Let's discuss aluminum heads... BTW: Dumped the Chevy

ratio411

ratio411

Founding Member
Apr 21, 2002
3,870
73
109
Pensacola FL
#1
I am going to start focusing on my old Ford again.
I have a Maverick... never could seem to afford a Stang.
I hang out here because so many parts are the same and most things that apply to a 65-66 (dimensionally, weight, shape, etc...) apply to the Maverick, so I tend to watch those posts.

Anyway...
I keep modeling different engines on the puter and I cannot build an engine that averages more torque or hp below 6000 rpm with aftermarket heads.
I get the flattest, highest, and 9 of 10 times best peak to 6000 by using ported early 351w heads (1.94 valves).
As soon as I model larger valves or any aftermarket head in the database, the power average, and most of the time, the peak hp drop drasitcally...
Remember I am modeling up to 6000 rpm, after 6k it is a different ball game and the ported iron heads get whipped like red headed stepchiles.
I have never built a 351w, normally I would expect to spin higher as I have always been most into SBFs or Clevelands.
So this has me floundering a bit.
I am torn between 3 setups:
1: 351w with 400 rods and all the goodies. (Models to 540 hp @ 6000 with ported stock heads, numbers get worse with aftermarket because of too much flow.)
*I have always wanted to build an ultra long rod engine for giggles.

2: 393 with all the goodies. (Haven't modeled YET, but look at the price advantages.)

3: 408 with all the goodies. (Again, pulls better numbers with said iron heads until 5.5k. This one will pull a better peak with aftermarket heads, but only slightly... Average torque and hp are still low though.) This engine will pull the exact same power curves as the long rod 351, just 40 hp higher across the chart.)

So...
Let's discuss:
Is it a waste to put fancy heads on an engine that you don't want to turn over 5500-6000 rpm?

Is the computer model missing something? It seems very comprehensive. It is Engine Analyzer 3.0 and I find it much more informative and exact than Desktop Dyno. I have used both. You can enter far more varibles with EA.

Also, I will note that the heads that are getting the most power are 69-74 351w heads with Chevy valves and porting to the max. NOT stock heads... stock heads model miserably and choke out around 4.5k rpms!

Ideas?

Thanks
Dave
 
#2
You will never achieve 500 plus horse power with 351 w ford casted cyl heads, ever!!! even on a big cubed 351 They just wont flow the kinds of numbers to make that kind of power. I dont know what program you are using to come up with those numbers but if you would like to check out some interesting reading MM&FF just did a huge cyl head comparo and bassiclly covered every cyl head for the small block ford they could get there hands on and did all kinds of testing on different motors to find out what the best cyl heads were for each application, the article spanned about 6 different issues. I reccomend you check it out.
 
#3
he said they were "NOT stock heads" and that he was using engine analyzer 3.0...

I'm not sure that I am so surprised that the bolt on Al heads aren't producing more than the cast heads ported to the max w/ larger valves...
Isn't the general consensus that the iron heads (all things being equal) will out-perform the Al heads due to heat retention? The primary reason for going to Al being the ability to run higher compression or boost w/a lower chance of detonation due to better thermal conductivity?
 
#4
I use the EA3.0 software also, I always get the same results as you Ratio411. Honestly, I think its wrong. There should be a way to enter a flow chart showing cfm at different valve lifts, instead it gives you valve size, average runner size, and flow efficiency. Every time I model an engine I get best results with the 1970 351W heads, aftermarket heads only seem to decrease power unless you build a really all out engine. Real world dyno tests don't support the numbers EA gives when it comes to head swaps. It's also off when ti comes combustion chamber cc's, the 70 351W heads are 60.4 cc and should give roughly 10.5:1 compression on my engine, to get the software to work properly, I have to enter nearly 80cc to get the same compression.
 
