302 Build Ideas

[Ryans67]

So I bought a couple 67 coupes yesterday and they came with a few different goodies in terms of spare engine parts. I want to build a nice engine for one of the cars. I try not to do anything with engines and leave it to the pro's, but I want to atleast have some background before I start looking for a shop to do the work. The parts I got were;

-stock 302 block that has some damage to one of the cylinders. I think it will be reusable if I want.
-brand new set of Edelbrock victor Jr heads. I can pull the PN if there is a big difference.
-A Weiand tunnel ram intake with dual 4barrel edelbrock carbs. Not sure how great the carbs are, they are basically new, but I will not use this intake.

So should I just buy a shortblock from CHP or Ford and throw these heads on with a decent intake? I want to keep the car very streetable, but would like to get around the 400hp mark.

Should I sell everything and start fresh? If I were, what is a good 302 block to start with, the newer 5.0's?

Thanks for any advice.

-Ryan

 

[kilgorq]

85 and up Mustang 5.0 blocks have a lower rotating mass. (The Crank counterbalances are smaller.) This will make them rev faster. Also in most cases they are set up with roller lifters. Roller lifters reduce internal engine friction and follow the cam more accurately.

The only snag that I know of would be your Flywheel or flex plate. If you get a 5.0 make sure you get the correct flex-plate with it. Also if you are having someone build up the block for you. Pay the extra and have them balance rotating assembly and radius the crank journals. This will make your engine run smoother and last longer.

 

[woodsnake]

Here's a free opinion.
Keep the aftermarket heads.
Decide how you are going to use the car.
Is it going to be a street car that may go to the track, or a track car that may get some ice/beer/soda/chips/whatever...

400 horse at the fly wheel today is pretty easy, and with an overdrive trans, you can get some decent mileage with a set of performance gears.

I.E., "fresh" 302/5.0 (rebuilt bottom end, rings,pistons and bearings)
'street able cam', something in the .500~ range, and a set of 3.5?~ish gears.

For me, I'd build a 327 stroker, with a lumpy cam, and take advantage of an over drive transmission. 750 Holley, 2 1/ inch pipe, magnaflows.

 

[57fairlane]

You could build a good 347 with those heads . . . been around plenty of 347s that ran low 7s/high 6s in the 1/8 and were friday/saturday night cars.

 

[stonecoldtx]

85 and up Mustang 5.0 blocks have a lower rotating mass. (The Crank counterbalances are smaller.) This will make them rev faster.

I'm not quite sure where you are getting this information. I'm pretty sure that Ford changed the 302/5.0L crankshafts in 1980 and went with a hollow crank (someone here please correct me), which required the use of a 50-oz imbalance as opposed to the 28-oz imbalance previously used.

The counterweights are not smaller, and this will not make them "rev faster".

For the record, the counterweights and imbalance on the flywheel/flexplate and damper are there to counteract the weight of the piston/rod assemblies.

That's why when engines are internally balanced, more weight is placed in the counterweights and taken off of the flywheel/flexplate and damper.

Also, reducing rotational mass is not intended to make an engine rev faster, it is intended to make it live LONGER at high RPM's, because the stresses encountered by the parts involved are increased by factors of magnitudes as RPM increases.

Pay the extra and have them balance rotating assembly and radius the crank journals. This will make your engine run smoother and last longer.

Well, this is sort of correct; smoothness will depend on the camshaft used up to a certain RPM. Balancing the rotating assembly will help make sure that no unwanted harmonics are introduced to the rotating assembly that could increase the chances of failure as a result of the increased stress that would occur.

A side benefit of that is that the engine may be smoother and have less vibration through the RPM range to the point where it would be noticed.

In other words--it might be difficult for the average person to detect any difference in vibration amount between a factory-balanced engine and one that was balanced at the machine shop.

Radiusing the crank journals just means that square edges are removed, and thus eliminating a potential area for stress to occur and fail as a result of that stress.

