bob p

I've got a 1962 Super 88 that has the Sky Rocket 394. I'm trying to figure out what aftermarket carbs (if any) are compatible with the original manifold.

The car had it's original 4GC until last week -- when I pulled the car out of winter mothballs to get it ready for summer driving, I found that squirrels had made a nest in the carb & air cleaner. I've pulled off the 4GC for a rebuild, and for the time being I'd like to find an aftermarket carb that will be compatible with the manifold while I tinker with the 4GC.

Are the Edelbrock Performer carbs compatible with the 4GC bolt pattern? I think that both the 4GC and the Edelbrock Performers use square mounts, but I've read so much conflicting information about carb fitment and adapters that I need some help clarifying this.

I'd really like to know if something like an Edelbrock 600 CFM model 1406 will fit directly on the manifold. I'm aware that the Sky Rocket air cleaner won't fit on the Edelbrock, and that an aftermarket Edelbrock air cleaner assembly will have to be used with the Edelbrock carb ... that is, if the carb will fit.

It'd really be helpful if there was a direct bolt-on carb available that doesn't require some sort of spacer/adapter. I'm trying to avoid a solution that involves spacers because I'm concerned about topside clearance.

Thanks.

5998DownUnder

Hi there,


If it is of any help, I have put a Holley 600 (temporarily) on my 394 as I have a 1959 98 Oldsmobile.


I used a spread bore adaptor flange as flange has a number of holes to bolt on with as the Holley holes do not line up.


I have a 14" diametre air cleaner and is 3" high.
The base is a recessed base so it fits down around the carby more. I use this usually on Chev motors, but it works here too. Gives more bonnet clearance.


Just an idea.

bob p

I'm having trouble understanding how a 1959 98 with a 394 could have a spread bore manifold. My understanding is that the 4GC is a square bore carb, and that any manifold mated to it couldn't be anything but square bore. You've lost me.

59-59-59

Take it from someone that actually has a 1406 Edelbrock on a 394 intake- it fits without any spacers. Now hooking up the kickdown linkage is another story....

5998DownUnder

It doesn't have a spread bore.
I had to get an adaptor as the bolt holes from the manifold to the Holley did not line up otherwise I would have bolted the Holley straight on. Would have been no dramas.


The adaptor I got sent to me was a spread bore, I needed the adaptor to get the holes lined up to the bolts, so instead of sending it back I just used it. Works for me.

bob p

Thanks everyone for your input.

If I understand this correctly, then the news is good -- a 1406 Edelbrock *is* a direct bolt-on fit for the stock 394 intake manifold.

This beings up some more questions:

1. It seems that the problem is going to be adapting the linkages. Would I be correct in understanding that the throttle linkage is going to be straightfoward / isn't going to be a problem? How about the connection for the automatic transmission kickdown linkage?

2. This is my first 4-bbl rebuild, so I'm having trouble visualizing everything without the hardware in hand. I'd really appreciate hearing more about what sort of problem you ran into with the lockdown linkage and how you solved it. I guess this is one of those situations where a picture is worth 1000 words.

3. Are you happy with the results from fitting the 1406? If you had to do it all over again, would you select the same carb or something else? As far as I can tell from reading data sheets it seems to be appropriately sized for the task, but so far I've only read specs, and I haven't heard from anyone who has real-world experience with the actual setup. Real world experience always trumps reading about the subject, so I value your opinion.

thanks again for your help.

bob p

Thanks for clarifying that for me.

joe_padavano

The original 4GC is NOT a spread bore carb, it's a square bore carb. The only difference is the bolt pattern. A spreadbore adapter on the original manifold will create a really bad turbulence and is a bad idea. As noted, the E-brock (Carter) carbs have both bolt patterns and go right on without any adapters. You will likely need to fabricate linkage, and the TV rod to the trans will be a problem.

bob p

Can anyone clarify what the term "lockdown linkage" refers to? (post # 4)

I'm not sure what that term means, and that nomenclature isn't used in any of my reference materials.

joe_padavano

I suspect that is supposed to be "kickdown linkage", with is not the correct term anyway. It should be "throttle valve linkage", or TV linkage. This trans uses a throttle valve, similar to that on a 200-4R, which replaces both the kickdown and vacuum modulator functions typically seen on other GM transmissions. As I noted above, getting this linkage correctly fabricated and adjusted for a non-original carb on these cars is both difficult and extremely important for proper functioning of the transmission.

bob p

Joe, when you say "this trans" uses a throttle valve, you're referring to the Roto Hydra-Matic 375, code OA, which was the stock transmission on the Super 88 in 1962, right?

