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304 Power and Potential

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amcfool1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcfool1 Quote  Post ReplyReply Direct Link To This Post Posted: Sep/22/2016 at 10:03pm
Hi again, i built up a pretty nice 304 with forged pistons about 20 years ago, for my 80 J10. That was the last time you could find "off the shelf" forged pistons for a 304. (btw, same piston as a 258) Forged pistons for a 304 or 258 are not available anymore, except from specialty houses like Bulltear, and they are priced accordingly. Also, unless you are adding an artificial atmosphere, you don't really want or need forged pistons. They expand at a different rate than cast, so have to fit "looser" in the bore, and as a result can be noisy. Nothing wrong with a good quality cast piston, unless you plan to hit the Bonneville Salt Flats. good luck, gz
george z
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Sep/23/2016 at 6:59am
Originally posted by Rambler Mexicano Rambler Mexicano wrote:


Some AMC models I would like to own in the future if I have the chance are the 1977-1979 AMXs, 1978-1979 Pacer coupe, 1974-1975 Gremlin X Rallye and 1974-1975 Hornet Rallye X .

The main feature of these models is they were available with the 304 V8, that'd would be the engine of choice to buy any of them. I could opt for a factory 360 V8 in both Hornets but that would extremely rare and highly unlikely to happen.

In regards to accessories and appearance I'm with the crowd that supports full originality without being a purist. But in regards to the mechanical department, that's another story.

I always like to make cars better performance-wise. That's what I've done to my current car (1981 VAM Rally GT with a 282 six), all original parts and looks but I threw in dual exhausts, flat pistons, reduced the height of the head, ported head and intake manifold, performance carburetor, performance distributor, etc.

Canadian/American-made AMC cars with V8 engines (not available in Mexico) mostly get the following treatment, the 304s (and 290s) most times get removed (and discarded) in favor of 343/360 or 390/401 units.

In my case, I would like KEEP all 304s BUT would like to build them into higher performance units. I'd keep the 360s and 401s for higher performance models (AMX, Javelin) and heavier larger sized models (Rebels, Matadors, Ambassadors).

It would have been cool for AMC to offer a dual-exhaust, four-barrel, four-speed version of the 304 like they did with the 1966-1969 290 V8s. When the GEN-3 engines were introduced they opted instead for a 2-barrel version of the 360, but, alas, no four-speed in this one. The 1979 AMX was the only time the 304 had a four-speed transmission.

If I build a 304 from the ground up with performance parts (heads, cam, pistons, four-barrel intake, four-barrel carburetor, ignition, headers, dual exhausts) what results can I expect from it performance-wise?

Does anyone have 0-60 and quarter miles numbers on customized/modded 304 units?

I'm Not planning to BORE OUT any of the engines (at least so far), but I rather ask the PROs and CONs of such a decision first.

How much can a 304 block be bored out? Are there differences between blocks through the years? Most of the ones I'd be working with are the 1974-1979 units.


In regards to the added power of the engines and how could that affect the transmissions, my plans would the following.

I am mostly a STICK driver myself, I'd rather get floor-shift manuals on the Hornets, Gremlins and 1979 AMX, but I'd keep the automatics on the Pacer and the 1977-1978 AMXs.

I know the 1977-1979 SR-4 four speed manual is not a performance transmission and is practically nothing more than MARGINAL in regards to high amounts of torque. I wouldn't keep the 150-T three speed manuals either. I would have them swapped in favor of five speeds (WC T-5, AX5, AX-15) or Hurst linked four-speeds (T-10).

As for the A998 TorqueFlyte automatic, medium duty unit, how would it stand out against a highly modded 304?

Would you recommend swapping it for a very-high-torque A727 unit?

The A999 models used in Eagles, higher torque resistance than the A998, can be used as an alternative to the A727?

Thanks in advance for any information you can provide.



Page 3 at the bottom shows actual dyno data from a +.030" overbored 304 with a Comp268H cam, Edelbrock performer intake and 500 cfm Edelbrock carb and Free Flow exhaust manifolds. This would be a typical street build with 8.5:1 compression ratio.
http://rebsamcandjeep.proboards.com/thread/144/dyno-time?page=3
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scipii Quote  Post ReplyReply Direct Link To This Post Posted: Oct/07/2018 at 1:08pm
I'm working on a daily 727 (moderate upgraded) with a stock 304 and a big cake air filter; still have the stock 2-bbl and respective manifolds, but I cut the muffler off and am running free-flows. Made a difference taking the nasty smog pump off and the over-back pressure muffler.
Looking to install a free flow X-pipe to keep the back-pressure away whilst gaining some scavenging and getting a bit more on the even pulses with torque.

So point is; I've found just bringing it up to spec with our tech and knowledge we have now seems to actually make the 304's happy; granted it'll never be a 700hp Nascar worthy engine, but for a balanced daily/fun car, I do believe with simple bolt ons, electronic ignition sway it'll respond better, give you slight increases all around including mileage (I noticed a small gain even with my heavy foot).
I wouldn't give up on it for daily stuff but like several people have pointed out, AMC V8's are all exactly the same block and heads (390's & 401's use forged steel internals?) just bored and stroked different (as far as I can tell, please correct me if i'm wrong)

I wouldn't doubt one could get 300hp out of them, but with just basic bolt ons, what are the actual number's we're getting?

Sorry for reviving a dead thread, but just like AMC, it'll always be back!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Class Guy Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2018 at 7:10am
Originally posted by Ken_Parkman Ken_Parkman wrote:

I repeat the 304 heads are amazingly good.

Spend some time on 304 heads (517, 990, 086, etc.) you will come to the conclusion that the basic ports are the same as 360-401 heads, just the bowls are reconfigured to accommodate the smaller valves.  Chevy did the same thing with heads of the 305s.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2018 at 10:03am
Does anyone happen to know the AMC Head Runner Volumes in cc's ?
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