#5
I dont care what you do to any stock 351 w head it wont make 500 plus horse power N/A they cant support any where near enough air flow to make those kinds of numbers. Now a dart iron or world sr. head could accomplish those kinds of numbers.
 
#6
you can get 500hp out of a set of "power heads" 351w cnc ported heads with chevy valves (can't remember if they are 1.94 or 2.02) hot rod or car craft did an article a few years back and got like 480 something hp out these heads. www.powerheads.com check'em out. no they are not stock heads, they are "ported to the max" as ratio was saying he was modeling with. i plan on using these heads or maybe some gt40-p heads due to the improved combustion chambers. my mototr will also be done and out of breath by 6k or less probably more like 5500.


ratio, i like your long rod idea, that's what my next motor will be, hopefully not too far away. i'm going to use a 94-up roller block with the one piece rear main seal with the 400 rods and KB pistons, i'm going to shoot for around 10.5:1 compression, and i think i can get away with that using the power heads have you checked out speedomotive for their long rod kits?


http://www.speedomotive.com/ford_351_long_arm.htm
 
#7
Great info guys!
Couple responses to comments:

Modded stock heads will support good HP, the drawback is that potential decreases with an increase in either rpm or cubic inches. 351, even 400 if you think about it, are relatively small V8s. 6K rpm is also a low rpm for an SBF.
The deciding factors on how high you can get the power curve below 6k is in the details.
I won't spill all the beans on my engine combo, I have been tossing these ideas in my brain for years, but I will disclose some things that I suspected and the models confirm, as much as they can be trusted:
Large heads need very small cams to perform at lower rpms.
Smaller (modded stock) heads need large cams to have a well rounded power band.
Small cams in mild heads fall on their face too soon, while with large valves and runners work well because they raise port velocity needed for street use.
All the models with aggressive ports tell me (in the report) that port velocity is too low. This is a sure sign that the heads are too aggressive.

I am not saying this is right, I am playing 'devils advocate' and trying to have a thoughtful thread with ideas floated.

302 coupe:
The model includes all clearances in your cylinder.
Not just the 60cc chambers, but:
Deck clearance
Gasket thickness
Valve pockets/dishes
even the gap between the top of the piston and the top of the 1st ring.
The idea is that YOU measure all these clearances, add them together, then load them into the program.
The other way is to model the compression ratio you want, then use the cc's they give you to figure what clearances you will have to build into your future engine.

slackr:
Aluminum makes more power because you can run higher compression. That factor outweighs all others. Add to that the fact that 100 lbs weight loss equals 10 rwhp. That is equivalent to almost 15 fwhp, which is what we are talking here. 1 point of compression is worth 10 fwhp. So aluminum heads, though not showing it on the dyno, will add 15-20 rwhp in the real world, red light to red light.

Bnickel:
I have had high hopes for a long rod engine for a long time now, but I am nervous about doing it.
In theory it will make much better power, but the model doesn't take them into account other than piston velocity. It doesn't model the dwell from what I can tell.
Yet you can see enormous gains with a stroke increase...
Really 400 rods in a W would be very cheap to do...
Polish them up, ARP bolts, bush, resize... Should be plenty stout for a steet app.
The piston needed would be around 1.18" tall... there is an off the shelf chevy stroker piston with that height. That would be the most expensive part of the bottom end.
I just wish there was more info to justify the trouble.
Some other pros would be the fact that long rod slow the piston, which puts less pressure on the rod bolts and main caps while still producing more power. Also the piston thrust side of the block does not wear nearly as much because the rods don't get 'angular' due to their length. The block lasts longer, stock rods are stronger, the piston dwells longer (better breathing), and the block is stronger due to less rod angularity...
There are a lot of pros there and the only con is that this engine models 40 hp/tq lower accross the rpm range compared to an engine 40 cid larger with rod angularity issues.
It's a tough choice. That is why a productive discussion is in order.

