304 Power and Potential
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=82721
Printed Date: Apr/18/2024 at 11:33pm
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Topic: 304 Power and Potential
Posted By: Rambler Mexicano
Subject: 304 Power and Potential
Date Posted: Sep/20/2016 at 3:40pm
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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. ------------- Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V. |
Replies:
Posted By: 304-dude
Date Posted: Sep/20/2016 at 3:56pm
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When I did my simple bolt on mods to my 73 304, it livened up well. mostly because dual exhaust an better intake with a 650 cfm carb. Adding a cam would even bring more power. I think if you put more effort into torque around 4500 RPM would be more beneficial than trying to get 300 hp out at 7000 RPM. It weighs as much as a 360, and has smaller valves and pistons. Over boring won't do much and stroking is to costly compared to obtaining a 360. If you do want to run 300+ hp, a 100 shot of NOS would do the trick and you don't have to run high octane or go to radical with the build. ------------- 71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
Posted By: Traveller
Date Posted: Sep/20/2016 at 4:07pm
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The 304 is an under-rated engine in my opinion. It's a solid performer with some upgrades. With a Performer 4 barrel manifold, some work in the heads and a better piston choice, it can be quite a good engine. The engine can be overbored (a lot) in relation to the other blocks. .125 is not a problem usually, but it needs to be sonic tested. The factory said max overbore was .155, but I'd test any block first due to core shift and corrosion over the years. The 998 is the same trans used behind the 360, and you won't have quite the peak torque with the 304. It can be built to take a lot of power. So, just depends on budget. How much do you want to spend? I have a 325 incher in our blue car making over 300HP, and it's a hoot to drive. Just need to do a couple things with the front end to make me happier and I'll take it to the track. I run a 4 speed auto made from the 42RE Jeep case. I run the 3.54 rear gear, and the RPM is 2600 at 80MPH on the freeway. About 2000 at 60MPH. As far as times, hope to know that in October. Trying to get the front end stuff done the next couple weekends so I can take it to the track. My 360 powered Hornet runs 13.50-13.70, and the blue car feels faster. I'm crossing my fingers. I'll probably post times once I have them. |
Posted By: tufcj
Date Posted: Sep/20/2016 at 4:23pm
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I had a 304 in my mud-bogger Jeep. It was bored .030", rods shot peened, 10.5 forged pistons. Balanced. Heads were polished/ported with bronze guides and 1.94 and 1.50 Chevy valves. Don't remember cam specs, but around a 290 duration with a .500 lift. Edelbrock Torker with a Holley 600. Easily revved to 6500. I never had it dyno'd but it was easily 300HP. Lots of people thought I was running a SBC conversion until I'd open the hood. Bob tufcj ------------- 69 AMX 74 Javelin AMX 67 Rogue If you need a tool and don't buy it... you'll eventually pay for it... and not have it. Henry Ford |
Posted By: uncljohn
Date Posted: Sep/20/2016 at 5:22pm
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I would have no problems deciding to build a 904 transmission or a 998 for a street performance AMC V8 engine of any size. And my preference would be the later versions with a lock up torque converter and I would have a 2200 rpm stall lock up converter installed at the bare minimum. By the by, any size includes a built up I-6 which I have done and put so far 50,000 miles on with out the slightest inkling of a problem with it. As to a 304? Unless I had a specific reason to build one, my preference would be a 360! ------------- 70 390 5spd Donohue 74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam |
Posted By: purple72Gremlin
Date Posted: Sep/20/2016 at 6:27pm
| I put a performer /edelbrock 650 and dual exhaust/ stock manifolds in a 1979 AMX. this car has a 998, and 2.87TG. It had a bit better driveability. but on the track, it was no faster. I have another 1979 AMX, but this one is completely stock and has the SR4 4 spd. 2.87s open, I want to put a Holley Z intake on this one. and duals with free flows. I very seriously doubt Ill drag race this one. based on my experience, the small bore is the big limit on making good power. a 360 has the same stroke and it runs rings around the 304, and the 360 also responds to mods better too. Ive had 3 cars that came with 304s. 2 1979 AMXs, and one 1972 Gremlin. |
Posted By: 53w
Date Posted: Sep/20/2016 at 6:59pm
| Stock 304 Rods and rod bolts are weak link. Without addressing that problem must stay in stock rpm range. |
Posted By: Ken_Parkman
Date Posted: Sep/20/2016 at 9:25pm
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The 290/304 have tremendous potential and can make some serious power. The heads are very good stock and shockingly effective prepared right, and if you want they can rev fine. For example they are a far more capable engine than a 302 Ford, and look at what people think of those. If you want real proof look at something like Garrett Ghezzi's SS car with a 290, one of the fastest traditional SS cars there is for running under index. The only problem with a 304 is a 360 is the same physical size, weight, and fit, and has 56 more inches. A little better parts availability, but that really does not matter much. You just can't argue with 56 more cubic inches at the same cost, weight, and installation; bigger is always better. It will make more torque and power, and deliver the power at a lower rpm. That's why almost everyone will suggest a 360 or 401, although a 401 is a lot harder to find and takes more money. Just tell them it is a 304, no one will ever know. Unless there is some rule requiring a 304 a 360 is a better plan as it is more cost effective for power. But the 304 is a terrific engine.
