Bone stock 440 magnum - Dyno Carter AVS vs 850 vacuum secondary carb

[StockMan]

This test claims that swapping to the bigger carb on the stock 440 was worth almost 10hp, and more than 10lb/ft.

http://www.hotrod.com/how-to/engine/mopp-0104-buildup-1969-440-magnum-engine/

[StockMan]

I guess I should have made note of why I posted this.  I've been wondering about moving to a larger carb, from the AVS 625CFM unit to the AVS 750 unit.
This article reported that the dyno sheet showed 1.4-inches Hg of vacuum being developed at WOT, in the manifold by 5400 rpm, suggesting that even the larger carb was a restriction at higher RPMS.

[c00nhunterjoe]

I have always said the mild 440s will benefit from an 850. Some claim that throttle response will suffer, but i feel that loss is negligible and probably wont be felt in the seat-o-pants meter.

Heck, i borrowed an 850 to try on my 383 and it LOVED it. Couldnt talk him into selling so i stayed with my 750.

[c00nhunterjoe]

I guess I should have made note of why I posted this.  I've been wondering about moving to a larger carb, from the AVS 625CFM unit to the AVS 750 unit.
This article reported that the dyno sheet showed 1.4-inches Hg of vacuum being developed at WOT, in the manifold by 5400 rpm, suggesting that even the larger carb was a restriction at higher RPMS.

Are you leaving power on the table with the 625?    Yes, but it is mostly upper mid- top end power. If your car is strictly a cruiser, then in my opinion, buying a bigger carb just because its bigger, is a waste. This is also assuming that you have decent pistons in your "stock" 440. You could be as low as 7:1 depending on whats in it.

[StockMan]

I'm running a freshened up 68 440 magnum with the original pistons/bore everything else stock including cam.  
Your probably right about gains in the higher RPMs only, I'll likely be giving up some fuel efficiency to.
It was going for a good price (150) so I picked it up already.  Hopefully it makes some noticeable difference.

Thanks

[Canadian1968]

Good post . I always like reading articles like that .  Pretty basic , straight to the point , you do this - you get this !

[John_Kunkel]

If you're driving on the street you won't feel the added 10 hp on the buttmeter and, possibly, you'll lose some drivability.

[BSB67]

I'm running a freshened up 68 440 magnum with the original pistons/bore everything else stock including cam.  

Curious as to what was done then.

[StockMan]

I'm running a freshened up 68 440 magnum with the original pistons/bore everything else stock including cam.  

Curious as to what was done then.

The 440 I have was a low mile bone stock motor, I re-ringed the original pistons (with a light hone), new mains and rod bearings along with a new MP magnum cam, that's it.
I picked up the larger AVS carb, but haven't had a chance to put a kit into it yet.  I have a friend that has done this swap before, and said that I'll feel more power in the mid range and higher RPM, and I will lose around 3-4 mpg from the smaller AVS.  The 440 has lots of power even with the smaller AVS on it.  Impressive carbs, the AVS.

One thing that I always wondered about, when I pulled the original rings off the pistons, there were thin flat metal spacer rings under the compression rings.  To me these looked like a great idea, in terms of adding more stability to the piston position in the bore, potentially even reducing piston noise.  I couldn't find any modern ring sets that had these supporting rings, and I was afraid the put these old ones back in, under the new rings.  The 383 I have has then to, when I put that motor back together I'm going to consider putting them back in.

[BSB67]

One thing that I always wondered about, when I pulled the original rings off the pistons, there were thin flat metal spacer rings under the compression rings. 

Could you elaborate?  Top ring is for compression, second is oil scraper (sometimes call second compression ring) and the third is the oil control ring. The oil control ring is usually a three part assembly with thin outer rails.  Is this the ring you are talking about? 

[StockMan]

One thing that I always wondered about, when I pulled the original rings off the pistons, there were thin flat metal spacer rings under the compression rings. 

Could you elaborate?  Top ring is for compression, second is oil scraper (sometimes call second compression ring) and the third is the oil control ring. The oil control ring is usually a three part assembly with thin outer rails.  Is this the ring you are talking about? 

They are thin corrugated shims in behind the top two compression rings.  They create outward pressure from the inside part of the rings, pressing the ring against the bore.
Maybe they were in there because of the cast material used for the rings at that time.??  Good idea though.  I'm not sure now if I have any of them to show in a pic.

