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Unread 08-07-2012, 10:22 AM   #46
Dadamsnv
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Quote:
Originally Posted by lucdog View Post
I run a 470 on a Chevy 305 trail Jeep. I also run a Quadrajet on a 360. I prefer the Q-jet. The reason being, the Q-jet doesn't flood out as soon. The 470 is good to 45°, the Q-jet will go over 50.

On your calculations for carb size, Hollys website say to multiply your final CFM by 80%. This is because the engine is roughly 80% efficient.

Bill
I've heard great things about the Q jets for wheeling, is there a good source for new or refurbished Q jets online?? I guess the reason why I liked the Holley TA so much was because I already have a Holley, and it works pretty good.

I searched for what you said about the efficiency online and I found this which agrees with what you said.

Quote:
CID x RPM x V.E. / 3456 = CFM
that puts me at...

(304 x 5000 x .80) / 3456 = 352 CFM

Right now I have a 350 CFM, but I also have an intake, headers, and eventually a torquey cam. Plus, like was said before, if the 2 bbl test was done at a higher depression, it would less flow than advertised.

So, if anything, the 470 should be bigger than the 304 can use. BUT there is a line between bigger and too big. I think the 470 fits neatly in the bigger but not too big category, but I'm really no expert.

Matt,

sounds like somebody is a Q jet fan eh??

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Unread 08-07-2012, 10:31 AM   #47
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Shoot Matt a PM he just bought one. It's supposed to be jetted for his altitude.
Matt's Q-jet was bought partially on my recommendation. Check out his thread on "the worlds ugliest AMC 360" . It's about to get more interesting , it's going to the Dyno in a couple days.

Bill
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Unread 08-07-2012, 10:43 AM   #48
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Dada,

Based on a bunch of research, and some advise from guys who know, like Bill, I chose the Q-jet for my 360 re-build. My engine is sitting at the dyno shop right now. I hope to fire her up, for the first time, later this week.

I got mine from National Carburetors. It was reman'd, but you'd never know it, and it came with a warranty. They even jetted it specifically for my elevation, or so they say. We'll see on dyno day.

Great thread.

Edit: I see Bill and I were typing at the same time.

Matt
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Unread 08-07-2012, 10:49 AM   #49
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I still have the stock MC carb and intake. When I get to it should I just get a different intake and carb? Will that help get more HP or stick with what I have. I will have to rebuild that carb anyway.
Oh and 304 no idea how long it had been since it ran I would guess 6-7 maybe even 8 years. But that is anyone's guess.
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Unread 08-07-2012, 10:58 AM   #50
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Last night I tuned the base timing to 11* to account for a bit of the 5000 ft altitude I'm driving in. I also checked my mileage, and was surprised to find it was at about 10 MPG. I would've figured I'd be up in the 12s by now with all the tuning I've done. This got me to thinking my vac advance wasn't working properly, so I pulled the vac adv line off of my carb while it was running, and there was no change in RPM, and I couldn't feel and vac when i put my finger over the hole. I pulled my cheapy vac gauge out of the cab, and I hooked it up to the manifold, and then to the carb. Pic 1 shows the manifold vac, and Pic 2 shows the carb vac. I made a hose extension with some silicon fuel tubing and hooked the manifold vac to the vac advance on the distributor. Right away the RPMs went up to about 1100. I turned those back to 700-800. I then took a quick look with the timing light and the idle timing was at 30! I don't know a whole bunch about this, but that seemed pretty high. I didn't get any knock while it was sitting there, so I closed the hood and cruised around. Still no knock. However, I had a bit more power off the line than I had before because of the advanced base timing, and in coasting and cruising situations I had a ton more power and the motor was MUCH more quiet and smooth. I pushed the throttle slow off of 55 MPH cruise, no hesitation, the CJ wants to rocket off. So I punched the throttle off of 55 MPH cruise, no hesitation, she still wants to rocket off. Things are looking good at this point, so I stopped on the side of the road and waited for traffic to clear. Then, I did as hard a takeoff as I could up to 60 MPH. At this point I was testing the added base advance, because I'm sure my vac was at 2 or 3 in Hg. No knock!! I'm getting much closer to that perfect DD tune!

I can still smell a bit of fresh fuel cruising down the road, and the CJ feels a little sluggish off vac, so I put in the #58 jets (one step leaner) last night and called it a night. This morning, the CJ felt a bit better climbing the hill out of my hood, but I still smell that fuel smell. I will cruise for a few days while I experiment with how the tune feels at this moment. I should also see a drastic improvement in fuel economy with the vac advance working properly. The last pic is my initial curve and my curve how it sits now.
image.jpeg   image_1.jpeg   8-7timing.jpg  
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Unread 08-07-2012, 11:06 AM   #51
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Quote:
Originally Posted by Matt1981CJ7 View Post
Dada,

Based on a bunch of research, and some advise from guys who know, like Bill, I chose the Q-jet for my 360 re-build. My engine is sitting at the dyno shop right now. I hope to fire her up, for the first time, later this week.

