Sam's build thread

[sambb]

Thanks for that Gary. yeah ill see if the extra camber will tuck the top side under and if not then i'll have to break out the hardware.
Yeah surprised me - I thought with such stout springs that dropping the bar wouldnt have that massive effect like it does on street level springs, but it still did. Killed the handling having no rear bar.

[sambb]

I need compression ratio advice as I'm choosing pistons soon. Now I've decided on this engine being a pump 98 RON engine. Given that i'll stick with the ME7.5 which more or less demands non-real time tuning ie with respect to ignition timing logs are interpreted and a moded file is reflashed in before each test run, tuning more or less has to be based off knock sense voltages and c.f's. This tuning method however isn't applicable with E85 as timing advance can continue will past 'minimum best timing for best torque' and still not knock so I think we'd be in the dark without making a million different logs at all the different load points. I just don't have that kind of dyno money. Also E85 is just too scarce for me for a car that is daily driven on my routes and drives regionally to/from race meets. So pump petrol it will be. That's the first decision out of the way.
So I can say that in my experience the 1.8T 20V is knock limited. I've only run a K03s which runs at 20+psi but being so small is not really pushing much air yet during the boost ramp up/spool has always struggled with timing pull at anything approaching WOT. This has also been evident in the top end even as boost trails off I presume because by the turbo is just pushing scorching hot air. Also it responds very well to water and water/meth injection. Even the most rudimentary water injection can see a log full of 5 degrees pull go to next to no timing pull on the next run despite the car being more heat soaked. And on the track you can really feel it fall away with timing pull. And this is all at 0.82. So I might be wrong but I'm pretty sure you could call the engine knock limited.
So if the K03 and K03s cars 150/180hp OEM had 9.5:1 CR @ 10psi and the bigger K04 S3/TT 225hp cars had 9:1 , then I cant understand why the vast majority of peoples building 300hp engines with nearly double any OE boost seem to choose the 9.25:1 pistons over the 8.5:1 ones. I'm shooting for 280hp and will most probably go with a K03 hybrid. Yes it will have bigger wheels, and a bigger K04 comp housing but by retaining a stock turbine housing it is going to push heat rapidly once it moves out of its efficiency range. So knock limited engine + turbo setup that can cause high EGT's - I'm thinking that the aim of the game will be to get as much timing into it on the least possible boost.
Sooooo Isnt an 8.5:1 piston going to be better for what I'm doing? ie pump petrol, hybrid turbo That would be an advantage wouldn't it for spool as you'd be more able to get lots of timing into it to get the gases driving the turbine and everywhere else in the rev range the extra timing would help lower EGT's and strengthen the top end as boost falls away No? Assuming that the 1.8T 20V is knock limited an 8.5:1 engine will outperform a 9.25:1 (maybe even at the same boost level?) as you'll be able to run more timing without timing pull intervening which really robs you when it happens. I realise that 8.5:1 isn't going to be as efficient in lean cruise low load mode, but surely the idea that spool is inherently slower on a lower comp piston is a bit generalised isn't it given that any K03 framed 280hp wheeled turbo is inherently fast to spool, and the timing stuff I've already mentioned.
I cant help but think that these were euro 3 emissions engines with a big motivating factor behind the high comp ratio (for a port injected turbo) being to help meet emissions/economy at pedestrian loads.
anyway I'd really like to hear from in the know people on what they think.

[HaydEn]

I would agree on going for the lower comp Pistons. As you’ve said, these engines are constantly on the brink of knock and love to pull timing.

It’s not like you’ll notice losing out on the 10kw below 2800rpm before the turbo kicks in. On a gt28/30 you’d go with the higher comp pistons and use E85 or water meth.

The low comp 1.8t pistons have been used with aftermarket rods for 600hp often. So getting a set of them would be a good more cost efficient move than aftermarket pistons.


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[sambb]

By low Comp 1.8t pistons do you mean the 9:1 comp S3/TT ones?

[HaydEn]

Yeah BAM/AMK pistons.


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[Sydneykid]

Static compression ratio is not as relevant as many believe and it's getting even less relevant as controlling inlet air temps becomes more sophisticated and hence accurate. Lowering the static compression ratio is a bandaid over the real problem, which is excessive inlet air temps. Very inefficient turbos create extremely high levels of heat in the combustion process especially when pushed beyond their design limitations. You have already hit on the alternatives;

1. E85, you work within walking distance of 2 of the biggest outlets of E85 in Sydney so I don't go much on the limited "availability" issue. For sure it's pain not having every servo selling E85 and it's extra PIA having to plan ahead when travelling to events. But having used E85 for over 10 years you just get used to looking up where E85 is available and planning the route and timing in advance. For sure it's an inconvenience but the gains are well and truly worth it.

