Engine Internals and their TQ/WHP Thresholds

[lo-lyfe]

Doing more research on the pros/cons of turbo options for Stg3. Also debating on rebuilding the bottom end while the motor is out. I know my rods/bearings will be my initial limiter in terms of max WHP based on where the torque peak occurs within the RPM range. I also realize I will most likely be restricted to under 500 WHP if retaining the stock bottom end. My question is this: assuming the turbo I choose can (hypothetically) attain 600+ WHP and assuming I want to be somewhere north of 500+ WHP, what would be the next part, after rods and bearings, that would require an upgrade. Is it valves, and if so, how much more WHP can be squeezed by upgrading those? After valves, what would be next (pistons??)....and so on and so on until lets say a max 600+ WHP is reached.

I think it would help a number of members in my position to know the progression of engine internals upgrades and what these upgrades are good for (WHP and TQ) when added to the bottom end. In my case, it would allow me to determine whether or not doing these upgrades makes sense $$-wise for the additional WHP gained. I know there's a number of ppl here that are knowledgeable enough to contribute and maybe have even done so in prior threads, but it would be nice to have all those thoughts/suggestions/opinions in a devoted thread.

I intend to retain the stock 2.7L displacement. However, if someone wants to add a 2.8L or a 3.0L I'm sure that info will be beneficial as well. It would also be helpful if we could categorize the data according to fueling options: 93 octane, e85, 93 octane with W/M, etc.....

Apologize if a similar thread already exists, although I haven't been able to find one. Thanks!

[JDM EJ1 95]

pistons and rods are main concerns.. rods being more important.

then after that you probably are fine unless you plan on revving higher than stock.. in that case your valves/valvesprigns are limited.

[bigern45]

rods, intake ported, 2.8 heads/cams with ported heads. valvetrain upgrade.

and a really, really good funnel..

[JDM EJ1 95]

rods, intake ported, 2.8 heads/cams with ported heads. valvetrain upgrade.

and a really, really good funnel..

'

hes asking what the limits are... having an intake ported or 2.8 heads while may increase power.. will not add to the power potential and ability to handle stress of the mechanicals

[bigern45]

limit is a relative term. he asked what he would need to do safely to reach 600 whp. without intake/valve work i doubt you can achieve those levels. he said, and i quote, "what would be the next part that would require an upgrade".

re-read it...

[JDM EJ1 95]

limit is a relative term. he asked what he would need to do safely to reach 600 whp. without intake/valve work i doubt you can achieve those levels. he said, and i quote, "what would be the next part that would require an upgrade".

re-read it...

why would the valves be compromised at 600 vs 400? the stock valves will be fine.

[bigern45]

Nope, heat will be an issue for sure at that point

[JDM EJ1 95]

Nope, heat will be an issue for sure at that point

with factory exhaust valves being sodium filled.. i dont think heat is an issue. unless your tuner sucks. the only issue with the factory valves is getting past the stock rev limit.. while sodium filled are great for heat. the tradeoff is durabiltity with a high revving/high lift valve train.

[bigern45]

Again, stronger springs may be too much for the stock valves even at that point. IMO this discussion/argument has been redundant and a waste of time. Sorry that we disagree.

[Meow]

If you plan on spending a lot of time near the red line you will likely float a valve on stock valve springs... That's what happened to me.

Rods are good to 450-500wtq, I have never seen limits for stock pistons. Never seen anyone post an actually number for their limit. Once you do rods your limit will be turbos. Without head work rs6 and 605 turbo setups will have a hard time reaching 600whp on Pump gas. Even with e85 and 2.8 built heads about 570whp is about right. You will want to go with rs6-r or 770 turbos of you want 600whp consistently. I feel that can be done on upgraded rods, stock pistons, stock head with upgraded valves and a good tune. When you look around at cars, the rs4 k04's and rs6 k04's and tial 605's cant really cut it after 500whp, there are some guys who push the rs6's into the mid 500's range, but to top 600 you really need larger turbos.

Head work becomes really important after 500whp. 2.7 heads can really hurt a car when trying to get that last bit of power...

I still suggest upgraded valve springs and retainers. Plus 7800rpm is fun...

