Q-jet

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Postby NixVegaGT » Sun Oct 28, 2007 9:26 pm

Cool. Thanks Shred. I went off to a business meeting and read a couple tech papers and an entire Q-jet manual on the plane ride! lol.

My $20 Q-jet carb came while I was gone. It turns out it's an 800 cfm version. A little big for my application. I know they are variable but I'd like a 750 cfm version to start with. I also found out some guys don't like the later carbs because of the ATC feature. SO I peeped ebay again and found a nice '68 750 for $75. NICE!

I'm really interested in the tunability of these things. I found a great site with a tuning explanation for each feature: Primary jets/rods, power valve, secondary jets/rods, and the secondary doors. I really dig the vac operated power valve so. It adds more fuel based on demand instead of throttle change. That's cool!

I'll keep you all posted how it goes.
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Postby NixVegaGT » Mon Oct 29, 2007 8:45 pm

OK guys. SO I was looking at my Q-jet next to my square flange intake and it seems like it would really impede flow... Anybody have a take on this?

Should I grind some aluminum off to smooth the transition to the square flange intake? It looks like half the primary barrel runs into the flange...

The problem is I don't have many options for my engine choice. Thanks guys...
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Postby Sirshredalot » Tue Oct 30, 2007 4:26 pm

Biggest problem you hit when you do that is vacuum leaks at the mounting flange.....Some of the performers have enough meat to do it...but some would cut it really close.

What i would do is bolt the adapter/spacer to the manifold with the gasket and then port the manifold and spacer to suit. it would be very easy to leave the primary holes alone and just hog the larger secondary bores to a better/softer transition.

The casting ridge in the plates also causes some fuel shear...that should be cleaned out too. Dont make the holes too big or youll loose your sealing surface. Just work on the taper of the spacer towards the bottom of the spacer in the hard turn into the plenum.

Also when you finish...take the spacer off and smooth/round out the edges on the bottom/intake side of the spacer to help combat turbulence.

Thats my .02

God bless
-Shred
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Postby NixVegaGT » Tue Oct 30, 2007 6:24 pm

Thanks man. I was thinking the same thing. I looked at the performer carbs but I really want to use the Q-jet. Most agee that they don't perform well with a hotter than stock cam.

I'm sure the performer/carter is a great carb it just seems there is more room for tuning and better efficiency with an old Q-jet... Then again I haven't done a great deal of research on the performer...

Thanks for the input, Shred.
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Postby Sirshredalot » Tue Oct 30, 2007 10:54 pm

All it takes are a few small mods to make a Q-jet really wake up with a hot cam.

How big of a cam are we talking here?....Duration @ .050?
LCA? LSA? gross lift? Solid? Hyrdaulic? roller? Ramp rate?

If youre running a buick 215 its not advisable...psshh.

But if youre building a 350-ish inch motor it wont really be hard at all.

The Q-jet tunes alot like an eddy/carter.

If youve got a cam that has a wide LSA like a 112-114*, than youll be fine with durations up to about 228 @ .050 without needing too much modification. The Q-jets really like a good vacuum signal....or else theyre bog machines.

Lemme know what youve got planned and well see if we cant help out some.

God bless
-Shred
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Postby NixVegaGT » Wed Oct 31, 2007 9:07 am

Sweet. I've bored and stroked the 215 to almost 300 now so it should have less impact... Here's the cam specs:


Cam is a Crower 50232 with an intake lift of 0.488", an exhaust lift of 0.490", Duration 276º, Duration at 0.05": intake 214 degrees, exhaust 218 degrees. Lobe separation angle: 112 degrees.

At first I didn't see your "@ 0.050" and I was thinking OH NO! because my advertised duration is 276º. Cool though. I may be good. I might have a lead on a single plane intake for my car that will fit the Q-jet... Hopeful.

I've got to remember to add this to my CarDomain page... Thanks for the help, Shred.
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Postby spyder_xlch » Wed Oct 31, 2007 8:19 pm

Wes has a good point about the vacuum signal. I never really thought about it til he just mentioned it. With a real "hot" cam a Q-jet probably isn't going to respond well. I've always been a fan of Q-jets (i guess it's the under dog thing) and they always seemed to work good for me. But I've never had a full out race motor.
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Postby NixVegaGT » Wed Oct 31, 2007 11:23 pm

WOOOO HHOOOO! I scored that intake! Here's a pic:

Image

I got it for $350 AU. (like $320ish) Sweet find for my engine. Parts are a bit more expensive than the SBC. LOL! I'm pretty keyed up.
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Postby Sirshredalot » Mon Nov 05, 2007 1:04 pm

Im not sure what i think about that,

what kinda gears are you gonna run? Automatic or stick?
Drag drace? Road race?

