What turbo - 2023 edition

[greenMachine]

Big decision coming up - that little IHI has passed its use-by date, but what am I going to replace it with?

I am price-sensitive, so basically the choice is which churbo. Currently looking hard at a Pulsar Garret 2680 clone, price is right and stock available. Mania use AVO, not sure about price (probably similar to Pulsar?) no supply atm but that could change.

Been looking for user experience, found a lot of love for Pulsar on a jap car local site, and I believe Ford people like them - no horror stories (yet). Alex2550 has one, he may chime in on his experience I hope. Anyone else use either?

Other thoughts?

[ManiacLachy]

I assume you're working on a T25/28 manifold? I also hear good things about the Pulsar 2860, hopefully we're talking the GTX Gen2 clone. Should give good spool and response, while giving you that nice 300whp you'll want with the built motor.

[greenMachine]

I assume you're working on a T25/28 manifold? I also hear good things about the Pulsar 2860, hopefully we're talking the GTX Gen2 clone. Should give good spool and response, while giving you that nice 300whp you'll want with the built motor.

Yes and yes Lachy, Pulsar, definitely Gen2, probably .64 - Mania (David) reckon that keeps drivability on stock compression, but pulls well.

That has got me thinking, I set my revlimiter at 7000 with the IHI. another 250-500rpm would probably be on offer depending on the valve gear. I haven't discussed valve springs yet ... , that might be another item to discuss when I drop off the rest of the engine bits.

[ManiacLachy]

I think that's the best bang for buck turbo on our cars at the moment, .64 is what I hear is good too for a quick response.

You probably want to at least install heavier valve springs, like the Super Tech heavy doubles, so they can resist the boost pressure in the head.

[StillIC]

....You probably want to at least install heavier valve springs, like the Super Tech heavy doubles, so they can resist the boost pressure in the head.

I don't understand why you'd want heavier valve springs to *stop* boost pressure getting to the combustion chamber. If the pressure behind the valve head is greater than the pressure in the combustion chamber, surely you'd *want* to let that boosted air/fuel through? Like a reed valve.

[rascal]

I don't understand why you'd want heavier valve springs to *stop* boost pressure getting to the combustion chamber. If the pressure behind the valve head is greater than the pressure in the combustion chamber, surely you'd *want* to let that boosted air/fuel through? .

Not sure if you joking, but definitely not if it’s in the wrong part of the combustion cycle, piston at bdc for example..

[StillIC]

I don't understand why you'd want heavier valve springs to *stop* boost pressure getting to the combustion chamber. If the pressure behind the valve head is greater than the pressure in the combustion chamber, surely you'd *want* to let that boosted air/fuel through? .

Not sure if you joking, but definitely not if it’s in the wrong part of the combustion cycle, piston at bdc for example..

The piston is at BDC twice per cycle:
1) If the piston has just sucked in air and fuel and is ready to compress it, then, it *isn't* the wrong part of the cycle to let in boosted air. Any extra incoming air/fuel will add to the charge that will be ignited in 60-80 degrees. This is why standard intake valves close *after* BDC. This is *good*.
2) If the piston has just completed a power stroke and has a bunch of hot exhaust gases already ripping out the barely opened exhaust valve but still quite high in pressure (~50psi), then *good luck* to the boosted air getting in.

Where in the below graph, where the in-cylinder pressure is below a boosted pressure, would one *not* want the turbo adding pressure?
https://www.performancetrends.com/Definitions/Images/Cylinder-Pressure-Lrg.gif

PS: Sorry for thread hack, but it is close to topic>

[ManiacLachy]

I was basing my recommendations from word of mouth, 949 Racing and Flyin Miata both recommend heavier springs. I admit, I don't understand all the physics behind it.

So, prompted by StillIC's questions I tried some googling. and well, there's many discussions on the topic it seems, and a lot of people posit that you do not need heavier springs, and they cite all sorts of technical jargon that I do not understand. All I can now say is, I don't know

I didn't read too heavily into the topic, I was hoping for a simple summary of why/why not, but it doesn't seem to be that straight forward. I guess I'd just take an engine builder's advice.

[greenMachine]

I raised the question with David (Mania), he said standard is fine. Bad line, I was planning to ask him to explain further on Thursday when I drop off another tub of engine bits for the reassembly, will definitely do so now!

[rascal]

1) If the piston has just sucked in air and fuel and is ready to compress it, then, it *isn't* the wrong part of the cycle to let in boosted air. :

I disagree.
The initial air/fuel mixture would be the required ratio and then letting in extra air after the fact will lean the mixture out. Not good for engine longevity..

[StillIC]

1) If the piston has just sucked in air and fuel and is ready to compress it, then, it *isn't* the wrong part of the cycle to let in boosted air. :

I disagree.
The initial air/fuel mixture would be the required ratio and then letting in extra air after the fact will lean the mixture out. Not good for engine longevity..