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Posted By: Buzzman72
Date Posted: Sep/21/2016 at 6:33am
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In a "run what you brung" world, the 304 should be acceptable for a performance build. Do you hear the Ford guys telling the novices to ditch the 302 and build a 351? Not as often as AMC folks dismiss the 304. And in the Ford universe, there are a lot of built 302's. Aren't the 304 rods the same as the 360 rods? Same deck height block, same journal diameter, same piston pin diameter, same length. So why are we telling folks the 304 rods are inferior? My questions about the 304 concern how much overbore, if any, is necessary to install larger-diameter Chevy valves. Can you use the 1.84" Chevy intakes without boring the block? The stock AMC heads start out better than stock Chevy heads, except for valve sizes. ------------- Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects. |
Posted By: 304-dude
Date Posted: Sep/21/2016 at 6:53am
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Most built 5.0L have boost of some sort. Having thicker walls helps on the 304. Having smaller valves good boost will compensate. So, dollar spent should be on bolt on stuff. A turbo and NOS should get 450 HP on a stock built motor, with a nice mid range cam on pump gas. Building a stock 304 is too costly in HP return over grabbing a 360 and living with stock head setup. Stock 360 heads flow better by valve size, no machining needed. So how it all depends on how you want to spend your money. The Ford guys may stroke kit an engine, but most will bolt on performance of some kind as it is not just easier, just plain cost effective for the gains. ------------- 71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
Posted By: DaemonForce
Date Posted: Sep/21/2016 at 12:19pm
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Ken has this spot on. Here's the thing, I come from a world of L6 AMC. Not that fond of V8s of any kind since my family is so big on Ford FE garbage. Seriously, 390 after 390 is junk and I've never seen these in any decent shape. Considering that my grandfather was a journeyman mechanic that knew what he was doing with big Caterpillar engines most of his life, I'd say he knew what he was doing with the Fords, but even I don't understand what he really wanted. My first taste of an AMC V8 is currently sitting in a 1970 Ambassador with a Holley carb that likes to flood and puke itself after the first minute of use. Doesn't sputter or misfire, just drowns the engine with extremely rich mixture. I'm still thinking of buying this vehicle from a guy North of the capitol but until he gets this issue under control, probably a non-runner. Which is a shame considering that it's a really great powerplant despite sitting for 12 years. It's a big bore skinny stroke engine which I immediately relate to the 232's design made into a V8 reality. The square is about 84% which makes this a nice revver and feels about as torquey as my L6 stroker. I'm tempted to say it's a preferred engine but it can be better. The current V8 I'm messing with comes from a Javelin SST that I bought earlier this month and it is in fact a 304 2v. That's a medium bore skinny stroke engine that is the most square of the entire AMC lineup at 92% and I'm still struggling to get it to stop misfiring but this thing is absolute gold. I'm honestly not a fan of V8s but something about this 304 feels exciting and I'm directly comparing that to the 360. I wonder if a 290 would be the same but seeing how my one trouble spot with these engines is their age, I'll have to find a later 304 from a Grand Wagoneer or start swapping distributors, intakes and cranks just to get this mated up to a more modern transmission like a torqueflite or TH400. The stock Borg Warner 3spd has to go, that's the first line of business with this thing. The most unmentioned thing I think about these engines is the flow rate in the heads. The stock 304 heads are appropriate for what it is and I wouldn't change anything about it unless there's some sort of design issue I don't know about when I finally put on a 4 barrel intake. These are great performing heads that can BREATHE. It's the crossflowing pattern that I find to be appropriate engineering and it's probably the exact same kind of heads that I find on the 1 year earlier 360 that seems to hit some kind of flow limit but with all these tuning issues going on, it's hard to say. Maybe I'll give it Indy heads. |
Posted By: 53w
Date Posted: Sep/21/2016 at 1:14pm
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Over 20 years ago i had a really hot 304 built. Balanced, Ported heads, cam,intake,headers, 600 carb. All good parts. Shifted it at 6000. This was before internet and had no manual or amc expert. Had a ford buddy that built hot ford 302 in local street racing. Used his ford recipe on my 304. Was very fast won alot of street races even took down some mild 350 with it. Problem was the rods we lost 2 engines in 2 years do to rod failures. Both times it looked like the rods fell apart..... remains of rod bearing where perfect, crank perfect. We gave up on the 304/360 and i parked the car for 15 years. As years went by ran into amc engine guys and internet and had amc experts to ask about my 304 build and failures. All said same thing stock 304/360 rod and bolts are good only in stock rpm range they will fail if constantly ran over rpm limit. That was years ago. Currently arp makes rod bolt kits and there is good aftermarket rods advailable. If you get the rods setup right you can build a dam good 304/360. The rods are the weak spot on a 304/360 build, fix that first and build away. |