[Meow]

Tial 770 car making 637whp

Engine size: 2.7L
Rods: Integrated Engineering
Pistons: Stock
Heads: 2.8 (Slight Polish)
Cams: 2.8
Valvetrain: Supertech
Intake Valves: Supertech Stainless Steel Black Nitrided
Exhaust Valves: Supertech Inconel
Head Gaksets: 034 Compression Dropping ~8.8
Intake Manifold: Ported RS4
Intake:Custom by 666 Fabrication
Y-Pipe: Custom by 666 Fabrication
Throttle Body: 80mm Hemi with 034 TBB
Turbo kit: TiAL R770
MAF: EPL GT MAF
Fuel Rails: 034 Motorsport Fuel Rails
Injectors: Bosch ev14 83 lb
Fuel Pump: Bosch 044 In-Tank pumping to custom surge tank with twin Bosch 044s in parallel
Surge Tank: Custom by 666 Fabrication
Fuel Pressure Regulator: Aeromotive A1000
Tune: EPL
Water/Meth Injection: Aquamist HFS-3

TiAL 770 powered avant... this was on 5 gal of 100oct with a gallon of 93 still in the tank. Car is a fairly simple 2.7L, with stock manifolds, pistons, and 2.8 heads with Ferrea valvetrain parts. 618awhp and 567ft/lb

[bigern45]

^ Mike's car was on race gas, no??

[Meow]

^ Mike's car was on race gas, no??

nope, that was on pump gas.

[JDM EJ1 95]

Again, stronger springs may be too much for the stock valves even at that point. IMO this discussion/argument has been redundant and a waste of time. Sorry that we disagree.

What?..... Stronger springs aren't needed for 600awhp.either

[bigern45]

to rev higher it is, that was my point



do you know of any 6xx whp cars without upgraded springs and valves?

[Meow]

What?..... Stronger springs aren't needed for 600awhp.either

Well stock springs on most of are cars have seen a lot of miles, and a lot of high rpm abuse. Spring fatigue is very difficult to calculate, without knowing a ton of very specific detail about the engine load conditions the car has seen, the properties of the material used in the spring, and the potential for heat to alter the conditions of loading. Its really tough to say "these will not break or float" because there are so many unknowns. One good known is that people have (myself included) floated valves because of fatigued springs. Now, if I were building an engine that cost me a lot of money and was considering replacing the heads, I would for sure replace the springs with either stock OEM ones, or stronger aftermarket ones. The issues of tolerance quality of aftermarket retainers is a big thing to consider. Having friends who work both in the OEM and in the aftermarket, I can be sure and tell you the OEM quality of tolernacing is better than aftermarket companies. I still chose to go with aftermarket springs and retainers because I took into account the fact I won't be trying to get 200k miles out of these springs and retainers like an OEM would. I took the risk of worse tolerancing for better spring performance because it seemed like a fair trade off for my needs.

Now why you say they "are not needed for 600whp" you are correct. You do not technically need them. However, it would be foolish not to upgrade them IMO.

[Meow]

to rev higher it is, that was my point

This is the point that is most important. Larger turbo setups will favor RPM, thats just the dynamics of turbo sizing. So in order to get the widest power band, tuners often up the rev limit. The stock rev limit is fine for stock springs. 8k RPM is not so fun with stock springs and valve float... It is fun when you have the right equipment.

[JDM EJ1 95]

Just because its beneficial doesn't mean its necessary... Op was asking the weak links at 600 whp... Horsepower has no affect on valvesprings. You can easily make 600whp on a factory rev range.. considering even 770s on stock bore spool well before that limit..

[lo-lyfe]

Appreciate all the input, fellas. Been pricing out the different options you guys mentioned. Planning on visiting George Mazuro (www.mazuromotors.com), an experienced engine builder in my area who specializes in Porsche engines, next Saturday. He was recommended to me by one of his former drivers who happens to be a friend. Budget-wise I may be able to swing rods, bearings, valves, springs, and retainers (around $2700 total parts cost) but have to see how much the labor will run me. Anyone care to chime in with their estimate, just so that I have a realistic range once he starts to quote his fees?? Again, we're talking rods, bearings, and valves. The motor will already be broken down once he gets his hands on it so the whole dis-assembly does not have to be factored into the price. Thanks!

[Meow]

Op was asking the weak links at 600 whp...

I consider valvesprings a weak link.

Horsepower has no affect on valvesprings.

Not true, the effect of horsepower on valvesprings is very important when looking at air flow rates in engines. The main cause of valve float is spring rates but also high boost applications can actually pull the springs down and float them that way. Many people push the upper limits of pressure on small turbos to try to get a broad power band. Pushing rs6's or gt28s' or 605's at 30+ psi this can be cause for concern of floating a valve because of this high pressure. Now I am not sure this has been exactly proven on s4's but it is very common on stuff that is naturally aspirated from the factory with weaker valve springs.