I am trying to see your point: I think you are saying that if the injector has stopped firing, and all the fuel/air mixture has been sucked/blown into the cylinder, and if then somehow more air gets in past a leaky intake valve, the engine leans out?

But I don't understand in what circumstance this can possibly happen. There is no "after the fact". If the valve is still open, it's still open. It wouldn't close then open again due to a weak spring, because the weak spring wouldn't have closed it in the first place. The boost acting on the valve would determine when the fact (the valve closing) ended. That is, the valve will close when spring load plus cylinder pressure overcame boost pressure.

At BDC after intake, the intake valve is still open in any case. You don't need a stronger spring to ensure it is shut at BDC. At some point just beyond intake valve closure, cylinder pressure is increasing such that it exceeds boost pressure after not too many degrees of crank turn. If, by chance, boost pressure leaked in past the intake valve just after the cam let it close, the engine tuning should account for this, based on speed load characteristics. And again, this is a *good* thing, as it would mean that the cylinder gets extra filling it wouldn't get had the closing intake valve stopped this from occurring.

A general comment: the only reason intake valves exist is to stop the cylinder pressure escaping during compression and during the power stroke. That is, they exist to stop flow in the direction of cylinder into the intake runners, not the other way around.

[rascal]

[And again, this is a *good* thing, as it would mean that the cylinder gets extra filling it wouldn't get had the closing intake valve stopped this from occurring.

The ecu would have already injected the reqd fuel based on the fuel map and the position of the crank, the ‘extra filling’ would just be adding air, which leans the mixture out, which is not a good thing.

If extra air is creeping past a non closed or held open valve, then the ecu isn’t going to magically squirt another lot of fuel to compensate, as it’s already been triggered to squirt fuel this cycle, and so will wait for its next trigger to squirt.

Eg, if you had a continuous stream of air from the boost pressure pushing open the valve then this would only be a good thing if you also had a continuous stream of fuel, but you don’t. It is only supplied fuel at predescribed times, based on engine timing.

[StillIC]

[...
The ecu would have already injected the reqd fuel based on the fuel map and the position of the crank, the ‘extra filling’ would just be adding air, which leans the mixture out, which is not a good thing.

If extra air is creeping past a non closed or held open valve, then the ecu isn’t going to magically squirt another lot of fuel to compensate, as it’s already been triggered to squirt fuel this cycle, and so will wait for its next trigger to squirt.

Eg, if you had a continuous stream of air from the boost pressure pushing open the valve then this would only be a good thing if you also had a continuous stream of fuel, but you don’t. It is only supplied fuel at predescribed times, based on engine timing.

Yes, that's what you said above, but I don't understand what you mean. If boost is keeping the valve open, then the engine control system will either:
1) in closed loop, note the air flow and inject the appropriate amount of fuel. A leaky valve is just like having a longer cam duration but only at the exact engine speeds you want it. Any leak can only possibly occur just before the beginning of, or just after the end of the intake valve opening, as the pressure in the cylinder is too high at other points in the engine cycle.
2) in open loop, one ensures the engine is tuned for the conditions (load, speed, boost etc.). You wouldn't tune your engine deliberately to run lean. It's not as if boost isn't known (well, should be) or predictable. And it's not as if the spring pressure on the intake valve, when closed, changes from one revolution to the next.

[rascal]

Yes, that's what you said above, but I don't understand what you mean. If boost is keeping the valve open, then the engine control system will either:
1) in closed loop, note the air flow and inject the appropriate amount of fuel. A leaky valve is just like having a longer cam duration but only at the exact engine speeds you want it. Any leak can only possibly occur just before the beginning of, or just after the end of the intake valve opening, as the pressure in the cylinder is too high at other points in the engine cycle.
2) in open loop, one ensures the engine is tuned for the conditions (load, speed, boost etc.). You wouldn't tune your engine deliberately to run lean. It's not as if boost isn't known (well, should be) or predictable. And it's not as if the spring pressure on the intake valve, when closed, changes from one revolution to the next.

The point I was trying to get across (obviously poorly), is that at the point of firing the injectors, based on timing, the ecu measures the air and injects the reqd fuel Once per cycle. If you continue to supply extra air then it cant feed it extra fuel until the next cycle, so your A/F would be off.

[The American]

Hi GM,
I understood AVO used Garrett unless they have moved to own brand? My car with an AVO kit has a Garrett 2560. It’s outstanding for initial response, but runs out of puff.

Setting aside how valve float occurs in a turbo application, I satisfied myself that it does based on others picking up top end power after only swapping to heavier springs.

I was also mindful that 180,000km valve springs (in my case) had already done a lot of work, so I replaced with heavy doubles. My head was the NB8B version which allegedly has the lowest tension stock springs.

I think there is a good argument for spending less and having more fun sooner (and avoid falling too far down the ‘while I’m there’ rabbit hole. Bludy Rabbits.)