Impco 600

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Helmet
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Impco 600

Post by Helmet » Sat Dec 23, 2017 6:54 pm

Hi guys,

I've managed to snag 2 of the big Impco 600 mixers of ebay. I've done some reading on these things, and most of it mentions that a 600 can't be used on an automotive engine. Guess what I'm going to do....? ;)

I have a BIG block Chevy coming my way, it should be here in Feb/March. It has a 1050 CFM Dominator type carb on it. So the 600 with its 960 CFM should not be to big for this engine.

My plan is to feed the mixer with a Model E converter as its primary converter, with a H420 as secondary converter. Thoughts, opinions? I've read that a converter can be 'tuned' with springs, how much of that is true? Mostly concerned with startup of the engine.

There are not a lot of tuning possibilities on the 600. IIRC an idle screw and that's about it. I will be adding an AFR guage to see what it does through the RPM range.

Is there anyone here with hands on experience with on of these beasts?
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454


BigBlockMopar
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Re: Impco 600

Post by BigBlockMopar » Sat Dec 23, 2017 7:10 pm

I've changed (leaned) the output curve on a vaporizer with an added light spring inside the current one.

The light spring I used came from under the acceleration pump cup from a Carter/Edelbrock gasoline carb.
Have no experience with the larger IMPCO stuff.
An AFR-gauge is mandatory when tuning an engine. The gauge in my car was a big help getting things sorted out.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

Helmet
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Location: Holland, Europe

Re: Impco 600

Post by Helmet » Sun Dec 24, 2017 4:56 am

Very true on the AFR guage, I just bolted the 425 I have on a 454, and I know its wayyyy to rich at idle, and propably lean at WOT.

So more spring pressure in the converter leans it out, good to know!
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

C3H8
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Re: Impco 600

Post by C3H8 » Wed Dec 27, 2017 4:27 pm

Darn!! Just wrote a reply to this and hit the wrong button and deleted it. Here goes again.

Back in the 80's we had a dealer that ran a GM BB in a race car. Special engine. Huge heads and something like 750CI. He ran two 600's on it. It took a lot of experimentation to get it right. It could run an average of a 7.5 second 1/4 mile. He calculated the HP at about 13 to 1500. The 600's had to be modified. Typically there are no idle screws on a 600 since they're made for large industrial engines that don't idle. Starting was the first problem. Initially we had to lift the gas valves manually to start the engine. Once started the engine idled at 13 to 1500 RPM so that was fine. He also had to machine in an idle air bypass to allow mixture adjustment at idle. He solved the starting issue by feeding fuel into the intake from the primary pressure of the model E directly into the intake with solenoids to stop the flow once started. He used 4 model E's. The second issue was sluggish response. These mixers were not made to respond instantly for generator use. He solved that by modifying the strength of the mixer spring to allow the gas valve to lift quicker. He kept varying lengths of springs to use depending on the altitude of the track. I think that any mixer can be used for automotive but there are many difficulties to be addressed. The key with the 600 is an idle circuit and strong enough airflow to lift the gas valve quickly when demanded. If you have an idle circuit it was probably machined in by a previous user. As implied in your first post it sounds like fun to try. I would not modify the E's initially. They will supply fuel as long as the mixer is reacting properly.

BigBlockMopar
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Re: Impco 600

Post by BigBlockMopar » Wed Dec 27, 2017 6:46 pm

Whenever you (have) type(d) a large reply, try to get into the habit to occassionally do a "CTRL-A" + "CTRL-C" the entire text (Select ALL + Copy).
So whenever something goes wrong during the actual reply, forum-issue or anything else; you always have (part of this text) in your PC's clipboard, which be easily CTRL-V'd into a new reply again.

Just make sure to reposition the cursor again AFTER the selected text before typing any further, as if you don't, the selected reply-text will otherwise be replaced by your further typing.
https://www.bigblockmopar.com
'73 Dodge Dart - 318ci - IMPCO E vaporizer / 425 mixer - A518-OD trans - 3.55 gears - 225/50/17" tires.

Frank
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Re: Impco 600

Post by Frank » Thu Dec 28, 2017 7:27 pm

Let's not forget CTRL Z to undo. I've been able to go back several steps and I think this works in most browsers.

Helmet
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Location: Holland, Europe

Re: Impco 600

Post by Helmet » Tue Jan 02, 2018 10:30 am

C3H8 wrote:
Wed Dec 27, 2017 4:27 pm
Back in the 80's ..... They will supply fuel as long as the mixer is reacting properly.
I think I remember your post of the 750 CI BB from quite some years ago!
In the 80's a 706 CI mountain motor was the popular size in Pro Mod and the like, so with 750 CI back then he must've been king of the hill!

Anyway, I should take some pictures. I believe idle will not be problematic, or atleast easily solved. There is the idle screw, and a long arm attached to the butterfly valve. Fabricating some brackets for a throttle return spring and the like will not take long.
Airflow to lift the gasvalve and sluggish respone: this will be interesting. The camshaft is rather large, and ground for nitrous use. With over .7xx inch of lift at the valve, I am pretty sure intake manifol vacuum isn't going to be the greatest. So a different spring(s) seems to be in my future to.

Offcourse, I don't expect this big block earlier than march, as it's currently still in California. So I'm still a few months away from this project. I'm pretty excited though!
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

storm
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Location: NSW, Australia

Re: Impco 600

Post by storm » Tue Jan 02, 2018 9:44 pm

Will a 600 accept a Holley, or any other carburettor, baseplate like a 425 does?
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

Helmet
Posts: 72
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Location: Holland, Europe

Re: Impco 600

Post by Helmet » Wed Jan 03, 2018 7:15 am

No, the mixer itself has a flange at the base, at which the the butterfly valve portion bolts on. That portion has the same flange size as the mixer. Flange size sits neatly between a 4150 and a 4500 carb base. Luckily, I have an early procomp victor style intake with a flange that doesn't fit a 4500 carb either, but with drilling and tapping some bolt holes can fit this 600 mixer.
'72 Cutlass Supreme, 455 BBO (out of order)
'85 CUCV, HO454

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