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Searching for the golden tuning

39K views 683 replies 23 participants last post by  Matt1981CJ7 
#1 ·
I am beginning the saga of fine tuning my amc 304 for best performance. I will be working on both the carb and timing to make my tired old motor perform to its fullest.

As for equipment, I have a freshly rebuilt holley 2300 2bbl carb (similar in tuning to a motorcraft carb), an unknown brand HEI, an edelbrock performer intake, and unknown brand tube headers.

I will be using JeepHammer's "tuning amc v8s" instruction thread as my guide. I will list part numbers of all my tools, parts, and kits as I use them. I will post everything I do, even the embarrassing srew-ups.

This thread is for people who are interested in tuning their motors at home using good, old fashioned elbow grease, and for those looking for a laugh I'm sure.

Wish me luck, here I go! :2thumbsup:
 
#32 ·
Dada,

Good work. Your centrifugal curve is much improved.

I'm at 6000' elevation and run my initial at 11. It runs fine at 12, but I like to be on the safe side.

So, when do we get to see a video of the "Golden Tune". :)

Matt
Thanks Matt :D

Right now my tune is more like a bronze tune (Olympic joke) :laugh:
I have a few more things (dial in main jets, experiment with vac advance) to get done before I will consider it golden.

Also, I have an embarassing header leak I need to take care of before I post a video. :rolleyes:

I'm glad to know you also advance your base tuning for elevation! That validates the research I did this morning
 
#33 ·
I can feel that the ol 304 could use a bit more carb at about 2700 RPM. She tends to have a very predictable climb in speed right up until that point, then she climbs speed linearly and a bit slower. I can certainly get by with the holley 350 without a single problem, and I bet I can get pretty good mileage out of it, but a little bit bigger carb might give me everything I want (power, economy, 4x4 prowess).

I've been eye balling the Holley truck avenger 470. Holley states that the 470 is for six cylinder motors, but there is no reason a small v8 like the 304 couldn't manage one just fine. Have any of you guys used this carb, or do any of you have any ideas/opinions on this carb?? It has everything done to it already that I would do to my 2300 (350 CFM 2bbl) for wheeling. I feel 470 CFM should be perfect for it because it has the performer intake, tube headers, and will eventually have a torquey low end cam. The Summit CFM calculator puts a 304 race motor with a 5000 RPM max at 484 CFM (not that mine will be all raced out with high RPM goodies). I feel like anything larger will be past the point of diminishing returns.

Thoughts? Ideas?
 
#555 ·
I can feel that the ol 304 could use a bit more carb at about 2700 RPM. She tends to have a very predictable climb in speed right up until that point, then she climbs speed linearly and a bit slower. I can certainly get by with the holley 350 without a single problem, and I bet I can get pretty good mileage out of it, but a little bit bigger carb might give me everything I want (power, economy, 4x4 prowess).

I've been eye balling the Holley truck avenger 470. Holley states that the 470 is for six cylinder motors, but there is no reason a small v8 like the 304 couldn't manage one just fine. Have any of you guys used this carb, or do any of you have any ideas/opinions on this carb?? It has everything done to it already that I would do to my 2300 (350 CFM 2bbl) for wheeling. I feel 470 CFM should be perfect for it because it has the performer intake, tube headers, and will eventually have a torquey low end cam. The Summit CFM calculator puts a 304 race motor with a 5000 RPM max at 484 CFM (not that mine will be all raced out with high RPM goodies). I feel like anything larger will be past the point of diminishing returns.

Thoughts? Ideas?
I just installed this carb on my 304 ran great out of the box a little rich dropped the jets two sizes for primary and one size for secondaries I'm at about 4000 ft. The fronts and rears on the 470 are both 57's. Was a little flat off idle but as you I set my base timing to 8* before tuning. Went back to 11 or 12 and was set. Also installed the lighter spring so the secondaries open earlier. Will watch fuel consumption for awhile might go back to the original spring. Overall this carb does what it says and is great for a near stock 304.

Sent from my XT907 using AutoGuide.Com Free App
 
#34 ·
Don't forget that the Holley 2 barrel and 4 barrel carbs are rated at different depressions.

If you were to compare them both at the 1.5 inch depression that 4 barrels are rated at for a more apples to apples kind of deal, it'd be more like a 271 carb vs. a 470 carb. I think the 470 is probably about right for a 304 grunt.


Shawn
 
#36 ·
swatson454 said:
Don't forget that the Holley 2 barrel and 4 barrel carbs are rated at different depressions.

If you were to compare them both at the 1.5 inch depression that 4 barrels are rated at for a more apples to apples kind of deal, it'd be more like a 271 carb vs. a 470 carb. I think the 470 is probably about right for a 304 grunt.

Shawn
Ha ha. I feel dumb, I have no idea what that means, what is depression??
 
#39 ·
My bad.

To rate a carb's airflow, they have to pull a vacuum through it and measure it. They also have to pull the same vacuum (depression) through different carbs to know which one flows more in a fair and accurate way.

4 barrels are usually flowed at a 1.5 inch pressure drop (same thing as vacuum or depression, just sounds more engineerier :)) while most 2 barrels are flowed at a 2.5 inch pressure drop.

For example, they'll hook a 4 barrel up to a flow bench and turn up the juice till a fancy sensor or a simple manometer tells the operator that a 1.5 inch pressure drop between atmosphere and the vacuum under the carb has been achieved. Then the machine tells how much air is flowing through the carb at that depression.

2 barrels have always had the flow bench cranked up to a 2.5 inch drop. You have to mathematically convert the readings if you want an apples to apples comparison between a 2 barrel and a 4 barrel.

Clear as mud?
 
