13mm pump Q, boost Q

P

PRattenbury

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Jan 28, 2007
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I sure am glad to have my truck back. I'm pretty sure sliding the plate all the way back, AFC housing all the way back, and not letting the AFC move till 20PSI or so will not be one of those things that causes the pump to bind, correct? With the plate set midway and the AFC disconnected, I still have too much fuel to run on the street. I'm runnng a 64/71/13 as a single for now. I figured the thing would be screaming its guts out with the fuel I have. Not true. When I had my Towing Twins (PS62/K31) I could get 40 or so PSI boost at WOT. With the 64 as a single I could only manage 20 pounds. When I had the motor built I did so with maximum airflow in mind. The valves are bigger, the head is ported, the cam is huge... Anyway, this is the second turbo configuration I've had on it, so I think the turbo side of the boost factor can be eliminated as a cause of low boost. I have the waste gate disconnected on the 64. On the intake side of things, I do have the ZZ Fab manifold as something unusual, but the IC tubes, air horn and so forth is all stock, with heavy boots and clamps. The IC itself is a Cool Twist and it's only got maybe 1000 miles on it. I'm nearly inclined to just accept the possibility I just have great air flow through the motor and call it good. Once I get the RPMs to come up (through great care with the skinny pedal) I do get to where I hit the governor pretty quick somewhere north or 3000, and it runs silky smooth up there. Does it seem reasonable the engine could flow air so well I'd have boost numbers this low?
 
Yep, I've had it right on the governor. I've got 4.10 gears and 32" or so tall tires. So I can get WOT pretty easily once I get it rolling.
 
I just brought mine home from getting the pump swapped. With the plate and afc just slightly off the rear I see 72/73psi with 43psi from the primary and about 85psi of drive. That's with 64/71/16ss over GT4718/1.08 twins. I have a cam and mildly ported head.
 
Well, that's wierd. The plate's definitely going all the way back. I'll go from there. I admit, I don't know anywhere near enough about these animals to be able to reach in and perform the majic fix. I'm just learning as I go. :frown:
 
Paul, have you pressurized the system yet to check for leaks???????
 
you might (but unlikely) just have awesome flow.......remember that boost pressure is just the measurement of the resistancee of flow......
 
I hope that's the case. But Warpig is right. He and Signal73 have been telling me to check for leaks. Just because everything's brand new doesn't mean something doesn't have a leak. The plate is all the way back now. So is the AFC housing. I'll get something to plug the turbo inlet tomorrow and pressurize the system to remove that possibility (up to the intake, at least).
 
Hey, Ron A

What kind of cam are you running? Mine is big enough to need deep fly cuts, and .020" thicker gasket to ensure clearance pistons to valves. Is yours big like that, or a street type grind?
 
I would take it to a shop and have them smoke it. Plug the exhaust and fill the intake with the smoke a smoke machine makes and watch for smoke to escape. Any place smoke can get out you have a boost leak.
 
I think you need more than a 64mm turbo for that pump... though I'm sure all the porting will help immensely.
 
yea, that is a pretty big pump. I would of at least got a 66mm turbo if not bigger/twins
 
The 64 turbo is actually the top turbo for my twins. I ran into some fitment issues that are going to cause me to make a new hot pipe, I guess, before the S480 is able to join in for the fun.

Ron, once I get up to 2300 RPM or so she smooths out and pulls pretty hard. But then I run out of RPMs pretty fast with the 4.10 gears. Still put out a pretty heavy haze even up in the higher RPMs. You told me before to back off on the smoke screw, and I haven't yet, that I recall. I went out and pulled the plate all the way back, and the AFC housing all the way back. I'm going to take it for a ride to see how that does, and if I can still snuff the fire out at will, the smoke screw is next. Boost leak check is in the plan as well. I do not know of a shop around here that has a smoke machine. Sounds like a decent concept, though. I'm going to plug the turbo inlet, put a scrader valve in the compressor housing where the port for the WG is, and plug the flex joint at the air horn. That'll at least check from the turbo to the air horn, unless somebody's got an even better way (short of the smoke machine).
 
Back off all your intake valves, and don't worry about plugging it at the air horn. Then you are also testing the boot to air horn connection, as well as the grid heater and gaskets, intake plate and gasket, and the valve seals.
 
Cool! I gotta find a plumbing cap or something about 4-1/8" diameter to stop up the turbo inlet with. I'll do that tomorrow.
 
So, I got all the stuff I needed to pressurize my charge air system. I split the system up into 2 parts. First I plugged up the turbo inlet and the tube at the air horn. I was able to blow that up to about 10 PSI without the plastic cap blasting out of the turbo inlet. I discovered the compressor housing was loose and leaking pressure. I tightened that up, and it'd hold pressure solid. The next half was from the air horn on through. I didn't undo the intake valves, because I was told it wouldn't leak enough to worry about anyway. I could blow that up to about 50 PSI, and then watch the boost gauge drop off pretty rapidly. I found one of the spray rails in the intake that still had a plastic cap on it was leaking pressure. I put an adapter and plug on that, and it held. I was also hearing pressure from the rig I was using to hook up to the compressor, but it was dropping down slower. So I hooked the CAC tube back to the air horn, and blew up the whole system using the schrader valve I put in the turbo compressor housing. I could hear some faint hissing coming from somewhere around the valve cover at #1 cylinder. But I'm not sure it wasn't the cylinder itself letting off pressure. It would lose pressure at 2 PSI every 10 seconds. Does this sound like I've got the system tight enough where I should be getting normal amounts of boost??
 
Paul, take that thing out for a real good rip and report back. Where are you getting your boost reading from?? It is possible you have an issue with your gauge. That thing should scream with that little 64!!!!!!!! I would say you should max out just shy of 50 psi. You will never clear that thing up with the single 64, even with the plate and AFC all the way back. I don't even come close with my 66 and the plate back, but I do hit 50psi in an instant. Also, I had the plenum gasket blow out, and even with the leak there I still hit 50 psi. The air you hear escaping is air leaking from your open intake valves.
 
I think it's amazing how what I would consider a small leak has so big an effect on the ability to hold pressure. I was looking at my gauge inside the truck to see how fast the pressure drops off. No problem with it. I saw it up around 50PSI when I was testing. I'm gonna take it out for a ride tomorrow to see if there's any improvement. I agree the 64 by itself is way too small for my fuel, but I should still see boost. I can tell when it starts snuffing out the fire. The sound is distinct, RPMs don't increase, and the world goes black behind me. But if I'm careful with the loud pedal I can get the revs to come up, and boost. The Towing Twins would get me 40PSI. The 64 would only get me 20. Tomorrow will tell if I can get any more than that with better boost holding power. I see RonA pumps out huge boost with his 13mm. I have an aftermarket IC and a bigger cam, but dayum. I should be doing much better for boost. If my single turbo ever shows up, we'll see how that does. If that fails, I got no choice but to get my fabricator hat on and get that S480 under the 64. Just don't have a lot of confidence in myself for that.
 
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