Thoughts on raising compression verses peak cylinder pressur
Discussion
My question relates to static compression verses peak cylinder pressures, we all know with E85 becoming more avaliable there is benefits to be had by raising compression to become a more effecient engine.
With the raise in compression you can get to the point of having head lifting issues, normally in that case you would simply put head studs in and clamp it down.
I do not have that option and my head bolts are 16" long M9......to save going over it with everyone multiple times, they cannot be replaced with anything larger or stronger period.
The head isnt the best for flow, around 130cfm at 10".
On pump fuel(v power) we make 400ftlbs and 562bhp(8000rpm), using a hx40/35 turbo with a compression of 7.8:1 and 36psi of boost, this is with 19 degrees of timing and hitting MBT, exhaust back pressure from 7500-8500rpm is 39psi.
We have initially limited the engine to 400ftlbs to see how the engine does but we have noticed that it takes 6psi to so from 510bhp to 560bhp, so the effeciency is really dropping off.
We monitor coolant pressure coming out of the head and exhaust manifold back pressure
With that in mind I need to raise this up to 700bhp and the only way i can see this is by raising the compression and switching onto e85.
We dont want to increase the turbo size as the powerband is already fairly narrow and again pulling overlap out of the cams while does help with peak power, massively hurts boost threshold and anything up to 7000rpm.
Due to having 131.1mm rods which means the rod/stroke ratio is awful so while i have been revving it to 8500rpm, its pushing it.
The potential problem with this is that it may lead to an increase in peak cylinder pressure which since i cant change head bolts could lead to head lift issues.
Since this isnt an engine anyone really turbocharged if i need 'off the shelf' pistons my real only other choice is 11.1:1 which is a big increase in compression, this combined with e85 should widen my powerband, also one advantage through is it will allow me to the run the 133.1mm rods, meaning the extra 2mm of rod length will make me more comfortable revving to 9000rpm.
I suppose my question would be has anyone increased compression on their engine and run the same peak torque but suddenly had head lifting issues from the change in compression?
Sorry for the long post but ive spent alot of time researching this online but with most being able to put ARP studs from the start they dont suffer this issue to much unless we are talking really big power
With the raise in compression you can get to the point of having head lifting issues, normally in that case you would simply put head studs in and clamp it down.
I do not have that option and my head bolts are 16" long M9......to save going over it with everyone multiple times, they cannot be replaced with anything larger or stronger period.
The head isnt the best for flow, around 130cfm at 10".
On pump fuel(v power) we make 400ftlbs and 562bhp(8000rpm), using a hx40/35 turbo with a compression of 7.8:1 and 36psi of boost, this is with 19 degrees of timing and hitting MBT, exhaust back pressure from 7500-8500rpm is 39psi.
We have initially limited the engine to 400ftlbs to see how the engine does but we have noticed that it takes 6psi to so from 510bhp to 560bhp, so the effeciency is really dropping off.
We monitor coolant pressure coming out of the head and exhaust manifold back pressure
With that in mind I need to raise this up to 700bhp and the only way i can see this is by raising the compression and switching onto e85.
We dont want to increase the turbo size as the powerband is already fairly narrow and again pulling overlap out of the cams while does help with peak power, massively hurts boost threshold and anything up to 7000rpm.
Due to having 131.1mm rods which means the rod/stroke ratio is awful so while i have been revving it to 8500rpm, its pushing it.
The potential problem with this is that it may lead to an increase in peak cylinder pressure which since i cant change head bolts could lead to head lift issues.
Since this isnt an engine anyone really turbocharged if i need 'off the shelf' pistons my real only other choice is 11.1:1 which is a big increase in compression, this combined with e85 should widen my powerband, also one advantage through is it will allow me to the run the 133.1mm rods, meaning the extra 2mm of rod length will make me more comfortable revving to 9000rpm.
I suppose my question would be has anyone increased compression on their engine and run the same peak torque but suddenly had head lifting issues from the change in compression?
Sorry for the long post but ive spent alot of time researching this online but with most being able to put ARP studs from the start they dont suffer this issue to much unless we are talking really big power
First off...I dont believe for one second the studs cannot be either made larger, or from a better material, unless they're already made from unobtanium...
There are always options...but M9 is pretty small
And as above...would hardly say E85 is readily available.....any different than simply buying race fuels. That said, it really does seem to be the fuel of choice.
