sixtentouge
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- Aug 28, 2023
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GR Yaris Balance of tuning and durability limits
- Thread starter Onehp
- Start date
That's high but a good way to make power. Some more cycles then, for the load on the rod it's bit the same, either power from cylinder pressure or from rpm still is an incredible load... the amount of fuel (E85?) should be pretty amazing too...They were turning it 9,000 rpm
Greenthumb
Totally Hooked
No Joke, I just thought to myself, hey, when did I write that, I can't even remember. I even forgot the video... Until I realized that the quote wasn't mine. Puuuuh wanted to call the doctor . But look @ the Username of the quote
. But look @ the Username of the quoteAttachments
LittleMav
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- Jul 22, 2023
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A question from a non-tec guy who is interested in long term durability and is following this thread closely:
Apart from a HJS DP and exhaust the car is - and will stay- stock. What impact would an upgrade to the Kelford valve springs and camshaft have on the on drivability and power - without touching the software?
Apart from a HJS DP and exhaust the car is - and will stay- stock. What impact would an upgrade to the Kelford valve springs and camshaft have on the on drivability and power - without touching the software?
Good Q.
With the EZ cams I've read that it can work on the stock ECU, but don't know how well that is validated. Maybe just a run to the dyno from the shop before car was tuned, haven't seen any reports from anyone running like that long term.
Expected effects are some less mid range torque and more top end power. But not sure if driveability is affected...
Not much sense in doing so, stock boost top end is barely above 1 bar, you're safe. Unless you want security from better valvetrain but bit far fetched if not planning to do more (later)...
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Hi there, if you’re not doing ECU software (more boost, more power and maybe raised rpm limit) is pointless to do valve springs and camshaft, and I would add it’s probably detrimental to engine life (anything you do on this car, by someone else, you risk doing it below factory standards, and that’s a big risk for me) and a waste of money.
The car in stock form is quite bulletproof engine wise. Yes, there’s been “loads” (not that many in the grand scheme of things) of engine failures reported, but I wonder how many of them have had the ecu flashed, used the wrong oil or just the use wasn’t really the ideal -meaning abused without respecting warming up times, cooling down periods…-
I would argue it could potentially rob you of power. The aftermarket springs are several uggaduggas springier than stock, which require more umph to boing up and down
It would be interesting to see if the Stock ECU will compensate for the higher lift of the cams and give you more powaaah or a nice lean Jehovah witness mixture
The other thing to consider is that you're pulling apart an engine that was put together by Toyota's best inside Toyota's best factory. Absolute best case scenario is that it will be put back together almost as good as before
You're taking on all the risk, but don't want the benefits of that risk
Finally the way I understand it, valve float under normal conditions will give you a fluffy high end, not the piston interference *kaboom* kind. Obviously once you go above factory parameters you can blow anything up with enough revs and boost
It would be interesting to see if the Stock ECU will compensate for the higher lift of the cams and give you more powaaah or a nice lean Jehovah witness mixture
The other thing to consider is that you're pulling apart an engine that was put together by Toyota's best inside Toyota's best factory. Absolute best case scenario is that it will be put back together almost as good as before
You're taking on all the risk, but don't want the benefits of that risk
Finally the way I understand it, valve float under normal conditions will give you a fluffy high end, not the piston interference *kaboom* kind. Obviously once you go above factory parameters you can blow anything up with enough revs and boost
Sekred
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- Dec 18, 2021
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Usually with a camshaft upgrade (for want of a better term) you loose some torque down low but the gain at the top of the rev range exceeds this. You probably going to need the right supporting mods like exhaust and intake.
I'm not into this valve float/ bounce theory unless you exceed the factory redline or change the cams. I see no link between valve float and increasing boost.
I'm not into this valve float/ bounce theory unless you exceed the factory redline or change the cams. I see no link between valve float and increasing boost.
But it's pretty well established there is? If not, tuners could just run 2 bar at 7000rpm and not need to change the springs...
Having difficulty imagining how the physics work is another thing, I imagine it is simply the increased amount of exhaust stroke gas that simply doesn't have enough time to evacuate the cylinder above ~6500rpm, keeping the valve open together with the sheer inertia from the valve weight, both working against the valve spring.
What I don't fully get is at what boost this happens, to me it should vary depending on the backpressure and thus what kind of mods one has exhaust + turbo side, as that clearly should influence how easy said exhaust gasses can evacuate the cylinder...
Sekred
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This is the way I look at it. Increasing boost pressure increases cylinder pressure and the engine makes more torque. More twisting force on the crankshaft. Out of interest peek cylinder pressure occurs 15-20 degrees after TDC. Maximum twisting force on the crank shaft occurs just before 90 degrees after TDC which make sense if you have ever ridden a bicycle. Increasing boost pressure by lets say 20 percent does not increase peek cylinder pressure by 20 percent. The reason we can increase the OEM boost pressure by a large amount and the engine survives (generally).
Noe the valves are closed during the majority of the compression stroke and the power stroke.
So how does boost force the valve(s) open?
Are we talking about the increase in exhaust pressure in the exhaust manifold holding the exhaust valves open . Exhaust manifold pressure and it's hard to find information regarding this but I have seen figures around 2 to 3 times boost pressure. The bigger the turbo relative to engine size the lower the exhaust pressure in the manifold. The lower the exhaust pressure relative to boost pressure the better generally. I am talking about exhaust pressure before the turbo.
