: Holley on a 1970 500?

06-10-13, 08:41 PM
Hey all,

I'm looking for any experience, wisdom, etc. regarding my Eldorado's 500c.i. Engine and Holley carbs.

Basically, I want to replace my old divorced choke Q-jet with a vacuum secondary, electric choke Holley.

The 1970 Q-jet for the Eldorado was Eldorado-only. Meaning all other Caddy's that year (except for commercial which had their own) had a different carb. The Eldorado had an 800cfm carb.

Now, I've used Holley's carb selector, read through various model specs and am still not sure which model would be best for my application.

My engine has no modifications. And I'm not planning to race it or do burn outs. I simply want it to effortlessly take off and purr smoothly through all gears and speeds.

Anyone have any Holley experience they'd care to share?



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Chris Cornett
06-10-13, 08:57 PM
Im assuming that Qjet is a spreadbore? I dont think Holley makes a spreadbore larger than 650 cfm which will starve that engine. You will have to swap intakes or run an adaptor which is less than optimal. I like the Avenger series because they come with electric choke, quick change secondary springs, clear sight plugs, and reusable gaskets on the bowls and metering blocks for jet changes.

06-11-13, 12:50 AM
Yes, they sell adapters to go from square bore to spread bore. I don't know what the implications of that are on efficiency/performance. That said, the intake manifold is nearly flat in order for everything to fit under the hood. So fuel and air literally make a 90 degree turn already.

So, yeah, I'm looking at an adapter above 650cfm. I just have to make it all fit under the hood.

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Chris Cornett
06-11-13, 10:53 AM
I still think your best option is to find a good Qjet builder. If done properly they are great carbs. I have been running them on my Buick Gran Sports for years. Get with these guys http://www.thequadshop.net/

06-11-13, 03:47 PM
Thanks for the info. I sent them an email inquiring about my Eldorado-only carb and divorced choke. Lol. Curious to hear back.

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Chris Cornett
06-11-13, 04:46 PM
They are top notch. I am running carbs from them on both of my Buicks.

06-12-13, 12:33 AM
I would stick with the qjet it is a really good carb. Rebuilding them aren't that bad when you get used to them, just more parts than edelbrocks and holley. Just becareful not to bend the rods when putting back together. If you don't like the chokes you can run it without them no problem.

06-13-13, 04:58 PM
Back in the 80s when I was younger I wanted to hot rod my old caddy. It was a 68 Calais. I dueled out the exhaust, put the adapter on the stock intake and slapped a Holley 750 on it. Aside from the normal stuff I remember having to change the front bowl to a side loader to clear the AC compressor and dremeling the exhaust manifold to fit the throttle. In hind sight I'd say it probably suffered from too much carboration. It didn't bogg out or run poorily, a matter of fact it was a little quicker off the line. But that was negligable compared to the smell of all that exhaust/unburnt fuel flooding the car when you took it for a cruise. For what it's worth I'd stick with the Quadrajet. I've had a 70 Coupe since 2000 and ran the same Quad on it all this time. It does fine. It's not a race car.

06-13-13, 07:01 PM
I know I posted them in other threads as well, but these guys helped me out with a lot of questions on the 500cid and I just received new (custom) headers from them for my 70 eldo, so i really like to recommend them:


They have a lot of parts especially for the 500cid and have a lot of experience and knowledge on tuning and racing with them. They can help you out with the Q-jet or other carbs as well.

06-20-13, 09:10 PM
does anybody know if the edelbrock intake/carb combo for a 472/500 will fit under the hood without modification? What about trans kickdown swithch?

06-20-13, 10:17 PM
Swede dog,

I have yet to find an intake manifold, other than original, that will fit under my 1970 Eldo's hood. In fact, until I put new rubber bumpers on, the air cleaner hit the hood insulation with stock parts. And I haven't quite talked myself into cutting a hole in the hood. Lol

06-21-13, 08:01 AM
The original manifold is so low profile for a good reason ;)

Tomorrow I will have new headers from cad500parts installed. I will post pictures!

06-21-13, 01:39 PM
Yes, but that has to be the most inefficient intake I've ever seen. The air/fuel literally has to make a 90 degree turn. Lol

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06-24-13, 06:48 PM
Yes, but that has to be the most inefficient intake I've ever seen. The air/fuel literally has to make a 90 degree turn. Lol

Unfortunately the good-as-it-gets without cutting the hood.