cjb80

OK, so here is my idea that I am going to share with everyone.. I think it's worth a couple bucks, but I don't have the $$$ to do it (all of my money is in the turbo engine rebuild)

Here's the deal.. getting a pulley is relatively cheap, you'd have to do the math or experiment with it, but you could get a pulley that would boost at 6psi or more at 2500 RPM right. Now, buy some pre-bent piping and rubber fittings and a front mount air-air intercooler and run the piping. Before the piping gets to the intake manifold you have a wastegate, or similar device my shop called it a pop off valve. Apparently the POV is similar to the wastegate except it is designed to work at different temps (not hot as hell exhaust temps) Now you can hook up your boost controller to the POV.

The trick is to have it boost at low RPM, but also not lose efficiency at high RPM. So you'd have to run some tests to figure out how low RPM you can reach full boost with out the thing crapping out at 9000 rpm.

Someone do this and credit me.

Thanks

Your friend,

Chris

krazik

I've been telling SilverSurfer and DavePK this for eons.

krazik

I believe you can get a max of 12psi out of the current paxton.

Comptech (heresy) did claim that they had detonation problems with higher boost in the lower rpms.

cjb80

Yeah well we know that's BS now since the turbo spools at 3500 RPM .. in fact Speedcraft said that 8psi works fine with stock internals until you hit VTEC and then it starts detonating.. so, perhaps it has to do with the fact that the super isn't cooled, but I dont see any other issues with it..

I have never heard of a pop off valve, does someone actually make this product? Or would you have to modify a wastegate?

If there was a more efficient blower then alot more would be possible (full boost at 2000 rpm?) but it looks like you'd have to figure out what pulley size that the super outputs 12 psi at 9000 rpm.. I bet it would reach 6psi boost at 4000 RPM or less.. or get the better blower and you could spool at less RPM.. that'd be cool..

krazik

Maybe they meant it detonated at vtec. Like I said, I didn't hear it directly from comptech, but from a pretty reliable second party.

krazik

So a BOV blows off exhaust pressure? I thought it did it on the intake after the turbo.

cjb80

I am confused about how you came to that conclusion from what I said?? oh well...

The wastegate moderates how much exhaust pressure gets to the turbo so it cant spool up past a certain point.. this is the same concept that needs to happen after the super .. a blow off valve is a different concept..

A BOV is after the turbo, before the intake, and is meant to relieve pressure when the throttle body closes.

krazik

So then why wouldn't you use a BOV on this setup?

You basicly want to get to 6psi early and keep it at 6psi right?

marcucci

Something to consider is how fast you'd have to spin the blower to do that. The blower is the smallest (if I remember) that Paxton makes now and will probably be well out of it's efficiency range to be spun that fast to produce that much boost that low.

Also, are you considering the additional pressure drop of the intercooler (or is that what you mean by spinning it faster, to overcome the drop?)?

From what I've read, a wastegate is designed to dissipate any boost beyond what's desired for engine safety/max boost (say, 8psi) and a blowoff or popoff is designed to vent between shifts to prevent damage. I didn't think they had any basis in temperature (though I admit some ignorance in this area).

ultimate lurker

You don't want a blow off valve to modulate boost pressure because they really aren't designed for that. They're either open or shut in most cases (which is why you usually hear that flutering sound - open to bleed off pressure, close when pressure drops, open again cause the turbo is still spiining, etc.).

Rather, you'd want something that performs similar to a wastegate. This would allow you to do some very precise manipulation with the electronic boost controllers out on the market. You can set boost by gear, rpm, etc. Thus, you might run less boost in 1st gear, more in 2nd and 3rd, and then start backing off a bit in the higher gears to keep the engine together.

I don't know if current wastegates would operate in the flow range you'd see on the intake side vs. the exhaust side. The only time I've heard of pop off valves is in CART, where they use spec valves to ensure the competitors don't run too much boost. Getting into the pop off valve was always considered bad in CART, so I don't know how effective they'd be to continuously modulate boost. Guess you'd have to investigate.

As for detonation issues, what it really comes down to is the ignition maps on the ECU (and to a lesser extent the fuel curve). With a single plane manifold the F20C has some poor intake resonances at certain rpms. From a boost perspective the worst is probably right at 4500 rpm. To compensate for this and keep the torque curve as flat as possible, the ECU boost the timing there dramatically. This is common on all single plane Honda manifolds (and probably any single plane manifold in general). More timing is required because the mixture is less dense, less homogenous, and less energetic, which means that it takes longer to ignite and burn. When you add forced induction, the intake manifold resonances really don't mean as much because the effect of boost masks them. Thus, you've now got a ton of mixture where before you didn't and the timing curve is too aggressive - hence detonation.

AFAIK, Comptech really doesn't do much with ignition timing controls in their kit, hence the problem. The lack of an intercooler doesn't help either. I don't know how Speedcraft does their ignition issues, but I assume they trick the ECU into thinking the charge is hot, retarding timing. As for detonation at VTEC, Honda ECUs usually boost timing when you go into VTEC, which might explain Speedcraft's experience.

The best thing to do is get a good engine control system that allows control of ignition timing dependent on boost. The 11:1 compression is still going to hold you back on pump gas (maybe 8-9 psi max with good ignition control on pump gas), but you could at least bring up the low end.

UL