End result is that the engine should be stronger, and as a result, perhaps last longer, but it is not a given, and a big part of whether it lasts longer is dependent upon the quality of work by the machine shop and the stresses placed on the parts.

It's been proven that the weak area of stock 5.0L engines isn't the rotating assembly, it's the block, so while performing the additional machine work would be helpful if planning for more than 450HP-500HP, unfortunately the stock block will fail before reaching beyond that level.

 

[65ShelbyClone]

It's been proven that the weak area of stock 5.0L engines isn't the rotating assembly, it's the block, so while performing the additional machine work would be helpful if planning for more than 450HP-500HP, unfortunately the stock block will fail before reaching beyond that level.

Right, and it seems that RPM is a large factor in their failure. Even the Sportsman blocks have failed by 450bhp, but that seems more likely with a high spinning NA build.

Personally, I would keep the heads and put them on a 331 stroker that won't see much over 6000rpm. I love roller cams, but they're not mandatory. You just have to run a good oil with higher levels of zinc and all that.

 

[Wicked65]

I think you should first sell me those heads... LOL

Figure out what you want to do with the car. But im pretty sure a 10.0-1 compression motor, with a good cam and a 331-347 stroke would make you happy.

 

[rbohm]

my advice is to have the block looked over carefully by a good machine shop to determine what kind of condition it is in. if it can be used then i say build a 331 stroker with an xe268h comp cam. use flattop pistons, drop the heads on with the tunnel ram, and two 500cfm edelbrock carbs. make a nice healthy street machine out of one car, with some bling in the engine compartment.

 

[kilgorq]

I'm not quite sure where you are getting this information. I'm pretty sure that Ford changed the 302/5.0L crankshafts in 1980 and went with a hollow crank (someone here please correct me), which required the use of a 50-oz imbalance as opposed to the 28-oz imbalance previously used.

The counterweights are not smaller, and this will not make them "rev faster".

For the record, the counterweights and imbalance on the flywheel/flexplate and damper are there to counteract the weight of the piston/rod assemblies.

That's why when engines are internally balanced, more weight is placed in the counterweights and taken off of the flywheel/flexplate and damper.

Also, reducing rotational mass is not intended to make an engine rev faster, it is intended to make it live LONGER at high RPM's, because the stresses encountered by the parts involved are increased by factors of magnitudes as RPM increases.

I may have the year wrong on the lower rotating mass. The machinist that rebuilt mine said it was 82 and a friend that I have that has built 5 of them said 81. So it was probably the early 80's

But Comparing the 2 cranks side by side. The counterbalances are smaller and one them has a notch out of it and the counterweights are hollowed out.

Also rotational mass does change how quickly a motor revs. It also reduces the amount of time that it takes to return to Idle. Think the laws of motion on this one. An object that is in motion will stay in motion. And an object at rest will stay at rest. The greater the mass of that object the more force required to change the state of the object. Furthermore an object in motion will travel in a straight line unless acted upon by an outside force. When speaking the internal workings of any engine. The heavier the internal parts are the more likely those parts are to want to go in a straight line. Which in turn requires more force to change the direction. This is why you see aluminum rods on race cars. They are lighter therefore decreasing the rotating mass and increasing the amount of usable power.

The advantage of rollers in a block. Are basically based on the same principles. They decrease friction in the moving parts therefore making the motor more efficient. Less power (AKA Force) Wasted in friction. The other advantage to rollers is accuracy. The valves follow the cam more accurately.

 

[D.Hearne]

I'm not quite sure where you are getting this information. I'm pretty sure that Ford changed the 302/5.0L crankshafts in 1980 and went with a hollow crank (someone here please correct me), which required the use of a 50-oz imbalance as opposed to the 28-oz imbalance previously used.

The counterweights are not smaller, and this will not make them "rev faster".
.

