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Unzipped Composites

High CR Pistons

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Hey guys,

 

I apologise if this has been discussed before, I was sure it must have been but I just can't find anything recent and up to date in a search.

 

I am currently building my RB25 Neo for use in a dedicated Time Attack car, and I want to bump the compression ratio up to at least 10:1. I'm sure this is fairly common practice these days, but I just can't find what pistons people are using to achieve it? Any 'off-the-shelf' forged piston I look at are quoted at most a 9:1. Now I know that relies on some assumed figures and may not work out that way, so is it the case that people are using these pistons and bumping the CR another way? Or using custom pistons? Or is everyone actually still building quite low CR engines?

 

Of course my machinist is going to CC the head and can work out what we need to achieve 10:1, but I just wanted to find out if this is definitely going to be a custom piston job or what others are doing?

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Generally people are using custom Pistons I think, places like CP would have done them enough that it wouldn't be a major delay to get them, nothing new would need to be designed i'd have thought. They aren't off the shelf in terms of stock but the design would be so to speak?

10:1 seems like a good spot, i did 9.5:1 and kind of regret not going that little bit further.

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Thanks Pete. Really I'd be keen to go as high as 10.5:1, but I'm trying to reign it in a bit haha. 10.25:1 or 10:1 would be ideal. I'm a little bit surprised they aren't more of a stock item these days with the availability of E85, I would have thought everybody would be looking to bump their CR.

 

I did actually email CP about it, but they haven't got back to me in the 3 weeks since. I do intend to run CP's, but that is sort of all I have been looking at. I wasn't sure if maybe someone else do some 10:1's that would be an easier option. But if they're a custom job then CP it is!

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If you're running E85/race gas full time you can bump CR up, but if you're running pump gas only 9:1 CR is pretty much as high as it gets. If you want to run 10-11:1 CR on pump gas you need direct injection. You would have to dramatically drop boost if you used a flex fuel setup when using pump gas, with PFI engines 10-11:1 CR is pretty common for 98 PULP.

 

Edited by joshuaho96

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Yeh I know, I will only be running E85. Not sure why you would run anything else in a track car regardless of what CR you have. And with the number of flex setups getting around I just find it a bit odd that 10:1 isn't the norm these days even for street cars.

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1 minute ago, Unzipped Composites said:

Yeh I know, I will only be running E85. Not sure why you would run anything else in a track car regardless of what CR you have. And with the number of flex setups getting around I just find it a bit odd that 10:1 isn't the norm these days even for street cars.

10:1 or 11:1 is normal for GDI-T. With PFI-T you can probably only run 6-7 psi boost when not running E85 with that kind of CR. Most people want to make more power on E85, not less. So you see relatively low CRs.

Personally one of the bigger pet peeves I have is how rich these RBs run, either on pump gas or E85. Hopefully someone comes out with a proper water injection kit for these cars at some point.

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29 minutes ago, joshuaho96 said:

Hopefully someone comes out with a proper water injection kit for these cars at some point.

What are you talking about? A kit especially for RBs that you don't have to do any thinking about? I mean, it's not as if the 3 or 4 different WI manufacturers don't already have kits that you could just drop directly onto any RB with only 3 brain cells functioning. It's really not that hard.

And 10:1 CR with decent boost on 98 is no trouble, with decent attention to management and not grinding out all the quench pads, etc. Cams to help relieve some of the dynamic CR is always an option too.

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5 minutes ago, GTSBoy said:

What are you talking about? A kit especially for RBs that you don't have to do any thinking about? I mean, it's not as if the 3 or 4 different WI manufacturers don't already have kits that you could just drop directly onto any RB with only 3 brain cells functioning. It's really not that hard.

And 10:1 CR with decent boost on 98 is no trouble, with decent attention to management and not grinding out all the quench pads, etc. Cams to help relieve some of the dynamic CR is always an option too.

Not a fan of any of the easily available water injection systems. If you're going to do it, you should do it right. PWMing the motor to get the desired flow rate is really, really slow and imprecise. Aquamist is the only company doing a "fast acting valve" so you can control the injector more precisely but the flow isn't to individual injectors, it's to all cylinders all at once. I've seen a lot of literature about injecting water during the low lift phase of the intake cams leading to crankcase water contamination and scuffing of the cylinder bores so it seems unwise to have such poor control over when you're injecting water. 

Bosch's water injection system is one injector per two cylinders, so it's semi-sequential which is probably ok, but I'm unwilling to spend 2000 USD per injector to find out.

The only other option is Nostrum Energy, and they don't actually have a real product to buy, just the director of R&D's testbed R35. We'll see if they manage to ship something as promised. 

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I think you're over-thinking/worrying about it. Whilst you can keep injecting water almost up until the point where the combustion is quenched out.....you really don't have to. You can get at least as much knock prevention/resistance/whatever you want to call it from WMI as from E85 without having to inject anywhere near enough water to cause the effects you're worried about.

Whilst I agree that better control is better, the control that we have is certainly fit for purpose.