Thanks for the intelligent ideas!
Keep em comin
Dave
 
#8
The flow numbers on the Powerheads look good.
How many folks run better than .550" lift on a 6k rpm street engine?
Does anyone know off the top of their head what some aftermarket head flow at these low lifts?

I checked Speedomotive...
That is what I have in mind, but I think I can do it myself with forged pistons for less dough.

Fwiw: I have seen the early W heads worked to a point that you would think they were WP heads until you looked hard.
 
#9
ratio411 said:
slackr:
Aluminum makes more power because you can run higher compression. That factor outweighs all others. Add to that the fact that 100 lbs weight loss equals 10 rwhp. That is equivalent to almost 15 fwhp, which is what we are talking here. 1 point of compression is worth 10 fwhp. So aluminum heads, though not showing it on the dyno, will add 15-20 rwhp in the real world, red light to red light.
Click to expand...
Agreed.... thus the stipulation of 'all things being equal'. If you have two heads where the only difference is in the construction material (including compression, boost, runners, valves... whatever else), then the only differences realized will only be due to the qualities of those materials. I was going after your idea that your modeling of the 'maxed' cast heads vs. the 'fancy' (assumed Al) heads and not seeing much of a difference.

Of course the power gains realized through the ability to run higher cylinder pressures w/o detonation (or any other) problems due to the thermal properties of Al, outweigh the benefits of iron (cost and mass excluded).

Pardon my amateur mathematics, but if I remember right, HP is the integral of torque w/respect to time, no? Torque (angular force?) on the power stroke (related to breathing ability for now, my knowledge of long rod dynamics relating to engine forces is limited at best), would be directly related to the amount of fuel/air that is burned, yes? The ability to flow that mix into the cyl seems to be the big question.... volumetric efficiency. I think VE is a measure of the pressure inside the cyl (after the intake valve closes considering the total volume of the cyl) and dividing it by the ambient air pressure..

To flow more air into a cyl, you need bigger ports/valves, but these things in excess are typically associated with lower velocity and thus lower atomization of the fuel w/the air.... thus not completely burning the mix of the stuff that we are desperately trying to get into the cyl... counter productive.

I think that most of the atomization can be achieved best by turbulence of air about the valve inside the cylinder where it is most utilized. All this is leading up to the statement you had that large heads need small cams to perform well. If you had a large head with low lift, the atomiization around the valve would increase....

What if, you had a decent sized head and a low lift longer duration cam? I wonder if keeping a large valve open @ low lift longer could achieve a better average air flow while maintaining the turbulence needed for the best atomization.

You said you wanted it to be a thoughtful thread... barring the validity of the thoughts, I put some in to this post anyway...
 
#11
Great post.

Just so you folks know, I have decided on Trick Flow T/W heads. This discussion is totally academic due to the things I noticed on the engine modeling program.
I am using the T/Ws because they are not huge ports, but decent. Aluminum material of course. The exhaust ports are stock bolts and position, which will matter significantly in my tight engine compartment. And the chambers are unique.

I wouldn't use iron for the weight factor alone.

I would like to note that the idea of heat being good in an engine is a misconception.
I thought this was true for a long time too...
I read something by Smokey Yunick though that changed my mind. BTW, I highly recommend folks reading anything by Smokey that they find, he was, and still is considered THE performance engine master.
Anyway... the idea of a standard I/C engine is that ONLY potential heat is power. Once the combustion has taken place, the residual heat that is absorbed into the engine is good for nothing and must be dissipated, faster the better. In other words, residual heat, though power if harnessed, cannot be harnessed by the inherent limitations of current designs, is only a liability.
I know this is not how it was told to me, I hope it makes sense. Bottom line is that if the engine was totally ceramic and air cooled, as well as oil free, then heat is good... but technology is not there and therefore the engine must lose this heat for it's own good. Only the potential heat entering for the next stroke is what matters.

