Author Topic: E4ME questions and ideas  (Read 9637 times)

Offline Peer81

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E4ME questions and ideas
« on: January 27, 2009, 01:48:23 PM »
Hello everybody,

I'm Peter from the Netherlands and bussy with a body off Corvette from 1981. This Corvette is the first and only year with a E4ME Q-jet.
Of course i read Cliff's book on Rochester Q-jets and I have a few questions.
I'm trying to get the best out of this carb but in the book I get the feeling there could be more to this.
Is there some other info to tweak this carb that isn't in the book?

I'm (or was) bussy with the idea to change the ecm and prom. The 81 is the first car with a ecm and also the lowest ecm. There aren't any (exept a hypertech) other prom's to change the original with. So i tought change the entire ecm and get a newer one with a newer prom. The '87 camaro and '88 monte carlo were the last cars to have the E4ME carb and hopefully a faster ecm with a different prom. I already have the ecm and the prom and I also know what to change in the wiring harness. What do you think of this idea? I think speeding up the "refresh rating" of the ecm/prom will also improve the accuracy of the carb.

Greetings Peter

Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #1 on: January 28, 2009, 04:06:18 AM »
Peter, the only output the ECM has for the carburetor is to control the part throttle A/F ratio.  It sends a signal to the Mixture Control Solenoid to provide fine metering control when cruising.

The idle and full throttle A/F is still non ECM controlled, aside from the amount of fuel that goes by the primary jets and metering rods at full throttle.

Any ECM upgrades, would make the most power by improving or providing control to the spark curve.

The good news is that those carburetors are still very good for high performance use.  We have set up quite a few of them for the later Monte Carlo SS's, some of those guys still use the ECM and run those cars deep into the 12's, with a few into the 11's and still get over 20mpg's for "normal" driving.

Those later carburetos can also be set up to run straight off the jets and all the electronic stuff removed, for serious high performance work.  They don't look as "clean" as the earlier units, but work equally as well once correctly set-up......Cliff

Offline Peer81

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Re: E4ME questions and ideas
« Reply #2 on: January 28, 2009, 01:56:40 PM »
Hello Cliff,

Thank you for your reply. And my compliment on your book, its a very good and easy to follow read!

Are there also differences or improvements within the E4ME line (later models better then the early ones)? I'm almost certain I have the Monte Carlo SS ecm, but my ebay search for a wiring harness isn't so easy as i thought  :-\

I'm a little in doubt to rebuild it myself or let you guys do it. I've rebuild the entire car from cratch and with the original service manual and your book I think it shouldn't be a very big problem.
My Corvette isn't primairly build for speed but is more a nice cruiser but it would be very nice to get it under the 6 sec from 0 to 60mph.  ;D
Something about the engine. Original 350ci. Original aircleaner with dual snorkel, original alu intake. Hypertech pistons around 9:1 compression, Mild comp. cam, still the original heads but could be changed to iron eagles in the future. Original shortstyle headers and a 2.5" true dual exhaust with x pipe. All the emissions stuff is still in place but only for show (airpomp is empty for example). Behind all that a 700R4 (4L60).

If you could give me an idea about a rebuild and the price, please send me a pm.  And please the price for a E4ME rebuild kit with a throttle shaft bushing kit.  :)

If somebody has some other ideas or thoughts please don't hesitate.

Greetings Peter

Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #3 on: January 29, 2009, 05:19:57 AM »
The electronic q-jets are pretty much the same thru the years of production.  They are excellent high performance units, no need to dump one for a older model provided the cam chosen for the build produces enough vacuum to keep the computer happy.

Raising the compression helps with those engines, as does installing better flowing heads.  Cam choice is critical, and must be well chosen to produce good vacuum at low rpm's.  Avoid "tight" LSA grinds, common to the aftermarket.  We use and recomend hydraulic roller cams for engines built here, and there are some excellent choices for the small block Chevy engines.