Whoa there big guy. I agree with everything you posted south of here, but I got's to set you straight here. The change to the 50 oz cranks occured sometime in 81 or 82 (even Ford is fuzzy on this) and the change did include removing material from the crank counterweights. Just setting a 28 oz crank next to a 50 oz crank will confirn this with the naked eye. The hollow crank you describe was intended for the 255 V8, there's a possibility some ended up in 302's , but not likely as the imbalance would have been off with the 255's smaller diameter pistons vs a 302's larger ones. The change to a 50 oz crank was likely to reduce material costs in production (less iron in the crank) The faster reving may or may not be true, the 50 oz motors do rev pretty quick, but the difference would need an electronic measure to confirm.

 

[stonecoldtx]

Whoa there big guy. I agree with everything you posted south of here, but I got's to set you straight here. The change to the 50 oz cranks occured sometime in 81 or 82 (even Ford is fuzzy on this) and the change did include removing material from the crank counterweights. Just setting a 28 oz crank next to a 50 oz crank will confirn this with the naked eye. The hollow crank you describe was intended for the 255 V8, there's a possibility some ended up in 302's , but not likely as the imbalance would have been off with the 255's smaller diameter pistons vs a 302's larger ones. The change to a 50 oz crank was likely to reduce material costs in production (less iron in the crank) The faster reving may or may not be true, the 50 oz motors do rev pretty quick, but the difference would need an electronic measure to confirm.

Thanks for the correction on the crank, D.Hearne--I was a little fuzzy myself on the changeover.

Kilgorq--I stand by my statements regarding the fact that reducing the crankshaft counterweights will NOT allow an engine to rev faster.

To help you better understand, as I mentioned before, the counterweights are just that--counterweights. That means that their use is to counter the weights of the connecting rod/piston assemblies.

Let's talk a minute about basic engine operation.

When an internal combustion engine operates, during the power stroke (the point at which the ignited fuel expands, creating force on the top of the piston), there is reciprocating weight (inertia) and friction that acts against that force.

The entire reciprocating assembly has to be taken into account here--that means that the connecting rod/piston assemblies must match the counterweights of the crankshaft.

For the engine to be "balanced", they either have smaller counterweights and larger imbalance weights on the flywheel and/or damper, or the entire assembly is lighter.

In the case of 302/5.0L engines, they didn't reduce the weight of the connecting rod/piston assembly when they changed crankshafts, they simply reduced the weight of the counterweights and added weight to the imbalance they used on both the flywheel/flexplate and damper.

Therefore, without reducing the entire reciprocating assembly, the same resistance to the force applied to the top of the piston remains.

Bottom line--the elements that cause (or help) an engine to rev faster aren't simply to reduce the size or weight of the crankshaft counterweights, they are to reduce friction, reduce the entire weight of the reciprocating assembly itself (which Ford didn't do here), and provide more power within the cylinder to create more pressure on the piston top.

I hope that helps illustrate why simply changing the crankshaft counterweight size doesn't have the effect you have been led to believe it did.

 

[D.Hearne]

There would be some lessening of windage in the crankcase with the 50 oz crank's smaller counterweights, but again, that's something that would only be able to be proved electronically. The early 50 oz cranks were weak and had a tendency to break in half in normal operating conditions (I've personally seen two failures, one in a half ton F series truck, the other in a Lincoln Town car both had AOD transmissions) The later ones exhibit excellant casting quality with smoothly contoured counterweights much like a forged piece.

 

[kilgorq]

So you are saying that the rotating mass was essentially unchanged. They moved the mass that they took off of the crank out to the flywheel or flex plate. Is this correct? I was under the impression that they had changed the whole rotating assembly at the time. And that all of the components were lighter. Not Just the crankshaft.

Reducing the rotating mass does increase throttle response and engine efficiency. I may have been misinformed on this change that ford had made.

But I do have a question then. Why did they make this change? What other benefit would it have besides changing the rotating mass?

