Dustin1706

Hi guys,

I am working the bugs out on a 68 Delmont convertible that I picked up over the winter. It seems to run really well though it occasionally has a minor hesitation when punching it from low RPM even when warm.

Anyhow, I'm looking to pick up a handful of ponies and get her running perfectly. I have no idea what, if anything, has been done to the motor, but the car was rebuilt about 10 years ago and appears to have been taken care of and not driven much. Engine is clean, has no leaks and has good compression. I think there may be some restriction in the muffler as it is bulged slightly, so I am going to dual the exhaust and I am thinking that maybe I should replace the sad little two bbl and stock manifold with a 4 bbl setup.

This is the first big block I've ever owned or worked on and I am trying to sort out which carb I should be running for this (probably) stock engine. Is there a go to aftermarket carb for these 455s that works well or should I pick up a rebuilt Q-Jet? And if so, who do you guys trust to pick up a rebuilt Q-Jet from? Also, recommendations on an intake manifold that will let me close the stock hood and give me some streetable performance? Not particularly concerned with price, but also not looking to drop $2500 on an EFI system for a stock engine. Also bear in mind I'm in very rural Canada so there is no chance of being able to take the car somewhere to have it tuned by a real pro.

D1.jpg
20140415_204850.jpg

oldcutlass

Very nice car. To be honest there are many threads that discuss carbs, a Quadrajet would be a good choice for a carb. As far as manifolds, you could replace yours with a stock cast iron as they can be had on the cheap, or keep an eye out for an aluminum stock replacement like an Edelbrock Performer.

Oldsmaniac

All these boats respond nicely to a dual exhaust system.

Dustin1706

I had done quite a bit of reading up on this forum and I was a little bit shocked to see how many times the Q-Jet carbs were recommended. In the small block Chevy world most guys are trying to get away from Q-Jets. I guess a better question would be will it make any appreciable difference going to the 4 bbl? Also, I see warnings in many threads against going with a standard rebuilt card from the likes of Jegs or Summit, but who do you guys reccomend getting one from that will be setup for the 455?

69ishHoliday

Bob Stone of Classic Carbs did a perfect job with rebuilding a quadrajet for me. He made it turn-key. I provided him with what other engine aspects I had and he taylor'd it to work best. classiccarb@aol.com He said he does the carb restorations for Thornton's. I sent him a wretch of a core and he returned it looking oem new. It was about $250 including an electric choke which he recommend for everyday use. - Steven

P.S. A friend of mine master mechanic that had won winternationals in J-class drag racing more than once used to say that "You can put as much gas through a Q-Jet as you can anything else."

47 Convertible

re. Q-jet for 68 455. If the information I got a few years back on this forum was correct the Q-jet for 1968 455s is 7028251. It also has the following letters: RJ G7.
I looked a few months and finally got one from a member, sent it off to Cliff Ruggles along with information on engine modifications, waited about 6 months, and back it came. Since I had the Edelbrock Performer intake which has no provision for a heat pipe type choke I elected to have a manual choke. I'm having second thoughts on that now thinking an electric choke might have been a better choice. We'll see.
I'm still working on the car but think it will be ready to start the engine about June.

Dustin1706

Awesome. I appreciate the info! Any clearance issues with the Ed performer manifold + carb and the stock hood?

hookem horns

Definitely get the duals and mufflers depend on your noise tolerance. Glasspacks are loud and so are Flowmasters. Most folks here prefer Magnaflows or Dynomax's.

Butt dyno and sound will be better with the 4bbl over the 2bbl, but probably not much measurable improvement. May actually get better mpg if you drive nice and stay out of the secondaries but what fun is that. The Performer intake will be a lot lighter and easier to wrestle into place than a stock cast iron boat anchor but not much performance difference. You may need a 1" spacer for the carb linkages to clear.

Car probably came with tall highway gears, so lower gears in back will be big help off the line. Not cheap but a logical next step if not making bigger engine mods beyond easy bolt-ons.

My opinion only, you get what you pay for.

455man

I think it's about a 15hp increase over the 2bbl.

442rocketdave

I have a 69 W30 and I have run 11.67 with a rochester 4bbl, and I could get 20mpg if driving real easy and taking off in second. Rochesters are a little tempermental but when adjusted and fine tuned they run great. They are not the best choice for drag racing but are very good for street driving. An edelbrock performer will fit under the hood and with a good rochester it will greatly improve your performance but dont forget the dual exhuast!

jag1886

I'd use a stock iron manifold and a Holley 650 spread bore carb with vacuum secondaries, Holley makes direct replacements that bolt right on and have electric chokes I used this set up on a 68 Riviera with a replacement 455 and it worked very well, ran strong and got 18 MPG on the highway and it worked perfect right out of the box.
I'd also use Dynomax Super Hemi Turbos for mufflers in a dual exhaust system, they offer very good interior sound quality, I've used Dronemaster's and Magnadrones before on they just ruin the sound quality inside the car.
I'd also look at your ignition, that swollen muffler tells of hard back firing through the exhaust at some time in it's past.