And as long as you keep timing conservative, stay clear of detonation then there is no reason cylinder pressures should pose any difficulty as such other than the engine making more power...is to some degree going to have higher cylinder pressure at some point in the cycle. But good tuning should ensure it remains sensible.
And if you want more power, wider spread of power, better efficiency....a simple option would be a more modern turbocharger. As well as good boost control etc you could try and limit torque vs rpm yet still shoot for higher power ranges overall using the higher rpm's if you can safely.
I'm sure you could very safely push into the 9's CR with ethanol, or keep it very safe at say 9.0 or thereabouts.
There are always options...but M9 is pretty small
And as above...would hardly say E85 is readily available.....any different than simply buying race fuels. That said, it really does seem to be the fuel of choice.
And as long as you keep timing conservative, stay clear of detonation then there is no reason cylinder pressures should pose any difficulty as such other than the engine making more power...is to some degree going to have higher cylinder pressure at some point in the cycle. But good tuning should ensure it remains sensible.
And if you want more power, wider spread of power, better efficiency....a simple option would be a more modern turbocharger. As well as good boost control etc you could try and limit torque vs rpm yet still shoot for higher power ranges overall using the higher rpm's if you can safely.
I'm sure you could very safely push into the 9's CR with ethanol, or keep it very safe at say 9.0 or thereabouts.
227bhp said:
Where are you going to find E85 in the UK? AFAIK the only way to find high octane fuel is to buy race fuel.
I can buy it about an hour away from where i live, well actually pretty pure ethanol but i have a flex fuel sensor in my setup so i will probably run wastegate(10psi) on pump fuel which based on making 300bhp/200ftlbs on 7.8:1 i would imagine its going to be around 330-340bhp which will be fine for road use then add the ethanol when i want to go drag racing, the other option is using the flex fuel sensor to mix 20-25% methanol with my fuel to make my own race gas but since e85 high compression tuning is generally more well known in 4 cylinder applications i used that as an exampleYour question is so non-sensical I'm not sure where to start. You don't make more power or efficiency from turbo engines by raising the compression ratio. That just increases the propensity to detonate and limits boost. You do it by raising the boost and if necessary lowering the CR even further. My calculations say you'll need about 50 psi plus to get to 700 bhp. E85 will help by virtue of its higher octane value. CR might need to come down to low 7's or so.
As Stevie has said, you can get any fastener made from any material if you specify a custom design. I see no reason why you can't helicoil the block out to 10 mm and get appropriate studs made from a fastener manufacturer.
As Stevie has said, you can get any fastener made from any material if you specify a custom design. I see no reason why you can't helicoil the block out to 10 mm and get appropriate studs made from a fastener manufacturer.
Because of the nature of construction of the K series, stronger studs dont increase the clamp load, intially maybe, but after the block/ladder sandwich has gone through a number of heat/expansion cycles the pillars in the head that support the through bolts start to deform and collapse reducing the clamp. Ask me how I know. The stock bolts deform into the plastic zone and allow the block sandwich to expand and contract with heat.
Dave
Dave
If those power figures are genuine i'd be happy that it's still in one piece, I think if you push it much more something will let go. You've chosen the wrong engine for those kind of outputs.
Also, as has been pointed out to you before you need the full and intricate spec of your engine and put it into a simulation program, that will tell you what you want to know.
Apart from the onset of det', it won't tell you that.
Or if it's going to blow up, but it will give cylinder pressures.
Also, as has been pointed out to you before you need the full and intricate spec of your engine and put it into a simulation program, that will tell you what you want to know.
Apart from the onset of det', it won't tell you that.
Or if it's going to blow up, but it will give cylinder pressures.
Edited by 227bhp on Thursday 13th September 18:23
turbotoaster said:
Since this isnt an engine anyone really turbocharged if i need 'off the shelf' pistons
What? There are plenty of companies that can supply totally custom pistons for any engine ever made from a lawnmower to an DFV!!(if you can't afford those pistons, well, that's an entirely different matter! a genuine 700bhp from a k series is a) going to be hugely expensive and b) hugely un-reliable and likely to grenade expensively at the drop of a hat. If you are already genuinely running 36 psi (2.45barg) without going bang then you are already doing extremely for an engine with a max design power of 134 bhp in std trim........)
Mignon said:
Your question is so non-sensical I'm not sure where to start. You don't make more power or efficiency from turbo engines by raising the compression ratio. That just increases the propensity to detonate and limits boost. You do it by raising the boost and if necessary lowering the CR even further. My calculations say you'll need about 50 psi plus to get to 700 bhp. E85 will help by virtue of its higher octane value. CR might need to come down to low 7's or so.