You can easily make 600whp on a factory rev range.. considering even 770s on stock bore spool well before that limit..

Stock rev limit is 6500... that means you would be shifting right at peak power, that would be terrible! 1500 rpm of power is a garbage power band. You want to rev out way more than stock to use larger turbos.

[lo-lyfe]

So if my rev limit remained stock (say I chose faster spooling turbos w/a lower top end, like FT21s), and wanted to run e85, I could push slightly past 500 WHP and do so relatively safely with just rods, correct? In other words, my restriction would then be the turbos, not the internals?? (by safely I'm referring to the engine only, not whether or not the turbos would be pushed past their efficiency range and thus more prone to failure).

[FlaS4]

Rods are good to 450-500wtq

FAW ran stock rods at 537 wtq for a while before they went and EPL ran 518 wtq before the same.

[Meow]

So if my rev limit remained stock (say I chose faster spooling turbos w/a lower top end, like FT21s), and wanted to run e85, I could push slightly past 500 WHP and do so relatively safely with just rods, correct? In other words, my restriction would then be the turbos, not the internals?? (by safely I'm referring to the engine only, not whether or not the turbos would be pushed past their efficiency range and thus more prone to failure).

Yes, you can push the turbos well past their efficiency range when you use e85. With just rods, stock pistons and head, a bit over 500whp would be no problem.

[Meow]

FAW ran stock rods at 537 wtq for a while before they went and EPL ran 518 wtq before the same.

How long is "a while" lol. Most tuners and enthusiasts agree, over 500 wtq is a big risk on stock rods. One bit of bad gas, or one bit of harsh knock and that rod will snap real quick at over 500wtq.

[JDM EJ1 95]

I consider valvesprings a weak link.
Not true, the effect of horsepower on valvesprings is very important when looking at air flow rates in engines. The main cause of valve float is spring rates but also high boost applications can actually pull the springs down and float them that way. Many people push the upper limits of pressure on small turbos to try to get a broad power band. Pushing rs6's or gt28s' or 605's at 30+ psi this can be cause for concern of floating a valve because of this high pressure. Now I am not sure this has been exactly proven on s4's but it is very common on stuff that is naturally aspirated from the factory with weaker valve springs.

Stock rev limit is 6500... that means you would be shifting right at peak power, that would be terrible! 1500 rpm of power is a garbage power band. You want to rev out way more than stock to use larger turbos.

when have you ever seen that happen.. i have never seen that happen.. not on any platform..... ever.. and certainly not on the s4 which has barely even come close to pushing the envelope of the 2.7T motor.


ill say it again.. yes its beneficial to upgrade the valvetrain.. but wether or not the car makes 600whp or 400 whp.. on a stock rev limit the valves are NOT A WEAK LINK nor are the valve springs.

[somebody5788]

Stock rev limit is 6500... that means you would be shifting right at peak power, that would be terrible! 1500 rpm of power is a garbage power band. You want to rev out way more than stock to use larger turbos.

Mine is definitely not 6500.

[Meow]

when have you ever seen that happen.. i have never seen that happen.. not on any platform..... ever.. and certainly not on the s4 which has barely even come close to pushing the envelope of the 2.7T motor.


ill say it again.. yes its beneficial to upgrade the valvetrain.. but wether or not the car makes 600whp or 400 whp.. on a stock rev limit the valves are NOT A WEAK LINK nor are the valve springs.

Valve float because of boost is very common on other platforms. 4.6 mod motors have this happen, 5.3 ls motors can have this happen, this happens to a lot of honda motoros as well, not to mention all the diesel platforms that this is a problem ... there are many many other platforms that have valve float issues due to boost.


Its not just about if higher boost pressures hold the valves open, but also if they slow the return, also called floating a valve. It doesnt have to stick open to be floated, it can just not return fast enough, potentially causing major damage. You ever float a valve on an s4? I have! It sucks.


Some info about 944 turbos and valve float: http://www.lindseyracing.com/LR/Part...VESPRINGS.html

When you start increasing the boost pressure, you also increase the force that is trying to prevent the valve from closing. The stock intake valve is 45 mm in diameter and has a 9mm-stem diameter. The factory valve spring has a seat pressure of 130 pounds and an open pressure of 230 pounds. When you calculate the surface area of the valve, it comes out to be just over 2.3 square inches. This means that when the valve has 11.8 pounds of boost pushing against the backside of the valve, it takes approximately 27 pounds of spring pressure to counter the effect of the boost pressure.

