gmoran1469

I've been looking at the modmax stroker forged assemblies for the 4.6 and the thought has me squirming in my seat. I don't have the scratch to lay into a project like this right now but it's the first step towards a 2.8l mammoth setup for me I feel. I'd like to learn more about FI and compression ratios etc, anyone have good resources for this? I'm scouring google as I type this. I understand the basics of AFR, 14.7:1 is stoichiometric, usual fuel ratio is somewhere around 13:1 but in boost you need to run richer to prevent knock. So should I use a lower comp ratio when using boost or a higher one? Does this all just depend on if the engine can handle it?

danzcool

Ah, the question of keeping it safe.
I haven't found a good resource to put all the variables into a formula, and I don't know all that I'd like to know.
1st is having the components that will handle the extra power, this is the pistons rods, crank, bolts, and the rest of the power train. When your bottom end can hold up, the main other issue is preventing detonation, which several things affect.
air/fuel ratio...
you hit on this one, richer for when WOT, this makes the fuel mixture harder to ignite (less oxygen), which protects against detonation, it also makes the charge air coolerdue to the extra fuel being sprayed in.
compression...
the lower the compression, the more boost you can run (all other things being equal)
octane rating...
the higher the octane rating the less likely the fuel is to detonate, higher octane rating means a slower burning fuel.
intake air temperature....
the higher temp the charge air is = less protection against detonation, every degree warmer is 1 degree closer to the flash point of the air/fuel mixture. This is where larger intercoolers and water/methanol injection come in, reducing the temps of the intake charge.
coolant system...
If your not keeping the engine cool enough, then your again closer to the flashpoint of the air/fuel mixture.
timing...
retarding the timing also protects against detonation.

If you detonate, things get real hot and the expanding gasses try to find a way out of the cylinder before it gets to the exhaust stroke, so blown head gaskets, blown rings, bent rods, meltdown of cylinder walls and pistons, etc.

if you find some resources that quantifies how these things interact, be sure to post back here.

gmoran1469

My cousin sent me this:

http://www.powernationtv.com/episode...n-turbo-coyote

Was very interesting. The Helion kit with the dash input for on the fly boost control is very appeasing.

tx_zstang

One thing at a time here.

First of all, the engine. Two big factors will be: how much boost do you plan on running, and what fuel do you intend to use? With the mammoth, and with a build engine, you'll probably eventually end up going to small enough pulleys to max out the blower, so assume boost will end up at over 20 psi.
For fuel, well, at this level, it is very risky to run 93 octane pump gas, but if you intend to use E85 if available, that is something to keep in mind, too (e85 has different stochaic value than regular gas).

As boost goes up, and the risk of detonation increases (as boost increases while fuel can't handle the boost as well), you'll get recommendations to lower the compression ratio.

Let's take a slightly milder approach, and say your target is 15psi and 93 octane.

Now, these are real-world observations and results that I've seen on my own cars and on friends' cars.
Go with a near-stock compression ratio, such as around 9.5:1 to 9.7:1. For a little added safety if you plan on using 93 octane, 9:3 or 9.4 to 1 would be acceptable. DO NOT go with an 8.x:1, as that is too low for these engines and you'll loose some low-end torque and won't be running enough boot to make that a reasonable cr for your goals.

If you're going to use E85 or higher octane, you can get far more aggressive and run 11:1 compression ratio pistons and make a lot more power; but that's pushing it a little


You personally should not attempt to worry about the actual AFR and such, as the person tuning your car will take care of that. Yes you will need custom tuning with a blower, and you'll need a wideband sensor and gauge installed in the car to do that.

If course the engine is just one aspect of the whole picture. You'll need a fuel system setup that can deliver enough fuel, along with proper injectors. The GT500 dual pump setup is a good option for lower-boost levels, where you're around 500-550 hp, but above that, you'll need either different pumps or use of a boost a pump, with the gt500 pumps.

Take your time and do your research on everything, every aspect of what you are planning, and understand the power potential that is there along with your goals. Do everything right the first time to handle your current and future needs, and you won't have to change anything other than a pulley and tuning as you desire more power.

Simon1

I would also consider the 2.6H from KB. I have a seen a few with the 2.8 and the smaller motor not do so well. I have the 2.6 and I love it, but regret not getting the 2.6H version.

It's the same blower, but a slightly different outlet on the blower (I think) and the manifold is designed differently.

It is designed to be used at 15 psi and higher. Similar to how the 2.8 is designed.

gmoran1469

Well, in my mind at least, the plan is to upgrade my swaybars (will do that soon) then start saving cash to swap the bottom end to a 5.0L forged stroker assembly and upgrade with a full header/exhaust swap. Run that for a while until I can save the cash to put do a gt500 pump swap w/ boost-a-pump and get the mammoth with as massive an intercooler as I can fit. The rwhp goal being 600-650. I don't have easy access to E85 so maybe water/meth injection if needed.

Simon1

You won't need water or meth injection.

The key to the twin screw blowers is heat. Having a good heat exchanger and a large tank for the coolant is what is needed. The injection stuff works. It just not a normal route to go to get the results you want. Some of the KB blowers come with a liquid cooling feature that runs coolant through the SC it'self.

A 5.0l motor, good exhaust, cams and a good throttle body, 2.6h or 2.8h blower will get you to 600-650 easy.

gmoran1469

I am trying to understand the graph on the modmax stroker assembly page. The very top row is what heads you have, right? What are the stock heads on the 09 gt?

tx_zstang

I disagree with Simon1 on methanol injection, especially for our hot part of the country. I use it for additional cooling more than the octane, to keep intake air temps cooler, timing higher, and power higher.
With 93 octane, I'm "pushing it" as it is on 18-19 psi, and methanol injection helps keep things a little safer for me.

I do not yet have access to E85 either, but there are some places getting close enough where I may be able to get some and use it, and then not need to worry about it.
GMoran, if you intend to run higher boost (over 16 psi), you'll need some way to keep things together and safe.

FYI, I'm using stock '09 heads, with custom cams and different springs; I'm sure I could pick up some nice power if they were ported/polished!

gmoran1469

Would you post some details of your setup and HP/TQ #'s? I'd love to look over that info just to see what kinda power it makes and what the curve looks like. Trying to determine the benefits/cons of stroking vs keep it stock and boosting.