408 swap

[mwalls54]

Can I ask why you are wanting to go to a 408?

[BenKey]

Nothing better to do. He wants better gas mileage.

[cadowns]

Nothing better to do.  He wants better gas mileage.

<{POST_SNAPBACK}>

 

 

Something doesn't add up to me. But, Hey we all want a 408, I just want mine to work, the first time.

 

CD

[zippy]

Nothing better to do.  He wants better gas mileage.

 

 

is that why you went bigger? i mean, you already had the 6.0L and the radix, why not stick with that?

[j4nash]

Can I ask why you are wanting to go to a 408?

<{POST_SNAPBACK}>

 

i need more hp and tq

[BenKey]

is that why you went bigger?  i mean, you already had the 6.0L and the radix, why not stick with that?

 

I didn't have much of a choice. I would have gladly kept the 6.0L and the Radix. Since I had to take it out, I wanted forged parts. I would have stayed stock crank even, but if they are forged, they are like $100 less than a stroker crank - easy choice to go bigger.

 

No way would I ditch a blown, perfectly working motor and s-chgr, just to go bigger cubes. Too much wasted money, IMO and not all that much power gained. And, probably worse gas mileage to boot. To each his own though, I guess.

[zippy]

my experience with radix trucks is that if you drive a modified radix truck they average around 12-14mpg at best unless you're strictly doing highway driving. this is with little to no wide open runs. i'd bet you'll find that once you're done tuning (man does that get expensive) you'll find 14mpg daily driven is cake. any improvement at all over a radix is good to me if you can run with them since you are left with alot more room to grow. aside from having to have a very rich a/f ratio at anything above roughly 40% throttle or more, take a look at these numbers...

 

 

[TBSS]

aside from having to have a very rich a/f ratio at anything above roughly 40% throttle or more...

<{POST_SNAPBACK}>

Please share what you mean by 'rich.'

 

How fat do you need to be running above 40% throttle? (and why, if you don't mind elaborating... )

[zippy]

the two important things here that stand out with the milage issue i speak of. before i go into the a/f ratio, look at the power to turn the radix issue. anytime you get into the throttle hard enough to close the bypass valve (which with a smaller pulley happens quickly), you suddenly have to use about 25-50hp to turn the radix (considerably more with small pulleys). hell some people don't even run the a/c to save fuel...

 

on the a/f ratio issue. if you have a truck that makes lets say 6psi (about a base kit). from .7psi to 6psi, you have the same power enrichement setting and the same V.E. setting. in order to get the truck to run say a 11.7:1 a/f ratio you need to have a commanded of around say 10.5:1 or so. you see on a system with a 1 bar map, it doesn't know what boost is and therefore doesn't allow for a different v.e setting for 6psi as .7psi. if you look at the chart below you'll see that the volumetric efficiency increases quite a bit as boost comes on. well, without being able to compensate for that, at 6psi you may have a true a/f of 11.7:1. unfortunatly to do this you need to have an a/f ratio that is around 10's or so at 1-3psi of boost. this really shows up in a truck like your avalanche kevin. with your 4.10 gear, almost any change in throttle gets you into power enrichement. at 2400 (about your highway rpm if i recall), you are spinning the blower fast enough that it will tip into boost under almost any load change. i found in one of the trucks i did that with the 2.8 pulley the blower spun fast enough to cause the bypass valve to shut at 84mph almost every time and around there it was in p.e. almost instantly. this means at anything around 85mph or so crusing speed it just fueled like a pig and could have been driven without knowing down the highway at around a 9:1 a/f ratio or so. this certainly indicated itself in the economy meter. lol at 85 it showed 2mpg with the cruise set.

 

 

 

 

 

 

i will add that doing a 408 as an economizer is just rediculous. doing it for future modifications and the possiblility of gaining milage over a smaller supercharged setup isn't a bad idea. in a light truck the blower rocks. in something that requires almost 30% throttle to run down the highway at 70, it's not so cool.

[TBSS]

Ahh, sooo.....so it's not just RPM's that are killing my mileage with the 4.10's, it's the power enrichment & A/F....

 

All I know is that my mileage really be suckin' right now.

 

Maybe I should go back to the beginning and take your original advice to me, zippy - leave the 3.73's in and get a converter.

[big hack]

Yeah i used to do everything in hotel parking lots.  cam/headers/shiftkit/ well everything except engine swap.  it took me more than 1 full day to pull the engine and tranny.  I pretty much did it by my self.  The install is alot more easier as long as it will start after you are done   oh well got that fixed though

<{POST_SNAPBACK}>

BY MYSELF!!!!!!!! You had a little help. And it wasn't in a parking lot. And a real mechanic got it started.. Right Zippy.

[zippy]

next time you get a chance, log yourself during normal driving and watch it later to see how many times you've went into p.e..

[mwalls54]

Can I ask why you are wanting to go to a 408?

<{POST_SNAPBACK}>

 

i need more hp and tq

<{POST_SNAPBACK}>

 

 

Thats great. I just hoped you didn't decide on the 408 because of gasmilage. With the 6.0 I was getting between 17-20 mpg on the highway going up and down hills (zippy calls them mountains). I dont plan on seeing the mpg to be that high with the 408. I know you say you are on a budget but expect some addional costs that might be unexpected. I had planned on being on a tight budget but that flew out the window. And label every bolt you and who ever helps you takes out. I tried to label all my bolts but ended up missing a few.

[haynss]

i know we are still not talking about mpg and a 408

[zippy]

someone else brought it up so i got in on it. i didn't see you talking about it though. my point is that the radix which has been the big suggestion doesn't get any kind of decent milage in an SS. going naturally asperated of any type has a better chance to. matt's truck with the 6.0L still in it went as fast as many radix trucks and knocked down some very usuable mpg.