differance in 258 and 304

[Incommando]

Either way you go make sure you are careful with the cam & dizzy gears matching when changing either component in an AMC V8. I usually re-use both of the originals.

 

[1986cj7]

Thanks for reminding me about the difference in hardnes in the gears would hate to go though all the trouble of rebuilding and end up chewing the cam gear up.

 

[jasonmark1993]

I think best bang for the buck would be running a little higher compression and porting the heads yourself. I strongly recommend contacting one of the several AMC engine specialists or visiting an AMC specific forum; there a couple more in tune to race engines/hot rods.

Id also research into porting the heads; not sure if youve done it before?

Depending on the size of the valves/vs port, you may not want to take much out of there. If you take too much material out, you can actually slow down air flow=hurt power. Sometimes you just take out a little hump and then polish everything rather than making the whole port bigger. Opening up the port at the last half inch before the intake/header helps too; just use the appropriate gasket as a stencil. Aftermarket intakes/headers are typically larger by about 1/8" all the way around.

 

[1986cj7]

Yeah Jasonmark I've read about how to port the heads but never tried it yet. It may be the way to go to keep cost down.

 

[jasonmark1993]

Its a bit of work and if you dont have the tooling, you may be able to buy a set of heads for the money. You'll need a pretty serious air compressor; the die grinder will be running full bore for like 8-10 hrs and maybe up to 20.

Not sure if they make an electric die grinder that will get the job done.

Pretty sure the bits are like 30 bucks or something.

 

[tarry99]

Yeah Jasonmark I've read about how to port the heads but never tried it yet. It may be the way to go to keep cost down.

1986CJ7

I believe the first and only question one should ask is: What are you going to use this motor for?...........if you are going racing then having discussions about induction systems ,cams,porting cylinder heads, port speed, flow, compression ratios & cam & ignition timing ETC, should all be considered.

Torque simply is a derivative of horsepower period. Torque is the static measurement of how much work and engine does, while power is a measure of how fast the work is being done. Simply put Torque moves the car while Horsepower keeps it moving.
Horsepower and Torque are always equal at 5252 RPM's.
Increased displacement is the easiest way to increase torque.
But remember torque is measured at the crank shaft and not at the wheels.

In this application of a very basic AMC 304 V8 motor it is highly unlikely that one would build a motor that see's more than 3000-4000 Rpm's maximum at which point porting cylinder heads and having a longer duration cam shaft would be of such an insignificant advantage that one would surely wonder why it would even be considered since the operating range off road is maybe 10-15 mph @ say 1200 Rpm's and on road maybe 65 mph @ 2200 Rpm's?

If you have a grocery getter and part time 4-wheeler ...........I would think that one should be concentrating on Torque but only at the wheels.....and not the crankshaft.........simply put "Gear Multiplication" or torque at the wheels is what Jeeps need most.

Simply , the Transmission multiples the torque coming from the engine by a factor equal to the overall gear ratio.

Either one of those motors coupled with the right gears will do a pretty good job.

Now don't get me wrong, If getting to the grocery store a little faster is what your after then by all means have at it!

 

[1986cj7]

1986CJ7

I believe the first and only question one should ask is: What are you going to use this motor for?...........if you are going racing then having discussions about induction systems ,cams,porting cylinder heads, port speed, flow, compression ratios & cam & ignition timing ETC, should all be considered.

Torque simply is a derivative of horsepower period. Torque is the static measurement of how much work and engine does, while power is a measure of how fast the work is being done. Simply put Torque moves the car while Horsepower keeps it moving.
Horsepower and Torque are always equal at 5252 RPM's.
Increased displacement is the easiest way to increase torque.
But remember torque is measured at the crank shaft and not at the wheels.

In this application of a very basic AMC 304 V8 motor it is highly unlikely that one would build a motor that sees more than 3000-4000 Rpm's maximum at which point porting cylinder heads and having a longer duration cam shaft would be of such an insignificant advantage that one would surely wonder why it would even be considered since the operating range off road is maybe 10-15 mph @ say 1200 Rpm's and on road maybe 65 mph @ 2200 Rpm's?

If you have a grocery getter and part time 4-wheeler ...........I would think that one should be concentrating on Torque but only at the wheels.....and not the crankshaft.........simply put "Gear Multiplication" or torque at the wheels is what Jeeps need most.

Simply , the Transmission multiples the torque coming from the engine by a factor equal to the overall gear ratio.

Either one of those motors coupled with the right gears will do a pretty good job.

Now don't get me wrong, If getting to the grocery store a little faster is what your after then by all means have at it!

Thank you for your insight. MY jeep already has 4.10 gears and 33" tires which is as low in gearing I plan on going and largest tires I'm going. This jeep sees about 50/50 trail/highway so the 4.10 are trade off for more highway friendly driving. One question though the increase in hp also increases the response time this torque can be unleashed, or I'm I wrong. Now I'm not looking to break any 1/4 mile speed records just want to uncork the potentially of the motor by increasing the stroke with a 390 crank cam, and shuck, with out breaking the bank. So 360 heads are not out of the question instead of porting the AMC 304 heads. But also if the porting I can do my self to save a little money buy doing it my self may be an option. Also compression I would like to keep to 9:1 or little lower to be able to use 87 pump gas. And I know some are shaking there heads wondering why I don't go with a 360. But I'm looking to increase torque and hp and mpg which will be a tight line to walk and some compromises will have to be made. The only thing I need to upgrade in the drive line beside the motor in my opinion, is beefier drvie shafts which are stock to hand the extra hp and torque. Again thanks for your input and keep it coming. The next question is under square motors to over square motors that should open up another can of worms. Here's a great site for stroker basic and theory for those new to strokers like me.http://www.fordmuscle.com/archives/2003/09/stroker/ Now this is a ford motor site but still has alot of good info.

