General Category > Quadrajet Carb Talk and Tips

E4ME questions and ideas

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Peer81:
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

Cliff Ruggles:
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

Peer81:
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

Cliff Ruggles:
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

Peer81:
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

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