turbovette80

help please,

I'm running 5 psi boost drawing on a rochester quad fitted to a Gemini inlet .

The problems begin at 4000rpm the secondaries start to open with full turbo boost the engine stumbles and spits back through the secondaries, (air valve spring at 3/4 turn, "J" metering rod hanger,"CJ"metering rods )it just won't go past 4000rpm.

any suggestions would be much appreciated ,if I had any hair I would be pulling it out!

comp

got any pic's of this ???

Star79

Sounds like timing, more than carb problems (Just guessing).

Let me be the first one to ask for pics and details of the turbo setup

*edit dammit comp! Okay 2nd for pics!*

turbovette80

OK

timing is 6deg btdc.stock distributor,vauum advance signal from inlet manifold see pics

BigBlockk

It almost sounds like the turbo is surging. Are you sure it is sized correctly?

BigBlockk

Later.....

my72vette454

Maybe your running out of fuel?

Yellow73SB

Did this just recently happen? After any mods?

big_G

turbovette80

OK

what might be the most likely cause fuel starvation, delivery pressure delivery rate,or float levels.It's got a standard mechanical pump.

Kalway

Upgrade to a pump that has a higher flow rate?

PolishMike

while your in there get rid of those pathetic worm gear clamps. T-bolt is only way to go on turbo setups. Im WAY too used to turbo setups on FI engines, so cant help you out besides suggesting an electric fuel pump. Any idea on your AFR? A wideband setup would help you out a lot.

Edit - Are you sure on the 5 psi?? Do you have an accurate boost gauge? What wastegate setup are you running? Ive never seen one that opens up at 5, especially with a turbo that size, unless you got one somewhere specially made to open that easily. (im used to 20-30lbs of boost on the cars I work on).

edit again - Looking over this again im gonna have to go with timing. Ive seen this kind of thing happen in cars with computers that pull timing when they see knock. (i know this doesnt apply to you).

To fully 100% fix this i would look into a knock meter, something along the lines of the msd knockbox. A wideband setup, innovative and zeitronix have nice setups. Or a EGT gauge. If you hook up an egt gauge i think you will see that you will be running perfect temps right until 4000 then the temps will shoot down due to timing, or up due to a lean condition.

Anyway i know this probably didnt help but good luck.

enkeivette

I don't know that much about turbos, but I do know that lean spitting through the carb generally means not enough fuel, or not enough advance. Maybe both.

If you take it up slowly past 4K does the engine still spit? If not, I'd guess that you're draining your fuel bowls. I could drain the fuel bowls of my Q-Jet after a few seconds of WOT when I had it on my 383.

mongo6901

An electric fuel pump may be in your future...

turbovette80

OK guys

Assuming I've got fuel starvation at WOT(it seems I can increase maximum rpm if I feather the throttle)is an electric pump the only option or are there any high flow mechanical pumps that can do the job?



thanks for the info polish mike but that diagnostic kit sounds a bit expensive!

63mako

Holley High Flow Mechanical 130 GPH. Should be enough. I got one from Summit

Twin_Turbo

a knock detection box is very easily made from simple parts. The easiest is an early 80s ESC box like used on 81, 82, 84 and the early TPI vettes. Those boxes have the following pinouts:

De pinouts zijn A B C D E F G H J K

A = shielding ground (the outside of the knock sensor wire, a shielded coax type cable)
B = sensor input (wire to knock sensor)
C,D & E empty
F = 12V (ign switched)
G,H empty
J = digital out (retard)
K = ground

hook up the 12V and ground, wire the knock sensor cable up and then all you need is a 1K ohm resistor in series w/ a led connected to the digital out and presto a knock detection box. The signal puslewidth depends on knock intensity.

You can also build one from a weatherpack memcal ECM, remove the plastic memcal cover and carefully remove the interpreter/decoder board.

You'll need:
2x 1KOhm R
2x 10KOhm R
2x BC548 transistor
1x LED


[1][ 2]------[]-------[]
|knock sensor board|
[3][4]-------[]-------[]

1 = 12V
2 = digitaal out
3 = knock sensor wire
4 = ground

note that these don't have the shielded wire, that's a thing only the early ones had..not really needed.

wire it like this:: XXX = 3 pinouts of BC548 (1),(2),(3),(4) are the pinouts of the interpreter board. .... is nothing...just for the spacing of my excellent ASCII drawing so draw it on paper and forget the dots

(1)
|
|
R = 1K
|
|................................X__led_ __R=1K___(1)
|__________R=10K_____X
X................................X__(4)
X--R=10K--(2)
X
|
|
(4)

shafrs3

Another pin out schematic, seems to be a little different.

WashingtonRacer

Have you tried disconnecting the inlet line from your turbo, so it will run NA? If you can take it past 4k then it's fuel/timing related. "well it's almost always fuel timing related isn't it."

Anyways you should have at least a mechanical pump with a boost reference port. If you don't have on, I do have one that I can sell you. It simply references from a ported source somewhere above the carb and adds pressure to the pumps diaphrame in a 1:1 ratio, so lets say you have 8lbs of fuel pressure at 0 boost, you will have 13lbs of pressure at 5lbs of boost.
As far as your timing is concerned, 5 pounds really should not be affecting your total timing. What is your total timing? The only way it will affect it is if your somewhere south of 36degs. I have a MSD boost timing retard box that I need to get rid of as well. "I used to have a turbo setup much like yours, but it managed to destroy every piston in the block before I became the wiser. Now I have learned from those mistakes.

BSeery

Why would a draw through setup need a boost reference port on the fuel pump? As long as he is getting 5-7 PSI and plenty of flow that should be enough. The carb is never seeing boost and jamming 13 PSI of fuel will cause the needle to stay open when the float is trying to close it.

Just hook a fuel pressure gage to it and place it where you can see it while driving (not in the passenger compartment). Take it for a drive and make sure you have at least 5 PSI at all times. Recreate the problem and see if you have enough pressure. If you do, then you don't need to worry about different fuel pumps or anything like that.

When this problem occurs what is your boost gage doing? Do you maintain 5 PSI boost? Maybe this problem is only between the turbo inlet and the carb and not from the engine intake all the way back.

turbovette80

since repairing gasket leaks boost is running at 8psi and holds steady once acheived,did a flow test on fuel pump seems ok,reset float level made slight improvment,my distributor gives 22deg @4200rpm + 6deg static gives me 28deg overall. I don't understand how you reach the magic 36deg.
Is there a way to make the power piston boost referenced and do I need to do it?

ps there is a strange sound over 4000rpm sounds like the air valve is having a fit,it clatters like fury,there is about an1/8th inch slap on the spindle!

thanks for the help sofar.