D. Yaros

Are you doing the rebuild yourself? If so, the car should not be down that long. Certainly not long enough to justify putting a temp carb on and have to hassle with the more than touchy TV linkage.

This will give you an idea of what is involved in doing a rebuild of Rochester 4 bbl -

joe_padavano

Yes. If you look at your engine, you'll see one rod that goes from the accelerator bellcrank to the carb, and a second one that goes from the carb to the trans.

bob p

You're right, a normal rebuild shouldn't take that long, but I'm not looking at a normal rebuild.

Take my word for it, I need a replacement carb that I can get parts for. The original carb has been extensively damaged by rodents; the butterflies are heavily pitted and rusted in place, immobilized by corrosion with rodent urine. All of the rebuild kits for a 4GC are incomplete, and some replacement parts do not seem to be available.

I don't know that this 4GC is worth the effort. It's a screwed up specimen of a type of carburetor for which service documentation is hard to find and many parts are just not available. Those are plenty of good reasons to replace it with a modern carb that's reliable and has 100% parts availability. If I keep the 4GC, my worst case scenario is that the car is immobilized all summer. The best case scenario is that the car runs like crap because I can't get all of the parts that I need for a full restoration.

rocketraider

Rebuilt 4GC are not that hard to find. Worst to worst, send it to Sparky's Carb Service as he's doing 4GC now, or contact Don Monroe in Washington state who generally has some quality 4GC rebuilds on his shelf. Last contact info I had for him Don Monroe in Tacoma WA 253-566-8488 evenings.

Justintiime had Sparky do a ratty 4GC for his 65 Starfire that turned out really well. Here's the thread with pics https://classicoldsmobile.com/forums...starfires.html

I'd go that route before I'd go thru the aggravation of trying to set up Slim Jim TV linkage for an Edelbrock. Put it this way- you think the carb problems are bad, misadjusted TV linkage can end up as a trans rebuild, which will make dealing with a 4GC look like a Sunday school picnic.

bob p

Maybe these things bother me more than they should, but I'd want those throttle valves replaced.

a7_zps9e768645.jpg

5998DownUnder

.

bob p

thanks, that's a great picture. i looks exactly like what i've got on my car, but that diagram is not in my 1962 olds service manual. can you tell me where you found the picture? is it from an earlier olds manual?

joe_padavano

As discussed before, the 1962 manual is NOT complete, it is only the changes from the 1961 manual. You must also get the 1961 manual to get all the info you need to work on this car.

As for adapting an E-brock carb, the problem is the aux bellcrank, shown to the right of link B in that drawing. The bellcrank is mounted to the carb body and not easily transferred to an aftermarket carb. I eliminated it and fabricated my own throttle and TV links on my 62 F-85 when I changed carbs.

1970-W30

Joe, What part number Edelbrock (Carter) did you use on your 62 F85 215? Is it a 500 cfm?

joe_padavano

Yes, 500 CFM with electric choke. Model 1403.

D. Yaros

I would tend to agree with others, that if you are going to go to all the trouble of finding/installing a replacement carb, why not just buy a replacement 4GC and be done with it?

Daytona Parts Co, is reliable carb rebuilder supplier. Am sure there are others. Cannot hurt to check with them? You give them yours and they give you a good/working one.

5998DownUnder

Yes, from my manual.


Like Joe, I adapted mine, photo not shown as mine is an abysmal dogs dinner and an embarrassing slap up job meant as a temporary fix only.


The photo shows why mine is only temp, reco carb on reco engine to go ready in.


(I have just put a parts wanted thread on if anyone can please assist)


Thanks
John.

bob p

I rebuilt my 4GC yesterday. I don't need to send it out to an expert.

Part of the reason that my car was having problems is that the secondary float failed the hot water dip. It had a small / invisible crack at the heel. This crack wasn't visible to the naked eye, or with magnifiers. I had to use a microscope on low power to see it. I soldered it.

The other part of the problem is that the "expert" carb restorer who had rebuilt the 4GC for me years ago did several things improperly. He used the wrong bowl to throttle body gasket, which resulted in a manifold leak above the throttle body. He lost the internal airhorn mounting screw. To me that's a sign of shoddy workmanship. (I was able to come up with the exact 1950s screw to replace it.) He also got the float adjustments backwards for the main and secondary floats. The result is that the two floats were horribly out of spec. It took quite a bit of time to reverse them. I didn't like the amount of stress that I had to put on 50+ year old floats to get the heel, toe and drop adjustments back to where they were supposed to have been before the "restoration expert" screwed them up.

