Scorpion

So I've been thinking about adding a little more boost on my stock motor. I've been looking at what others have been running with lower comp pistons and head gaskets and from what I've seen I think it can take it. Follow my train of thought here and tell me if I'm nuts. Stock compression of the F20c is 11:1. That's also what the "effective" compression is. Now stock 11:1 with 8psi, the effective compression rises to 16.9:1. Which so far I have been running no problems. Now take the Inline Pro kit, it runs at 18psi with a 3mm head gasket. The gasket drops the compression ratio down to 8.8:1. With 18psi of boost you get an effective compression ratio of 19.6:1. Same thing if you run CP or JE pistons at 8.5:1 with over 20psi of boost.

So with a stock 11:1 with 12psi of boost the effective ratio is at 19.7:1. I think that should be safe, considering I'm running EMS and can retard the timing, where Inline just uses a map defender.

Am I crazy or does this make sense to anyone else?

Scorpion

No opinions on this?

slamar1

I think it was fperra that said he ran 9 psi for 2 years on a stock motor as a daily driver. I was thinking of doing that myself. I would go from 7psi to 9psi. I think I could hit 370-380 rwhp with that

Why not try 10 psi first and see if you can get an effective tune? I would think you would want a good balance of timing and boost. I have not heard/seen anyone doing 10 as of yet. Do you think you have enough injector for 12 psi? I am not sure, that's why I ask.

Baby Steps, Scorpion... Baby Steps..

Scorpion

LOL the problem with baby stepping it is that I'm going to be using the GM 3-way solenoid and EMS for boost control. And after a lot of research I have found that the solenoid is not very affective for small increases. So the fact that I have a 8psi wastegate spring doesn't allow me to go much less that 12psi. My injectors are a little on the small side. However, that's nothing that a 10psi increase in the fuel pressure system won't fix

Tinker219

actually Brian, you have a .4 bar spring, which I believe is a 5.5psi spring. The efficiency of the GT series turbos throws the TiAL ratings system right out the window; and there is about a 1psi creep-factor built into the manifold(not on purpose, but the wastegate has to fit somewhere!).
I say turn it up! And put fuel cut low in the PSI(Setup, rev limiters) so that if you make a b00 b00 in figuring out the GM Boost control selenoid, you dont see 20psi of boost
BTW, I miss boost. I just got my car running again, all-motor. 10:1 compession on stock exhaust(and cat) is REALLY slow; especially when running on the same boost map that I always have been
Hopefully by Thanksgiving Ill have my car up and running, on the way to the tuner with some good basemaps for you all to mess with(boost control selenoid).

spoiled@21

I have over 8000 miles on my stock motor SCd at 9psi the whole time. Tune it right and it will run right.

Scorpion

Actually I have a .5 bar spring (tial small green) which is just a tad over 7psi. I have aabout a half psi drop though the intercooler (tested with two boost gauges, one on the intake mani and one connected to the compressor housing) and I am getting one psi of creep which I can understand due to the 90* angle of the dump into the downpipe. So the system works exactly the way it's supposed to in my mind. I would like to try and understand how you think efficiency can change the physics of a spring. It's a pressure system in which boost pressure pushes on a diaphram and once it over powers the springs pressure rating the gate opens. Is there something I'm missing?

My plan for the EMS was to set fuel cut at 13psi. That way if there is any spikes or I set the sloenoid up wrong it won't tank the motor . I just finished installing the solenoid last night, it's connected to a switch mounted under the dash, so I can run hi/low boost. Tomorrow I will be cranking it up and doing a quick street tune. Hopefully by the weekend I can get it on the dyno and see what she makes with the extra 4psi.

MickeS2K

We also have the same question
When we had the vortech supercharger we boosted daily about 1bar~14Psi and we allso tried a while on 1.3bar we had no problems.
But the SC doesn't put down at the same boost as the turbo.
We have AEM EMS 720cc spridare injectors stock engine with 3mm Cometic gasket running on 8.8-9.0 CR, lovefab GT1, GT35R how much you guys think we can boost?

spoiled@21

One of the reasons that Honda and Toyota did so well there last two years making turbo 6s for cart was that developed a manifold that created airlow vortices in such a way that it would fool the "pop-off valve" (Cart tech speak for wastegate) that was league mandatory set to 14psi. Ford raised a big fuss about being slow and it was found that the Honda/Toyota motors actually boosted 15-15.2 psi. Since their designs were within regulation they had to change the pop off valve design to accomodate these new airflow patterns.

thus, placement of the wastegate on the manifold can negate some of the actual boost pressing against the wastegate spring by means of "laminar physics." I am not in a position to say that Tinker did this on purpose but seeing as it is not an equal length manifold it makes this happen much more easily. When all the tubes are not equal then there are 4 different airflows that are going to have 4 different "angles of attack" on the inner walls of the manifold just before the wastegate opening which creates turbulence in the airflow that can fool the wastegate. So is short, yes it is possible to create greater boost than the wastegate should theoretically allow.

So all that said in explaining creep you still have this turbulent air. The GT turbos are effecient enough and spin easily enough that the turbulent air spins then just as easily as clean air.

spoiled@21

I am not 100% on that so easy on the flaming if you think I am an idiot.