Crate engine swap advise please?

[MadOgre]

The Qjet uses vacuum operated secondaryies. What this means is that the secondaries are opened by the manifold vacuum of the engine. This means that the engine is only fed as much fuel as it will suck by vacuum.

The Edelbrock does not it has mechanical secondaries which means that regardless of the engine vacuum a predetermined amount of fuel is pumped into the engine.

The Qjet has small primaries that help give real good throttle response as well as very good fuel economy.

The Edelbrock has all 4 throttle bores the same size.

Because the Qjet has small primaries and the secondaries are vacuum operated you never over fuel your engine which means that your Air/Fuel mixture will stay tuned through out the whole RPM range and provide the best fuel economy possible aside from EFI, where as the Edelbrock does not stay tuned through out the RPM range causing all kinds of quirky manners, poor perfomance and horrible fuel economy.

The Holley Street demon uses the same small primary bores and vacuum operated secondaries. But incorporates some design features from the Eddy carb that makes changing rods and jets a whole lot easier then a Qjet.

The Qjet comes in 750, 800 CFM as well as Edelbrock manufactured brand new Qjets for a while and these could be had in 850 CFM.

A 350 only uses something like 575 CFM at WOT

The holley Street Demon comes in 625 and 750. The 625 is what a 350 uses.

 

[MadOgre]

OK. Your talking like what I thought I wanted to do, but with the specifics I needed. Thanks.

If I give this to my son someday will it handle a little Nitrous. The kids into that. Would it change the cam needed?

My thoughts after listening to you guys are to grab the cam mentioned 12-300-4. I see it at Summit. I see kits.

What's the difference between it and the 12-300-2? I don't see it. I just put a double roller chain and sprocket set in, so I see they have three size kits.

What if I just get the cam a lifter (small) kit?

What if I just swap the heads now? Then I don't need the springs in the bigger kit right?

If I can get this figured out I order the cam today. I need some 2 deg. axle wedges for the pinion angle anyway and with the cam the shipping will be free.

What head options are there for this build? $$$ Dart, or built Vortec? I'd like to get one set and be done with them. It would be nice if what ever they are the would swap nicely onto the next block someday. Maybe a Gen 1 short block with mechanical fuel pump and roller cam previsions.

Are there other budget minded heads that are any good? I see Edlebrock heads on the shelf at the Irish.

This pro comp RV cam will work fine with your stock heads. Don't buy preassembled heads except maybe from GM. They will put cheap valves and springs in them and you will have problems. This is why I suggested doing the heads as a later upgrade.

The 12-300-4 is pretty much stock for valve lift. This means the whole cam assembly should last as long as a stock cam would. The 12-300-2 has a little more lift for a little more power. but runs the risk of wearing out faster and definitely needs the upgraded springs.

 

[MadOgre]

I think I would save any nitrous for the roller cammed engine

 

[MadOgre]

FYI you don't need angle shims on the front or the back.

 

[MikeB]

The Qjet uses vacuum operated secondaryies. What this means is that the secondaries are opened by the manifold vacuum of the engine. This means that the engine is only fed as much fuel as it will suck by vacuum.

The Edelbrock does not it has mechanical secondaries which means that regardless of the engine vacuum a predetermined amount of fuel is pumped into the engine.

Not picking on you (really), but the Edelbrock Performer series carbs use air valve secondaries. You're right in saying the secondary throttle plates are opened mechanically, but the air valves above them stay closed until engine "demand" is enough to overcome the counterweights. Then again, maybe EFI is the future.

From the manual: "Air flow through the Secondary side is controlled by Air Valves. These valves are located in the secondary bores above the throttle blades. They are balanced against a counter weight and open to admit additional air flow only if there is enough air velocity to allow the proper operation of the Secondary Metering Systems."

On another note, I'm really surprised the aftermarket hasn't developed a carb with small primaries and larger secondaries to mimic the Q-jet. Holley makes a couple Q-jet replacements, but as I recall, one is emissions-oriented and the other has mechanical secondaries. And both cost nearly $500. If GM, through their Performance Parts arm, started reproducing a couple Rochester Q-jet models, I doubt they could keep them in stock!

 

[Old77]

I personally don't see crate motors being a economically viable option unless.

You forgot several other reasons why a person would choose a crate engine.

