318 build problems & new direction

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BTW, for what is may be worth... I ran a spreadsheet on the energy absorbed by a lighter versus heavier piston/rod assembly; i.e., I looked at just the bobweight change spinning around the crank, and the associated lighter weight of the crank counterweights.

With a bobweight drop from 2326 grams to 1893 grams (what my son and I did for his 340 with KB pistons and SCAT rods), then revving from 3000 to 7000 RPM saves 2080 joules that can be put into accelerating the car.

This translates to roughly a 1/2 HP to 2 HP range; the exact HP loss varies with how fast the motor revs, and the RPM range, which is all gear and weight dependent when in a car (both mass AND other rotating parts). But 1 HP is a ball park range. It would drop 1/4 mile MPH by a coupla tenths for cars in the A body weight/power range. For reference, it takes around 1.5 million joules of energy to get a 3300 lb car moving at 100 MPH from a dead stop.

So this acceleration/HP improvement with lighter rods+pistons is in the range of crank scrapers, or using a standard oil pump vs HV pump, and will vary a lot on the particular parts and the exact use.
 
cudaracer said:
Just checked RPM and they have 390 kits for $1049.
Add balancing and shipping and price is under $1500. Not bad.
Click to expand...
At those prices, I'd be wondering about what you are getting. I am not much of a fan of buying 'unknown brand' parts. Any idea whose parts?
 
nm9stheham said:
BTW, for what is may be worth... I ran a spreadsheet on the energy absorbed by a lighter versus heavier piston/rod assembly; i.e., I looked at just the bobweight change spinning around the crank, and the associated lighter weight of the crank counterweights.

With a bobweight drop from 2326 grams to 1893 grams (what my son and I did for his 340 with KB pistons and SCAT rods), then revving from 3000 to 7000 RPM saves 2080 joules that can be put into accelerating the car.

This translates to roughly a 1/2 HP to 2 HP range; the exact HP loss varies with how fast the motor revs, and the RPM range, which is all gear and weight dependent when in a car (both mass AND other rotating parts). But 1 HP is a ball park range. It would drop 1/4 mile MPH by a coupla tenths for cars in the A body weight/power range. For reference, it takes around 1.5 million joules of energy to get a 3300 lb car moving at 100 MPH from a dead stop.

So this acceleration/HP improvement with lighter rods+pistons is in the range of crank scrapers, or using a standard oil pump vs HV pump, and will vary a lot on the particular parts and the exact use.
Click to expand...

Well done. Thanks for putting that info together for us.
 
toolmanmike said:
Well done. Thanks for putting that info together for us.
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You're very welcome, sir! It's nice to know the general principles of HP savings (or cost savings or whatever), but it is nicer to be able ballpark quantify something like this. The question of "Is it 1 HP or 10 HP?" makes a big difference in how important it is when making decisions.

Of course in this case of lighter rods/pistons, the benefits of less stress in the crank and parts is a separate benefit. NOW someone is going to ask: How much lower IS the stress? The discussion never ends... LOL
 
nm9stheham said:
You're very welcome, sir! It's nice to know the general principles of HP savings (or cost savings or whatever), but it is nicer to be able ballpark quantify something like this. The question of "Is it 1 HP or 10 HP?" makes a big difference in how important it is when making decisions.

Of course in this case of lighter rods/pistons, the benefits of less stress in the crank and parts is a separate benefit. NOW someone is going to ask: How much lower IS the stress? The discussion never ends... LOL
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Sure, every time you remove weight from the car, it gets faster. ESPECIALLY rotating weight, like torque converter, wheels and tires, and for sure the rotating assembly off the crank.
That is why on my post above, I said there are several changes that can be made to the car that will make it "feel" faster without it showing up on a Dyno. This is why on the "2017 318 race", I have a penalty for using the magnum block (not much of a penalty though).
 
nm9stheham said:
At those prices, I'd be wondering about what you are getting. I am not much of a fan of buying 'unknown brand' parts. Any idea whose parts?
Click to expand...
RPM claims to be a leader in stroker kits, with more offerings/combos, for 20 years or so.
When I look at the parts list, they are all name brands anyway.

