Have been reading up on QJets in the Archives, and have worked a little on them a few years ago. With better heads, intake, headers, and cam (but retaining decent vacuum) is this carb tuneable to match the engine mods? Also, does the available Hypertech upgrade chip (that controls the carb and timing) work with a performance engine? Not real radical - Vortec heads, Comp Cams XE262 hydraulic, headers, GMPP Performer style EGR intake. Need to retain EGR and AIR at least if possible.

Lars - I understand you're the expert on these - any suggestions?
Thanks much!

 

macx, the e-qjet should be able to handle the mods your talking about. despite what some people think: 1) these carbs really don't have that much control over total engine operation (rather they respond to the input of the computer), and 2) already support somewhere in the neighborhood of 750cfm.
the biggest concern you will likely have is the readings to the Ox sensor as they have the most impact on the operation of the engine. this primarily restricts the cam overlap you have. if overlap stays reasonable, like the cam your considering, it should easily fall into the Ox sensor/computer parameters.
the chips don't really do much as far as the carburator is concerned. i think they might have a slightly revised fuel map to cycle the M/C solenoid but primarily they control the timing curve. at this point, you may have a hard time even finding one for these computers but it should just be a generic chip. the new computers need to be recalibrated on several different levels depending on the mods made. i think they just sell one or two chip for our computers regardless of the changes made.

 

Hi,
The Hypertech chip (Thermomaster) is for mildly modified engines. I'd read a lot of bad press on the chips where people hadn't noticed any difference after fitting one. I fitted mine after I'd changed the cam, intake, fitted duals, etc & noticed that it improved low end performance appreciably. So I'm guessing that the advance curve it gives is tailored to non-stock engines?
With all the above mods my E4ME Q-jet seemed fine. Then I fitted headers & an "H" pipe in the exhaust & the more I drive it, the more I think that the mixture is a bit lean. It just feels like it's got a bit more ooomph locked away & the exhaust note sounds a bit flat. I'm currently looking at tweaking my Q-jet & will let you know if I get anywhere. The biggest problem I've got is finding jets, rods, etc where I am. The next biggest problem is that Lars doesn't touch E4ME's :lol: From another post of mine it looks like Headers need an increase in primary jet size (go up 2) on a normal Q-jet, so I think the same will be required on the E4ME. "All" I've got to do is find out what jets are fitted & get hold of some richer ones. Will let you know if I get anywhere with it.
:cheers:

 

oh yes, paul reminded me. although he didn't come right out and say it, another function of the aftermarket chips is to go into closed loop at a lower temperature. if you install a 180* thermostat with the factory chip, it will not normally go into closed loop as i believe the computer has to see a temperature reading of something like 195-205 before it switches to closed loop operation.
i have installed one of those digital air/fuel mixture gauges in my car and you can actually see a difference when it goes to closed loop. it's actually pretty neat, but i use it as a gauge to tell that the computer is actually working correctly.

 

First, really appreciate the thoughtful and informed responses!

It would seem to make sense that the chip would primarily alter timing,
the standard route of richening the primaries a couple steps to
step up to the increased breathing would make sense also.

The only chip(s) I've found are the Hypertech chips for that application.
There's one intended to work with the stock tstat, then one series that will work
either with a 180 or 160 (I think they're different chips within the series).
The info on closed / open loop makes sense in that context as well.

I was also worried about any impact the computer might have on EGR esp and
maybe also AIR systems. Apparently this early computer system is pretty basic and so likely just "works" the timing and the fuel mixture when it gets to specified temp.

Sounds like it's worth a try. I understand Edelbrock can supply jets and metering rods and some other QJet parts. Now we just have to find out what we've already got in there stock, and go to Lars' chart to see what's 2 steps richer for the primaries.

I haven't looked at mine closely yet, but had worked on changing the primary metering rod plunger adjustment on a couple Chev pickups some years ago, although all don't have adjustments for that. That and secondary air valve tip in adjustments. Those alone helped throttle response throughout the range and highway mileage. I'll have to dig out all my old articles and reacquaint myself
with QJet basics.

Thanks again - it'll be a few months (next spring likely) before I get to those
engine mods - first upgrading rear suspension, tires, gears to 3:55, beefed auto OD with 2500 stall, and headers/exhaust. Then the engine gets the treatment.
One step at a time, the "framework" first, then finally the power.

Good luck with yours, and keep me posted on your results.

 

I was reading Doug Roe's book last night & he says that the primary jets can be changed in the E4ME as long as they keep the mixture within the ECU's acceptable range. So, looking good, I just need to find out what primary jets are fitted as stock.
Clutchdust, I saw an A/F meter in the Summit catalogue that hooks into the stock O2 sensor & it's just what I need to take the guesswork out of all this. It's about $35, is that the one you've got & is it accurate enough to use to set the carb up?
macx, The ECU is pretty basic & doesn't do a lot. I don't think you'll have any problems with the AIR & EGR systems. My EGR remnants shared componants with the TCC lockup & I think the ECU allowed lockup when a certain coolant temp was reached.... & that was as far as its decision making went! The other lockup functions were controlled by a pressure sensor in the Th350c & a switch on the brake pedal. What I had left of the EGR system looked like it used the normal controls with very little input from the ECU.
:cheers: