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500, 472, 425, 368 Discussion, Lets have a vote... in Cadillac Engine Technical Discussion; I am stuck on whether or not to go multiport EFI or a performance Quadrajet from JET. With the EFI, ...
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    terrible one's Avatar
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    Lets have a vote...

    I am stuck on whether or not to go multiport EFI or a performance Quadrajet from JET.

    With the EFI, I have to use the stock manifold. I can get one of these, fuel rail, and throttle body. Pretty expensive. However, I have been told the EFI manifold is crap for flow, and even with a lot of porting would barely catch up to a stock carb manifold. Also, the EFI system is much more expensive of course.

    With the carb, I would get a pre-EGR manifold for the better flow, port it, and run a JET Quadrajet on there. Everyone is telling me this is what I should do, and save money and get better performance.

    Now, the catches.

    Others tell me that the runners on the EFI manifold are about the same. No one has proof of either. I am almost tempted to buy it just to see for myself. I also was looking forward to the tuneability of the EFI setup, and just the sheer broad powerband performance and coolness. However, it has been said that it would come back to bit me in the ass because it would be such a pain and if something went wrong I have to troubleshoot, yadda yadda yadda. The guy helping me is really wanting the EFI thing to happen.

    Now, with the carb, I know I will always wonder how the Megasquirt/EFI setup would have worked out. Plus the fuel economy wont be as good. Some people say big difference, others little. Also, a carb is always a carb, and won't have the computer tuning the MEgasquirt has, the awesome response, the almost limitless powerband, etc etc. Also a carb is just simple.

    Okay, feels good to get all of that off my chest. This has been killing me guys. I don't know what to do.

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    Re: Lets have a vote...

    Ah crap forgot to add the pole. Oh well who cares, just type your response. I'll get more info out of that, and everyone always does anyways.

    Thanks guys.

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    Re: Lets have a vote...

    I have an EFI manifold here. Find out just what is supposed to be so restrictive on it and I'll have a look.

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    Re: Lets have a vote...

    Runners are supposed to be the problem, the size and curves. I would really like to make this thing work, but then again it is a MUCH more expensive route, dunno if it would be worth the performance gain in the first place...

    Thank you

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    lux hauler is offline Cadillac Owners Connoisseur
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    Re: Lets have a vote...

    Really, how much difference will there be over a well built, well tuned carb?

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    Re: Lets have a vote...

    Not a ton of difference, but there WILL be a difference. Thing is Quadrajets aren't known to be easy to tune. A computerized system that's able to take feedback from the engine will always outperform a carb.

    I've heard from some people that Al at MTS says the EFI manifold outperforms a carb one by a big margin. I've heard from some people that the Torque Inc crew says they don't flow for crap. I also know the factory rated the EFI cars 20hp higher than the carb ones, but that the factory ratings aren't exactly that accurate either. So really who knows. If you get the EFI unit you could have it and your carb intake on a flow bench and let us all really know what's up.

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    Re: Lets have a vote...

    Wouldn't a holley or eldebrock be better. I always heard they were Quadrajunk. Could be wrong though.

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    Re: Lets have a vote...

    Nah, a well tuned Quadrajet will out perform those carbs hands down. But it needs to be well tuned (not as easy as an AFB, or Holley)... I used to have a PDF that explained performance tuning of a Quadrajet in detail... I'll hunt it up and if I can find it I'll post it.

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    Re: Lets have a vote...

    One thing I do wonder is that even if the carb manifold and EFI manifold are neck and neck, is the performance gain worth the extra $900-1k?

    The people who don't like Quadrajets are the ones that don't understand them.They are tuned in an entirely different way than a Holley or Edelbrock or Demon. Once they are tuned right and happy with what engine they are sittign on top of they will outperform a same class Holley in performance and ecomomy.

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    Re: Lets have a vote...

    Here are some of the guides I used, I'm still looking for the one that actually made modifications to the carb (drilling) for maximum performance... I know I had it downloaded at one time for my '70 Camaro/454 project...

    Hope this helps... Be a LOT cheaper than EFI...

    http://www.nastyz28.com/~ericf/tech/qtune.pdf
    http://www.carcraft.com/howto/57178/
    http://www.geocities.com/gtopercy/Pi...rajetTech.html

    And a whole lot of links about nothing but Q-Jet tuning (about half of the links are dead):
    http://www.buickpartsdirectory.com/carbs.htm

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    Re: Lets have a vote...

    Here are some pictures of an EFI manifold which was originally from a 1978 425. It was last on my 500 which lived under the hood of a 1982 Trans Am.

    Dunno where the runners would be restrictive. Maybe I need new glasses.
    Attached Images

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    Re: Lets have a vote...

    Even if the EFI and carb manifold are identical (that manifold looks pretty similar to me) you will have an advantage to the EFI because there is only air flowing through those twisted runners so you do not have to worry about fuel fallout. Plus, you can fit a huge throttlebody that will flow more air than a Q-jet without hurting your street manners. Getting over 800cfm through a carb without resorting to huge bores that kill response gets tough, although a carefully ported Q-jet can get up in the 900+cfm area. .
    How much do you use the car, especially in cold weather? I would go for EFI hands down but for the $$$ issue. A well-tuned Q-jet car is darn close to EFI in terms of driveability and response, so rest assured you will not me giving up very much if you go that route.

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    Re: Lets have a vote...

    I don't see much wrong with the EFI manifold from the pictures except for the fact that it is flatter.

    BluEyes, this is a question I asked myself. Even if the EFI manifold was identical and EFI would be better than carbureation, would it be worth the money?

    The car is going to be a daily driver, but not used on short trips where the moped can be due to gas prices. (What can I say, I'm broke)

    It seems to me that the Q-jet is darn close to the EFI, with the EFI still being better. But is it worth the money. Even after I get decent figures from the EFI manifold, is it still worth the money?

    Would you say that the Q-jet will be plenty for my engine right now? I am going to be working with JET on this one who builds a Q-jet specifically for your engine.

    Anyways guys, this is what the vote is for. There are just too many factors.

    Will this well tuned Q-jet have good power throughout the entire band like the EFI?

    This shouldn't be as complicated...

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    Re: Lets have a vote...

    Personally, I would prefer all my vehicles to be EFI. Reliability, cold weather starting, accurate A/F ratio throughout the rpm range, mpg...

    But is it worth the cost to retrofit? Not in my eyes, unless you are going to build the Megasquirt system over time.

    My vote would go for Q-Jet... Unless money isn't an issue, then EFI hands down.

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    Re: Lets have a vote...

    Well money is an issue. It doesn't get cold here really either. Almost never snows, just ices. Not like I would be driving in those conditions, so there you go.

    The RPM range power was what I was seeing through the EFI. That and the crazy easy tuning and effieciency. But for over a grand more, I'm kind of just not seeing it. It's still a hard decision to make, but I am only 16. I'm not made of money and the rest of the engine needs tending to as well.

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