Pressure in the exhaust manifold is different to Force. We can calculate force using the formula Force = Pressure x Area.
Considering the area of the exhaust valve and this excludes the diameter of the stem I just do not see enough increase in force to cause a problem.
I could be off track here and there maybe other things I have not considered.
Of course more boost increases torque and load and peak cylinder pressure, all related, but you need to use absolute pressure (atmospheric + boost) . How that relates to how an engine holds up is an entirely different subject I don't want to tap into now other then that of course survivability (on what time scale?) is affected.
Anyway, point is, if you increase power through boost which means more air crammed in the same space, this increased amount after combustion needs to evacuate the engine in the exhaust stroke but you haven't changed the hardware. The valve opening is the same and at high rpm the time to do this is reduced and flow losses increase exponential. So as the exhaust cam stops pressing the exhaust valve down, there are just more highly pressurised exhaust gasses around that somehow are forcing the valve to remain open. The flow dynamics of this are very complex and actually I'm not sure what exactly happens, a three pot should be completely seperate in evacuating the exhausts but maybe at high rpm there is some interference from other cylinders also in the exhaust manifold from pressure peaks that haven't fully evacuated?
Anyway, point is, if you increase power through boost which means more air crammed in the same space, this increased amount after combustion needs to evacuate the engine in the exhaust stroke but you haven't changed the hardware. The valve opening is the same and at high rpm the time to do this is reduced and flow losses increase exponential. So as the exhaust cam stops pressing the exhaust valve down, there are just more highly pressurised exhaust gasses around that somehow are forcing the valve to remain open. The flow dynamics of this are very complex and actually I'm not sure what exactly happens, a three pot should be completely seperate in evacuating the exhausts but maybe at high rpm there is some interference from other cylinders also in the exhaust manifold from pressure peaks that haven't fully evacuated?
Michael Knight
Totally Hooked
total amateur here but turbo kits seem to run longer exhaust manifold runners maybe to help this topic. This is not a good read in terms of keeping engine stock - is there an option to hide certain forum threads from UI?
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sixtentouge
Committed member
- Aug 28, 2023
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Minus the valve stem, the stock exhaust valve has an area of roughly 1.21 square inches.
Logging the stock boost curve, it seems to mostly go to around 1.7 bar by 4,000 rpm and then the ECU pulls it back to about 1.2 bar by 7,000 rpm. Changing the target to maintain 1.7 out to 7,000 rpm will (just rough calculations) decrease valve seat pressure by 18psi if we assume a 2:1 turbo pressure ratio. If a "tuner" is taking the boost up to 2 bar, that's a .8 bar increase in boost. Again, assuming a 2:1 PR, that's 1.6 bar increase in EP, or 28psi less valve seat pressure. This is why, IMO, so-called hybrid turbos are garbage. On an efficient race engine, I look for absolutely no higher than a 1.5 PR. Using teh stock exhaust housing and just putting bigger wheels in it can send the PR to the moon. I've been building engines professionally since the 1990s. SAE member...yadda-yadda.
The Kelford standard springs are 87lb. on the seat, and I assume the stock springs are quite a bit less. While boost won't affect separation over the nose of the cam, it will certainly affect valve bounce on the seat when closing (float).
Exhaust pressure on the valve is an issue in turbo engines. With bucket followers, it's just a loss in power. With non-shaft-mounted followers, it can have disastrous effects, as the follower can "jump" off the valve or pivot. Any kind of misfire that lights in the exhaust (like when "tuning") and it's game over.
I've been following this with interest as I've just installed cams and springs (EZP) on the stock ecu and I'm looking at a hybrid turbo solution for later on...
The reason I want one is because it's plug and play, compatible with the oem ecu, can offer a reasonable bump in power (400bhp total) and the turbo won't have to work so hard to my exhaust and more importantly intake temps will reduce which is a problem I'm hitting at the moment with the oem turbo having to work so hard on track. I appreciate they may be not a perfect ultimate solution but do you think they're garbage for all applications?
Not sure if something is lost in translation, but this makes no sense to me, as usually pressure ratio has nothing to do with the exhaust side, only the compressor side. Even if it did, I don't understand where the 18psi comes from as 0,5 bar x 2 = 1 bar = 14psi.
Not all hybrids created equal. Unfortunately not so easy to get good information. A good one has an uprated ball bearing shaft and larger compressor and turbine (some leave the turbine stock - cheap) that both allow for more flow but at the same time don't sacrifice spool too much. Also efficiency plays a big role and can't be seen from the sizes of the wheels. Basically need to be able compare torque curves on like for like tunes, not easy.
From an OEM+ perspective hybrids are great, but for someone expecting min 600hp the suck b*lls. 400bhp is a very reasonable goal on a hybrid and is possible without silly large wheels that look out of place in the housing.
Well mine will get a tune the 29th Feb, so I'll know what the score is then with additional power etc.
Car already has an OEM ecu tune and intake and exhaust mods.
Car already has an OEM ecu tune and intake and exhaust mods.
Sekred
Dedicated member
- Dec 18, 2021
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Sekred
Dedicated member
- Dec 18, 2021
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Cheers. I don't know of anyone in Australia tuning the OEM ECU at the present time.
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