I got mine from National Carburetors. It was reman'd, but you'd never know it, and it came with a warranty. They even jetted it specifically for my elevation, or so they say. We'll see on dyno day.

Great thread.

Edit: I see Bill and I were typing at the same time.

Matt
Thanks Bill and Matt !

I'll keep my eyes glued to Matt's 360 thread for sure! dyno testing is right up my alley. I'll also look into the Q jets too.

Daniel
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Unread 08-07-2012, 11:10 AM   #52
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Quote:
Originally Posted by 8pitcher View Post
I still have the stock MC carb and intake. When I get to it should I just get a different intake and carb? Will that help get more HP or stick with what I have. I will have to rebuild that carb anyway.
Oh and 304 no idea how long it had been since it ran I would guess 6-7 maybe even 8 years. But that is anyone's guess.
I've also heard good things about the MC carbs. If the CFM of that carb fits the 304, I'd just rebuild the carb. Also, manifolds are pretty pricey, but I really like my edelbrock performer. I could immediately tell the difference when I put it on. So far the best performance gains I've gotten out of the 304 have been the product of proper tuning. I'd say get her all tuned up, then think about a new manifold and carb. That'll let you know exactly what you need/want
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Unread 08-07-2012, 11:20 AM   #53
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Dada,

Congrats on coming over to the "bright side". Manifold vacuum to the vac advance is the only way to go, IMO. I thank Shawn and McMudd for that lessen.

The only practical difference between manifold and ported advance is at idle. Manifold produces full vacuum at idle, ported produces zero (if the carb is setup correctly). In all other off-idle situations, the two vac sources are almost identical.

The reason your timing showed 30 at idle is you're probably dealing with a 20 degree head on your dizzy. So, the manifold vac is adding a full 20 degrees to your initial at idle, as it should.. The advanced timing at idle creates a cooler combustion chamber and smoother idle. It also produces better cold starts, and low end performance.

Your engine will never see those high timing numbers in any load situations, since manifold vacuum goes lower under load, so you shouldn't have any problems with pre-detonation.

I switched to manifold about a year ago, and will never go back.

Matt
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Unread 08-07-2012, 11:22 AM   #54
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Quote:
Originally Posted by Dadamsnv

I've also heard good things about the MC carbs. If the CFM of that carb fits the 304, I'd just rebuild the carb. Also, manifolds are pretty pricey, but I really like my edelbrock performer. I could immediately tell the difference when I put it on. So far the best performance gains I've gotten out of the 304 have been the product of proper tuning. I'd say get her all tuned up, then think about a new manifold and carb. That'll let you know exactly what you need/want
Thanks just tryin to plan out expenses. As far as I know everything is stock.
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Unread 08-07-2012, 11:30 AM   #55
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Quote:
Originally Posted by Matt1981CJ7 View Post
Dada,

Congrats on coming over to the "bright side". Manifold vacuum to the vac advance is the only way to go, IMO. I thank Shawn and McMudd for that lessen.

The only practical difference between manifold and ported advance is at idle. Manifold produces full vacuum at idle, ported produces zero (if the carb is setup correctly). In all other off-idle situations, the two vac sources are almost identical.

The reason your timing showed 30 at idle is you're probably dealing with a 20 degree head on your dizzy. So, the manifold vac is adding a full 20 degrees to your initial at idle, as it should.. The advanced timing at idle creates a cooler combustion chamber and smoother idle. It also produces better cold starts, and low end performance.

I switched to manifold about a year ago, and will never go back.

Matt
I had heard, and it was probably from you or Shawn or McMudd in another thread, that it was a good idea to switch to manifold vac, but I never understood why until now. You are right, my idle is SIGNIFICANTLY quieter and smoother. Plus the benefit of it running cooler is a big no brainer. I'll never run anything off a ported vac again!

And thanks for setting my mind at ease about the 30* advance at idle. That had me a bit worried it was too much.

Daniel
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Unread 08-07-2012, 11:40 AM   #56
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Yes, welcome to the wonderful world of manifold vacuum! I'd been keeping my yappy trap shut but I'm glad you found it


Shawn
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Unread 08-07-2012, 11:45 AM   #57
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Yes, welcome to the wonderful world of manifold vacuum! I'd been keeping my yappy trap shut but I'm glad you found it


Shawn
haha, thanks.

I get the vib that this whole ported vs. manifold vac is somewhat controversial.
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Unread 08-07-2012, 11:45 AM   #58
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As a side note, I can't find a Q jet in anything under 750 CFM
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Unread 08-07-2012, 11:52 AM   #59
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Originally Posted by Dadamsnv View Post
As a side note, I can't find a Q jet in anything under 750 CFM
Pssssttt......

I've been told Q-jets can be made to run with a wide variety of engine cc's, but I don't know the specific setup for a 304. Shawn?


Matt
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Unread 08-07-2012, 12:03 PM   #60
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Pssssttt......

I've been told Q-jets can be made to run with a wide variety of engine cc's, but I don't know the specific setup for a 304. Shawn?


Matt
PM sent

And it looks like you already beat me to the punch.
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