--if your truck came with a tired/worn out 305 that isn't worth rebuilding a crate motor makes sense because by the time you find a good candidate for rebuild, gather parts and then put in the time to freshen it up it costs the same as a crate but you've spent a lot more time going through the rebuild

--if someone's truck came with a 350 but the block has a crack in it or some other issue that renders it useless then see above for why it makes sense.


There's at least a dozen more reasons why crate motors make sense but I don't feel like typing all that out especially since it sounds like the OP is leaning against that direction now anyway so it doesn't really matter lol

 

[MadOgre]

There's at least a dozen more reasons why crate motors make sense but I don't feel like typing all that out especially since it sounds like the OP is leaning against that direction now anyway so it doesn't really matter lol

Oh, do tell!

 

[MadOgre]

Not picking on you (really), but the Edelbrock Performer series carbs use air valve secondaries. You're right in saying the secondary throttle plates are opened mechanically, but the air valves above them stay closed until engine "demand" is enough to overcome the counterweights. Then again, maybe EFI is the future.

From the manual: "Air flow through the Secondary side is controlled by Air Valves. These valves are located in the secondary bores above the throttle blades. They are balanced against a counter weight and open to admit additional air flow only if there is enough air velocity to allow the proper operation of the Secondary Metering Systems."

On another note, I'm really surprised the aftermarket hasn't developed a carb with small primaries and larger secondaries to mimic the Q-jet. Holley makes a couple Q-jet replacements, but as I recall, one is emissions-oriented and the other has mechanical secondaries. And both cost nearly $500. If GM, through their Performance Parts arm, started reproducing a couple Rochester Q-jet models, I doubt they could keep them in stock!

You may be right and I am just remembering it incorrectly. The old noggin seems to be failing me lately. Aghh maybe just the fact that I consume enough pain killers each day to sedate a full grown Elephant. Not even kidding I am gonna have to put a little more thought into this Edelbrock carb if that is truly the case.

 

[MadOgre]

Ha Re read my 1806 manual lol you are right! Don't know how I got that turned around in my memory lol Oh well. I was looking at my calibration kit too. and its not making sense with which ones I have in my box and which ones I should have in my box! So Im gonna pull that 1806 apart this week and see if I stuck the wrong jets in or something.

Thanks for the correction Mike You may have just fixed my problem if I have the wrong jets in there!

 

[MadOgre]

'73 C10 Cheyenne Short Fleet, 2" front spring drop/5" axle flip drop w/ Caltracs traction bars, 1973 350ci base timing is 12* BTDC, HEI w/ 10* Vac. Adv. and 20* centr. blu/ylw springs, Vac. Adv. on carb mani. port, Eldelbrock 1406 98 primary (stock) 95 secondary (stock), 6557 rods, 8" springs), Holly Contender, Cam, '74 882 heads 76cc 1.94/1.5, 1.5" OD header 2-7/8" collector, 142-148psi dry comp., dual exhaust (no crossover), th400 w/ shift kit, 12 bolt Eaton posi, 3.73 gears, 28" tires.

What tuning combos have you tried?

Those 8" springs are probably some of the problem. You should be using the 5,4 or 3" springs. If you have a lopey cam you will have less vacuum at idle which requires lees spring tension. Rich was using an RV cam which pulls really strong vacuum at idle so he would have used a stronger spring. I don't know why he wanted you to run a stronger spring.

The rods I would go with would be 070x037 with a 098 jet and 101 or 104 secondaries and either a 4" yellow or a 3" blue step up spring.

 

[MadOgre]

No. I'm just sick of it running like crap. And it's weak. I would guess it's under 200hp. I doubt it will spin the tires now that I put posi in it. That's good and bad.

A couple of you guys stuck with me through this (it should explain why I don't like my engine):

http://www.gmsquarebody.com/forum/showthread.php?t=11085

But I never got the issue to go away. I thought Rich had me going in a good direction, but after a while, I think I was just masking the problem. I ended up smelling rich, and I had the timing as advanced as I could get it without pinging and it wouldn't start well. I tried everything that was suggested I think, and I'm grateful for the help. It just didn't solve anything, so I set everything back to stock and gave up on fixing anything.