 

[tarry99]

Thank you for your insight. MY jeep already has 4.10 gears and 33" tires which is as low in gearing I plan on going and largest tires I'm going. This jeep sees about 50/50 trail/highway so the 4.10 are trade off for more highway friendly driving. One question though the increase in hp also increases the response time this torque can be unleashed, or I'm I wrong. Now I'm not looking to break any 1/4 mile speed records just want to uncork the potentially of the motor by increasing the stroke with a 390 crank cam, and shuck, with out breaking the bank. So 360 heads are not out of the question instead of porting the AMC 304 heads. But also if the porting I can do my self to save a little money buy doing it my self may be an option. Also compression I would like to keep to 9:1 or little lower to be able to use 87 pump gas. And I know some are shaking there heads wondering why I don't go with a 360. But I'm looking to increase torque and hp and mpg which will be a tight line to walk and some compromises will have to be made. The only thing I need to upgrade in the drive line beside the motor in my opinion, is beefier drvie shafts which are stock to hand the extra hp and torque. Again thanks for your input and keep it coming. The next question is under square motors to over square motors that should open up another can of worms. Here's a great site for stroker basic and theory for those new to strokers like me.Stroker Motors Basics and Theory - FordMuscle Now this is a ford motor site but still has alot of good info.

1986

I'm still not quite sure what you hope to obtain? A faster Jeep to go down the highway or a more capable Jeep off the road......there is a balance somewhere that only you can answer.

In answer to your first question if you have more horsepower the acceleration rate of the motor or rise time will be faster in most cases.

You also mention that you would like to make more power and torque while
at the same time keeping compression low and burning 87 octane fuel?? If I was interested in making more power adding compression is free energy.

Porting without a flow bench and the ability to measure port & combustion chamber volumes in each port would be akin to walking in the dark.

The basics of making Horsepower are quite simple and only require one thing and that is burning fuel or gas to create heat. All fuels burn at a given BTU mixed with oxygen at a rate of about 14:1......the more fuel you burn the more heat you create and the more power is generated in a given 4-stroke cycle "Period"...........getting the fuel into the combustion chamber , compressing it and then igniting it has always been the biggest challenge in a normally aspirated motor.

The motor's ability to RPM and generate more combustion cycle's in a given time period thus burning more fuel in that period is where Horsepower comes from.

Adding a stroke to a motor adds cubic inches & perhaps some horsepower but also takes away from the ability of the motor to RPM and reduces it's efficiency as compared to a short stroke high RPM motor. More Torque yes more power maybe.

Figure out where you want the most gains and build the motor to fit those needs..........

 

[jasonmark1993]

I think for bang for the buck, using the AMC 304 you have with some inexpensive upgrades will be the best bet.

You probably dont want to reuse the same cam or pistons so thats a no brainer to spend a few bucks there. 8.4 CR is pitiful. Id just find out what CR you get with the 290 pistons. From what Ive read they dont make flattops for the AMC 304 . If you end up in the 9.25-9.5 range and dont run excessive timing, you probably wont need the highest octane fuel, but if you want the most power you want to run the most timing you can.

Porting the heads is the cheapest route; just takes a little time.

If you do stroke the engine you are probably going to increase the cost quite a bit; some engines are cheaper than others so you'll just have to look into it. I really dont know on the AMC 304 .

The drivelines arent that big on there but unless you are dropping the clutch or trying to launch your jeep, the stockers are fine. I ran the stock driveshaft in my turbocharged 5.0 that dynoed 503 ft lbs of torque at the wheels; I had no traction but it held up fine under hard acceleration once I was moving.

 

[CJ]

~~~ increasing the stroke with a 390 crank cam, and shuck, with out breaking the bank. So 360 heads are not out of the question instead of porting the AMC 304 heads. ~~~

What is a 390 crank cam? Do you mean 390 crank?

The valves on 360heads will hit the AMC 304 cyl walls unles the walls are notched. Then the valves become shrouded negating the benifit of the larger valves.

 

[1986cj7]

What is a 390 crank cam? Do you mean 390 crank?

The valves on 360heads will hit the AMC 304 cyl walls unles the walls are notched. Then the valves become shrouded negating the benifit of the larger valves.

Yes a 390 crank is what I meant sometimes the connection between the brain and the fingers typing don' match sorry for the typo. And info on th e valves I'm a little new to building motors and trying to learn as much as I can, reading on the internet as much as I can. Also I've look into the parts for stroking the AMC 304 it is about $1500 for parts including crank, cam pistions ect. I'm not wanting any more then 9;1 or 9.5;1 to keep from having to run higher octane fuel. Thanks for all the info as always and keep it coming, all opinions are welcome.

 

[CJ]

Did the $1500 include chevy rods?

 

[1986cj7]

Did the $1500 include chevy rods?[/QUOTE
The info I got was forged H beam 3d super rods rod length 5.7" 4340 steel match weight set +- 2 grams magnafluxed and sonic and x-ray tested heat treated stress relieved. Not sure yet if going with this just checking prices now and seeing whats out there.