As Stevie has said, you can get any fastener made from any material if you specify a custom design. I see no reason why you can't helicoil the block out to 10 mm and get appropriate studs made from a fastener manufacturer.
In the modern world....CR's of 9...10..and even 11.0:1 are not uncommon with ethanol, and lots of boost too !! It really seems to be a very forgiving fuel.As Stevie has said, you can get any fastener made from any material if you specify a custom design. I see no reason why you can't helicoil the block out to 10 mm and get appropriate studs made from a fastener manufacturer.
And people using 50...60..70psi boost for the really fast stuff on 4cyl engines..again, it getting more common
Here's a recent one at around 65psi boost with E85..although it's probably making 13-1400hp lol
https://www.youtube.com/watch?v=9Jr4OneRjq8&
stevieturbo said:
First off...I dont believe for one second the studs cannot be either made larger, or from a better material, unless they're already made from unobtanium...
There are always options...but M9 is pretty small
And as above...would hardly say E85 is readily available.....any different than simply buying race fuels. That said, it really does seem to be the fuel of choice.
And as long as you keep timing conservative, stay clear of detonation then there is no reason cylinder pressures should pose any difficulty as such other than the engine making more power...is to some degree going to have higher cylinder pressure at some point in the cycle. But good tuning should ensure it remains sensible.
And if you want more power, wider spread of power, better efficiency....a simple option would be a more modern turbocharger. As well as good boost control etc you could try and limit torque vs rpm yet still shoot for higher power ranges overall using the higher rpm's if you can safely.
I'm sure you could very safely push into the 9's CR with ethanol, or keep it very safe at say 9.0 or thereabouts.
Its not that studs cant be made, infact you can buy them for this engine from ARP but since this engine works by the bolts also holding the main round when the engine changes from cold to operating temperature it can effect bearing clearance and as such damage main bearings.There are always options...but M9 is pretty small
And as above...would hardly say E85 is readily available.....any different than simply buying race fuels. That said, it really does seem to be the fuel of choice.
And as long as you keep timing conservative, stay clear of detonation then there is no reason cylinder pressures should pose any difficulty as such other than the engine making more power...is to some degree going to have higher cylinder pressure at some point in the cycle. But good tuning should ensure it remains sensible.
And if you want more power, wider spread of power, better efficiency....a simple option would be a more modern turbocharger. As well as good boost control etc you could try and limit torque vs rpm yet still shoot for higher power ranges overall using the higher rpm's if you can safely.
I'm sure you could very safely push into the 9's CR with ethanol, or keep it very safe at say 9.0 or thereabouts.
Just like what im currently doing with the boost pressure, im using it to maintain a flat torque curve to ensure i dont simply have a big massive chunk of torque at 6000rpm that i dont really need, you can see im adding boost as rpm increases because my engines VE is dropping off, the issue we will come across is i will simply run out of turbo effeciency before hitting my target power level.
to be able to hit my target i will need 430ftlbs, which while isnt much more than what im peaking at now, being able to keep that level of torque at 8500rpm is alot more difficult, im making changes to the head/cams to try and help the situation but i know thats not going to be enough to reach the level im looking for.
Hence compression seemed the next choice, i built the engine with pretty low compression specifically for pump fuel, but now i seemed to have reached a limitation from compression and head flow that i am working to overcome, I agree that somewhere in the 9s would be a more suitable choice, I would need to have a custom set of pistons made which can be a pain(though i know companies like wiseco will do it)
Max_Torque said:
What? There are plenty of companies that can supply totally custom pistons for any engine ever made from a lawnmower to an DFV!!
(if you can't afford those pistons, well, that's an entirely different matter! a genuine 700bhp from a k series is a) going to be hugely expensive and b) hugely un-reliable and likely to grenade expensively at the drop of a hat. If you are already genuinely running 36 psi (2.45barg) without going bang then you are already doing extremely for an engine with a max design power of 134 bhp in std trim........)
I know that, I just worked with Omega Pistons and had 40 custom k series turbo pistons made for myself and customers which are 8.3:1, this took 4months to do(ive got 7 of these) they had a minimum order of 20 pistons which is alot.(if you can't afford those pistons, well, that's an entirely different matter! a genuine 700bhp from a k series is a) going to be hugely expensive and b) hugely un-reliable and likely to grenade expensively at the drop of a hat. If you are already genuinely running 36 psi (2.45barg) without going bang then you are already doing extremely for an engine with a max design power of 134 bhp in std trim........)
