than an outright advantage. Look up carlos sienz and colin mcray, they battled it out and carlos often used right foot only for gas/break -- won a couple championships. then look at the racing video i linked you, guy's otherwise known as 'the drift king' -- very accomplished race car driver -- one of the most accomplished. tons of other examples just youtube professional drivers.

[Dan[FN]6262]

Any kind of racing seems to be a stretch... Unless you're doing parking lot time attacks or some similar shenanigans, I don't see why you wouldn't want to have a bigger turbo. K04's run out of breath pretty quickly in the top rev band.

If you're doing laps on a proper road course bigger for sure.

This.


What race is won under 5k rpms?

[james 408]

again, not really about rpms bra. autocross being the most common example

[Dan[FN]6262]

[Zba]

No revs were used in autocross, ever

[james 408]

for those still struggling with understanding turbo lag, Matt F actually does a pretty good job explaining the sensation. He's partially wrong in how he describes it as 'a narrow power band' (he likes LSX motors, deal with it), but he is describing turbo lag quite well in terms of it going in and out of the power all the time and have to row gears (or pop clutches) to get the turbo delivering the right power when you ask for it. But just goes to show you, even a bit of a handling oaf like Matt has enough seat of the pants understanding of the concept to know he doesn't like it in the twisties. It gives the same sensation as a 'power band' like you'd see in an older dirtbike or something, and the lag makes the driver think it's the rpm, but it's just time for the turbos spooling (as long as you aren't actually below rpm to provide max boost, say 3k rpm, but you've got to be terrible to be racing below 3k rpm, i don't want to hear about your 2nd 3rd gear gap).

See 8 min 30 second mark



I was gonna find a nice japanese touge video I've seen where it goes into great detail about it including lap time support for the conclusions, but I gave up and this came accross my autoplay. Hopefully we've kinda fenced the concept in so most people kinda understand what it is.

[NOTORIOUS VR]

Turbo lag is really, really not an issue if you're in high RPM's and past your boost threshold.

Down low sure, turbo lag is the most significant place you will notice it as you need the exhaust temperature and velocity to build up. But when you're in the sweet spot "lag" is so minimal and makes zero difference

[manimal]

Turbo lag is really, really not an issue if you're in high RPM's and past your boost threshold.

Down low sure, turbo lag is the most significant place you will notice it as you need the exhaust temperature and velocity to build up. But when you're in the sweet spot "lag" is so minimal and makes zero difference

+1

You can have lag with a big turbo where it wont make any power bellow 4200 rpm but when you build the valvetrain so the motor can rev to 8500 it really isnt an issue. it's kinda relative. However I do sit with Flybo and think that the TTE550 turbos are the best bet though I have gone through and cant find any power data from him about those turbos.... and when I say data I mean something more than just 2-11 psi based on engine speed. what is a dyno run, where are the efficiency limits, what kind of times can you achieve (1/4, FATS, really anything that someone coming into this platform can understand)? And most importantly, how do they hold up after some abuse. These are touted as the best turbos with greater tolerances than come from BW and should be abel to take continuous abuse beyond say Frankenturbos, standard K04s and any other brand. Sorry I was extremely excited to see that you were going to test these turbos as they are the ones I want to replace my K04s with and then was disappointed with how little you actually did with them...

[james 408]

Fact is turbo lag is real, it exists, and it's around us every day.

(and you're right about the mechanics of rpms and velocity, but real world driving there are situations this happens, and terms like 'minimal' in higher rpms are not the same as 'nonexistant')

want a real world sample? go look at some of the s4 shootouts. several companies swapped to smaller turbos for the road course compared to what they used on dyno king -- and yet another setup for dragstrip. maybe all these pro drivers, winning companies, and lifelong enthusiasts are completely wrong about it, or maybe you're a little wrong.

it may seem i'm arguing for the contrary, but if I were in this decision, and cost wasn't a factor, i'd go gt28s(or another larger turbo) for road course use or roll racing or dragstrip or just showing off to my buddies -- just don't buy into this there's no drawback crap, it's bs. They say the same thing when you're first offered illicit drugs.

[genecan]

EFR 6258 x 2 = spool + tons of HP

Might be good to build a 3.0L stroker, but if you get a good tuner might not experience the surge issue.

[james 408]

as a rough guideline for horsepower and turbosizing for a given application:

350hp for autocross/tight canyons -- k04 or high strung k03;
550hp road course/smooth high speed canyons -- rs6/gt28r/pick your poison i'm not an expert on turbo offerings, but you can 5 min google to see what many tuners chose, maybe even why
800hp+ dragstrip/rollrace -- Naw, Naw, bigger bra

[james 408]

a bit nerdy, but explains the basics. if you layer in the rpms affecting it as well as the throttle body, you'll get a more complete picture. Then if you were to cross-reference this against throttle positions and rpms in different racing applications, you would understand why me, and many experts, are saying the same thing BIGGER ISN'T ALWAYS BETTER.

If you really want to get into it, youtube it. there's videos on compressor maps, efficiency ranges, etc. These are the arguments guys like flyboy are making regarding the efficiency ranges on where our engines line up with a turbo. Going this route, it gets very complicated, very quickly. I have no idea if these calcs are right, but high-level, the video will give you a good introduction to compressor maps and turbo efficiency and what type of variables there are:



An easier route: You could also pick up the phone and talk to these guys, there's experts out there and tuners who have been there and done that -- on our platform no less. I know who I'd call.