RW99

Please predict the two dyno curves for me from 3000-6500 rpm, valued experts: on a front-mount T67 (A/R 0.81), A2A intercooled, 346 ci w/-8 cc pistons, AFR 225's 72 cc. 60 lb injectors; plenty of fuel.

Setup 1: 15.5 psi boost, 12 degrees timing

Setup 2: 10 psi boost, 20 degrees timing

Assume that each setup is tuned to proper AFR.

Theoretically, what curve profiles would you expect on a dynojet?


Thanks in advance for your opinions.

CHRISPY

Why would you only run 12 degrees timing with 8.8:1 compression and 15.5#'s boost?

What octane would you be running?

With proper timing and your comp ratio 15.5 pounds boost should make 85-100 plus more RWHP than 10#'s imo

kp

iTrader: (34)

14-15 psi with 15-16 degrees of timing is all I run with 104 unleaded @ 9.5:1.

Honestly going from 13 to 18 degrees of timing makes little difference in my car as far as ET/MPH, air/fuel makes a way bigger difference.

The more boost with less timing will definately make more power, my same combo ran 10.40@129 with 10psi and 22 degrees of timing. Cant help you with dynojet curves

fletchls1

iTrader: (10)

I thought it was the other way around? With boost dont you make more power advancing the timing, and nitrous you make it retarding the timing?

RICE ETR

iTrader: (3)

agreed.....and a lot safer too. 13 degrees peak tq, 18 peak hp for me.

fletchls1

iTrader: (10)

Can someone explain to me why so many people would be running higher timing when its safer PLUS makes more power lower?

kp

iTrader: (34)

That depends on so many factors, combustion chamber, dome design, inlet temp, fuel used etc. You retard the timing to avoid detonation with both. Naturally with higher cylinder pressure (more boost or nitrous, whatever you prefer) you need to reduce the timing depending on fuel used. I could probably make more power running C16 and 5 more degrees of timing but on 104 unleaded it may not be a good idea..

fletchls1

iTrader: (10)

Understood! Thanks for clearing that up!

LTLHOMER

iTrader: (10)

How about more boost and more timing?

67Firebird455

iTrader: (27)

Then you end up like me... nuclear f-ing meltdown. Poor car. With the 8.8:1 I would run at least 16-18 degrees at 15# boost, assuming your intake air temperatures don't sky rocket with the increased boost. There are a lot of variables that must be filled in. No meth to cool the charge? I am planning on running about that same compression with the new motor, was also thinking meth (better safe than sorry) with more timing, and the same amount of boost. You should be perfectly fine as long as 1 your IAT and EGT don't fly through the roof and cause meltdown. =)

LTLHOMER

iTrader: (10)

Were you on pump gas or something?

I have the same compression, same boost, but 6-7 more degrees of timing.

67Firebird455

iTrader: (27)

Yes sir, I was on california famous oxygenated 91 octane fuel. That was on the stock shortblock with 97k on it, had oil come in the top end when the stupid body shop ran the car without the mocal scavenge pump 12v hooked up and it ended up detonating big time after that and grenaded. I was 16 and would KR down to 12.5 under boost. Knocked the boost down to 5# and that's when the motor came apart.

RW99

I was mostly curious if running the low timing/higher boost (setup 1 above) could result in the turbo running out of steam at about 5000 rpm... sounds of the turbo maxing out, torque dipping off, etc. Making good rwhp and rwtq at that point, but you wouldn't be able to use the motor above 5k without damaging something, I think. This is on 91 octane Cali gas (dammit). I will be running methanol, but I want a good safe tune prior to crossing that bridge. On the plus side, I'm pretty certain that there aren't any leaks and that the FAST intake is just fine with over 15 psi...

Or are there other more probable causes for a dyno graph that looks great but just ends too soon?

DeltaT

iTrader: (5)

Sounds like your problem was not due to more boost and more timing, it was due to an incompetent shop, right?

That must have sucked.

Jim