The set i have at the moment in the engine were part of a group buy from wossner so if something were to happen to one of them basically they are scrap as i cant get replacements.
i know companies like wiseco do one off sets but its still a pain if something were to go wrong, the nice thing about a k series is if you kill a piston you can simply hot swap it with a new liner pretty quick, I would like to try and keep that ability, hence it would be nice to be able to simply order a piston/set and have it within a couple of days.
Its not an issue of money, more things like time if i do want to use it competitively.
I thing the engine genuinely does have potential, its a fully girdled crank, runs ductile liners, forged pistons and rods(though rod/stroke ratio is awful) the things i think holds it back is poor head flow compared to other manufacturers and potential issues with head lifting but again i have not reached that point, that may come at 450ftlbs, maybe 500ftlbs but until i start to see spikes in the coolant pressure I wont know.
Everyone assumes its a weak piece of rubbish but until i reach a mechanical failure point i dont know where the limit is, i used to run 25psi of boost on a completely OEM bottom end making 380bhp and that saw track work without an issue, so again that surprised alot of people.
You know of course that boost is just a level of restriction being in your industry, that really just shows how poor the head flow is to be only making 562bhp at that boost level for what is a reasonable size turbo, put the same turbo on a honda/4g63 and it would make alot more power
Most of the US piston makers will do smaller orders than 20 !!
There have already been other threads, but I've had JE and Diamond make me custom sets before. Or Gibtec got recommended too.
If the cost aspect is less of a concern vs keeping running...then dont buy 4, buy 8, then you always have spares as overall cost probably wont be that much difference anyway.
But keeping things simple, higher CR, ethanol and a better turbo could see a big difference. Even if you got stuck at that CR and were happy....try the ethanol anyway and a better turbo
There have already been other threads, but I've had JE and Diamond make me custom sets before. Or Gibtec got recommended too.
If the cost aspect is less of a concern vs keeping running...then dont buy 4, buy 8, then you always have spares as overall cost probably wont be that much difference anyway.
But keeping things simple, higher CR, ethanol and a better turbo could see a big difference. Even if you got stuck at that CR and were happy....try the ethanol anyway and a better turbo
RobXjcoupe said:
Is it possible to re-engineer the head securing bolts so that they can just clamp the head on with separate bolts holding the crankshaft bearings in place?
Not really as the block isnt designed to be a 'tension' engine so the block is pretty much enough meat in it to stop the liners moving and keep coolant around them, if you tried it the block would massively distort i would expectstevieturbo said:
Most of the US piston makers will do smaller orders than 20 !!
There have already been other threads, but I've had JE and Diamond make me custom sets before. Or Gibtec got recommended too.
If the cost aspect is less of a concern vs keeping running...then dont buy 4, buy 8, then you always have spares as overall cost probably wont be that much difference anyway.
But keeping things simple, higher CR, ethanol and a better turbo could see a big difference. Even if you got stuck at that CR and were happy....try the ethanol anyway and a better turbo
I my current turbo can make more power, in the US they are making 700bhp flywheel with it on 4g63 engines(either 560whp on mustang or 700whp on dynojet) at 40psi/e85 and running high 9s so there is more left in it and 36psi of boost and 39-40psi of back pressure shows its not done yet, but since it took 6psi to go from 510bhp to 560bhp it shows the returns are dropping fast, for example it was 300bhp at 10psi and 400bhp at 17psi, while i think 600bhp can be achieved at 42psi we ran out of time on the day, but thats still 100bhp off where i want to be.There have already been other threads, but I've had JE and Diamond make me custom sets before. Or Gibtec got recommended too.
If the cost aspect is less of a concern vs keeping running...then dont buy 4, buy 8, then you always have spares as overall cost probably wont be that much difference anyway.
But keeping things simple, higher CR, ethanol and a better turbo could see a big difference. Even if you got stuck at that CR and were happy....try the ethanol anyway and a better turbo
My thoughts were ethanol will help a little with boost threshold but that while higher compression doesnt spool the turbo faster, what it does do is make more power per psi while spooling, so i maybe able to hit a target 430ftlbs at a lower rpm purely because its a lower boost target im aiming for.
For basic maths on what to expect i dont really know if it would work this way but to go from 7.8:1 to 9.0:1 is a 16.8% change, if that carried over to the power output at the same boost, that would equate to 656bhp then maybe the extra from better head/cams and ethanol to crack 700bhp.