Long rods:
They 'dwell' longer at the top and bottom of the stroke. I learned this produces power because the intake and exhaust movements are caused more by ambient air pressure than by pushing or pulling of the piston, contrary to what most folks think.
The valves are actually better off if they are open most while the piston is dwelling than moving. Filling and emptying of the cylinder is done more by air pressure than piston movement is what I am saying and if you study valve timing you will see that other than combustion, the valves move differently than you would imagine.
Anyway... longer dwell equals more time for cylinder emptying and filling, more effieciency and, in a way, more displacement without additional bore/stroke.
Rod angularity:
If you have short rods, they push the piston into the cyl. walls harder, as they push up.
This creates frictional power loss and wears parts faster.
Long rods don't get sideways as much, so they wear the engine out slower and cause less friction for the rotating mass to overcome.
I am far from an engineer, so I might be all wet...
Math gets me confused :D,
I know some makes sense on paper, but I have found different in engines I have built.
IE:
Everyone is so scared of overcarbing...
I tested and got better power with a 750 dp on a 302 than some different smaller brands and sizes of carbs. Very few folks here would recommend a carb that size for an SBF, quoting all sorts of math and websites, but it sure worked for me.
That brings me to another thing about the EA program, it gives a detailed mathematical report on the engine you have modeled, nearly every time it suggests a larger carb than what mags and websites would ever recommend. If I didn't find it true from experience, I would say the program is wrong.

Keep talking. I want to hear from some folks that have put their car on the track with ported heads, then later with aftermarket heads.
Dave
 
#13
ratio411 said:
I would like to note that the idea of heat being good in an engine is a misconception.
I thought this was true for a long time too...
I read something by Smokey Yunick though that changed my mind. BTW, I highly recommend folks reading anything by Smokey that they find, he was, and still is considered THE performance engine master.
Anyway... the idea of a standard I/C engine is that ONLY potential heat is power. Once the combustion has taken place, the residual heat that is absorbed into the engine is good for nothing and must be dissipated, faster the better. In other words, residual heat, though power if harnessed, cannot be harnessed by the inherent limitations of current designs, is only a liability.
I know this is not how it was told to me, I hope it makes sense. Bottom line is that if the engine was totally ceramic and air cooled, as well as oil free, then heat is good... but technology is not there and therefore the engine must lose this heat for it's own good. Only the potential heat entering for the next stroke is what matters.
Click to expand...
It makes good sense... I guess I never took the time to scrutinize the idea before.

I am of the mindset that airflow is caused by differences in pressures in 2 or more areas. You say that filling and emptying of the cylinder is done more by air pressure than piston movement; it is the piston's movement that is responsible for the differences in pressure due to volume changes. The flow is enacted when the valve opens to expose the 2 different pressures to each other. In this respect, I am not intuitively grasping how a rod length change significantly affects breathing ability (VE to be more specific) in a cylinder with a static maximum volume.
However:
ratio411 said:
Rod angularity:
If you have short rods, they push the piston into the cyl. walls harder, as they push up.
This creates frictional power loss and wears parts faster.
Long rods don't get sideways as much, so they wear the engine out slower and cause less friction for the rotating mass to overcome.
I am far from an engineer, so I might be all wet...
Click to expand...
Nope, you're not all wet as far as I can see... This not only has that affect on the upstroke, where these ideas are sound, but also on the downstroke. This is where I see the most power gain from a longer rod, where the rod angle to the crank can be leveraged against the crank for a longer time (I'm having a hard time explaining).... the duration of the best rod angle against the crank where it can have the most force on the crank rather than the force being applied to the opposite side of the cylinder wall. This angle duration, I think, might be why long rods are known for more torque.

