RedBlazed

My next, and hopefully last engine related project for about a year (next is weatherstripping and door issues, interior, and then paint/body once everything is done) is to add the MSD 6al and tachdrive dist, an Edelbrock performer intake, and my carb.

My only real question in what do to with my carb. My initial thought was to get a new Edelbrock Q-jet 750cfm, but I've checked through a lot of the posts saying the E Q-jets are too generic. Would I be better off getting my stock q-jet rebuilt or going with the new Q-jet? Another option is of course a Demon carb, but I'm not sure if that's what I want. I'm more going towards getting at least brand-new stock performance or better, while trying to enhance fuel economy (I know I know, laugh it up).

Oh yeah, its a 1970 454/390 BB, PW, PB, PS, A/C, #'s matching t-top coupe. I've only had it for about 6 months, the guy I had it before didn't pay too much attention to it I think, except for storing it in a nice place when it wasn't driven and taking care of minor maintenance stuff, but he did keep the engine strong and it definitely has an aftermarket cam, I don't know what though. I've already taken care of the suspension (spring, bushings, etc) and heating issues (new waterpump, therm, and fan clutch). I'm going with this current project because the guy I bought it from even told me the carb was on its way out, and I've been having problems with it and dist related problems too. Nothing distasterous, but definite signs that they need to be replaced.

Unfortunately, I do go to a corvette-only mechanic for all this, whom I actually trust and have talked to a lot of C-3 owners that like him too (the majority of cars I've seen at his shop have been C-3's, and he prefers a new Q-jet, but he's a big Edelbrock lover. I wish I could work on it myself, but I'm 24 and live in an apartment building where garage working space is an issue. Once I get a house, it'll be all better, but I have to cope with this for now, and like I said, my mechanic's a good guy.

Phew, long post :eek:, but my first post here (woo-hoo :crazy:). Thanks guys, I know I'll get some good advice here. Oh, and you can critique the other parts I'll be using in this project if you see fit.

Alwyn678

I think you should talk with LARS.I would recommend a Demon For sure I love mine. But you can set-up a q-jet to run quite well

Roscoe

Lars, :thumbs: He rebuilt my Q Jet turnaroung time about 2 weeks. :thumbs:

Ryan77

A q-jet can run very weel when setup right, but they can also be a pain in the azz when not working correctly. I will be using a Speed Demon 750, with mechanical secondaries and no choke on my new 383 that I will be installing. I talked to Lars (our resident carb expert and performance Q-jet rebuilder) about my decision and he told me he has dyno tested many carbs, and the carb I described above (with your choice of cfm) was better than all the others by 15-20 horsepower :eek: . Without a choke you have to feather the gas for about 90 seconds on cold starts, but other than that, there is no problems. As for your other parts that you would like to install, I've heard of some reliability issues with the MSD 6A, 6AL's, etc., but don't personally have one so I can't say for sure, but when working correctly, they should be a good choice. For the intake manifold, a Performer may not be what you want if you have a somewhat radical cam. The Peformer is for idle-5500 rpm, and the Peformer RPM is for 1500-6500 rpm, and your aftermarket cam probably operates in this range as the even the milder ones usually don't come on until about 1,500 rpm. But it also depends on what rpm range you drive in also, if you always stay in the low rpm's then the Performer is for you, if you're in the mid or upper rpm somewhat often then the RPM is probably for you. My vote would be for the RPM intake. It can get confusing, but I hope this helps, and feel free to IM me or post with more questions :cheers:

scottw

Lars is the man when it comes to carbs. :thumbs:
Contact him and get it rebuild.

RedBlazed

whoops, knew this would happen but forgot to add this part. Let's suppose I didn't have Lars rebuild it, then what would you say about my situation... :blueangel:

scottw

If you don't have lars do it then it depends on your or your mechanics abilities to rebuild your carb and tune it.
Why wouldn't you have lars do the carb? Just wondering.
I installed a MSD dist, box and the performer intake myself also. Very nice improvement, you should like them. I also put in a new cam. What kind of intake does it have now? If it has a good intake now, you may want to see how it does with the new or rebuilt carb. A properly tuned carb can make all the difference in the world.

