Here is the setup:
5.3 Gen III truck engine
Edelbrock 7118 conversion kit with MSD clone box and RPM dual plane manifold
Stock motor. no cam. no valve spring changes.

Going into a '71 C-10 with a manual shift. Used for work so it sits in rush hour traffic and actually hauls some weight (never overloaded though). I believe a 3.73 rear end.

Here is kinda my thoughts:

1. Just put a Quadrajet on with an adapter plate... They work and are reliable.

2. BG Road Demon 625 with Vac secondaries and electric choke.

3. Just go crazy and get a Holley or Street Demon 750

4. Call up ProSystems or Jet and go with whatever they recommend.

ANY input is greatly appreciated!

 

No advice on the carb, just a heads-up on your #7118. Be aware it can only use pre-programmed timing pills that all have too much timing for the LS-1 motors. The difference between the Edelbrock controller and the MSD are numerous, your 7118's (lack of) programmability being the main issue. Search around here, lot's of info on the differences...

Russ

 

I think you should call prosystems and post back here what they recommend.

A 750 seems to be the carb of choice for a 5.7/6.0 with moderate upgrades. Not sure what would be best for the lower output of the stock 5.3.

I would not mix a spread bore carb with a square bore manifold, if that is what your dual plane is.

 

>all have too much timing for the LS-1 motors.<

I was unaware of that issue. I knew most high HP guys did not like the lack of rev limiter, programming, and nitrous control. Good tip I will just plan on the real MSD kit and buy a Edelbrock RPM manifold seperately. The only other manifolds I am aware of are the single planes Victor and GM Performance Parts.

Also every manifold I have seen is a square bore... No spreadbore that I know of unless running the adapter plates... Which is cheesy and might not work right anyway.

I will post back next week after calling ProSystems for some insight.

Thanks!!!

 

I think the 625 road demon would be a nice match.

 

If you plan on any kind of performance just get a double pumper, those vacuum secondaries belong on tow rigs and motorhomes only. I would recommend a 650/750 double pumper, if you need a choke a holley, if you'd like a lot more tuneability then a proform/quickfuel/etc will do it. I have a 750 proform with 3 miles on it actually because I'll be stepping up to a 950 in the spring if you were interested. Original box, etc. I'd take $75 off the original price from summit and pay shipping. Not to sound like a sales ad, just figured I'd throw it out there before ebay gets it.

 

I think a Holley 650dp would be perfect. Since you have a stick, no need for the vacuum secondaries.

 

Not to start an argument, but I would think hard about mechanical vs. vacuum secondaries. I got this off the Holley website



Plus mechanical secondaries are one more thing to tune. Maybe not a problem depending upon your experience, but it is an added complication.

I have a 750 DP with mechanical secondaries on my 6.0, 440 HP LS2 motor. The idle circuits on the DP are way too rich for my stock cam. The DP I have seems to be meant for a more aggressive cam. Proving to be a learning experience for me anyway.

 

Pop N Wood, I'm guessing you don't know much about carbs. Having an adjustable rear jet in the carb only allows for more precise fueling than a vacuum secondary carb. If the idle circuits are too rich then you can turn in the idle mixture screws or just put a piece of welding wire into the idle circuit in the metering block, etc to lean it out. Chancing idle air bleeds will do the same thing if yours are adjustable like a proform, quick fuel, etc is out of the box. I would recommend going to a local library and taking out a book on holley carb tuning or buy one from borders or the like. It along with a wideband 02 tune will prove to be the best investments you can make.

 

Well I won't argue with you on that one, but I am learning. This site is a big help.

I do have a couple of Holley books. That is where I learned the trick of putting the wire into the idle orifice. Even with that and the idle screws at a half turn, my wideband is showing me rich at idle and dropping lean with light throttle. I have the accel circuits set such that I don't go lean with a big shot of throttle. Once the weather warms up I will try some thicker wire. I am finding it a little hard to check the WOT settings, cause 110 mph comes up too damn fast on this car. I still need to check the idle vacuum to make sure the power valve isn't contributing at idle.

