question for the blow-through guys...

[gravelrash]

i have a 250 2v turbo blow through system on my 65 falcon. after i have been driving it a bit then shut it off about 2 seconds later a loud pop is heard through the exhaust. wtf is this. my mate 350 chev blow through does exactly the same thing.
have linc200 or does10s ever experienced this?? if so how did you fix it.

i run a 600dp holley.

 

[xctasy]

Just live with it meantime.

I suspect it's most likely fuel bleed from the jets. The solution is the old 83-84 MustangGT 5.0 Holley 4180's series 630 cfm carb (also found on the 84 to 88 4-bbl 5.8 and 7.8 F150/250's) whcih may have had an anti dieseling valve. Option two is to drop the fuel pressure down when the ignition circuit is opened on tun off.

Falcon XE's and Jap cars from about 1975 solved it with reduced fuel pressure from the beloved retun line, and a 12 or seven volt solenoid which leaks a heap of air into the idle circuit to stop it dead.


The fuel presure can be controlled by an electric pump syphining off the retun line, and a good boost referenced Carter mechanical pumping.

 

[gravelrash]

i had a suspicion it was fuel bleed from the jets, as the turbine would still be spinning after i shut the engine off siphoning fuel out.
as you say live with it, but this is going to keep me thinking on this one. must be a way around it.

 

[Does10s]

gravelrash,
Yup! It occurs every 3rd or 4th shut down. I haven't really looked into it yet as it's not a big deal.
But my take on it is that if you shut the motor off without letting the turbo "de-spool" after running it hard, then the turbo will be trying to blow air through the carb even after the motor is shut off. This will push a bit of fuel/air into the chamber. If one of the cyl. is at the correct point where both valves are open (overlap) then you'll get the "pop".
This is my theory on it, but I'm not sure it's correct.
Try and let the motor idle for a minute of so before shuting it off and see if it still happens.
Later,
Will

 

[Funky Cricket]

yay desieling.

prolly just the extra pressure pushing fuel in to the engine and it is giving a little backfire due to puddling.

 

[gravelrash]

does10s, mate im glad to hear im not the only one experiencing this. i finally got that copy of car craft in Australia, good story.
i have though about using a lpg fuel solenoid to shut the fuel off when the ignition is cut. not sure if this would work though as it may still suck the fuel from the bowls.

 

[Does10s]

Gravelrash,
The solenoid thing won't work unless you let the burn all the fuel out of the carb bowl. That is if my "theory" is correct anyway.
I'll have to do some testing to see if this is the case.
Try and take some notes on your end to get some info. I'll do the same and maybe we can compare and come up with a solution.
Will

 

[gravelrash]

Gravelrash,
The solenoid thing won't work unless you let the burn all the fuel out of the carb bowl. That is if my "theory" is correct anyway.
I'll have to do some testing to see if this is the case.
Try and take some notes on your end to get some info. I'll do the same and maybe we can compare and come up with a solution.
Will

yeah mate i will do. the solenoid suggestion was just to start some lateral thinking. would need some sort of solenoid in the fuel bowl, somehow.
since i have started to let the turbo idle down it hasnt done it since. i just have to keep remembering its now turbo`d.

my email is gravelrash1@bigpond.com if you want to exchange any pics, plans and ideas.

catchya later Greg

 

[jahearne]

"Anti run-on" valve on some of the British sport cars I've owned in my high school daze opened up a vacuum line from the manifold to the fuel bowls preventing fuel from entering the the motor. This valve was found on my '73 Truimph GT6 and '76 Lotus Eclat. The valve has two wires running to it and two vacuum lines. Just a thought...

Good luck.

 

[Anonymous]

Usuallly excessive carbon that causes glowing partcles is the cause of all this.


Mine has never "popped" and never "dieseled", but I do run really high octane soup, too.

I always let it idle about 15 seconds before shutdown.

I also have a 3" downpipe after the turbo, maybe small pipe causes a pop?

 

[XFlow_Fairlane]

I have never had my turbo setup pop either. I always run 92/93 oct gas but I do have LOW compression (7.5:1) I am running a 2.5" dowpipe into a 2" tailpipe (no muffler) and it is all mandral bent sections

 

[Does10s]

We're also running a 3" downpipe with a 3" exhaust all the way to the rear with a Borla muffler.
The "pop" only seems to occur if we don't let the turbo despool. If we let it idle for a min or so it never happens.
Will

 

[Anonymous]

Just my .02c worth, but what about a turbo timer like the rice boys use? Not only will this solve your current problem, it will also extend the life of your turbo by giving it time to despool and cool off....

 

[Anonymous]

It takes nearly a minute of gentle run time to get from the end of the track to the pits, so that cools it down. I then let it idle for about 15 seconds. No biggie.