2. A lot of guys with combined track and daily driven cars have either 2 tunes or, the more simpler, 2 boost limits. From as radical as an E85 tune for the track and a Pump98 tune for their daily driving. I see lots of guys at track days whip their lap top out, load the track tune and fit their track tyres. Then do the reverse before they head off home at the end of the day. There are also a number (albeit smaller) that simply turn the boost up for the track day, often adding a % of E85 and/or turning the water methanol injection and/on or turning up the intercooler spray and/or adding some methanol to it.

3. Water to air intercooling will be the way I go next time around, then I can simply add ice from the esky to the water reservoir to get lower than ambient inlet air temps. For cars using an airflow meter and inlet air temp compensation that doesn't mandate loading different tunes.

Lowering the compression ration from 9 to 8.5 (for example) might make 2 degrees difference in the timing, whereas any or all of the above can make 10 degrees difference, as you have found. I'm not a big fan of bandaids, when fixing the real problem gives far better results.


Cheers
Gary

[sambb]

Availability of E85 is only part of it but the biggest stumbling block with E85 is the cost. I'd need a new pump, most likely bigger injectors if I wasn't needing to switch fuel regs every time I switched to an E85 tune, and the biggest problem remains that without a standalone ECU ($2k+ conversion) I wont have flex fuel sensing facility or any way to tune it correctly since the reflash method with my ECU will be much bigger stabs in the dark than it already is with petrol. Held on a dyno brake at every load point to find MBT and Re flashing throughout would just be impossible.
So assuming I do stay with petrol the other factor is IAT's temps. Now I'm the first to admit that the OE framed turbos push a lot of hot air but I can go out on a 15 degree night, activate the IC water spray so that the IC core temp is well below ambient, and do a 3rd gear pull and inlet air temps will rise from say 18 degrees and stay below 35 degrees and there will still be timing pull everywhere. Of course if I was flogging it on a track with its inefficient turbo I'd expect IAT's to consistently rise, engine temps to get out of hand and then of course timing pull will be massive. But even when the thing has been cruising along in 5th gear and is cool as a cucumber, timing pull is instantly there. This is a common issue not just for me and it is written amongst the tuner fraternity that the 1.8T 20V is knock limited. As I said the WM injection helps with that but in those cold run instances described above, the WMI is not really masking high inlet temps because the temps are fine. Is it just that the high CR on pump 98 has a specific knock limit and there's no getting past that. That's where I started to think that the comp ratio at 9.5:1 could be part of it. I started to look at the other turbo fours of that era (fixed cam timing, DOHC, port injected) and say EJ20T's, SR20's and 4G63's all had lower static comp yet they were built for a different brief - performance being a bigger consideration than say euro emission commuting. If the VAG brief back then had been to build the 1.8T 20V to be a stout track weapon in a horsepower war with the japs would they have picked such high static comp? I truly don't know the answer to that but It makes me wonder is all. Its true that if you look at the early 4G63's that even as they increased turbo outputs the comp ratios still went up, probably because efficient turbos and better intercooling had temps better under control, but they still topped out in the high 8's with their CR's didn't they with far more serious outputs.
That's where my concern came from - wondering if the CR is just inherently too high. Wossner, Wiseco, CP Carrillo and Mahle all offer either 9.25-9.5:1 pistons or 8.5:1. I cant help wondering if the high CR pistons are just offered for those that want to rebuild without straying from what the factory did (or for those who will be running E85). If most generic tunes are written for stock compression and that's where the market is at then it follows that this high comp will be well supported. But could the 8.5:1 pistons not purely be there for the tuner crowd. If mine isn't even a one run wonder when IAT's are well and truly under control and the turbo is pint sized, and assuming I do stick with petrol, I'm just wondering how on earth its going to be better on the knock front when it gets some serious cylinder pressures.
Theres no getting away from E85 being the better fuel and that getting IAT's under control over sustained periods is a massive deal. I may well still go with a Garret GT2560 as its the best turbo option open to me that I run any risk of being able to afford (all the hardware built around a gifted turbo) that also will help with IAT's. Failing that though due to packaging constraints it will unfortunately have to be a hybrid K03 frame turbo. So that's where I'm coming from - petrol + improved IC with WMI + not an ideal world turbo selection - Do I stay approx. 9.5:1 or drop to 8.5:1.