I don't wan't to change out air bleeds, because the Holley books are saying that is a good way to ruin a carb. They also say it is a pretty good indication you have the wrong carb. I am starting to think maybe a bigger cam will make the carb just right

There is a good bit to getting the carb right.

I still think a vac secondary would be a better choice in this application.

 

Vac sec is the way to go for a dd.

 

I have a vacuum secondary carb, its ok but a mechanical secondary isnt really eny less driveable. I actually and getting rid of my 750 holley vac secondary in favor of a Demon 750 mechanical. My secondaries dont open as fast as i think they should no matter which spring i run so i am going with a mechanical setup. My engine is somewhere around 500-550hp.

A 650-750 will be fine for you. Running a vacuum secondary carb in your situation wouldnt be a bad idea though since you have a heavier truck. My 2900lb car wont open the secondaries when i want them to no matter the springs i try.

I've heard nothing but good things about prosystems but they can be pricey. I guess if you dont own a carb already a few hundred extra wont really matter.

Also buy the MSD 6010 box as mentioned, not the edelbrock box so you can tune it. I think the RPM manifold is a good choice for your setup.

 

With a stick EVERY time he lets off the gas to change gears that secondary is going to take a while to open back up. Which will slow the car down considerably.

 

Changing gears with a 3 on the tree will slow everything down between shifts Really it is only out of uniqueness that I keep it in the truck.

WOW a lot of great advice to chew on here guys! Also you all are laying down some serious HP in LS motors. For me 300HP would be more than enough in a plain ol' truck. Also the efficiency in these motors should aid in some better gas mileage to boot.

I have to say though the Demon 625 with electric choke and vacuum secondaries is looking pretty strong. Again for a heavy DD I don't see a way around it.

I will keep you all posted on the info from ProSystems. Others have claimed that they make a mean LSx tune.

 

you will be very happy with this.



I've been through 3 carbs....my truck (81 c10) has a carbed 5.3 with a GM HOTCAM and GMPP intake

1. holley 650 d/pumper... truck ran great up top but WAY TOO rich at idle. Drivability average.
2. holley 750 vacuum sec.... not impressed... average drivability, average WOT performance
3. summit 600cfm vaccum sec. This is on my truck now... i love it. Drivability is EXCELLENT and WOT performance is just a hair less than the 650 dp.


FWIW, if i ever get the truck to the track... the 650dp will go back on....but for everyday cruising... 600 vac secondary all the way.


YRMV

 

sounds like you didn't spend the time to tune the double pumper properly. This would be the best performer overall and make more HP up top than either vacuum secondary carb.

 

Sometimes on a carb with a 4 corner idle setup smaller less radical motors dont like to idle well. There is an easy solution to the problem. Srew the rears all the way in and use the front only. Problem solved. My 700dp is only 2 corner idle and worked well on my 5.3 despite the ls6 cam. Accel pump tuning is what took the longest. Then I took it all apart cause I got a wiched deal on a lq9 go figure.

 

... i doubt it would out perform the 750 up top......

also it certainly is not the best overall performer.... if it was-- it would still be on the truck.

the only tuning done was on the idle circuit.. which was way too rich no matter what was done...

one can tune the thing all day long and eventually--i suppose--you will get close to acceptable "around town performance" with the d/p.... problem is the main jets are just too big in stock form for what is actually a relatively mild 5.3...

if i could knock 1000 lbs off my truck and switch to a ~3200 stall the d/p would be my carb choice no doubt.

 

I am having the exact same issue with my LS2 crate motor. Except my car is 2500# with 3.7 rear gears and a manual.

Car runs like a tourist in Mexico when it gets above 2000 RPM, but I am having a time adjusting the idle and off idle. I have tried 3 different sized pieces of wire in the idle jets, still don't have it right. Car doesn't run bad, especially when warmed up, but the wideband says it is not perfect. I will try shutting off the secondary idles next. Worth a try.

I am starting to think a milder carb would be a better choice for this street machine. Just save the 750 DP for when I upgrade the cam.

 

What have you done to the accel pump circut? Also what fuel pressure?