 

[D.Hearne]

So you are saying that the rotating mass was essentially unchanged. They moved the mass that they took off of the crank out to the flywheel or flex plate. Is this correct? I was under the impression that they had changed the whole rotating assembly at the time. And that all of the components were lighter. Not Just the crankshaft.

Reducing the rotating mass does increase throttle response and engine efficiency. I may have been misinformed on this change that ford had made.

But I do have a question then. Why did they make this change? What other benefit would it have besides changing the rotating mass?

I take it you didn't fully read what I posted before. The reasoning behind the change was most likely to reduce material costs. Taking 20 lbs of iron off 3 million cranks really adds up in dollars. (I'm guessing here on the actual weight savings, but you should get the point) I don't think an equal amount of weight was replaced though in the balancer and flywheel to offset the weight removed. I think in just looking at the size diffferences in the counterweights in the crank vs the balancer and flywheel/flexplate, that less weight was needed to replace the weight removed, to balance the asssembly dynamically

 

[2+2GT]

But I do have a question then. Why did they make this change? What other benefit would it have besides changing the rotating mass?

I believe he already answered that, windage.

Windage, from Wickipedia:

"Windage refers to parasitic drag on the crankshaft caused by oil splashing out of the sump at high rpm. At 6,000 rpm, for example, the crankshaft must rotate 100 times per second. As the crankpins and counterweights rotate at such high speeds, they create a swirling cloud of air around them. Windage is considered to occur when excess oil is caught up in this turbulent air, drawing energy from the engine to spin the oil mist. Windage may also inhibit the migration of oil into the sump and back to the oil pump, creating lubrication problems. Some manufacturers and aftermarket vendors have developed special scrapers to remove excess oil from the counterweights, and windage screens to create a barrier between the crankshaft and oil sump."

The BOSS 302 had a windage tray attached to the main caps, and the 351 Cobra Jet had an oil pan with a baffle plate for this purpose.

Windage tray:

 

[kilgorq]

I take it you didn't fully read what I posted before. The reasoning behind the change was most likely to reduce material costs. Taking 20 lbs of iron off 3 million cranks really adds up in dollars. (I'm guessing here on the actual weight savings, but you should get the point) I don't think an equal amount of weight was replaced though in the balancer and flywheel to offset the weight removed. I think in just looking at the size diffferences in the counterweights in the crank vs the balancer and flywheel/flexplate, that less weight was needed to replace the weight removed, to balance the asssembly dynamically

I agree with the 20 pound saving huge production costs. This makes sense.

I am not trying to contradict. I am trying to follow the logic. If the crank weighs say 20lbs less then the rotating mass has decreased. If you decrease the rotating mass then you change the characteristics of the motor. These are notable in Efficiency, Rev Speed and Peak output power. There are many other items that come into play on this whole equation like compression, Ring Width, Piston and rod weight, Etc etc etc. (Mostly friction and weight) But If all other items where equal except for the crank the motor with the lighter crank would be more efficient. This means it could put out more power and rev quicker. When combined with the windage improvements you will have a more responsive motor overall.

 

[D.Hearne]

I went back thru Ford's book on the 79-2001 5.0 (The Official Ford Mustang 5.0 by Al Kirschenbaum)and it states in chapter 19, on page 192 that the counterweights on the 82-and later cranks (the 50 oz crank) that the counterweights were trimmed to both reduce weight and windage. These cranks weigh 38.2 lbs. There's no figure given for a 28 oz crank, but seems I recall weighing one for shipping and it was something like 50 lbs. So it appears you're correct about the windage advantages, the book makes no mention of the benfits of the lesser weight counterweights, but it seems likely that too is a likely side effect of the weight reduction.

 

[stonecoldtx]

I agree with the 20 pound saving huge production costs. This makes sense.

