Starfox07

I've already ordered my intake manifold after unsuccessfully searching for a used unit. $150 isn't that much. Going with the weber 48 DCOE setup.

Anyways, aside from the carb, I figure I need to solve these issues/buy these parts:

-Fuel pump
-Throttle cable setup (no idea how this is handled really, just know it needs to be)
-Choke (?)
-Assorted gaskets (also removing aux ports, so taking off the entire intake manifold
-anything else?

For those who have converted an SE to carb, did you have any issues with efi/smog related vacuum systems? I believe most of that stuff is connected to the UIM and will just leave the car with that. General advice would be appreciated. Full write up is not necessary as I will not get the carb for another 2 months, but I'm just trying to get things in line to do so. I'm going to keep all the EFI wiring and such in place in case I should wish to convert back in the future

Sgt.Stinkfist

iTrader: (6)

You will need a good bypassing fuel pressure regulator. With a proper regulator you can retain your original efi fuel pump, no need to buy another pump

How much u want for your injectors?

Starfox07

Sorry, not selling any of my EFI stuff.

Also, I've heard using a FPR is not a good idea. :shrug:

Rogue_Wulff

I've got a carbed SE. EFI/emissions wiring harness, stashed in the storage bin. ECU, never seen it. Vacuum lines? Brake booster and vacuum advances. Fuel pump, some cheapo 6-7 PSI unit, no FPR needed.
It uses an RB holley intake and edelbrock 1405 (600 CFM) 4bbl, RB header, and the DIY direct fire ignition system (3 GM HEI & 3 MSD Blaster coils) firing FC plugs.
Super simple, super reliable, and massive throttle response from idle to redline (and beyond).

For the setup you are going to, your best bet for a throttle cable will be sourcing one for a 12A. They are longer than the FI cable used on the SE and NA FC. Just need to make sure the weber is setup for the proper type cable.

The weber 2 bbl will likely be less than optimal below about 3500 RPM, due to the aux ports being open, but after that RPM it should run like a raped ape. That's the one place a 4 bbl has an advantage, since the aux ports don't come into play until the secondaries open.

Are you buying an injector block-off kit, or just leaving the injectors and fuel rail in place to plug the holes?
Header or stock exhaust manifold? You really need a header to get the most out of this conversion.
A quick pic of my setup:


You can see the homemade throttle cable bracket near the oil filter. That is as far as the stock SE cable reaches. Hence, the recommendation for sourcing a 12A cable..... Also, the vacuum advances were not hooked up when this pic was taken by the PO.

Starfox07

Well the throttle plate should actually be in near the same location as the stock throttle body as it is a side draft.

I had not thought about the injector bungs. I don't want to leave them in there, because it looks messy. I'll see what's available.

The car already has full exhaust. Racing beat collected header with 2 mufflers. Sounds nice.

What did you do for the brake booster and vacuum advance?

The low RPM throttle response problem doesn't bother me too much as the car isn't a daily driver.

Sgt.Stinkfist

iTrader: (6)

That fuel setup may be fine for a Holley, but put 6-7psi unregulated to a Weber and she will be flooded over and the needle/seat will get worn/damaged quickly. Webers don't wanna see more than 3-3.5psi

I want to meet the person who says using fuel pressure regulators are a bad idea

Rogue_Wulff

Sidedraft, throttle cable might be ok.
As for the brake booster and vacuum advances, the RB intake has a booster port already drilled tapped, and the edelbrock carb has a "ported" vacuum port right on the front.
If you're retaining the lower intake, the stock booster port should remain. I think you're just outta luck for the vac advance though. Few side draft carbs have a provision for vac advance, as they are more thought of as a race-oriented part.

Sgt.Stinkfist makes a good point about the FPR. Weber's aren't fond of more than 3.5-4 PSI, much like an edelbrock doesn't like more than 5.5 PSI. My cheapo fuel pump puts out about 6-6.5 PSI for the first couple minutes, then it starts to drop. I have seen the PSI guage read as low as 2 PSI during extended idle periods. I can deal with the minor loading up during engine warmup, once it's warm, the PSI drops to to 5-5.5, and it's fine.

I'd recommend going with something like a carter pump that outputs 6-7 PSI and using a return style regulator to hold a solid 2.5-3 PSI. Just don't go with the cheapo mr gasket dial type regulator. They may hold a decent PSI, but tend to be a bit restrictive when the flow is at it's peak.
The stock pump will certainly provide plenty of flow, but the PSI will be a bit more than most FPR's can really cope with over the long term......

Starfox07

I think I'm going to call racing beat tomorrow and ask them. They generally have pretty good advice.

craaaazzy

iTrader: (9)

subscribing to keep an eye on this.

question though, u guys have stock ports?

PercentSevenC

The Mr. Gasket style regulators also have a tendency to cause fires. Stay away from them.

If it were me, I'd grab a return style FPR like a Mallory 4309 or Aeromotive 13301 and use the stock fuel pump. You should have no problem regulating it to 3.5-4 PSI. My Mallory FPR can regulate my MSD EFI pump down to 1 PSI, and your return line should flow better than mine since you have a GSL-SE tank.