When you increase the boost pressure, for example, by increasing the boost from 11.8 pounds to 18 pounds. Now when you multiply the 18 pounds times the surface area of the valve and you now need over 41 pounds of spring pressure to control the valve, that is an increase of 14.2 pounds. Larger intake valves or higher boost pressures will make this problem even worse.

If that is not enough to convince you, consider this: The valve spring actually does two things, not only does it control the valve, but it also has to be able to control the weight of the hydraulic lifter, which happens to be over 100 grams each. Porsche designed their spring rate to handle this very heavy hydraulic lifter at the factory red line of 6400 RPM. With the aftermarket chips today, a red line of over 7000 RPM is commonplace. The inertia of the heavy lifter at that RPM adds significant stress to the valve spring.

I have personal experience floating a valve. It is a bitch...



damaged the cam too...




This was on an off the shelf stage 2 tune with stock k03's and a 7100rpm redline. Valve float can happen, it sucks.

[Meow]

Mine is definitely not 6500.

You are on an APR tune, most of those raise the stock rev limit.

[jibberjive]

Assuming a stock redline, forged rods/ARP rod bolts are the only thing needed to handle 600+whp (chinese IE rods and the like are fine). After that, it's the stock pistons, but you shouldn't have to worry about that til higher cylinder pressures/more power than you're likely to make (over 600whp).

Edit: This is of course assuming no substantial knock, a good tune and whatever else to safely make that power. I'm only talking hardware limits.

[Meow]

I think I might be wrong about the stock rev limit. I always thought it was 6500, but looking around it appears to be 7000, sorry about that. I still feel it is important to upgrade the valvetrain, but that might be influenced by my past experience floating a valve...

[jibberjive]

There's no way I'd personally build a car to put out 600+whp and leave the heads stock, I'm just stating my opinion on the limits of the hardware. I read some really good testing on the stock heads regarding RPM and valve float the other week, I'll see if I can find that data again.

[Meow]

Assuming a stock redline (or say, sub 7200 RPM rev limit) forged rods/ARP rod bolts are the only thing needed to handle 600+a (chinese IE rods and the like are fine). After that, it's the stock pistons, but you shouldn't have to worry about that til higher cylinder pressures/more power than you're likely to make (over 600whp).

Edit: This is of course assuming no substantial knock, a good tune and whatever else to safely make that power. I'm only talking hardware limits.

Am I the only one to ever float a valve in an s4? Lol, looking through the forum with a quick search for "bent valve" turns up a lot of threads. Maybe no one likes to talk about it though... I feel it is something of concern when looking at high horsepower setups, especially on high miles cars where the springs have fatigued. Who knows what the previous owner did, maybe the ran a bit low oil at high temps and rpm, maybe they ran crappy oil that thinned out and caused more wear. Lots of potential problems arise when modifying high mileage old cars.

Then you get into raising the rev limit. Its hard to say where the stock valves will float, mine floated close to stock rpm, others might not float until 7500rpm, there are loads of factors that go into that... I just think its not worth the risk. Springs and retainers are cheap insurance against valve float. Some may think its not a potential issue, I think it is.

[Meow]

There's no way I'd personally build a car to put out 600+whp and leave the heads stock, I'm just stating my opinion on the limits of the hardware. I read some really good testing on the stock heads regarding RPM and valve float the other week, I'll see if I can find that data again.

I would <3 you long time if you could find it again. I LOVE me some data. Mmmm link me baby one more time.

[somebody5788]

You are on an APR tune, most of those raise the stock rev limit.

Even on the tac it says like 6850 or so RPM before it's in the red, however yes, mine will easily hit 7k

[rtl5009]

Shit breaks. Don't worry, it happens on every platform.

[JDM EJ1 95]

Valve float because of boost is very common on other platforms. 4.6 mod motors have this happen, 5.3 ls motors can have this happen, this happens to a lot of honda motoros as well, not to mention all the diesel platforms that this is a problem ... there are many many other platforms that have valve float issues due to boost.


Its not just about if higher boost pressures hold the valves open, but also if they slow the return, also called floating a valve. It doesnt have to stick open to be floated, it can just not return fast enough, potentially causing major damage. You ever float a valve on an s4? I have! It sucks.


Some info about 944 turbos and valve float: http://www.lindseyracing.com/LR/Part...VESPRINGS.html





I have personal experience floating a valve. It is a bitch...



damaged the cam too...




