|
|
| Re: Newbie Budget A14 Turbo Build & Expectations |
Subject: Re: Newbie Budget A14 Turbo Build & Expectations
by jmac on 2013/3/10 13:17:39
Trust me, the difference in runner lengths won't be any noticeable issue. It won't upset the pulses (esp since if you look at 'where' they draw from, it actually gives an even gap between when each runner breathes if we make the (admittedly not quite accurate) assumption that 1 and 4 breathe mostly from the outer barrel, and 2 and 3 from the inner. In contrast, the 'single' runner of the datsun manifold (front or rear) gets 2 pulses in a row (in fact potentially with some overlap if cam duration gets long enough) then a big gap before the next 2 in a row.
Having said all that I don't think there'd be enough difference for anyone to lose any sleep over. The main thing (and this is oversimplifying a bit I'll admit) is getting the air/fuel into the engine and the more you get in (assuming you can burn it properly, so a strong ignition etc) the more power it would make. A 'ghetto' turbo setup with less than perfect cam specs, less than ideal manifolds etc, well it might take (and these are figures I'm pulling out of thin air for sake of discussion) 14psi to make the same power as another a14 or a15 with ported head, really well specced cam, better manifolding etc might make with only 10psi, but rest assured it will still make the power.
In terms of welding cast iron manifolds, it's certainly doable. Definitely pre-heat both manifold and new flange section to practically red hot, then you can stick (or arc, depending where you are, some people call it stick welding, some arc, and I have no idea what else!) weld it. You can get welding rods for arc that are specifically for cast iron. There's usually 2 types (broadly speaking) - one is a little more 'flexible' and less likely to crack, the other type is a bit more brittle, but tends to be easier to attach to dirtier cast iron. I'd suggest cleaning teh weld area as well as can be so that the more flexible rods (and I know I'm murdering the proper terminology for this!) cna be used. I'm also aware of some people (one I've seen in person, and one I've seen online on another forum, by a regular poster there, I'll try and dig up the link if it is still there)have used welding rods meant for stainless steel and had similarly good results. Again the 'big' deal is to pre-heat a hell of a lot, then weld small lengths (perhpas 1 inch at a time or so) then peen it to help stress relieve it, and then let it cool VERY SLOWLY (or leave in the heat, and give it some time then weld the next bit). Done right and it'll last a long time.
Another 'trick' related to it is - since the flange to bolt the turbo to will be steel rather than cast iron, it is sometimes hard to get it to 'stick' to the steel. In this case the trick is simple, run a full bead of weld around the 'bare' flange where the cast iron manifold is supposed to attach, then put them together and weld them, so you are sort of welding the cast iron manifold to the newly added weld on the flange, not direct to the flange itself.
STill on a related note, I'd go even further. On the old garret drawthrough setups, they ran a custom cast iron exhaust manifold (custom alloy intake too, but that's not relevant here). And over time, with heat cycling they'd start to warp. So some people would try doing them up tighter but they'd tend not to seal at hte manifold face. No big deal. Don't overtighten, it'll only lead to them potentially cracking. Instead 'plan' for this to be a likely outcome, and around 1 month or 2 after initially getting the turbo setup running, unbolt the exhaust manifold and check for straightness, and if it is warped, then machine the manifold face back to flat. After that it will probably have warped as far as it is ever going to (or maybe if you were very unlucky, you'd have to repeat this step another month down the track) and after this final machining, it won't warp, and won't crack because it's been bolted down hard to try and seal the warped face, which puts it under pressure and invites cracks to occur..
Similarly, make sure any bolt holes/grooves have around 1mm clearance, It mrans you have to be careful lining up the manifold, but it does give ti the chance to expand just a little without the manifold boltsjamming it up and again inviting cracking of said manifold.
what else - a tip I picked up from the old blowthruturbo email list (which is now called 'carbureted blowers' on yahoogroups and has been dead for literally 4-5 years - but has massive amts of info in the message archives going all the way back to the mid-late 1990s when it was at its peak) was this - turbos weigh a bit, so the weight of the turbo itself can be a strain leading to cracked exhausts. So the trick simply was to run a steel bar with holes in each end, and bent at each end to suit the bolt locations, and it allowed this bar to go from a manifold bolt to one or two of the turbo to flange bolts and therefore it'd act as a support beam and take a decent amount of the total weight.
I definitely think an e15 turbo (nissan exa/et pulsar) would be the go and would suspect it would spool up even quicker than the approximate goalposts I suggested in an earlier post. I base this on my own experience (got full boost by 4000rpm, but remembering the exhaust was as bad as can be) but also on the nissan exa specs themselves. It was a 1.5 litre engine same bore and stroke as an a15 (and same bore but longer stroke than an a14). they made peak torque around 3200rpm (and I looked this up to help clarify things, I don't have a photographic memory!). Now there's no way they'd make peak torque 'off boost, so to make peak torque at 3200rpm it stands to reason they were spooling up earlier (perhaps 2500rpm?) and were at or very near full boost by 3200rpm. Not a bad thing at all, and would be similar on an a15, or perhaps starting to spool around 2600-2700 and full boost (or close to it) by about 3400rpm .
They made about 115bhp from memory, which would (to me) suggest you'd be able to get around 150bhp from them before they got ridiculously out of their compressor side efficiency. (mind you I wouldn't be wanting to try and find 180+ from said turbo). This is certainly backed up by how quick it ended up on the corolla I had, based on it's performance, it would have had to have been making around 150bhp. Considering how bad the exhaust setup on it was, it's probably fair to say that it killed off a good 10bhp extra (or even more) due to exhaust pumping related losses - in other words the same boost on the same setup with a better exhaust j pipe (and remember there's nothing wrong with a j pipe, just that in this case the particular j pipe that was run was absolutely craptastic) would make more power, just because it isn't being robbed by the exhaust restriction/issues.
another couple of turbos to consider - one from a ca18det. A touch on the large side but certainly workable. And one of the turbos off a late model 300zx - the twin turbo vg30dett engines. They are twin turbo on 3 litres producing around 210kw . In other words each turbo caters to 1.5 litres and 105kw (about 140 bhp) so getting 150-160bhp out of one of _those_ turbos would be easty and in general they'd be a bloody fantastic match.
|
|
