[Griffinspc]

I have my 1968 Ventura, stock 400 / 2bbl / TH400 but have converted it to dual exhaust. It has 82,000 original miles and doesn't burn a drop of oil. Tight.

I want to convert it to a 4bbl set up and was thinking about these parts:
EDL-1803 - Edelbrock Thunder Series AVS Carburetor
EDL-2156 - Edelbrock Performer Intake Manifold

I'm not looking to set the world on fire but obviously would like a boost in performance. My question is should I or do I have to look at a cam or other parts? I'd prefer not doing anything else other than the manifold and carb.

Thanks.

[Schurkey]

I'd WAY rather have a Q-jet than a Carter-clone.

[Griffinspc]

Originally Posted by Schurkey

I'd WAY rather have a Q-jet than a Carter-clone.

Reasoning in relation to my question and specs?

[Schurkey]

The Q-jet is a far more sophisticated design than the Carter stuff. As the Q-jet gets newer, the quality seems to improve--so a '76-newer Q-jet would be ideal if you can get the choke, fuel entry, and throttle linkage to work with your application. (Really, that shouldn't be any worse--and probably easier--than getting the aftermarket carb to work.) Get Ruggle's Q-jet book, and have some fun.

No, you don't "have" to change cam or anything else. How does the Ventura control the kickdown of the TH 400?

[Griffinspc]

"How does the Ventura control the kickdown of the TH 400?"

Are you asking mechanical or vacuum?

[gtofreek]

Originally Posted by Schurkey

The Q-jet is a far more sophisticated design than the Carter stuff. As the Q-jet gets newer, the quality seems to improve--so a '76-newer Q-jet would be ideal if you can get the choke, fuel entry, and throttle linkage to work with your application. (Really, that shouldn't be any worse--and probably easier--than getting the aftermarket carb to work.) Get Ruggle's Q-jet book, and have some fun.

No, you don't "have" to change cam or anything else. How does the Ventura control the kickdown of the TH 400?

X2!

You would get the most bang for your buck if you found a Q-jet and factory 68-72 manifold. Wouldn't cost much and would run much better than the Edelbrock stuff.

[Griffinspc]

Thanks to both of you. I've been doing some forum snooping and found many references to the Edlebrock not being liked much for this conversion. I'll start checking for a Q-jet setup. A follow up question though, do you agree that the cam can stay factory?

[gtofreek]

Sure, if it still runs fine, the stock cam is fine. Could it use more? Sure, but it will be fine the way it is. You will still have an improvement.

[b-man]

At that mileage the timing chain is certainly ready for replacement. Camshaft likely has a worn lobe or two.

Personally I would put in a new 066 or 068 cam and a top-quality timing chain set.

These two items will be worn out even if the rest of the original short block is in great shape. Big performance boost will be had from replacing these items.

I second the Q-jet and factory intake, big bonus from the use of factory parts is no cobbling throttle cable brackets, fuel or vacuum lines.

[Schurkey]

Originally Posted by Griffinspc

"How does the Ventura control the kickdown of the TH 400?"

Are you asking mechanical or vacuum?

No such thing as a vacuum kickdown on a TH 400; like every 400, it's going to be an electrical system. SOMETHING supplies voltage to the electrical connector on the trans case. Likely to be either a switch on the gas pedal assembly, or a switch on the throttle linkage. If it's at the gas pedal, changing carbs won't affect the kickdown. If it's on the throttle linkage, you may need to dick with it to make it work with the new carb.

[Will]

'73 and later Q-jets with the hot air choke are easily converted to electric choke which is a much better way to go than trying to make the old hot air system work.

[demonic68]

I also agree with every one else Q-jet all the way for Boulevard Cruisers get decent mileage and great performance stock 4 barrel intake also will work great for what you are trying to do. I would also. Replace cam lifters, cam chain

[steve25]

The factory manifold is better than the performer as by Edelbrocks own catalog info states that the manifols is done at 5200 rpm.
I would seperate the water crossover section to keep the front runners temp more in line with the rear ones on hot days if you dont mind the work it entails.
As posted before its high time for a new chain and gears and if not cam and lifters also, for sure new valve springs as the added rpm the 4 bbl will give and fater rpm INCREASE will let you know real soon how shot the stock old springs are even with a stock valve of .407"!
This fact I just posted about is also a reason to pop the oil pan off and install a 60 psi oil pump with its needed much larger 3/4" pick up tube, top this off with a far better race oil pump drive shaft and you are good.
Also while you are in there I would pop off number 1 and 2 rod caps and the 1 and 2 main caps for inspection.
In fact I would think about replacing all the rod bearings as I belive all the two bbl motors got the less robust GM moraine 200 serise bearings, where as all the four bbl motors came with the really good moraine 400 bearings.
Look at it in a real way, you are not swapping to the 4 bbl to give the motor a easyer life, so atleast intsall the basic parts needed to let it live as if you still had it breathing thru the 2 bbl carb!!

[Griffinspc]

Wow! Lots to think about here. Thanks to you all.

[2002Z4CSS]

My engine in my GT-37 was in a 1968 Lemans prior. It had the same carb and intake as you mention. The Edlebrock Carter type carb had an aweful stumble/bog when the secondarys opened. I replaced it with a Holley 750 dual feed I had laying around and the engine actually woke up nice when you floored it. I still have the intake manifold on my 400.

[PONTIAC DUDE]

Find a factory Iron Q-Jet intake and carb. 1967 thru 1971. The intake will make more power overall over the Performer intake

[PONTIAC LARRY]

May consider looking for a date code correct 68 intake since your on a hunt anyway and ditto on using a superior 76-78 Pontiac Quadrajet. Don't forget you will also need a 68 Four barrel throttle bracket, its differs slightly from the 68 two barrel one unless your car has the firewall mounted long adjustable rod so nevermind .. Is your engine the 10.5:1 premuim fuel engine with #15 heads or the 8.6:1 regular fuel engine with #14 ? heads ..?

You mentioned wanting a boost in performance so since it is a two barrel car its likely got a 2.56 rear axle ratio so since you did the duals and going to a four barrel the matching compliment to those parts would be a 2.93-3.08-3.23 gear just saying...

[geeteeohguy]

Another thing I'll add: with a Quadrajet, your fuel economy will actually increase over the stock 2bbl carb due to the Q-jet's miserly appetite when you are cruising at part throttle. They are amazingly efficient. When you need the extra power of the secondaries, a Q-jet will come alive right now, too. Can't go wrong with a Q jet and stock intake, IMO. The car will be more economical, more powerful, and more fun to drive. There is no down side to the swap.

[Griffinspc]

Thanks all again. I think I located a Q-jet / manifold setup about 30 minutes away. The guy has a bunch of mid 60's Pontiacs (several 67's included he said) and spare parts galore. I bought from him before. I'll drive up next week and take a look and post back.

[gtofreek]

I would try to avoid the 67 Q-jet intake as it has heat crossover ports coming up to the base of the carb. A special stainless steel shim gasket needs to be used with those. I usually just tap and plug the ports.