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11 minutes ago, joshuaho96 said:

. I've seen a lot of literature about injecting water during the low lift phase of the intake cams leading to crankcase water contamination and scuffing of the cylinder bores so it seems unwise to have such poor control over when you're injecting water. 

Theory doesn't matter. You don't need an OEM opproved system for performance aftermarket.

and as GTSBoy mentioned heaps of cars tuning 10-11 :1 comp ratios with 12 psi (or more!!!!!!) on 98 pump fuel (98ron)

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6 minutes ago, GTSBoy said:

I think you're over-thinking/worrying about it. Whilst you can keep injecting water almost up until the point where the combustion is quenched out.....you really don't have to. You can get at least as much knock prevention/resistance/whatever you want to call it from WMI as from E85 without having to inject anywhere near enough water to cause the effects you're worried about.

Whilst I agree that better control is better, the control that we have is certainly fit for purpose.

I'm not as sure, pretty much every tuner I talk to is not a fan of WMI due to reliability issues, every paper I read mentions water contamination of the oil and cylinder wall scuffing. WMI is really interesting to me as a concept but feels like the details aren't quite there yet. Not worth wrecking an engine over it. 

 

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I feel like WMI development pretty much hit a wall as soon as E85 became an easily obtainable option. I was ready to invest in it back in the day, but since then it just doesn't feel like it's as good an option. If a company was looking at developing a 'proper' kit for RB's, is there even a market for it anymore to justify it? 

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19 minutes ago, GTSBoy said:

It's been working fine since WW2. Who is writing these papers?

I dunno, random PhDs? Working fine is a relative statement. Even in the M4 GTS there are some reliability issues. If the design goal is OEM reliability and refinement I don't think the aftermarket systems are there. Even the OEM systems may be a bit touch and go. A fuel system just works for the better part of 200k miles or 15 years. A water injection system should be similarly expected to work just fine with just added distilled water for 200k miles or 15 years. The military is ok with 50 hours of maintenance for every 25 hours of flight or a total engine rebuild after 5 minutes of WEP, modern performance cars are basically expected to survive on not much more than fluid and brake changes for 15 years.

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Well, yeah, because E85 isn't available everywhere and it has significant negative effects on the range of the car. It's great when you've got it everywhere you go. It's great for many racers (but not for others where pit stop refuelling time lost might be an issue). It's not great if the car is E85 only (because it can't be made to run safely on 98 if you've gone crazy with the compression + boost, etc), and you can't use flex tuning to get you by.

E85 certainly made it easy to sidestep the hassles surrounding putting WMI onto a car, but only where any of the above are not application killers for you.

If you don't have easy access to E85, or you have to drive across Australia, etc etc, then WMI is still your leading option if you want to push well past what 98 alone can handle. A 10L WMI reservoir will last nearly forever in many applications. Certainly more than a few tanks of fuel. Unless you're caning it on the track that is.

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1 minute ago, joshuaho96 said:

I dunno, random PhDs? Working fine is a relative statement. Even in the M4 GTS there are some reliability issues. If the design goal is OEM reliability and refinement I don't think the aftermarket systems are there. Even the OEM systems may be a bit touch and go. A fuel system just works for the better part of 200k miles or 15 years. A water injection system should be similarly expected to work just fine with just added distilled water for 200k miles or 15 years. The military is ok with 50 hours of maintenance for every 25 hours of flight or a total engine rebuild after 5 minutes of WEP, modern performance cars are basically expected to survive on not much more than fluid and brake changes for 15 years.

Oh, c'mon. We're talking about systems for making stupid power out of dirty old RB engines here. We're not talking about OEM refinement and longevity. Put the crack pipe down and appreciate the fact that most people playing with this level of detonation prevention are going to take the car apart every few years and/ore break shit and/or do another engine transplant and/or get bored and move on to another car in far less time than you are worrying about.

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6 minutes ago, GTSBoy said:

If the design goal is OEM reliability

That is not the design goal

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3 hours ago, Ben C34 said:

That is not the design goal

How did you manage to attribute that quote to me?

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1 hour ago, GTSBoy said:

How did you manage to attribute that quote to me?

That's pretty special, didn't notice until now, this phone sucks balls....

 

Edit. I think I selected the quoted text from what you had quoted, and I then used the "quote selection" function. Seems like doing that there  is a glitch.

 

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1 hour ago, GTSBoy said:

Oh, c'mon. We're talking about systems for making stupid power out of dirty old RB engines here. We're not talking about OEM refinement and longevity. Put the crack pipe down and appreciate the fact that most people playing with this level of detonation prevention are going to take the car apart every few years and/ore break shit and/or do another engine transplant and/or get bored and move on to another car in far less time than you are worrying about.

I'm actually just hoping to be able to get an RB to be more modern, running something like high 13 AFR deep into boost and revs instead of 11.5 and maybe push back the knock limit enough to get power equivalent to 98-100 RON fuel with 95 RON. RBs also seem to be thermally challenged so water injection might help in that regard as well if it ever makes it to a track. But if the trade-off is I never actually get to drive the car or I have to pull the engine because water contaminated the oil and trashed the engine it isn't really worth it.

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