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| Re: Newbie Budget A14 Turbo Build & Expectations |
Subject: Re: Newbie Budget A14 Turbo Build & Expectations
by jmac on 2013/3/9 7:07:53
D - Is it possible to provide a quick link to an underbonnet pic of a datsun 1000 to show how much (or little) space there is and where the space is?
I'm making the assumption that you're particularly limited with space, but actually now that I think about it the a15 turbo you mentioned is in a 1000 wagon is it not? (I've got the video of it somewhere - a collection of pics with music from 'the spazzys' if I recall) - so there is some room for a lower mounted turbo.
Among my concerns would be the amount of heat radiated to the intake manifold (I'd also suggest you'd need to look at special paint on the bonnet directly above the turbo, on both sides (the garret drawthrough kits for toranas from the late 80s weren't quite as close as I imagine this design would be to the bonnet, and they'd eventually start to affect the paint. Certainly it wouldn't be outrageously hard to make up some pieces of sheet metal heat shielding (possibly out of stainless) and or that heat wrap tape (it won't survive around the turbo itself for long, but you could also wrap the intake manifold itself.
I'm not a big fan of the factory single carb intakes at all. I just don't like their relatively sharp turns (both under teh carb to go fore and aft then the turn 1&2 and 3&4 respectively and of course the very very late split from single runner out to each intake port.
If you look at the firing order, 1 3 4 2 it's also 21 34 if you think about it. That means it has an intake cycle like this - front front, rear rear, So if you feed 2, then just as it closes, 1 is about to be fed. From a common snigle runner. It's not as bad as something like a mini head, where even the port itself is shared, but it does mean that it would be emptying that runner then needing it 'full' to feed that next cylinder. Then there's a big gap as the rear two have their intake event. I'm thinking (and this isn't scientifically proven fact, just me thinking out loud) that having longer individual runners, under boost at least, means you can have the intake charge stacked up and waiting and it'll possibly get just that little bit improved cylinder filling when each intake valve opens, at technically the same boost/rpm level. The turns (and the Y shaped split near the head/manifold face of the intake manifold) are also less gradual than I'd like and i think it would lead to some degree of mixture distribution variation, not a good thing on a turbo setup.
The 'good old' log style intakes - if properly put together, alleviate almost all of this. Firstly, they can have a long (gently curved and partly if not mostly downhill) transition from the log section to each port. A curved runner per port means there's less likelihood of intake charge robbing from the paired cylinders. There is the slight 'uphill' journey to the log itself, but it happens immediately after leaving the turbo, where the mixture will eb at its best, and less (if any) fuel is likely to drop out of the flow. Extending the 'log' section a little bit further forewards and backwards past the edges of the front and rear runners is also good, it helps flow (a little bit) and arguably the shape actually leads to some amount of turbulence (not detrimentally) and this helps to prevent the suspended fuel droplets (tiny as they are) from falling out of the flow. Since the runners are downhill from that point, even if there was a tiny amt of fuel dropout, it won't 'puddle' into a small lake somewhere in the intake, it'll move into the cylinders (and since it'd be moving fast, it'd never build up or anything) that will remain there until the next time you floor it and the flow velocity is up and the mixture is better suspended etc . SO no flat spots/black smoke on the resumption of increased throttle openings.
Just out of pure coincidence, I've been thinking/looking into possibilities for manifolds. Obviously twin webers are the go for NA performance etc. But I was looking at the intakes on early corolla (the 3k and 4k motors in particular) engines, and looking into if I could copy the idea and turn it into an intake for a datto a-series engine.
http://www.rollaclub.com/wiki/images/3/37/Bigport_bent.jpg
http://www.rollaclub.com/board/topic/ ... ge__p__468972#entry468972
The basic idea would be that it would actually be a much better intake, as far as single carb setups go, than we can currently source for our dattos. They basically have a similar sized plenum, but the runners (on the better of the toyota variants) are separate from the plenum to the intake port in as gradual a C shape as is possible. If I could adapt that to an a-series (actually it'd have to be made from scratch, since the toyota runner dimensions are too small in diameter to work with an a-series - esp an oval port one. Might be able to adapt/use the original datsun plenum with a few tweaks.
FOr a single carb setup, this could work well I think. Additionally one could even experiment with putting a dividing wall inside the plenum, so that 1 and 4 are fed by one carb barrel, and 2 and 3 by the other (it would mean needing a 2 barrel carb where both throttle plates open at teh same time and each carb barrel is the same size) - sort of like a 'dual plane' manifold for a 4 cylinder (they tend to help midrange torque on v8s etc, couldn't hurt to try it , and the divider itself could be made to slot in or be removed practically instantly. And the carb I'd suggest would be a holley 2 barrel. As much as they are the 'fisher price' carby, they typically aren't hard to get a great idle and good power out of even on a smaller engine like this (in hindsight it was one of the few things done right on that turbo corolla - running the holley 2 barrel). And to follow on to the next step - the holley carbs are about the easiest to convert to run in a blowthrough configuration. I realise this thread is more drawthrough oriented, and there's nothing wrong with that at all, what I am saying is that if I was going to even attempt blowthrough on an a-series, personally I'd be making my own intake along the lines detailed in this post. If I couldn't run a 2 barrel holley on a 4 runner intake manifold, I'd honestly go with drawthrough - or put another way - I'd only run a blowthrough setup if it used a 4 runner intake manifold.
Again, in all fairness, there's enough people who have run blow and drawthrough setups with factory style intakes and gotten great results. Sure for all out racing, it's a situation where (potentially) 1-2% power differences can be the difference between winning a race or not even finishing in the top 10. In those cases you need it all - minimal lag, high power, high power across a wide enough rpm range, the most power possible for each and every oxygen atom you can get into the cylinder, etc etc etc. And for thatr application, you have to do it all - efi, well matched turbo, optentially aftermarket ignition, both intake and exhaust manifolds fabricated to optimise each, you name it. But on the street, where you aren't restricted by any rules(like having to run an intake restrictor that limits flow, engine capacity regs, etc) and where you aren't trying to send world records, well you can go a little more conservative - get the boost in there however you can - if you can afford a custom intake and exhaust manifold, do so, but if not, the j pipe exhaust and a factory intake is still going to get you a darn quick car
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