I did forget to add bearings/rings to the price. And I need a front damper and new flexplate, for internal balance. Total now puts me just under $2K. All that's left to do for the short build, is block machining and overbore. I figure about $300-400 for that, plus incidentals, I think total 392 stroker short build should be about $2700.
 
I ran camquest6 from comp cams, using the following parameters:

3.97" x 3.31"
XE268 cam (1600 to 5800)
DP high flow intake
600 carb
Large tube headers
9.5 CR
308 head flow numbers (max CFM 207) with 1.88 / 1.60 valves

HP seemed just a bit high at 364
Torque was at 394

I then replaced the cam with a retro roller, XR268 (1400 to 5500)
HP jumped 30 to 394
Torque also jumped 23 to 417

And not just the peaks, but much higher averages and sooner with that roller cam. I was not aware it impacts torque so much. And yes, I know the program is a bit optimistic, but I think the difference between roller and not is much more realistic.

Fun program. I played around and increased bore and watched only torque go up. Same thing happens with increasing stroke, just torque.
 
328 cubes.
417 torque
1.27 ftlbs per cube
A bit optimistic?
Try 15-20% or more optimistic. That program,with that little roller,is spitting out numbers that would make a 360 jealous.
 
AJ/FormS said:
328 cubes.
417 torque
1.27 ftlbs per cube
A bit optimistic?
Try 15-20% or more optimistic. That program,with that little roller,is spitting out numbers that would make a 360 jealous.
Click to expand...


I don't know, builders get close to those numbers without rollers.
 
The specs on that roller are tiny;218/224/110@050 with lift of .535/.531@ 1.5
I'm guessing, in a teener it will power peak around 5000 rpm, and torque peak about 1500 rpm earlier, at say 3500.
For a teener to make 417 flbs at 3500, with those heads and 9.5 Scr.......Why did I build a 360?, I must ask myself. I coulda had soooo much more.
 
I wouldn't get to caught up in numbers on dyno programs. To me the curves and when the torque comes in is more the strong suit of dyno programs so you can compare heads and cams combos.

Torque is some what an easy number to predict since it's mainly tied to engine size.
Most performance engines should be around the 1.2 lbs-ft per cid mark give or take .05 or so. But again it is curve and starting point that's most important especially if not running much stall or gears.
 
Here is an interesting output,

....as I played around with bore, going from 3.97" to a 4.07", hp only went up 1hp, but torque went up 20. If that is even remotely accurate, then there is your 318 to 340 difference, just torque. At least with the XR268 roller cam, and changing nothing else.
 
cudaracer said:
Here is an interesting output,

....as I played around with bore, going from 3.97" to a 4.07", hp only went up 1hp, but torque went up 20. If that is even remotely accurate, then there is your 318 to 340 difference, just torque. At least with the XR268 roller cam, and changing nothing else.
Click to expand...

Like I said torque is kind of easy to predict.
It don't very a lot like hp. In a N/A engine cubic inch is the main variable. Torque basically come from a per power stroke basis how full the cylinder gets (VE%) and how efficient the burn (CR, Chamber design etc..) HP is all the power strokes added up over time (RPM). Torque and HP are built by the same thing basically from Air flow and efficiency. So in a stock low power engine with low air flow and CR torque is around 1:1 to 1.15:1 lbs-ft per cubic inch. Once you started adding headers exhaust cams intake carbs decent heads etc... you start to get into 1.15:1 to 1.25:1. Once you get into professional built race engines above 1.4:1 is possible. So for us average guy 1.2 is a good guesstimate. Thats why people say build 360 or 408 over 318 cause that's the only really way to build torque in a N/A engine. So those cubic 42 and 90 cubic inch difference gives you about 50 to 110 lbs-ft more.