RedBlazed

No real reason about why I wouldn't have lars do the carb. Just looking at my options from all viewpoints. I already sent lars an e-mail to find out about the process. If it turns out to be something I don't want to do, then this posting will help me with the alternate decision.

The intake on there is the original stock intake. Of course not bad by any means, but I'm looking to upgrade. I'll be holding on to all these parts of course.

Oh, and about my mechanic, I think he would prefer the new edelbrock Q-jet as opposed to a rebuild. I think he might send it off or something, I didn't really question it. As of about 3 days ago, I was set on just getting the new carb, but I read some posts about the Edelbrock Q-jets being too generic and not getting the same results as the original Q-jets would


[Modified by RedBlazed, 1:27 AM 2/13/2003]

The_Dude

I rebuilt the quadrajet on my '76 Cadillac myself. It worked pretty well, but I never did get it adjusted correctly. It ran fine once it warmed up, but I didn't get the choke adjusted right and it ran extremely rich when it was cold. Adjusting them probably isn't that hard, but on a Cadillac, you can't get at the screws without removing the carburetor. The AC is in the way of pretty much everything. The rebuild process wasn't that hard either, but you need to follow the instructions explicitly. I have two books on Rochester carburetors and still ended up taking my carburetor apart 3 times before I got it put together correctly. I was going to do the one on my Corvette, but if Lars is rebuilding them again, I'll send it to him. If Lars rebuilds it, he also road tests it and gets adjusted spot on. That part of it, plus the knowledge that it was rebuilt by an expert, so I won't worry that I missed something, is worth an awful lot to me. :cheers:

LAvetteman

Either have Lars rebuild your Q(least expensive option) or buy a new Demon. Either choice is a good move in my opinion.

I would imagine the properly set up Q would be more efficient beings the demon is known to yield more HP. If efficiency is the same then its a no brainer, DEMON all the way.

RedBlazed

ttt

Tominator

If your mech. is going to do all the work I would go with what he knows best. If he really has a handle on Edelbrock and can tune them well that might be your best bet.

I would ask him what carb. he can set up best for your driving needs (street, strip, etc.) I know a lot of people recommend the carb. with the most ponies but I would look for the best one that fits your driving habits. For example if you mainly drive street I would go with vac. sech. might not have as many hp as a mech. sec. but much may be the fasted for your type of driving. MHO

Larry B.

I see that you have a BB... Unless you have an L-88 hood, a demon won't work unless you don't want to close the hood. You are pretty much limited to the Q-jet, stock corvette intake and air cleaner. (this applies to 68-72 BB"s only).

Milest

I put a brand new (not rebuilt) Edelbrock Q-jet (with performer intake) and it has performed perfectly for past 2 1/2 years, 12,000 miles. I put a MSD 6al at same time and it has never missed a beat. Car runs great for a stock 350 L-48.

Lars rebuilt and re-jetted my original q-jet and it works great, but not as well as the new one. I am speaking of idle and ease of starting, not performance. I only have the seat of my pants to gauge that. The great thing is that I have an excellent spare ready to go. This is not intended to bash Lars, he wanted me to send it back at his cost for some final tuning. I refused because it did the job I wanted. I am just relating my experence on a new carb out of the box.

RedBlazed

good, another opinion to think about. I'll have to talk to my mechanic more. Maybe I can put him and Lars into communication or something. We'll see.

How much different was idle and startup compared to the new Q-jet and the Lars Q-jet?

Oh, and the hood is the nice high rise L-88 type of hood with the cowl induction, so I'm not limited and can go to a demon if need be. Sorry, forgot to mention that before.