I thought in the end, maybe I had a soft exhaust spring, or a bad lobe on the cam. But just guesses. But if I bought vortec heads, a cam, intake, and carb, I would be spending a lot of money and maybe not even fix the problem or be better off spending the money on something with greater potential. I would like to buy one thing that make it run smooth and be done.

When I ask about changing a few things, guys say just upgrade with a crate. Not here, but on the street. Now that I'm asking about a crate, guys are saying just fix what I have. And I will, but I don't have much money to be just throwing parts at it. I know an intelligent person would test and measure to diagnose properly, but I'm dumb and poor. I can't afford to pay someone to recheck everything I already did.

I'm just frustrated because I like working on stuff but not when I'm getting no where.

If you guys stick with me and can put up with my occasional somewhat dumb reactions, I'd like to get my current motor pumped up. I just don't know where the point of diminishing returns is. Like the 2 bolt main.

Ahh OK so just read through that thread and just wondering where you got with everything.

Im thinking you just really need to get it set up properly from timing to good ignition to properly tuned carb, and then see where your at.

For starters do you have a Fuel regulator hooked up?

Did you set the floats to Edelbrock's specs?

Did you recurve the distributor? If so with what?

Good plugs?

Good wires?

New cap and rotor?

What is your timing at idle with the timing light? and @ 3000 RPM ?

 

[MikeB]

You may be right and I am just remembering it incorrectly.

As far as I know, all the original AFB carbs, as well as Edelbrock semi-copies of AFB carbs, used air valve secondaries. The latest 1800-series Edelbrock carbs have an adjustable air valve which can be tweaked to open with more or less engine "demand".

Sorry to hear about the pain killers.

 

[Joe383]

I think MadOrge has best advice for ya. I would get motor you have tuned proper. If you don't already have one I would get a vacuum gage. It will help with tuning. I would get one you can mount some were you can read it while in the truck while you drive. Use the vacuum gage for timing and your idle mixture setting. Play with different timing settings and make notes of the vacuum readings. You have to do all of your tests the same, same road, same speed. If you get a tune up kit for the carb you can do the same with it. Change step up springs, test, change metering rods, test. And for your full throttle jetting on the sec side you do it with a stop watch. What ever gives you the fastest 0-60 is how you pic your jetting. Also for idle and cruse you can look at the plugs and make sure there tan. Your edelbrock also is designed for 6PSI of fuel pressure so pressure more or less can effect float level. If these do not yield the power your after then do a compression check and if all cylinders are good pressure I say do a cam swap and see were your at.

 

[MadOgre]

As far as I know, all the original AFB carbs, as well as Edelbrock semi-copies of AFB carbs, used air valve secondaries. The latest 1800-series Edelbrock carbs have an adjustable air valve which can be tweaked to open with more or less engine "demand".

Sorry to hear about the pain killers.

Ya Thanks Mike. Sorry for being a jerk too. The pain meds mess me up pretty good. But I can hardly even move with out them!

Lol I don't know how I got that thought turned around backwards lol

And after looking at my tuning box it seems I currently have the wrong jet and rod combo in my 1806 so Im hoping changing that will make it run a lot better. Maybe my opinion of these Edelbrock Carbs will change lol

 

[MadOgre]

I think MadOrge has best advice for ya. I would get motor you have tuned proper. If you don't already have one I would get a vacuum gage. It will help with tuning. I would get one you can mount some were you can read it while in the truck while you drive. Use the vacuum gage for timing and your idle mixture setting. Play with different timing settings and make notes of the vacuum readings. You have to do all of your tests the same, same road, same speed. If you get a tune up kit for the carb you can do the same with it. Change step up springs, test, change metering rods, test. And for your full throttle jetting on the sec side you do it with a stop watch. What ever gives you the fastest 0-60 is how you pic your jetting. Also for idle and cruse you can look at the plugs and make sure there tan. Your edelbrock also is designed for 6PSI of fuel pressure so pressure more or less can effect float level. If these do not yield the power your after then do a compression check and if all cylinders are good pressure I say do a cam swap and see were your at.

Thanks Joseph. I don't see why he cant get some decent kick in the pants with his set up and a decent cam! Maybe something a little more aggressive then the basic RV cam ?

But everything he has going on now is from a bad tune! The rods are not gonna work with the jets he has, the step up springs are the wrong ones. And sounds like he as some kinda ignition tune problem. Once he gets that all figured out he might actually like is current Engine the way it is.