For my V8 build, I'm going to run 906 Vortec heads on a 305, resulting a lower CR, increased combustion efficiency, increased air flow intake and exhaust, and more power potential than using the stock heads. Other than that, I plan to use the #24 injectors that came with the engine unless I can get some cheap #19 injectors to use instead, and pretty much the rest will be a stock setup. I'm going to run a full 3" American Thunder exhaust system with headers and no emissions since I don't need it in my area, and maybe 1.52:1 Roller tip rockers if I can get my hands on a set.

Should I really be too worried about doing tuning? The biggest problem I can see if using the Vortecs...

 

My answer is yes, you should really be worried.. When you increase available air, such as your head changes will provide, you need more fuel to keep your AFR numbers from being too lean. You aren't sure if you'll use 19# or 24# injectors. You need to be.

By the way, your ECM would like to know as well.. There's a 25% difference in flow rates there. What if your current ECM goes unchanged and is set up for 24#, (you say it came that way) and you decide to use the 19# instead?

You'll be adding air via heads and cutting your fuel supply by 25%. Probably a 30% change overall. NOT a good idea. How lean can you go without destroying things? You might be on a path to find out. My suggestion is you'll need a re-tune to take advantage of those new parts..

 

Well at this point I don't even have a computer, and I don't have the engine built. I bought a 305 TPI that the guy put #24 injectors in and ran it that way. I didn't get the #19 injectors that he switched out so I'm stuck with the #24s unless I just decide to drop some cash on a set of #19s. Its all up the the air right now.

Would it be better for me to stick with the #24s and do tuning and possibly some P&P on the 906's to increase both my air flow and fuel or would it be better to keep the 906's stock and use #19 for my build? The first would probably put me a little rich without an adjustable fuel pressure regulator and the second would probably put me a little lean.

 

I wish someone would, but since no one else seems to be answering.....

Bear in mind, tuning a car is not a weekend event. As an admittedly poor example, it's taken me a few years to get to where my car is now. As I look back from today, I started knowing nothing about tuning via ECM's, but thought I was a genius who knew more than the average guyt, after all, I had read a few books on it already! How much else could there be! It would be a snap to learn. That wasn't the case. The more I learn, the realization becomes, the less I know. There is always more... a lot more.

I would take a bet that most of us here thought tuning our cars would be a challenge to some degree, but not a big deal. We're motor heads! We could handle it easily. That was wrong, at least for me, and I learned that sometimes it was overwhelming. That's not to say you should give up hope, or not try. Perseverance and patience are good virtues. (So is a large ball peen hammer, and something to pound into a bloody pulp with it).

My car is running fairly well now.

Am I done? No.

Do I have any clue as to how much more I need to do? Not really.

But every day that I can learn more about it, I get that much closer.

Just know this, that it will be a major investment in time and dedication to get it where you, (or anyone else) want the tune to be. It's not just doing something, it's WHAT you are doing, WHY did you do it, What problem were you trying to solve that created another that wasn't there before. HOW MUCH, what direction, was that a multiplier or factor, and why this, not that instead, and then it's "Crap, that didn't work the way I thought it would, and I got to get to work in ten minutes" and figure out how and why to do something else. Stuff you've never even heard of, much less thought of, will screw with your head, and haunt your dreams.

... and then there's the down side of it as well.

Did I mention a hammer is a good thing to have? Kittens?

Luckily for all of us, there are incredible people here, who are willing to share their immense accumulation of knowledge, AND A SEARCH BUTTON. I still re-read the stickies to glean nuggets of truth that I missed the first through fortyith time I read them.


Read more before you jump into it, to be sure this is what you want to do. When I started, I wasn't bald, but now the car runs, and the difference is my hard work and the collective efforts of this forum that got it that way.

Dave

 

X 2

 

X3 with Efi you really cant just go swapping parts around just because they fit like you can on a carburated application, Anything more than the most basic mods is gonna require you to "tell" the computer what you've changed or you will never get it to run right or be happy with the changes you have made.

 

Why would you want to reduce the CR? What is the resulting CR? I would consider a machinest to cut the heads to achieve 10.0/1 or greater.

Any other opinions on recommended CR??

 

The stock heads have 58cc combustion chambers, and the 906 vortecs have 64cc ones, that will result in compression being lowered from 9.3:1 stock to about 8.7:1. I did comsider getting them milled a bit to keep the stock CR or slightly higher, but it just cause fitting issues and I don't know how well they will all fit together if I do get them milled to achieve a slightly higher CR than what I can get with just using the Felpro 1094 headgaskets with 0.015" compressed thickness and 4.1" diameter.

 

8.7 to 1 would be kinda sluggish, unless your getting a supercharger. That would wake up a 305!

 

If your using cast heads 9.5 cr would work just fine anything lower would be pretty sluggish an you would not be happy . If you are using pump gas i would not venture into the 10.0 cr unless the heads are aluminum . There are incredible people here like said earlier by lakeffect2

 

Well if I mill the heads then I have to get different length pushrods for the valvetrain. Should I just get the block milled? If I get it zero decked then it will have 9.21:1 CR which is pretty close stock.

As for the supercharger, I don't want to supercharge it, I don't want to supercharge any engine, I want to make my power with nothing but pure mechanical might.

And yeah, I don't need to go to 10:1, thats too much for pump gas, and probably too much for the heads as well. The heads run 9:1 CR on a stock 350 though, just something to think about.

I debated about milling the block before but even with having a lower CR, the Vortecs will make me more power than the stock heads will, and I think that it would make the decreased CR almost unnoticeable. And I've never driven the car with the 305 in it so even with low CR on the V8, it will still be worlds better than the V6.

But do you guys really think that I should spend the extra time and money to get the block milled? Or how easy is it to get the heads/intake milled and just get different length pushrods to make it all work? Ideally, I think it would be best to mill the block and the heads, to get a little more than 9.2:1CR and something closer to 9.5 or 9.6. And I'm worried about valve clearance too if I do end up milling.

 

I'm of the opinion that its never a bad idea to make sure everything is square.

Due to the fact that these questions are no longer in the area of ECM's, DIY proms and programming, you'll likely get better/more responses from an appropriately different section if you post there instead.

 

Yeah, I'll be back with more questions about tuning though...

 

Glad to hear it!