The reason for the power output is there is a 9.55@156mph lotus record that i would like to try and beat from a honda k20 turbo elise with around 750bhp.
Im about 200kg lighter but i dont have a sequential box so im hoping to make it up in the first 1/8 on weight and tyres
ime, when a 700bhp engine doing 8.5krpm lets go, you are best sweeping up the remaining bits and putting them straight into the bin. The chance of getting a single cyi failure that only scraps one piston and liner is really pretty low. At the BMEP you are talking about, you are also almost certainly within the high cycle fatigue life of certain parts and probably within the low cycle life of some bits too, meaning you'll need to start pre-preemptively rebuilding the engine on a "scheduled" basis if you want to avoid failures in the field.
turbotoaster said:
Not really as the block isnt designed to be a 'tension' engine so the block is pretty much enough meat in it to stop the liners moving and keep coolant around them
Many people, me included, would suggest that it actually fails to even do that ^^ at standard levels of power ie 160bhp............)turbotoaster said:
in the US they are making 700bhp flywheel
Anyone who believes anything they read online about power figures is almost certainly being mislead ime.turbotoaster said:
The reason for the power output is there is a 9.55@156mph lotus record that i would like to try and beat from a honda k20 turbo elise with around 750bhp.
The k20 is a superior enigne in every respect to the k series. You're going to spend a LOT of money to go faster........turbotoaster said:
Im about 200kg lighter
200kg? really? out of an elise? hmmm i suspect not........227bhp said:
Why does the head flow so badly and what can or can't be done to make it better?
What are the flow figures?
This isn't a flow figure: "around 130cfm at 10"" Part of the info is missing - the valve lift, if indeed there was one fitted.
What are the cam specs?
sorry if im missing things out.What are the flow figures?
This isn't a flow figure: "around 130cfm at 10"" Part of the info is missing - the valve lift, if indeed there was one fitted.
What are the cam specs?
22.6 46.6 70.4 92.6 112 126.5 136.3 139.9 143
143 is at .500" then reduce by 0.050" each time.
my current cams are 274 degree with 11mm 0.433" with hydraulic followers
Since the porting was done with stock size valves but i simply put 1mm overside valves in(there wasnt much material around the valve seat area for the stock size valves so the seats were simply cut for the large valves) and not reblended to take advantage of them then 130cfm is a guesstimated figure.
My new cams that arrived today are 280/276 with 12.5mm 0.500" but are also designed for mechanical followers so valve accleration is a bit more aggressive
Inlet valves will be 2.3mm larger and exhaust 2mm larger but this time the head will be ported with these valves in place to make maximum advantage of them, the data for that head is below
23.2 46.5 70.6 94.4 114.3 130.4 140.1 145.6 150.25 153.1
Max_Torque said:
turbotoaster said:
Not really as the block isnt designed to be a 'tension' engine so the block is pretty much enough meat in it to stop the liners moving and keep coolant around them
Many people, me included, would suggest that it actually fails to even do that ^^ at standard levels of power ie 160bhp............)turbotoaster said:
in the US they are making 700bhp flywheel
Anyone who believes anything they read online about power figures is almost certainly being mislead ime.turbotoaster said:
The reason for the power output is there is a 9.55@156mph lotus record that i would like to try and beat from a honda k20 turbo elise with around 750bhp.
The k20 is a superior enigne in every respect to the k series. You're going to spend a LOT of money to go faster........turbotoaster said:
Im about 200kg lighter
200kg? really? out of an elise? hmmm i suspect not........to be doing over 140mph in a mitsubish evo over the quarter mile shows he isnt make 500bhp as i would imagine hes between 1200-1400kg, so the 550 at the wheels seems reasonable enough.
I understand the k20 is a much better engine in pretty much every aspect, they are making well over 1000bhp in drag race form, probably closer to 1300-1400bhp in the 7 second 4wd civics.
Thats not the point of the record, its lotus against lotus regardless of engine choice
My car weighs 650kg, plus allow 150kg for myself, bit of fuel and safety gear, his car weighs 1000kg with him in it(his is a series 2 which is alot heavier)
turbotoaster said:
Thats not the point of the record, its lotus against lotus regardless of engine choice
ok, so just slam in a nice turbo LS7 and be done with it? Almost certainly work out cheaper than doing it with a k series......turbotoaster said:
My car weighs 650kg, plus allow 150kg for myself, bit of fuel and safety gear, his car weighs 1000kg with him in it(his is a series 2 which is alot heavier)
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