#37 ·
ASteve said:
Love the thread. One question. Why is your distributer vacuum advance pointed straight at the radiator. All the 304's I've seen point to the driver side radiator and head light, unless your firing order has been altered...?

Sorry if this is stupid question but...just curious.

Again, love the thread.

SC
Thanks man :D

I'm just as curious as you, I don't know why it's like that. Haha
 
#38 ·
Big guy,

I don't have any personal experience with the Truck Avenger 470. But I read a post where it was the traditional rant about "fuel injection being god" and "engines can't run on carburetors" yada, yada, yada. This guy was commenting on the 470 and he was a jeep cross country racer. That is all he did for a living. He used one for four years (?) on his vehicle through all his jeep went through and never had a problem. It did what he needed it to do. From his reply, I would trust them. But I have no personal experience with the 470.

Take care,
 
#40 ·
1SASjeepster said:
Big guy,

I don't have any personal experience with the Truck Avenger 470. But I read a post where it was the traditional rant about "fuel injection being god" and "engines can't run on carburetors" yada, yada, yada. This guy was commenting on the 470 and he was a jeep cross country racer. That is all he did for a living. He used one for four years (?) on his vehicle through all his jeep went through and never had a problem. It did what he needed it to do. From his reply, I would trust them. But I have no personal experience with the 470.

Take care,
Thanks :)

I'm of the opinion that while FI is great for wheeling, a carb can be made to function just fine if you know what you are doing, and personally I'm a big carb fan.
 
#41 ·
swatson454 said:
My bad.

To rate a carb's airflow, they have to pull a vacuum through it and measure it. They also have to pull the same vacuum (depression) through different carbs to know which one flows more in a fair and accurate way.

4 barrels are usually flowed at a 1.5 inch pressure drop (same thing as vacuum or depression, just sounds more engineerier :)) while most 2 barrels are flowed at a 2.5 inch pressure drop.

For example, they'll hook a 4 barrel up to a flow bench and turn up the juice till a fancy sensor or a simple manometer tells the operator that a 1.5 inch pressure drop between atmosphere and the vacuum under the carb has been achieved. Then the machine tells how much air is flowing through the carb at that depression.

2 barrels have always had the flow bench cranked up to a 2.5 inch drop. You have to mathematically convert the readings if you want an apples to apples comparison between a 2 barrel and a 4 barrel.

Clear as mud?
Makes perfect sense :thumbsup:

I like things that sound engineerier. After all, I just graduated from UNR (university of Nevada Reno) with a BS in mechanical engineering. I would love to be involved in the development of these systems, but I'm a few years behind I suppose :(

The only thing that doesn't make sense is why they would take the CFMs of 2 and 4 bbl carbs at different depressions.

Thanks for the info man!
 
#43 ·
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
 
#46 ·
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.

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??
 
#47 ·
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
 
#48 ·
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. :thumbsup:

Matt
 
#51 ·
Thanks Bill and Matt :cheers2:!

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
 
#49 ·
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.
 
#52 ·
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
 
#50 ·
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.
 

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#53 ·
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
 
#55 ·
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. :thumbsup:

Daniel
 
#54 ·
Dadamsnv said:
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.
 
#63 ·
Shoot, GM put "big" Q-Jets on grannys Caprice Classic with a smogged-to-death 305.


Shawn

Ok, I got a little carried away with "granny's Caprice Classic" but they did use a 650 cfm Q-Jet on some Monte Carlos with a 305 HO option; which is kind of an oxymoron, lol.
 
#64 ·
Shoot, GM put "big" Q-Jets on grannys Caprice Classic with a smogged-to-death 305.

Shawn

Ok, I got a little carried away with "granny's Caprice Classic" but they did use a 650 cfm Q-Jet on some Monte Carlos with a 305 HO option; which is kind of an oxymoron, lol.
Hmm...

It seems more and more as I read that the 470 may even be slightly under powered for the 304, but there isn't any real science behind it, just opinions. And more than a few people are running Q jets on their 304s, and ALL seem to love it! Some even use the 750 CFM Q jets with great success. Looks like the way to go I suppose. I like the Holley TA, buts that a $400 carb, and even with the mods, the Q jets still seems to out perform.
 
#65 ·
Dada,

That's the same conclusion I came to. I believe there's something unique about the design that makes the Q-jet perform better than most at severe angles. When guys like John Nutter mention that many of his wheeling buddies use Q-jets on their 304s, and love them, I tend to pay attention. We'll see....

Based on the info from the thread I linked to earlier, it appears the stock Chevy 350 truck Q-jet setup works pretty well with the 304.

Matt
 
#66 ·
Dada,

That's the same conclusion I came to. I believe there's something unique about the design that makes the Q-jet perform better than most at severe angles. When guys like John Nutter mention that many of his wheeling buddies use Q-jets on their 304s, and love them, I tend to pay attention. We'll see....

Based on the info from the thread I linked to earlier, it appears the stock Chevy 350 truck Q-jet setup works pretty well with the 304.

Matt
Great!

All I need now is some spare $$$ :laugh:

until then, I will run the hell out of this holley 2300. Unfortunately, I need a new rad, hoses, and fan shroud. My JB welded rad just started to leak, it wont be long until it completely goes. Might as well beat it to the punch
 
#68 ·
I was planning on replacing timing set, and my cam gears if needed, but when I pulled the timing cover off today, I found an uncharacteristically clean timing set, cam gears, and timing cover insides. I'm not sure how sloppy a new chain is, I've only done a magnum 360 before. Does this timing set look as good as I think it does? I know it's hard to tell from the pic, but I'm almost certain this is hardly used.

I figure I'll post this here since it deals with my timing, plus I will be experimenting with why my HEI vac advance points at the radiator fan.
 

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