[John_Kunkel]

Thin spacers along side the compression rings are there to save the pistons when the ring lands wear out before the piston does. A machine shop uses a cutter to cut new wider ring grooves and the spacers are installed above the ring.

[BSB67]

Kind of afraid of that.  Is it to fix the slop in the groove, or worn land?

So to the OP, its likely you don't have a low mileage motor, and you probably need to put the spacers back in.

[StockMan]

Kind of afraid of that.  Is it to fix the slop in the groove, or worn land?

So to the OP, its likely you don't have a low mileage motor, and you probably need to put the spacers back in.

These spacers are in behind the rings in the groove, applying outward pressure to the ring to the bore.
Anyway, I'd have to post a pic to illustrate, and I don't think I have them anymore, I'm assuming Chrysler installed these in all of their big blocks from the factory, considering that my 440 had them and also my 383.  The motor I have has no bore wear at all.  I was lucky enough to score a very low mile motor from an older buddy that had been hanging onto it for years.

I'm hoping the larger carb is going to bring out a touch more mid-range power.

[Jaysick]

Here's another article I ran across when I was debating on whether or not the 850 on my 383 was too much carb.    Granted this article used a 383 for the tests but offers some valuable insight either way    
http://www.hotrod.com/how-to/engine/mopp-1207-carburetor-dyno-test/

[StockMan]

Here's another article I ran across when I was debating on whether or not the 850 on my 383 was too much carb.    Granted this article used a 383 for the tests but offers some valuable insight either way    
http://www.hotrod.com/how-to/engine/mopp-1207-carburetor-dyno-test/

Nice article, its hard to believe that the 383 would like all that carb.  The Chrysler engineers I think decided upon the optimal carb for the 68' 383 with the 625CFM AVS, good all around performance.  And for the 440 magnum the larger 750AVS (or whatever it was).  I'm eager to try this AVS carb I picked up, I have the 625 on my 440 now and I find it performs well, I expect the slightly larger carb to produce a noticeable gain.

[chargerbr549]

Here is some interesting info I remember coming across when watching some of the Chrysler Master Tech videos when I worked at the Chrysler dealership, at about 12 minutes into the video it talks about carburetor and manifold mods to do to 340 up to 440 motors back in 1969, it was recommending around a 700 Holley on 340's and 850 Holleys on 440's as a performance upgrade.

https://www.youtube.com/watch?v=rvzotL7DsnA

[StockMan]

Here is some interesting info I remember coming across when watching some of the Chrysler Master Tech videos when I worked at the Chrysler dealership, at about 12 minutes into the video it talks about carburetor and manifold mods to do to 340 up to 440 motors back in 1969, it was recommending around a 700 Holley on 340's and 850 Holleys on 440's as a performance upgrade.

https://www.youtube.com/watch?v=rvzotL7DsnA

Interesting information.

[Cooter]

If CFM requirements of a perticular engine under load were truly understood, there would never be another carb thread. Even though there's an 850 Holley on that 440, you do realize that many times the engine will only use what it needs. I've seen lot's of times where FUEL CURVES of larger carbs (NOT CFM RATING) is all a particular engine needed. But because that "850 Holley" ran better, 850 is "the sh*t" .....

[StockMan]

If CFM requirements of a perticular engine under load were truly understood, there would never be another carb thread. Even though there's an 850 Holley on that 440, you do realize that many times the engine will only use what it needs. I've seen lot's of times where FUEL CURVES of larger carbs (NOT CFM RATING) is all a particular engine needed. But because that "850 Holley" ran better, 850 is "the sh*t" .....

CFM requirements of a particular engine under load, sounds interesting, please explain.

[StockMan]

Kind of afraid of that.  Is it to fix the slop in the groove, or worn land?

So to the OP, its likely you don't have a low mileage motor, and you probably need to put the spacers back in.

These spacers are in behind the rings in the groove, applying outward pressure to the ring to the bore.
Anyway, I'd have to post a pic to illustrate, and I don't think I have them anymore, I'm assuming Chrysler installed these in all of their big blocks from the factory, considering that my 440 had them and also my 383.  The motor I have has no bore wear at all.  I was lucky enough to score a very low mile motor from an older buddy that had been hanging onto it for years.

I'm hoping the larger carb is going to bring out a touch more mid-range power.

So nobody has seen these spacer type rings installed 'Behind' the compression rings?  I'm just a little curious as to their intended purpose. 
I can't find any useful material on them.  I'd like to know if it makes sense to install them behind the new rings?  Or, were they there to apply more pressure behind the cast ring sets only?