this is prety interesting. not totaly suprizing that a log style manifold and 3" dp are a little restritive on a 408 but i am suprized how strong it is running with a 3-1 ratio.

i got on the interstate and started at about 8psi and floored it from 40 to about 80mph, then bumped it up, then again then again. all runs were with an open down pipe except for the last run i closed my cut out. below is a screen shot of the entire run and 2 links to some more close up pic's. the runs with a little KR are when it started to spin some, probably false but i never know for sure. i was going 40mph in 4wd on a dewy interstate and it was lighting them up.

here is a blow up of the last 3 runs >> http://www.neufamily.org/images/bigexhaustpresure.jpg
and then i put the boost/exhaust on a 3/1 scale >> http://www.neufamily.org/images/3xexhaust.jpg

 

That is pretty interesting Jim. I don't think that 3:1 ratio is very good for you engine though. Where did you put the pressure probe in the exhaust?

 

i put it in the middle of the cross over tube. i taped a hole and put in a brass fitting, then a 5' long 1/8" copper tube, and then a autometer presure sensor. i dont know if the copper will take that heat or if 5' away is enough to keep the sensor from dieing but we will find out. i stole that sensor of off my fuel rail so i need to get another one.

 

3:1 is pretty bad. Normally you shoot for 2:1.

Time for a different hotside setup. It gets to the point where you cannot get anything else out.

 

maybe next year, i am making more power now than i can handle. way more power than is safe for my current set up. i think this year i will work on a few thing to make it safer and smoother and more fun. shoot for some mid 10's or so and then do something nuts next winter.

 

probably a REALLY good idea!!! you already got stupid fast down, now its time to get stupid safe. that was . i need something to drink.

 

You cna crutch that with a cam change to help the situation a bit

 

i think thats pretty good...not perfect or ideal but not bad.

 

With that pressure its surprising you dont have blown exhaust gaskets. I know someone who would pay quite a bit for your current turbo, so you could help finance a bigger one.

 

parish8 I went from 5-6 psi of back pressure (before stock cats, with single magnaflow muffler, 3" mandrel bent single tail pipe) at 5500 rpms WOT to less than 1.5psi with the 4" diesel exhaust system...almost knocked off one full second off my quarter mile times with 8psi of boost!

Easy way to tell if you have to much back pressure...when your exhaust tone changes from it's nice mellow tune to a Jet engine taking off you have to much back pressure! Before I switched to the bigger exhaust system from 4,000 rpms on it would loose its tone and sound like rushing air out the exhaust pipe.

Also I found that Lightnings run less than 2psi of back pressure with the stock exhaust sytem.

I use a manual guage with an adapter that plugs into one of your o2 sensor holes and then tape the guage to the windshield.. http://jcsonlinetoolshed.com/product...e5acd59673bb70

Duel 3" Cats, dual 3" piping to a 4" Magnaflow diesel muffler, 4" mandrel bent tailpipe to 5" tip...





Ken

 

my problem isn't in the exhaust system although i am sure a larger downpipe would help a little. the outlet of the turbo is only 3" and then i have less than 2' of pipe to a 4" cut out.

i dont really know for sure where the worst of the restriction is, could be the log style header or the exhaust side of the turbo. like i said before though, probably just mess a little with it to make it flow better but not really sweat it for now, at this point more power wont make me any quicker, i need to figure out some other stuff.

 

NICE work! Keep it coming. Your truck is getting real interesting......