maximum safe boost?

[rmcdaniels]

I want to know how much boost it is safe to run on my engine on pump gas.

The guy who built it says anything under 30, but my Hondata tuner says under 20. Neither of them can tell me specifically why.

After doing some reading I found the following formula:

((boost psi / 14.7) + 1) x motor compression = effective compression

I think peak effective compression with good fuel management and forged internals should be around 18-20 if I want to keep it relatively reliable.

Doing the math for my engine, I get the following for my current setup:

((18/14.7) + 1) x 8.4 = 18.6857

Just out of curiosity, doing the math on my old engine/FI setup gets me:

((10/14.7)+1) x 10.2 = 17.1388

These values don't reflect the thermal efficiency of the FI solution, so figure the new setup can go a bit higher than the old setup because it puts out a lot cooler air.

Running a few other numbers through my new setup yields:

20 PSI = 19.8286

21 PSI = 20.4

22 PSI = 20.9714

25 PSI = 22.6857

28 PSI = 24.4

Looking at those numbers, 20 PSI seems to be about the max if I want to drive it every day. Of course that depends on my assumption that 18-20 is the max effective compression I should run on 93 octane pump gas.

Does anyone else have any information on or experience with this?

[john]

No idea. What I've done in the past is slowly up the boost until the knock sum is too high for comfort, then back it off a couple psi.

Or run 101. :)

Yeah yeah - I know that's no help, but...

[rmcdaniels]

How do you get the knock sum?

[12seccivy]

I would imagine it depends on a few things(I'm still learning as you are)
1. static compression
2. engine mgmt system
3. temps of the incoming air
All in all a lower compression(8to 1 or less)will handle a lot of boost without detonation.but off boost performance will suck.
you have a really good engine mgmt system,so detonation and ign. timing will be well controlled and monitored.
and last of all. If the incoming air is kept cool and consistant,you will have better control of detonation= more boost options.
I'd guess that your 9 to 1 compression(@sea level or close)would do 20 psi safely on hondata with 93 octane.
but you need to pay close attention to your engine and how it responds to the extra air you are adding.
Keep in mind that the more boost you run gives you less margin of error when things get out of hand..
this is one of the reasons i don't like nitrous

[ryanman]

How do you get the knock sum?
You don't until you set the boost somewhere and go drive the car and datalog it and then look at your knock count.

[rmcdaniels]

I didn't think a Hondata S200 on a P28 read the knock sensor. I'll have to check with Hondata.

[rmcdaniels]

I checked it out and it won't. I guess I should get a P72 or a p30.

[rmcdaniels]

Or maybe I should spring for a J&S Safeguard. That would give me a real-time readout of detonation and take care of it automatically. I'll call them and see if it will work with the Hondata ECU.

[exciv2000]

Or maybe I should spring for a J&S Safeguard. That would give me a real-time readout of detonation and take care of it automatically. I'll call them and see if it will work with the Hondata ECU.

I'll save you the time. It will.

[rmcdaniels]

I'll save you the time. It will.

Thanks, that thing is expensive, but it seems like some good insurance if I'm running 20 lbs of boost.