dizwiz24

Exhaust backpressure is supposedly a big deal on FI cars..

I read somewhere that the supercharger has to 'fight' exhaust backpressure during the overlap phase of the cam (when the exhaust valve and intake valve are open at the same time).

So if you make 12 psi boost, but have 8 psi of backpressure, then you are only getting 4 psi of boost effect during that cam overlap phase.

Hopefully you chose a cam with as high a lobe separation angle as possible. However, there is still overlap, thats why low exhaust backpressure is so important!

bogor

Back from the dead!

Finally got my new exhaust done. dual 3" with Flowmonster x-pipe. Loud but not unbearable...



Made a quick test of back pressure; about 3,5 psi at 5200rpms. Tested my old system at 5500 rpms so I suspect the new system will be around 4-5 psi at 5500-still a large improvement.

Have also added a second nozzle for the water injection. Put it on the airfilter and its now a straight shot towards the impeller.



I ahave also added a J&S Safeguard Interceptor to keep detonation under control. Still trying to set the right level of sensitivety but it looks like its doing its jobb (and its really great to be able to plug in headphones and listen to the knock sensors).

Managed to squeeze it into the glove compartment.

Its dyno time the 7th of June......

qwiketz

You definitely should be getting more hp out of a maxed out s trim. The nozzle pre blower should add a lb or 2 of boost also.

dizwiz24

Looking forward to your dyno results. I too added an exhaust (arh 3" w/ xpipes, same dynomax superturbo mufflers), no cats.

I'm interested to measure backpressure again.

I'm still in debt to you steering me into less timing means more power at low rpm.

Many peopple (lsx) think I don't know what I am talking about, that more timing down low makes more and more power until engine detonates.


They think I got the results I did because a knock sensor was pulling timing. However that's not true as I was datalogging the whole time.

do you have cats on your new exhaust? If so, why?

Either way, those look to be really low backpressure readings.

Are there any concerns with injecting methanol before the supercharger? What benefit is this?

bogor

my tuner recommended me to try out less timing. He was not very surprised about the outcome and he said this is not an uncommon result. Finding MBT is challenging and to my understanding, more timing does not always equal more hp. My particularl engine responded positive on less SA on high rpm/load and higher SA on medium load/rpm indicting its knock limited at peak hp- at least with my old crappy exhaust.. I will post info about the next dynorun.

Injecting pre blower is by some stated as a way of extending the efficiency zone of a blower. Could potentially mean some top-end gains, will soon know if this is true .
Have a look here: http://www.aquamist.co.uk/vbulletin/...read.php?t=251

Running dual random technology race cats due to quite strict emission requirements ( still borderline case though)

dizwiz24

ok. I didnt realize you had cats.

You sure your high-backpressure previous results werent just a result of either inadequete cats (did you use stock cats?) or clogged/damaged cats?

bogor

The cats are ok, see post 17. It was mainly the mufflers that caused the high back pressure.

bogor

Numbers from todays dynorun;

529 rwhp/ 543 ftlb

This shows a comparision with my previous best run in 2012 (470 RWHP)


This run gave the highest RWHP but it showed some slight indications of knock so I will not use this setting (it had 2 degrees more SA on the top).


Only physical change from previous year is a more free flowing exhaust (and some minor changes in the tune)-quite good outcome I think.

It looks like the rule-of-thumb I discovered was In the right neigbourhood-my combination: 59 RWHP increase and about 10 PSI less back pressure gives approx 6 RWHP peak gain for each PSI reduced back pressure.

Injection of water/ethanol straight in the blower did not give additional output. However, our test was quite limited so it cannot be ruled out it might be something beneficial in doing it.

mnstrlt1

Very impressive numbers! Especially with an S-trim!

dizwiz24

Great results! Way to go. Id be real happy if I was you.

What peak boost are you seeing? What'sthe boost curve like?

Can you share your wot spark advance vs. Rpm?
I'm really happy you got such a big improvement.

bogor

I put in some more advance and it seems have to payed off (thanks Dizwiz, this time your tests inspired me).
My WOT ignition and boost curve looks like this

2000 rpm; 19’ and 1,7psi
3000 rpm; 24,5’ and 3,8psi
4000 rpm; 22’ and 6,5 psi
5000 rpm; 19’ and 10 psi
6000 rpm; 19´ and 13,2 psi

Max boost was about 13,6 psi at 6300 rpms.
We added 2 degrees (21 degrees in total) as 5000 rpms and up but my tuner that was using a stethoscope listening to the engine said he heard some “suspicious sound”. This guy has tuned a huge number of cars and has probably a good ear for hearing knock. I have to highlight the fact that the J&S Safeguard really seems to work as claimed; the same time he heard the suspected knock, the Safeguard retarded 6 degrees. Even so, it managed to produce 538 RWHP (prob due to the individual cylinder retard)! Previous run with 2 degree lees timing, the unit did not retard at all so the unit seems to be able to filter out knock even at +6000 rpms, my tuner was impressed and he thought this unit was to be trusted.

I did some tests with an extra water injection nozzle. First dynorun blew off the intake pipe between the blower and the TB when releasing the throttle. Too small blow off valve I guess (will switch my plastic Bosch to a Vortech race). Pieces were flying and we got sprayed by etanol/water (top was down) and the pipe hit the inside of the hood and cracked the paint on the outside…It took some time to put everything back.

EDIT: i just found out that the hose going to the nozzle ahead of the TB was loose. I suspect there has been severe leakage making it impossible to draw any conclusions of my dyno runs with different injector nozzles.

BrianCunningham

impressive!

lcvette

What headers are you running? for supercharged cars running max effort, IK like the 1 7/8" American racing headers. also the cats are a restriction at this level, much more and you may start to get some melting occurring on a 3" metal substrate cat. upping the diameter of the cat will also help, some people are using the oversized metal substrate cats for the performance diesel applications. they are available in up to a 5" inlet and outlet.. these work great with the big headers, can use a cone to expand to the cat from the collector which also help initiate scavenging a bit better. the X pipe you show is also a restrictive type. a shallow bend with a small section assists in keeping exhaust gas velocity high and no tumbling it which creates a restriction and back pressure. such as the one below:



Just a few thoughts since you are looking for max effort on your setup.

Chris

bogor

Thanks again Chris, Im happy you are sharing your knowledge with me.
I running 1 3/4 " long tube headers from Exotic Muscle. Its been a real
pain getting an exhaust that works ok without too much noise (I think this is the 5th iteration...). The space
available is quite limited (its a vert so I have the X brace to deal with).
My current max back pressure is about 3-4 psi. I will check this again with
the new intake and if the BP goes above 5 psi I prob need to do something about it....it never ends....