TimZ

The pressure does increase due to the restriction - you're just confusing where the pressure increase happens. The pressure between the restriction and the pump does indeed rise, and the flow decreases accordingly. However, on the other side of the restriction you have less flow in the same size tube, so the pressure there is decreased. It works the same in the "thumb on the end of the hose" example. The pressure in the hose is increased, the flow is decreased, and the velocity of the water is greatly increased at the restriction, due to trying to flow the same amount of water through a much smaller orifice. As soon as the water leaves the orifice it's pressure becomes the same as the atmosphere around it.

Yep - that's what I was missing - I tend to think of base pressures as the zero vacuum settings. It's been a long time since I messed with carbs. Now I'm gonna ask another dumb question ... If you set the regulator to give ~4psi at idle, and your idle vacuum was, say, 16 in Hg, wouldn't result in ~12psi of fuel pressure at 0 vacuum (thus, 12psi plus boost)? Wouldn't that be close to enough pressure to blow the needles off their seats and flood the float bowl? Or did the Cagle regulators hold a static pressure until the manifold pressure exceeded atmospheric?

Thanks James - your $20 is on its way... Here's the thread... http://forums.hybridz.org/showthread.php?t=105832

I was thinking the same thing - I'm thinking either higher base fuel pressure or bigger injectors (probably the better option) should be the next change. ...but im guessing you already figured that out - I got similar comments when I posted my last dyno pulls, and it so happened that the one that I picked to display was an intermediate run from before I had addressed the issue, but it showed something like 2hp more. BUT, any way you want to look at it, those are some really impressive numbers, especially considering they were on a stock head and cam! Congrats!

Okay, that's good to hear - thanks, Tony!

Also, remember that the stock regulator is a bypass regulator - the quote you showed for me was referring to the non-bypass style. And, no, you should never be able to make more pressure than the pump can provide when deadheaded (i.e., zero flow). The stock n/a pump is internally bypassed at something like 45 or 50psi. The stock turbo pump is somewhat higher, like 55 or 60psi.

I agree on the plenum pressure spikes causing problems. My main reasoning for suggesting using plenum pressure was due to the low base fuel pressures involved - basically, any manifold vacuum higher than about 8inHg (-4psi) would result in zero fuel pressure to the carbs. If you use plenum pressure, at least when the engine is pulling vacuum, the plenum pressure is approximately 1 atm (zero vacuum), and the carbs will get the proper ~4psi. Am I missing something here? The bottom line here is pressurized carbs are just plain problematic, and any fix you try to make will have pitfalls. I ran a pressurized carb setup back in the late 80's too, and like Tony said, EFI is better. WAY better.

Niether type of regulator can increase the pressure above whatever pressure the deadheaded pump can produce. However, this "base" pressure is generally much higher than what you are probably used to thinking about for EFI systems. This could range from ~45-50psi for a stock n/a pump, to well over 100psi for some aftermarket pumps. In general, the more the pump is flowing, the lower it's output pressure gets. The bypass regulator regulates the pump pressure by bleeding the majority of the pump output back to the tank in order to acheive the desired pressure. This type of regulator can change pressures pretty quickly, since there is always fuel flowing through it, and it just needs to change the amount of fuel getting bypassed to adjust the pressure. The main limitation here is the size of the return line - if it is too small, the regulator will have problems reducing the pressure beyond some point. A non-bypass regulator is kind of the opposite of the bypass regulator. It achieves its pressure reduction by pinching off the fuel supply to the carbs. This will raise the pressure upstream of the regulator, but the pressure downstream will start to drop was the carbs fill with fuel. The problem here is that the only bleed mechanism is the carb itself. This works okay with the normal constant pressure needed for an n/a carb, but when you start trying to follow the manifold pressure (or carb inlet pressure in this case), there will be problems when the fuel pressure needs to drop quickly. For instance, when you quickly let off the throttle after a full boost run, the carbs won't be flowing much, so it will take a while for the fuel pressure to fall. In the meantime, you'll be flooding the bowls with 14-20psi of inlet fuel pressure - not good. BTW, if you use a bypass regulator to get to 4psi base pressure, a stock n/a EFI pump will probably be all you would ever need, since it will flow a crapload of fuel at 10-15psi. This is a much lower pressure than it normally has to supply, so that's about the best condition that you could ask for for that pump.