If youve got 300 cubes under that manifold you should be ok with a light car and a decent gear.

I have no experience with the buick family engine except for the 455's.

The plenum looks very shallow with a flat bottom which is good for the cubic inches and moderate cam.
Its going to like ignition timing.

The Q-jet is gonna be more picky with that open plenum but I dont reckon it will HURT you. Lemme look through some books and see if I cant remember how to get an increased pump shot to help fill that plenum.

God bless
-Shred

PS: What are those tubes in/under the manifod for?
Also....There was a buick motor that was a 300" or a 301" somthing like that...made for like 2-3 years.
What parts will fit it? Please and thank you.
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Postby spyder_xlch » Mon Nov 05, 2007 6:53 pm

Those tubes look like they'd be for water/coolant. Looks like you could drill and tap the bosses on the runners for NOS.
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Postby bugdewde » Mon Nov 05, 2007 11:07 pm

Those are water ports on the Buick/Olds 215s and Rover engines.

The Buick 300 cast iron engine was made after GM gave up on the aluminum 215 from '64 to '67.... it's deck height is larger than the Buick/Olds/Rover 215s..... so it's manifold won't fit on the B.O.R blocks.

The '64-only 300 heads were aluminum and have bigger valves and flow better than the 215 derivatives. They are used on the larger 3.7" bore later Rover blocks as an upgrade.

Intake choices are limited to the 215 derivatives, though.
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Postby NixVegaGT » Tue Nov 06, 2007 9:09 pm

Thanks for the posts guys. Those are, as Dwight was saying are the coolent ports. I'm not sure why the bosses are on the intake runners but it could be for expandability for NOS or injection...

I'm using a T-5 with straight-cut dog-ring gears: 2.94, 1.94, 1.34, 1.00 ratios in gears 1 thru 4. For 5th I'm likely going with the stock 0.68. My rearend is 3.42 torsen.

I'm building it for road race. Ultimately I'm shooting for running the Targa Newfoundland. I'm hoping tarmac rallies become more popular in the US... fun!

I'm looking forward to seeing what you come up with, Shred... THanks for the efforts.
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Postby NixVegaGT » Fri Nov 09, 2007 7:11 pm

I just got the intake. It is very close to fitting the Q-jet. It is off by about 100 thou in width for the secondaries. Maybe it was modified for an edelbrock carb... I will take some pix when I get the chance and post them. The tubes from the coolant ports turned out to be an intake heater. Kinda crude but functional. The floor of the intake is rounded. It looked more flat in the picture. The carb does sit right on top of the studs so it was made for some type of spread bore carb. It looks like it fits really well. That's a bit of a surprise. I have actually never heard of a single plane made for a spread bore for the type of engine I'm building. Hmmmm.

It looks like if I modify the flange a little wider to accommodate the secondaries it leaves me with just over a 1/4 inch to either side of the secondary barrels for vac sealing. Is this enough? I figure it should be. What do you guys think? It's pretty tall. That might be an optical illusion though I suppose with no heads to judge that off of.
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Postby HI WINDING MONZA » Fri Nov 09, 2007 11:25 pm

Nik, you could put a 4 hole aluminum Qjet spacer plate on top of that manifold, it may help some.

Back in the early hotrod days, they would weld aluminum in the floor of the manifold to get it to flow like they wanted. ( maybe change a single plane closer to a dual plane? )

My 425 manifold from the factory is a 4 hole - single plane but the runners sit lower than the heads and the fuel-air mix has to run uphill ( sort of like an upside down spider) Doug in AZ 8)
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Postby NixVegaGT » Mon Nov 12, 2007 11:08 am

Here's some pix of that intake I bought from Aus:

Here's a pic of the intake with the Q-jet sitting on top. BTW that is the Q-jet I got off ebay. It's going to need the flange to be bushed. The throttle shafts are sloppy enough to wiggle around so I figure it's time. I'm looking forward to modifying it:
Image
Image

The floor of the intake is pretty rounded. It's hard to get a good shot of that but I hope this isn't too different from what Shred was expecting. We'll see. This is also a nice close up of the flange modification for the Q-jet spread-bore. This is particularly hard to find for my engine. They just don't make them. The bottom pic is of the flange and the underside of the Q-jet. COOL!
Image
Image

OH one more thing to show is the custom intake heater. It's made from a hard line taped into the rear coolant ports and covered wiht braided line for show. I'm not sure this will work well but we'll see:
Image
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