Now that I think about it, I think I just figured out why piston dwell would help breathing.... and I think you said it, I just wasn't understanding...
The piston dwell @ the bottom of the stroke would give the a/f mix more time to fill the cylinder before coming back up.... conversely, the exhaust gases would be same the issue @ the top. Enlightenment.:D
ratio411 said:
Everyone is so scared of overcarbing...
I tested and got better power with a 750 dp on a 302 than some different smaller brands and sizes of carbs. Very few folks here would recommend a carb that size for an SBF, quoting all sorts of math and websites, but it sure worked for me.
That brings me to another thing about the EA program, it gives a detailed mathematical report on the engine you have modeled, nearly every time it suggests a larger carb than what mags and websites would ever recommend. If I didn't find it true from experience, I would say the program is wrong.
Click to expand...
I think you have some room to argue.... desired a/f ratios seem to change depending on use, as well as rpm's which could leave room for a range.
ratio411 said:
Keep talking. I want to hear from some folks that have put their car on the track with ported heads, then later with aftermarket heads.
Dave
Click to expand...
Sorry, I do not have this experience, and I seem to be hogging your thread.... nonetheless, I find it intriguing.
I do have something to add that might be interesting... a good source for head flow data:
http://www.jason.fletcher.net/tech/flowdata/castiron.htm
There is stock, modified cast, aluminum and cleveland info there...
It would be interesting to see this info graphed...

Clint
 
#15
One thing I forgot to mention...
Longer duration of dwell at TDC during combustion allows the piston to absorb more of the explosion that pushes it down to make power. Making a stronger push on the crank.
Again, all this is Smokey's theory... That is why I recommend reading his stuff.

I was going to use more radical heads until I did the models and thought maybe there was something to the program constantly telling me that port velocity was low.
I was going to use Victors until further thought. If I had room under the hood, I would have used Rs... Way too much.

I haven't decided on engine yet.
Either long rod 351 or going for the glitz of 40+ hp/tq with a 408.
The 393 is just too middle of the road for me... no good rod ratio and the 408 is just as easy with more power.
Dave
 
#16
Thanks for the discussion, I think I have a bit of a new understanding with regard to long rod benefits. I may look up Smokey's stuff.

I would be interested to know what you eventually do.... good luck!
 
#17
fastcoupe68 said:
I dont care what you do to any stock 351 w head it wont make 500 plus horse power N/A they cant support any where near enough air flow to make those kinds of numbers. Now a dart iron or world sr. head could accomplish those kinds of numbers.
Click to expand...

My N/A race 289 has run 11.08 @ 119 in a 3000# (w/ driver) '69 Mach I with a Jerico and 5.67 gears with 9x30 slicks. The motor wore '69 351w heads that had been mildly ported. Offy 360 with stock dual 660's. I have a time slip even. Tell me that's not close to 500HP at the flywheel.

:flag:
 
#19
1320stang said:
My N/A race 289 has run 11.08 @ 119 in a 3000# (w/ driver) '69 Mach I with a Jerico and 5.67 gears with 9x30 slicks. The motor wore '69 351w heads that had been mildly ported. Offy 360 with stock dual 660's. I have a time slip even. Tell me that's not close to 500HP at the flywheel.

:flag:
Click to expand...
your combo is probably making about 400 to 425 horse power at the wheels to lay down those kind of numbers and I am not doubting it one bit, it is still not 500 hp at the flywheel, say whatever you want, your close and to do it under 6000 rpms which was discussed in the orig post just not going to happen. I have been at this speed game quite some time myself back when there were not any aftermarket heads for our beloved smallblock fords, spent countless amounts of money on 351w heads (stock) probably more then most guys will spend on there entire cars and to achieve 500 hp with stock castings is just pushing the limits, unless you know someone with the magic touch, Good luck!!! And I never said you couldnt get close.
 
#20
This could be argued...

500 fwhp - 20% drivetrain loss
= 400 rwhp

And that is with a 289.

I pulled 310 rwhp with 302 cubes through 68 289 heads.
This was before they were ported, but after 1.94/1.60 valves.

I don't mean to drag out into a pizzing contest... I just think there is plenty of evidence the SBF heads don't have to be aftermarket to perform.
 
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