Posted By: mixed up
Date Posted: Sep/21/2016 at 1:28pm
Im with everybody on this forum 290 and 304 are vey reliable engine for performance I have a 290 in a rambler running 12.30 all day 6000 rpm launch and true the traps yes it has after market rod bolt and piston .030 over but other than that its just a amc im sure with a little work on any engine you can get the performance you desire I have a saying theirs no replacement for displacement  ------------- 69 amx 290 auto 65 220 290 4spd 80 ford fairmont |
Posted By: Rambler Mexicano
Date Posted: Sep/21/2016 at 2:30pm
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Thanks everyone for your responses. All of them have been very illustrative. Now I have a picture of what the situation is like. The idea of of opting instead for a 360 is fiarly tempting but'd love to build up a 304. Like you mention the bolt-ons are no problem (carburator, intake manifold, headers, exhausts, ignition), changing the camshaft and adding the 10.5:1 compression ratio pistons shouldn't be too. You already mentioned the solution to the small valve problem with the Chevrolet units and to find aftermarket conneecting rods and their respective bolts. I think it would be a neat experience if done right. ------------- Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V. |
Posted By: Ken_Parkman
Date Posted: Sep/21/2016 at 4:28pm
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Somewhat contrary to popular opinion (I do that) there is no problem with the 304 valve size, it's more or less perfect for the port size. It does help the ssr to put a little bigger valve in, but I would not overdo it, what is a nice combo is a 1.84/1.50 305 sbc valve set. One thing very often done wrong is too large a valve for the port, which can cause flow separation problems and poor efficiency. Of course this only matters in serious race use - a street application does not care much. Note that Ghezzi's absolute killer SS 290 must use a stock valve size. No problems at all for bore. Properly prepped the 304 head can achieve efficiency levels approaching dedicated race heads - do that with a Ford. I did one set of fairly max effort heads for a CI limited race class - I repeat the 304 heads are amazingly good. Part of the reason a 304 is capable of absolutely trashing a 302. But no one does it cause a 360 has 56 more inches. The rod problem is easy now - reasonably priced billet rods available and no sense in using stock. |
Posted By: 53w
Date Posted: Sep/21/2016 at 7:19pm
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I still have my blown up 304 mod in my bro shed. Kept it to some day rebuild or salvage cam and heads. I really been thinking about a redo on it with good aftermarket rods and run it on a dyno to see what it was making hp wise back then. with good aftermarket rods and other parts it would be worth doing a 304 or 360 if that is what you want. I just went with a 401 cause after my 304 rod failures i did want to mess with the small stuff any more. |
Posted By: Traveller
Date Posted: Sep/22/2016 at 8:55am
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The 304 and 360 rods are the same. Lightening the reciprocating parts will help them live longer. I really like 1.94/1.5 for a larger overbore. Reason being, the bowl can be blended the way I like. The 1.84 is where I would go on a smaller overbore. It's not hard to make the port go 230cfm@.500 lift. That's without porting the runner. On the flow bench the flow characteristics are awesome. Good flow right off the seat, smooth increase all the way up, no noise, no separation. Motor runs down the road very nice. |
Posted By: DaemonForce
Date Posted: Sep/22/2016 at 10:59am
| This is all great. I am about to have access to a Rambler parts car that just dropped. Possible 287 V8 + 3spd torque command combo. It would be a great temporary package for a Javelin while I build up a 304 or whatever else. Are the rods the only weak point? How many of us have dropped forged pistons into an early V8 or added speed parts? |
Posted By: Boris Badanov
Date Posted: Sep/22/2016 at 7:23pm
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304s are excellent, just a bit heavy for the displacement. 4.75 bore centerlines on a 3.75 bore..... On my bucket list is a 4" stroke 304 block engine. I have a 304 saved for that purpose. I just have no time..... ------------- Gremlin Dreams |
Posted By: amcfool1
Date Posted: Sep/22/2016 at 9:49pm
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hi, the 287 will not just drop in to a javelin, whole different beast, would be kinda cool though! good luck, gz ------------- george z |
Posted By: amcfool1
Date Posted: Sep/22/2016 at 10:03pm
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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 |
Posted By: SC397
Date Posted: Sep/23/2016 at 6:59am
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 |
Rambler Mexicano wrote:Posted By: Scipii
Date Posted: Oct/07/2018 at 1:08pm
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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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Posted By: Class Guy
Date Posted: Oct/08/2018 at 7:10am
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. ------------- Addicted to acceleration. Owner and Admin for www.classracerinfo.com |
Posted By: PHAT69AMX
Date Posted: Oct/08/2018 at 10:03am
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Does anyone happen to know the AMC Head Runner Volumes in cc's ? -------------  Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video |