I think you'll need to find a bypass-style regulator to mod for this. I don't think a non-bypass regulator could respond fast enough.

What is the base fuel pressure for those regulators? It looks like those are meant for higher pressure, like those used with EFI. I don't think you'll be able to make one of those do a base pressure of 4psi. $70 is only cheaper if it doesn't blow anything up.

No, there was still a mass damper installed on my '78. It was bone stock when I bought it in 1980 (yes I've had my car that long ). Most likely for curing some NVH issue - probably some resonance caused by gear whine. Mine fell off years ago (circa 1981), and I've never been able to tell the difference. So, to answer the original question, I'd say no you don't need it.

Sorry - I didn't explain this well enough. You will have to use a pressure referenced fuel pressure regulator, similar to those used with EFI, except the base pressure will be, say 4psi, instead of 38psi. Also, instead of referencing to manifold pressure like EFI does, you will want to reference to the pressure at the carb inlet. This way your fuel pressure will be 4psi until you start running boost, and then it will be 4psi plus whatever the carb inlet pressure is when you start running boost. You have to keep the fuel pressure 4psi (or whatever those carbs normally use for fuel pressure) higher than the pressure at the carb inlet at all times. If you let the pressure at the carb inlet (and thus the float bowls) go higher than the fuel pressure you will no longer be able to pump fuel in there.

I've not used those carbs, but it sounds like that would work. You will also have to regulate the fuel pressure relative to the pressure at the inlet to the carb. So, if you normally run 4psi to the carb, you'll have to get a regulator that regulates to 4psi over the pleum pressure. (4psi fuel pressure at 0 boost, 14psi fuel pressure at 10psi boost, etc)

I don't think they'd be flat tops then.

Seems to me that you'd be more likely to be able to live with the higher compression ratio if you went to a t3/t4. Not sure why you'd want to run a higher CR with a less efficient turbo.

Isn't Sunbelt around there somewhere?

Here's what you need for the fuel gauge: http://home.comcast.net/~pparaska/gagecalibration.htm

blu bk o grmr n pnctn

That one gets a lot of people. At least John didn't spell it grmr. The annoying text messaging grammar was only part of what made my head hurt, though. I saw that Steven apparently decided to go with dished pistons, but the reasons for the decision seemed pretty sketchy to me.

Okay so I read through all that and it just made my head hurt. What exactly did that clear up for you?

Yes - I have heard Tony recount that story, too. This was what made me decide to go to the slip joints. My manifold is also warped at the flange, but the nice thing about the slip joint placement is that the stiffness from the header tubes is no longer there. The manifold flange pulls down flat with minimal force from the mounting studs (it was pulled flat when the slip joints were installed, btw). I first looked into doing inconel bellows, but they were unbelievably expensive, so after talking it over with James, decided on the stainless slip joints. As you mentioned, hopefully the welds won't crack. Oddly, even with the cracks that I found in my header, it wasn't exhibiting any appreciable leakage.

Yes, it's mine. Well, the ITBs do flow really well and allow a bit larger bore runners than the stock manifold. They also offer a larger throttle area, which makes them pretty responsive. The Mikuni manifold sets the ITBs a bit higher which allows me some added room for the larger turbo. However, they don't like to pull much vacuum and can be pretty cumbersome installation and tuning-wise. My guess is that a well-made custom manifold like Yasin's (see - I'm trying to get back on track ) would flow just as well, and would most likely be easier to deal with and would pull more vacuum at idle. On the stainless/mild steel question, when I answered Yasin's post earlier I was thinking more along the lines of the lengthwise expansion. Radial expansion is another issue, for which I don't have a good answer, to be honest. I guess I'll find out soon enough - I don't think that this is the first time something like this has been done, so hopefully it won't be a problem.

Well, you would have to do some surgery on your SFP, but it can be done: If I'd known this was going to come up, I'd have taken a pic of the wastegate before I installed the turbo - DOH! That's an HKS 60mm gate with a GT42R - here's a pic to give some perspective:

You sure about that? The vertical flow IC will definitely flow better (at least in this application - shorter path, more cross section, less pressure drop), I'd be interested to hear theories as to why the horizontal IC would cool better.

All in all, that is a very strange mix of really nice stuff mated with really crappy stuff. The engine bay itself doesn't look like they spent too much time on it, either. Scraped up flat black paint. Weird.