[sambb]

so to put it another way if I'm to keep getting onto the track over the next 5 years, I only have a set amount of dollars. I cant rebuild with an affordable turbo upgrade and do E85 upgrade/tuning too. It would literally have to be one or the other. I cant do the E85 alone because I'd never be able to take full advantage of it on such a small turbo and it would most likely bend/break a stock bottom end anyway without having gained much at all beforehand. But the rebuild will actually give me some proper power up even if it has to be with petrol.
The other possibility is build it with the 9+:1 CR pistons. If it has to be held back on petrol then so be it but at least at that CR E85 remains and viable next step later down the track. 8.5:1 from the outset though would more or less lock me into petrol yeah?

[sambb]

Yeah Hayden that was the plan all along. I did sourced some S3 pistons. They cleaned up looking mint but the engine builder took about 5 seconds to tell me that they'd suffered ring flutter and were no good. He really wanted me to go aftermarket and it made a lot of sense what he was saying. He wants me to get pistons with anti detonation grooves and an accumulator groove all in the effort of lessoning the effects of knock on the piston/rings and he hated the delicate ring design of the S3 piston. He said it might make power but just wont last.
CP Carillos come standard with the accumulator groove but not anti det grooves or skirt coatings. I think JE's have both and also come standard with skirt coatings but he doesn't like their really sharp aggressively machined valve reliefs and big domes when all is needed is a small relief for the middle inlet valve on OE turbo cams. I'm yet to find out if the wisecos have anti det and accumulator grooves. I bloody hope so cos they're the last option that I can afford. Wossner and Mahle's are too expensive.
The cheapest way out might be if my 9.5:1 BJX pistons are mint. Then I could buy some IE 19mm pin end rods and provided I can then sell my 20mm pin end forged X-beams (which I'd bought for the S3 pistons), i'll come out in front...………..that's if 9.5:1 stock pistons aren't too high CR! I'm head ****ed you see.

edit: seems Wiseco only do an 8.5:1 with anti detonation grooves, skirt coatings, not sure on accumulator grooves though.

[Sydneykid]

I think I warned you early on that I'm really good at spending other people's money, it's a gift.

Some random stuff;
Evo X's are 9.0 to 1 compression ratio (22 psi boost).
Evo 5/6/7/8/9 are all 8.8 to 1 (19/20/21 psi boost)
R35 GTR's are 9.0 to 1 (15 psi boost)
R32/33/34 GTR's are 8.5 to 1 (9/11/12 psi boost)
I don't think it's a coincidence that the later engines use higher compression ratios, despite having higher boost levels. FWIW my RB30/26 uses 9.2 to 1 JE flat top pistons to retain the combustion chamber squish zones, which helps a lot with RB's in minimising detonation. If I lowered the compression ratio it would adversely affect the squish zones effectiveness.

Generally speaking the pistons with compression ratios below 9 to 1 are designed for drag racing with monster boost levels. It seems to me that 9 to 1 is kinda like a default compression ratio where its low enough to avoid detonation but not so low that the engine becomes unresponsive at anything less than maximum boost. It's so common that it can't be coincidence.

It's dead easy to machine (in a lathe) accumulator and anti detonation grooves, I don't know that I'd let that influence the buying decision. Ditto ceramic coating. Since you have them and as a cheapy, you could machine the S3 pistons to take a wider ring if available that would eliminate the ring flutter damage.

We always smooth off the valve reliefs to remove any sharp edges, ditto the combustion chamber, it's one of the value adds that a decent engine builder brings to the table. I've even done it myself using steel wool a number of times, it's gentle enough so even I can't stuff it up (too much).

E85 is the best answer but that doesn't escape the fact that it's not always the most affordable answer. Lowering the inlet air temps, as you know, is often the most cost effective detonation avoider. Plus as you know there are a range of options water and metho injection, larger intercooler, intercooler spray, etc. Another is lowering the boost level whilst maintaining the airflow by removing restrictions. For example in my son's RB25 I increased the exhaust valves by 1 mm and ported the head and it made the same horsepower (450) with 5 psi less boost. With the lower inlet air temps I could add around 5 degrees of ignition advance which made it far more responsive as well.

I really like to only "build" an engine once, do it to as higher spec as I can afford at the time, if that means compromising on the support hardware initially then so be it. Over time I then improve the hardware as funds become available, all the little efficiency gaining bits add up over time. Your situation is a little different as I don't have standard ECU limitations, so I can progressively tune appropriately.


Cheers
Gary