My 4GC rebuild is done. The only thing that I didn't bother to do was to soda blast it and electroplate it. Internally, it looks every bit as good as the ones in that other thread. Externally, I've decided not to refinish it because I don't want to keep this carb on my car.

Now that the 4GC is rebuilt, there's not really much point in discussing where to buy another one, where to send it for an expert restoration, etc. Getting back to the topic of this thread, I'm looking for information about replacing the OEM carb with an aftermarket unit.

Thanks to everyone for their helpful ideas!

bob p

Thanks again to everyone for your helpful ideas.

I understand that my 62 manual is incomplete, that's why I'm after that 61 manual on ebay.

I particularly appreciate the advice from those of you who have mounted aftermarket carbs and fabricated your own TV linkages. I understand that the changeover may not be the easiest thing in the world to do, but it's not the hardest thing in the world to do either, and it's certainly not the impossible task that some people make it out to be.

Joe, if it wouldn't be too burdensome, could you get me some close-up photos that show better how you fabricated your off-carb linkages? Or if you're not disposed to posting them on the site, could we discuss fabrication options in PMs? I'm very interested in fabricating my own off-carb linkage, and any help that I could have for a starting point would be greatly appreciated.

5898DownUnder, the same goes for your TV linkage -- although you might not think it's pretty enough for public display, I'd really like some help deciding what a good starting point is for building my own, and every piece of information that I can get my hands on would be helpful.

olds 307 and 403

A lot of people have had issues with Edelbrock carbs. Do yourself a favour and look at the Street Demon 625 or 750. They are based off the Thermoquad but are a 3 barrel that bolts to square and spread bore manifolds.

bob p

what kind of issues?

5998DownUnder

5898DownUnder, the same goes for your TV linkage -- although you might not think it's pretty enough for public display, I'd really like some help deciding what a good starting point is for building my own, and every piece of information that I can get my hands on would be helpful.[/QUOTE]

Been away, i'll get a photo up as soon as I can.

viper771

There are some good vids on a 4GC rebuild on youtube. I did my first ever carb rebuild last year on my 62 Starfire.. and it wasn't hard. The car runs awesome too. About to tackle my first quadrajet

bob p

I caught those Youtube videos by Mike's Carburetor Shop. They show how to assemble the carb after it's been totally disassembled, but they don't cover any aspects of actually rebuilding it. I was disappointed by them.

The best resource that I found was the color scan of the Rochester 4GC Service Manual on Mike's site. Even though it was specific to a much older 4GC than mine, that document was the most helpful of anything I've found.

My 4GC is all rebuilt now. Now I'm working on getting the engine started.

5998DownUnder

This is the linkage I spoke of, it was any more than a temporary job, I'd spend more time on it and pretty it up.


I did it this way so I can unpick the weld and re-use the linkage as I protected the thread from damage when welding.


You can see the other linkage sitting idle on the manifold below.
The car runs, drives, accelerates as it did before.

bob p

was it necessary to have a horizontal offset like that, or did that just happen because you needed to join two rods together? I'm just wondering if another approach might be to use one longer rod threaded at both ends, or whether the offset is necessary.

5998DownUnder

Because the Holley had the spacer under it, that lifted the whole show up so that's just the way it ended up after the operation. Offset not necessary if no spacer from what I can see. The Holley linkages being a bit higher there would be a slight incline with no spacer anyway.


Yes, thought of the threaded rod approach, had nothing the correct thread size in the shed at the time, (had the correct diameter rod though).

Nimrodinder

Indeed it's not. I've been reading this post with interest as I was looking to set up a new thread about my experience with this exact exchange. Quite surprising how many think it's a mission not worth trying. But Ive managed to swap the dog 4GC on my 62 Starfire (original 394) to a new sweet running Edlebrock 600cfm. It's not hard. The issue about the TV linkage is true but I figured the way round that is to not alter them at all... then there should be no issue. So the key is to make an off carburetor bracket that holds the aux bell crank in the same position it swings about with the 4GC. It's simply a matter of measuring the location of the pivot shaft, making a bracket and ensuring the new bracket puts the shaft in the exact same location. So now my 394 runs better than ever, using far less fuel and is far more responsive than with the 4GC, and I swear the gear changes from the sloppy slim are better too. 100% recommend the change over to anyone with a 394 Olds. Will post some pics for you from my phone once I figure out how to.

bob p

I'm looking forward to seeing your pictures. I'm thinking that my 394 would benefit from a similar upgrade.