Also keep in mind, that when you install flat top/high compressio pistons, or smaller chamber heads, the thick head gaskets found in most kits will lower the compression almost half a point compared to the factory style .020" steel shim gaskets.  The thick gaskets also increase the quench distance, which has negative effects on power production, engine efficiency, etc. 

Most SBC engines have the pistons about .015 to .020" below the deck at TDC.  If the engine is not zero decked during rebuilding, installing a stock replacment gasket (usually .039 to .050" thick, makes the quench distance as high as .070".  This leaves a lot of power on the table, and increases the octane requirements of the engine, despite lowering the SCR some, and in some cases makes them run much hotter than normal.

We zero deck all engines prepared here, and shoot for .035-.040 quench distance.  We have had exellent success with 350 SBC's such as yours, using World Products Sportsman heads with 64cc chambers, GM's HOT hydraulic roller camshaft, zero decking the block and using the Felpro .039" head gasket.   This combination makes 400-420hp, smooth idle, and strong power to at least 6000rpm's!  Best of all they are pump gas friendly, even with a relatively high compression ratio......Cliff

Offline Peer81

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Re: E4ME questions and ideas
« Reply #4 on: January 29, 2009, 02:22:01 PM »
Hello Chris,

Thanks for all the information! My engine has the Comp Cam X256H (256/262, 212/218, 447/462, 110)
I kept in mind that the cam should be ECM friendly to create enough vacuum, not a very wild cam but good enough for me. The smog heads on my 81 are the worst heads ever so in the future they will be changed, that would also be the time to figure out the quench distance.

In your book you show a couple of things I could do to improve the functioning of me Q-Jet. (Throttle plates at 90 degrees, notching the sec flaps etc etc.) I already checked my choke pull off and the release time is 3 sec so that is fine. But besides all the info in the book, are there some other (easy) things to improve my carb (DIY). Also the service manual says to connect a dwell meter and try to get it as close to 30 degrees as possible on the 6 cil scale. Do you agree with this or not?
Btw. my Q-Jet has all the plugs removed I even can reach the TPS adjusting screw.

Greetings Peter


Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #5 on: January 31, 2009, 08:26:08 AM »
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
« Last Edit: January 31, 2009, 08:34:09 AM by Cliff Ruggles »

Offline Peer81

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Re: E4ME questions and ideas
« Reply #6 on: February 01, 2009, 01:26:06 PM »
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

Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #7 on: February 03, 2009, 06:16:41 AM »
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

Offline Peer81

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Re: E4ME questions and ideas
« Reply #8 on: February 19, 2009, 01:33:03 PM »
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

Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #9 on: February 22, 2009, 04:16:16 AM »
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

Offline Peer81

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Re: E4ME questions and ideas
« Reply #10 on: February 22, 2009, 02:21:49 PM »
Thanks again Cliff,

Great to have somebody that gives good advice, this makes more sense to me then the bigger is better I hear everywhere. :) But first I need to read some books on the subject and of course rebuild my carb. :)

Groeten Peter

Offline Cliff Ruggles

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Re: E4ME questions and ideas
« Reply #11 on: February 23, 2009, 04:25:15 AM »
You are welcome.   We consider the carburetor a very important part of the total combination.  One still needs to have well chosen parts for the combination to be successful in the first place.

We get calls in here daily from folks with troubled engines, poor fuel economy, poor power production, etc.  Many simply have very poorly chosen parts, compression too high or too low, cam too small or too big, etc.

With the Small Block Chevy engines, poor flowing heads with big combustion chambers, adding a thick head gasket from a rebuild kit, and some big aftermarket cam is a very common problem call we get here.

Unfortunately, without good flowing heads and a decent static compression ratio, the cam choice, carburetor mods, etc, are NOT going to help the problem.  It's just difficult to get air in and out of an engine, and make good power when the compression ratio is low AND the heads flow poorly.

The good news is that the aftermarket has stepped up with dozens of cylinder heads that are excellent, and many are very reasonable in price.

The cylinder heads should be the first item on the list for upgrades to any engine project.  If the heads woln't flow well, and don't make much compression, no other parts you buy are really going to provide a good end result for the project......Cliff