General Category > Quadrajet Carb Talk and Tips

E4ME questions and ideas

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Cliff Ruggles:
Peter, that cam is really "small" for the cid and static compression ratio.  It should make plenty of vacuum and be computer friendly.  With only 256/262 degrees of off seat valve timing, and a 110LSA, it isn't going to make a lot of power in the upper rpm range, even with better flowing heads.  Still a decent choice for the application, being both user and ECM friendly.

As mentioned above, the only real function of the ECM is part throttle A/F, so anything done to improve the A/F ratio in that area will help with efficiency, which translates into smooth for normal driving and less fuel consumption.

The idle and full throttle systems are pretty much the same as the older q-jets.  This lets us install slightly larger cams and still bring in enough idle fuel and bypass air to keep the vacuum high enough to make the computer happy.  At WOT we can quickly change the total A/F ratio by using different secondary metering rods, and hanger height.

I'm not sure what cylinder head castings they used in 1981 on those engines.  The very best SBC factory castings (large chamber) were produced until 1973-74, castings 441, 487, 993, 336.  There are a few others but they are not as common.  The 041 and 186 castings were excellent small chamber offerings.  I didn't list the earlier casting numbers due to lacking the accessory bolt holes.

* Just a side note here, as good as some of the factory castings were, they are "thin" in comparison to most aftermarket offerings, and woln't flow nearly as well.  Most have 165/65cc runners.  The aftermarket has stepped up so well with aftermarket offerings, with low pricing, that it makes little sense these days to use old worn out factory castings, most of which are cracked someplace.  GM also offers "Vortec" heads, very reasonable.  However, we don't consider them a big bargain, as they are relatively "thin", and could use some upgrading to the studs, springs, retainers and valves.  By the time you get them up to par, a set of Iron Eagle or World Products heads could have been had for about the same money.

In 1974 the 882 castings came out, and a couple other really poor flowing designs.  They ran these heads on nearly every 350 and 400 that came down the assembly line to at least 1979, maybe even into the 1980's.  They are very restictive, and prompted cam manufactures to start pushing dual pattern camshafts with more exhaust than intake duration, and tighter LSA's (Lobe Separation Angles). 

I've never to date been overly impressed with any of those camshafts when used with good flowing cylinder heads.  All one has to do is to get some good cylinder heads, locate an "obsolete" 327/350 hp camshaft (224/224/114), and the power improvement will be amazing.  Yes, even the vast majority of the GM "high performance" grinds are on wide LSA's, and the run high static compression ratios with them as well.

Despite how well the factory parts work, aftermarket companies still push the tight LSA stuff with less seat timing, faster ramps and more advertised duration.  They advertise improved idle, improved throttle response, stronger mid-range and more top end power, even though their cams will have 20-30 degrees LESS off seat valve movements and quite a bit LESS overlap.  Makes one wonder how we can do "more with less"??

My testing doesn't show this to be true, as we've installed and tested a few aftermarket "high" performance flat cams with the "modern" lobe designs, and LOST power every single time just about everyplace!

Anyhow, I'll get back to carb stuff, as that's what this Forum is about.........Cliff

Peer81:
Hello Cliff,

Thanks again for this big wave with information!  :o :)
Compart to the states our gasprices are off the scale. So mile per gallon are more important for me then a 400hp engine that is a fuel guzzler. Besides that the 81 vette has a alu diff which isn't the strongest around so if I get 300hp along the way that is just fine for me.
I looked up the casting number for my heads and they are 462624. If I remember correctly they're the worst heads around. But if I can get my carb to function perfectly then I'm a happy person.
I also found a website with the original Thexton tools to set a CC q-jet so lets hope with a little more money I can order the rebuild kit and the rest :)

Greetings Peter

Cliff Ruggles:
Peter, 624 castings are OK as far as flow characteristics, still not nearly as good as any of the castings referenced above, but better than the 882 castings which are more common after 1973.

The only bad news with them is that every single set I've ever had in the shop here were cracked at the exhaust seats on the two center siamesed exhaust ports, no exceptions. 

We will NOT use them for this reason......Cliff

Peer81:
You got me thinking Cliff  ;D

I did some calculations on static and dynamic compression. Downloaded a desktop dyno to see what happens when I change a head or cam. Very interesting to see.
But as you said Iron Eagle heads are a good deal. I think I would go for the platinum versions with 180cc runners. Bumping the static up to around 10:1 and dynamic to 8:1 (depending on the cam choice)
A 2.5" true dual with x-pipe and high flow mufflers with block hugger manifolds. And a XE262 (262/270, 218/224, 447/462, 110) or XE268 cam, with the E4ME and stock alu intake manifold. But lets begin with rebuilding the carb :)

Groeten Peter

Cliff Ruggles:
Since fuel economy is a very important part of the goals for the vehicle, raising the static compression ratio will improve power and efficiency. 

The higher static compression ratio and improved combustion chambers will have the engine require less timing for best power production.  I would also like to see the block zero decked, and a quench distance established as close to .035" as possible/practical.

With the higher SCR, forget the "small" XE cams on "tight" LSA's (Lobe Separation Angles).  Follow the factories lead and look at cams on wider LSA's, with greater advertised numbers.  Those "modern" cam profiles became popular when compression ratios when in the toilette and GM started producing cylinder heads with piss-poor flow characteristics.

The better the heads and higher the compression ratio, the bigger the cam, wider the LSA, and tighter the lobe spread, just a general rule of thumb to follow.  Hope this helps some?.......Cliff

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