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Originally posted by Alaskaracer:

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Originally posted by wideopen231:
My question is. Why so much compression? Asking because you have more than one time told not that much extra power with compression and really very littl gain after 14.5 or so.

Had to ask after previous replys on my compression questions. i all hinesty I agree with not much gain after 14.5, especailly with waht it takes to get much more.

As for gas or alky. I have never seen why either would not work equally or slight edge to alky. If womething with heads and easily correct so could run both why would you not do it? Can see where coment on cam makes lot of since on working better with one than other.Fuel volue and burn rate being my thinking.

I don't recall myself ever mentioning there is little power to be gained with compression ratios above 14.5:1, but I do know it's been said. However, I will disagree with that to a point. When I built my last combo, my head guy and engine guy both wanted my compression ratio high. It helps to offset the loss of air pressure at altitude since I was in Denver, Co. My last deal was set at 16.5:1. When I switched to alky, it responded very well and clearly made more power as the et's dropped and mph increased substantially. My new combo was supposed to be the same compression ratio, but somehow we ended up a bit high...that's ok. What's happening now, is that my engine is making more power from less fuel than it did before. Yes, I have a larger pump and nozzle jets now. But I'm bypassing a lot more than I did with a similar tune on the old combo at sea level. The engine is wanting a leaner mixture which tells me it's way more efficient than my last build. Yes, the heads, intake, and cam are a major player in that, but so is the compression. I'm still at almost the same timing and the engine is telling me it wants more....I'll take more power on less fuel any day of the week.

Not aimed at you. Curly has told me this and just wanted to ask why he now sees it as need. Agree if in lousy altitude it is benifit.

I have both side of it. High compression woke engine up and where it did nothing much. Combo as always. That is why ordered new piston for 15.5 and had extra left in pockets. IK can swap gasket for 15 to 12:1. May need spacer for intake but that it.

agian was aimed to op.

I typically do not go for this high of compression but on this one I am taking the advice of a few who are familiar with this type combination. Generally I like to be around 14 to 1. With this SB2 and the small chambers I could get as much as I wanted.

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I am with Steve on this one, I realize the benefits of EFI. It will start up nice and clean like a carb, you can have all kinds of safeties built in, You can set it to warm up quicker and use a lot less fuel.

But I really do not know much about tuning them and need to get a set up that is competitive from the start. I do not have the time or the money to spend 2 years learning and tuning the thing.

A competitive set-up can be achieved on a chassis dyno or even a T+T at the track in EFI. If an engine dyno is preferred and can accommodate the EFI controls then this way.

The learning curve is as tough as you want to make it. Some prior reading, video learning instructions and laptop practice is all that’s needed. Laptop practice of just loading the program, understanding where to look for what you want is key. Once that is somewhat mastered, much falls in place as to how you program the system and continue on.

Data acquisition from EFI is excellent and some use an interaction of the DA to the program….ie an rpm position you view in the DA shows a cursor position of what you have programmed and where. I like and find this feature helpful.

You wrote in prior replies that you only use O2 readings, and one for each cylinder to tune with. Then somehow you mechanically try to achieve what you think is the correct/ best for each individual cylinder by changing a pill/ jet/ pressure/ relief to get what you want.

In EFI, one would use the table below. The programming manipulation of what you want is far superior to anything mechanical imho.



As I wrote in a prior reply……. Install the ECU with what you have now, continue to use MFI as always, collect all the run data in ECU and learn how to use the system without tuning. Use the ECU as your new DA. Then when comfortable (a yr from now, whenever, never), switch to EFI intake manifold, plug in the injectors and go.

Tuning with EFI using the Learn mode is easy. You program the AFR@rpm you want and ECU adjusts to achieve this setting and creates a learn table that you can use to correct the fuel map to run in open loop and tighter closed loop adjustments.

btw… I’m also writing this for the possible benefit of others that might be interested, read, but never write.

Markemark, You sure make it sound easy.

Part of my decision will be after Dyno. In the 4.60 outlaw class any electronics is legal. If I continue to run NE2 then very little electronics is allowed. If I make enough power to run the Outlaw class then I will be ripping all wiring out of car and starting from scratch. Plus new fuel cell and radiator to move weight around.

For O2 sensors I use a RPM data logger and tune to best performance we got on Dyno. Pretty easy.