I am not trying to contradict. I am trying to follow the logic. If the crank weighs say 20lbs less then the rotating mass has decreased. If you decrease the rotating mass then you change the characteristics of the motor. These are notable in Efficiency, Rev Speed and Peak output power. There are many other items that come into play on this whole equation like compression, Ring Width, Piston and rod weight, Etc etc etc. (Mostly friction and weight) But If all other items where equal except for the crank the motor with the lighter crank would be more efficient. This means it could put out more power and rev quicker. When combined with the windage improvements you will have a more responsive motor overall.

You can keep on believing that, but it doesn't make it a fact

Have you ever seen how engines are balanced?

When counterweights are cut down in size, something has to make up for the loss in weight. Racing machine shops regularly do this for a variety of reasons including providing more clearance to pistons in a stroker to reducing windage--BUT--when they do that, usually they "internally balance" the engine (no imbalance weight on the flywheel or the damper) by the use of heavier metal.

To do this, they drill holes in the remaining counterweights and add metal sufficiently heavy to replace the mass of the counterweight material that was removed.

In situations where the counterweight diameter was reduced, they have to use quite a bit of this heavier metal in order to get it close to the same "weight" (if you will) of that particular counterweight before it was reduced in size.

If the shop is only switching the rotating assembly from externally balanced to internally balanced, they don't need to use nearly as much--BUT--Because the location of the heavy metal is closer to the centerline of the crankshaft, it weighs more than it did placed further out on the flywheel.

When Ford removed the weight from the crank, they increased the imbalance to make up for it.

Now, you contend that this will make your engine "rev faster", but as I've already mentioned in a previous post--the resistance to the combustion pressure at the top of the piston due to the weight of the rotating assembly is the same (intertia) because the effective rotating assembly weight was not reduced overall--the connecting rods and pistons weigh the same, or are within a few grams of the assemblies prior to the reduction in crankshaft weight.

This is mostly due to centrifugal force, and the fact that while the actual weight of the crank was reduced, the placement of the heavier imbalance creates a situation where the same force is available to counteract the weight of the connecting rod/piston assemblies.

If you like, you can verify what I've described here with any physics professor . . .

 

[2+2GT]

If you want the engine to "rev faster", trimming the weights on the crank is a poor way to do it. The relatively small diameter of the crankshaft assures a small "moment" of inertia, resisting changes in rotational speed. On the other hand, reducing the overall weight of the flywheel (not the counterweight) being a far greater diameter, would have a dramatic effect on how "fast" the engine revs. I was in the pits at Road America one time, the guy I was watching qualify in his Japanese car cracked a flywheel in qualifying. He had only a few hours to get a junkyard replacement, and install it, no time at all to have it flycut thinner to match the damaged one. What a huge difference! The old one wasn't some exotic aluminum etc., just a thinner stock one. Compared to the old wheel, the new one responded with painful slowness. And this was on a tiny 4-cylinder engine, imagine the change from a much bigger 164T Ford wheel.

 

[stonecoldtx]

If you want the engine to "rev faster", trimming the weights on the crank is a poor way to do it. The relatively small diameter of the crankshaft assures a small "moment" of inertia, resisting changes in rotational speed. On the other hand, reducing the overall weight of the flywheel (not the counterweight) being a far greater diameter, would have a dramatic effect on how "fast" the engine revs. I was in the pits at Road America one time, the guy I was watching qualify in his Japanese car cracked a flywheel in qualifying. He had only a few hours to get a junkyard replacement, and install it, no time at all to have it flycut thinner to match the damaged one. What a huge difference! The old one wasn't some exotic aluminum etc., just a thinner stock one. Compared to the old wheel, the new one responded with painful slowness. And this was on a tiny 4-cylinder engine, imagine the change from a much bigger 164T Ford wheel.

Yep, and you can see this same effect if you have an engine on a stand, and change from a manual flywheel to an automatic flexplate, or vice versa . . . we did that in High School in Auto Shop class.