This was on an off the shelf stage 2 tune with stock k03's and a 7100rpm redline. Valve float can happen, it sucks.

ive had a few(beers).. but not enough to tell you that you didnt float a valve because of boost esp. on damn ko3s.. its just not possible.... .you floated a valve because of some other event.... and im sorry the mod motors are a platform that im not entirely familiar.. but like i said.. ive never ever ever seen a valve float because of FI alone... although its possible... yes... but in everyday normal builds.. i can honestly say it is not... its just an odd issue to bring up because it DOESNT HAPPEN.

i was a honda guy LONG before i was an audi guy.. and in those years in building, modding, and being in the honda building community.... I NEVER... Not once.... EVER seen a motor float a valve bc of boost alone.. wether or not its something that can be proven or not.... in my eyes.. you are the only one to ever bring this up... and in my eyes it just DOESNT happen.. and if anyone reading this can tell me otherwise.. and prove it.. be my guest.. but i will put money on it NEVER happenign on an s4...

and on top of things... not returnign a valve fast enough on stock rev limits... is not a issue with horsepower..... you either have something completely wrong with timing.. or you have something completely fubared with mechanicals in the first place.... saying the 2.7t ever had an issue with valves not returning fast enough.... thad be like saying audi designed this motor to grenade itself at the factory preset rev limit..


this is the only point i think i need to make.... in my ~10 years of being in the automotive industry.. ive NEVER heard of this phenomenon...EVER... and being in the communities that you have pointed it out being common in(besides the mod motors) im just asking you... where have you seen this issue...

it doesnt happen... and if it in fact does... it FOR SURE has definitely never happend on a 2.7T.. the hardware out there just doesnt support the theory..


stock vavles and valvesprings are perfectly fine @ 600awhp as long as the rev limit isnt increased like mad. and your tuner doesnt suck balls.

[jibberjive]

I would <3 you long time if you could find it again. I LOVE me some data. Mmmm link me baby one more time.

Here's the video




And I'm pretty sure the stock rev-limit is set to 6800 in the ECU, but don't quote me. Regarding rev limit, I'd probably feel fine with a redline 700-7200RPM. Of all of the bent valve failures I've heard of on our engine, I've only heard of maybe one or two that were potentially from valve float, and even those weren't for sure. If your damage was from a stock redline and K03's, I'd be super surprised if it was from valve float under normal operation. Maybe it could have been though, idk.

If I personally was aiming for 550+whp, I would definitely build the heads though, just my opinion. There have been questionable failures of the stock sodium filled valves (not necessarily related to valve float) that wouldn't leave me with an easy feeling on high horspower/high RPM setups, though it's definitely not required.

[BITRBO]

Valve "float" is cause by undersized valve springs and/or hydraulic lifters, and typically only happens in high-HP applications when when the engine speed is increased to a point that either the valve spring and/or the oil within the lifter cannot react fast enough (i.e. change direction) to keep up with the speed of the cam shaft. That's why pure race engines use super stiff valve springs and solid lifters so they can run 8, 9, 10k RPM reliably and not have to worry about valve-train float. But the trade off is solid lifters require constant adjustment due to wear on the tip of the valve stem and/or the cam lobe, so 99% of production cars have been using hydraulic lifters since the 60's cause they self adjust to the maintain the appropriate tolerances. They're aren't nearly as noisy either.

Meow, I'm not saying that you didn't valve float, but springs and lifters (more-so the latter) do fail from time to time, so that's probably what happened. I don't think your ko3 stage 2 setup was pushing enough hp/tq or spinning fast enough to get valve train float, and if it was... You'd have more than just one valve damaged.

[The_Auto_Tech]

It's not always spring or lifter failure that cause issues like that either. I just finished tearing apart a 2.5 VW engine at work to take in for scrap. It had 4,000 miles on it. One of the keepers broke and dumped the valve down into the combustion chamber. I've NEVER seen this happen on another engine but it goes to show you that anything can happen.

[The_Auto_Tech]

So, my question is this. I'm looking to build a very DD friendly setup, so I've decided to stay with the twin turbo setup to keep the power band down low with minimal lag. I'm thinking of doing Frankenturbos as I would like to help keep cost down. I plan on adding water/methanol injection as well. I'm looking for reliability for pure power. At that point would I need to be concerned about the stock rods? I figure I might be able to hit around 450 WHP with a good tune. The motor runs perfect and is in excellent health. I would just hate to tear it apart since it's having 0 issues.