Rogue_Wulff

Good points. The Mallory or Aeromotive FPR's are a bit pricey, but worth the cost, and they should have no problem handling the SE pump.


As for the porting question, yes my engine is a stock 6 port with over 200K miles on it. The last 100K or so have been with the holley type setup running premix only.
At last month's RallyCross Nationals, power was not an issue. Suspension, on the other hand was.

Starfox07

Mine is a stock port as well..for now

PercentSevenC

To answer your other questions, you'll probably just have to make your own throttle cable bracket. It's not hard, though.

Not sure what you're asking about the choke. If your carb is a DCOE, it'll have a rather useless cold-start enrichment circuit. I wouldn't even bother trying to hook it up, most people don't.

For vacuum advance: since you don't have a ported vacuum source, just hook it up to a manifold vacuum source. You'll have more advance at idle, but it doesn't really matter.

j9fd3s

iTrader: (3)

just to add my thoughts

1. i'd run the mallory regulator too. i've done the holley twice, and it was a mistake both times! it doesn't fit anywhere very well, and its not bypass!

2. the throttle cable and bracket are interesting. RB sells some, but i think its for a holley carb? peepers is using a slightly modded toyota 22R bracket, it was lying around and fit really well. the 12A cable is longer than the 13B cable, and i think there is a competition one too.

3. if you can use the EFI fuel pump that would be ideal, its in the car and it fits, not like that POS carter we all use. plus the EFI pump flows a TON of fuel.

4. forget the choke you don't need it. even the P port idles on it own without the choke after 30 seconds...

5. timing. i would leave the vacuum advances disconnected initially. you will want to hook em up, but after the fuel is tuned. the factory has the vaccum advances off at idle, but running timing @TDC instead of -5 is totally fine.

6. uselessly, the GSL-SE (and i think S4) intake length is 500mm.

Starfox07

The nice thing about the side-draft intake setup is that it retains a similar geometry to the factory EFI manifold, so the powerband should stay roughly similar. AKA a strong mid-range and top end.

Sgt.Stinkfist

iTrader: (6)

back when i was running a weber clone carb on my 12A, i was slowly building to a turbo blowthru set up and in turn needed a fatty fuel pump so i was running an inline walbro 255 EFI pump and used an Aeromotive A1000 carb regulator....long story short, the A1000 carb regulator is designed specifically for EFI cars converted back to carb, and i turn is designed to regualte an EFI pump down to acceptable levels. i was able to regulate a walbro 255 to less than 2psi. i think from experience, an A1000 regualtor would be a good option to go with

as for vac. advance, just run without it, using only the built in centrifugal advance. when i started runninf my weber clone, the vendor i bought it from advised me to do so


just outta curiosity, why are you going to convert to carb? is something not operating properly/running like crap?

Starfox07

Its running "ok" but I just can't see the EFI system making any more power. It's just far too restrictive. I would probably due an aftermarket EFI system, but I cannot afford to for a few years. I figure I can do the carb setup for about 1/4 the price of a standalone, and it will make nearly as much power.

PercentSevenC

Sure, you can do this. Enjoy your decreased gas mileage and cruise drivability with no real benefit.

I wish I could run vacuum advance with my FB's setup. If I were planning on keeping my carb, I'd look for a 12AT dizzy.

Starfox07

I have a vague idea, but can someone explain to me more in depth what the vacuum advance does? I know obviously it advances the timing, but how does it do it, under what conditions, and for what purpose?

PercentSevenC

It's pretty simple. As vacuum increases, the timing is advanced. This improves the engine's ability to burn lean mixtures and efficiency and power at low load. At WOT (zero vacuum), the effect goes away. I can't understand why anyone would not want it. It's only one extra vacuum line.

Look at any EFI spark map and you'll see it do the same thing.

Edit: Here you go. A stock TII ignition map.



Notice how the advance increases as load decreases, and increases as RPM rises. We do the same thing using a combination of vacuum and centrifugal advance mechanisms.

Starfox07

Now this is already on top of the built in mechanical advance?

Is there any reason I can't do a 'T' from the brake booster vacuum port on the carb and plumb the vacuum ignition advance into that?

PercentSevenC

Yep, the vacuum and centrifugal advance are separate mechanisms and work independently.

Nope, no reason that wouldn't work.

Starfox07

Seems like the easiest solution...no?

Rogue_Wulff

One issue though. The vacuum advance is designed to work exactly the opposite of how the manifold vacuum works. Manifold vacuum (like the booster port) is highest when the throttle is completely closed, and drops as the throttle opens. Hooking vacuum advance to this would actually make it become a vacuum retard....... Step on the throttle, and the timing retards.

The advance function is designed to work from "Venturi vacuum", sometimes refered to as "ported". The vacuum is created by placing a port just above the throttle plates, so that as the throttle is opened and air rushes past, it pulls a vacuum. The faster the air rushes past this port, the higher the vacuum "signal", so the more the timing is advanced.

pinoyremix

I have a dellorto 48 dhla on my 12a and I did a full gslse fuel setup swap...the tank lines and fuel pump...my dell only likes 3 psi, i was able to get it down to that using the mallory fpr