I ended up rebuilding my 4GC because it was the path of least resistance for me, in spite of the fact that there was no good technical information available for the later models. The carburetor rebuild books don't even cover the 4GC any more -- they've purged the 4GC chapter from the Rochester carb books. If you want to find a book on rebuilding the 4GC then your only option is to hunt for an older edition of the carb books. (unobtainable) All that I could find was a technical manual on an older model 4GC with the wrong float setup, and I had to adapt the information to my carb as best I could. During the rebuild I learned that not all of the parts that I needed were included in the NAPA rebuild kit, and they were not even available via the specialist carb shops. Floats, for example, just aren't available. Mine were leaky and I had to resolder them.

Having rebuilt my 4GC and having learned what I need to know about it, I still don't want that carb. But at least the car is running now, and my attention has moved to working on other things. I have no doubt that once I start driving the car I'm going to have to spend more time and energy on the carb. If the fuel efficiency improves significantly with the Edlebrock 600 CFM then that's reason enough to pursue the upgrade. How much of an improvement in fuel consumption did you get?

Nimrodinder

I was initially getting 26-27 L/100km (8.7mpg) with the 4GC which was sapping all the fun from driving the Starfire. I rebuilt it using a new old stock kit I brought on ebay years ago. No replacement floats but had almost everything else and my floats were fine. After putting it all back together according to the 61 Olds shop manual specs the thing still leaked through the gaskets and had flat spots on accelerating up right hand bends on the road. Could never seem to sort that out. Pulled it apart again numerous times and cleaned it out, adjusted it again to the specs and still the thing was a mongrel. Fuel consumption improved to around 23 L/100km (10.2 mpg) but that was the only benefit. My mate has a 1960 Cady, with 325HP 390ci and stock but rebuilt carter carb. he was achieving 17 L/100km (13.8mpg) yet his car weighs more. So I was sure it was my carb setup making mine a guzzler. As you know, the Edelbrock is same design as the Carter and everything I'd read was that the carter was far superior to the 4GC. In my mind its no wonder Cady used Carters while the cheaper Olds settled for Rochester. Anyways, i digress... pics below of the conversion. you can see the new fabricated bracket secured by the intake manifold nut and a new link from the bell crank to the edelbrock accelerator mechanism. The only other tricky thing is the adapter for the stock air cleaner. thats made from aluminium. no spacer between carb and manifold due to hood clearance issues. there may be room for 1/2" spacer but haven't checked that yet. I should do the simply plasticine squish test to find out!

Nimrodinder

oh, forgot to say fuel consumption is down to 17/100km with the Edelbrock so its a win all around.... better response, trans shifts better and I can no longer see the fuel needle moving down as the speedo worm moves up to 70mph. Mission accomplished.

Next upgrade on the cards... swap the slim jim for the 4 speed 56-60 Olds Jetaway trans!

1970-W30

I like guys that don't get discouraged and have the ability to improvise when needed. The ability to see what's required and then improvise to make it work properly seems to be a dying art, good job on the carb switch!

bob p

I'm used to thinking in terms of MPG. Looking at your numbers, it looks like after switching to the Edelbrock your fuel consumption matched that of your friend's Caddy -- 17 liters / 100 km, or 13.8 mpg. That's a 35% improvement from the 10.2 mpg that you got with the 4GC. Seeing numbers like this, I can't imagine why anyone would want to keep the 4GC on their 394.

Looking at your pictures, am I correct in understanding that you only needed to fabricate two pieces to do the linkage adaptation? It looks like you fabricated: 1) a simple L-shaped off-carb bracket to hold the aux bell crank assembly, and a 2) simple connecting bar made out of flat stock.

Is it really that simple? If that's the case, then the only complicated part would be the air cleaner adapter, which would require access to a lathe. It looks like the linkage bracket and connecting bar would be easy for anyone to fabricate without special tools.

Nimrodinder

Yes, those two pieces were the only bits needed to get the linkages connected up. The L shape bracket is the key, and the best thing is you use the shaft for the aux bell crank from the 4GC. It unscrews so u can reuse it on the new bracket. The bracket shape with notches out here and there came about so the aux bell crank can do its full swing movement without interference.
Yes the hardest part is the air cleaner adapter if you want to keep the factory look. I was very lucky in that a friend with a 61 Olds had this fabricated but didn't use it in the end. So I nabbed it. Can measure the height of it if you're interested.