Andy

V8yunkie

The easiest you could do is to buy a new Q-jet from Edelbrock and install the same jets, metering rods and power-valve spring from you old carb. This should do for a good primary adjustment. For Secondary, you need to some tuning, which is no big deal as it can be done in a minute (changing secondary rods and hanger and adjust secondary spring pre-tension).

I did the same an I am very pleased with the results - excellent throttle response, gas-mileage and cold-starting.

RedBlazed

Awww crap. I really should check things out before I assume things and make an azz out of myself. Just checked the carb cuz I'm having some idling/fuel issues. hehe, I have a Holley (4150 I'm assuming since that's what normally came with a 70 BB if the carbs a Holley), and if I'm not mistaken, that's definitely not a q-jet build.
:banghead: :banghead:
So, knowing this now, do I get the Holley rebuilt, or do I go with the Demon or the Edelbrock Q-jet? Don't worry about clearance or the intake cuz I'm getting a new one and I'll get one the fits my carb.

:banghead: :banghead: :banghead:

Also, how can I tell exactly what kind of Holley it is. The only numbers I found were 7832 6772, and a "36" on the top. I hate being such a n00b


[Modified by RedBlazed, 8:16 AM 2/16/2003]

V8yunkie

All Corvettes from MY 1970 on - except from the LT1's - came with a Q-jet rather than a Holley.
The Holley that you have got (according to the supplied number 6772 which should be taken from the front of the choke air horn..) is a 4165 model, rated at 650cfm - this is taken from the Holley carb list which you can find at http://www.holley.com.

Depending on your motor, the 650cfm is not that much actually. So if you opt for a new one, better go for a 750cfm Holley or a Q-jet (750cfm). I personally prefer a new Q-jet in combination with a Edelbrock Performer intake (should fit your hood, too).

Anyway, you could first try to throw in a Holley Renew kit for your carb (Holley part# 37-605, also take from the above list...) and see if you trouble is gone. Might be a blown power valve or bad gasket. It is about 3 hours of work (most of it is for cleaning all the parts clinically clean as the original gaskets destroy themselves upon dismantling).

Why do you actually want to change your manifold? Is yours the original, stock motor? If so, it would not make sense in my opinion to brake up a proven combo.

RedBlazed

I would change the intake to match the carb (if a new one) and to also get better performance and better gas mileage. The engine's original, though.

curious though, if getting a new Q-jet would be better than the Holley rebuild. I would think it would be, but I'm no expert.

But also, since I don't have an original Q-jet, shouldn't I just for an Performer RPM with a Demon? Or a Performer with a new Q-jet? best performance vs efficiency (fuel economy) trade-off...that type of thing

V8yunkie

To be honest I have no experience with the Demon... heard good and bad things about them.

I have had a holley 600cfm before I changed over to the new Q-jet.... and wow, what a difference: Better throttle response, better performance and MUCH better gas milage - admittedly after some playing around with jets and metering rods, as my motor is pretty far away from original.

But for you, you could opt for a new Q-jet, give it the jets and rods of the original carb (which should suit your original motor) an should be on a good way.

The Q-jet is a little more complex than the Holley and changing jets and rods requires a little practice (after the 3rd time, I learned to change jets and rods in 10 minutes) than on a Holley. But this more complex technique is the reason for its capability to give that good gas-mileage: I gain 16 mpg with a 3,55 rear going 90 mph on the Autobahn.

The Holley originally are carry-over from racing - fuel consumption is not a big deal there but time to change jets and readjustments is. The Q-jet was designed for street use, supplying good gas-mileage and throttle response by its secondary air-valve and smaller primaries. The airvalves makes it possible to use the one 750cfm size carb on small and big blocks as well (with different jets/rods of course).

BTW another alternative: Ask Lars to either rebuild a Q-jet for you or maybe let him tune a new Q-jet with jets, metering rods and power-valve spring for your particular application.

For the manifold: Stay away from the Performer RPM. It will reduce low end torque as it is designed for high-rev engines. The standard Performer is a good choice and a good combo with the Q-jet. Although I believe that you will also be fine with the standard manifold an the new Q-jet.