But not all is lost for a 318. It's not always doomed to loss against bigger engines since one major component is always left out of this conversation which is gearing.
If each engine has the same HP 318 vs 360 vs 408 if you gear basically a 318 .5 more than a 360 and 1full ratio more than a 408 you'll be putting similar power to the ground per mph than the other two. Eg. since 3.55 gear seems most popular so 4.10 to equal 360 and 4.56 to equal 408 and thats the real reason to go bigger most won't want to run deep gears. To me minimum gear for a 318 is 3.91 if you ain't willing to gear it go bigger.
 
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Plus

The main thing since peak torque is somewhat fixed is the torque curve and especially where it start. Especially in a street car where we spend most of the time below 3000 rpm. The more off idle your torque starts to come in the more lazy of a car you will have around town unless you gear it to spin it more than 3000 rpm at in town speeds :)
 
Thanks for the help and detailed thoughts, 273.


A couple of my own thoughts,

I do recognize the benefits of useful torque, but I really want to balance it with hp. Some will say, just build an engine for torque and don’t sweat the hp. Well, I did just that, after first installing a 1600 to 5800 cam. You really felt those heads breathe after about 4K and pull hard. But it was a dog out of the hole, so I thought, put a 800 to 4200 cam in it. Yup, I could spin the tire easy, but there was little excitement North of 3K. CamQuest6 says I gained 30ftlbs and lost about 25 hp.


So yes, a 360 will get me more of everything, especially torque. Pure fact.

But now I am intrigued with the XR268 cam numbers I listed earlier (394hp / 417ftlbs) on a 3.97” bore teen.

With the limitations of my 904 transmission, I have always thought that slightly less than 400hp and slightly more than 400tq is a good place to fall, for a tire smoking little screamer that impresses me more personally, than a 360 (no offense to anyone).


The other intriguing part for me, is how fast a 318 can spin, with lighter pistons/rods/bobweights combined with a roller cam. I imagine an engine that is easy to blip the tach for big grins and fun. Yeah, it might lose a race, but not by much. And in the end, it is a 318 (actually, a 328).
 
Thats the problem when people talk about torque and HP as two separate abilities.

Like I said torque is a single instance (one power stroke) and hp is all the power strokes added up over time (rpm).

So it sounds like 2 different functions.
But a running engine which is always doing revolutions per minute and making torque per revolution which is power an engine always and only makes power.
Power = torque x rpm those two never can be separated. And the power that we talk about is HP (hp= torque x rpm ÷ 5252).

I feel most people think torque does the work under 5252 rpm and hp takes over from there. But really since the hp curve is more like a staircase it's really hard to read what's going on down below peak hp.
So we look at the torque curve to get an idea cause it's more bell shaped. And it's not necessarily the numbers in the torque that's important it's the shape. Cause the more flatter the shape the more under the curve hp were making.

And since we know torque don't vary too much when they say build for low end torque (power) their talking between idle and 3000 where a street car is driven mostly. In a race car it don't matter if it makes low end power since it's geared and stalled to never go under the power band.

The way I see to build a street engine especially if your gonna under gear it.
Is to pick parts the will stretch the powerband far as possible without moving the low end to far off idle (depending on gears and stall how far you can go from idle)

If the one cam you picked was too big and the other too small it seems like in between would be the right choice or go back to the bigger one with Rhoads lifters.
 
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I wouldn't get to caught up in light weight revability. A well built 440 revs quite well and those pistons are insanely heavy. But yes if you can lighten up a bit all the better.

As for the 394 hp I'd think you would need a little more. The recipe I've come understand for a 400 hp small block is 10:1 CR, 750 airgap, xe285hl or similar and 220 ish cfm heads.
With a little more head you probably can get away with xe275hl.
 
I wonder how much quicker I could've gone with a modern lightweight bottom end than the stock 2000gm per pot 440-6 bottom end I ran in my 3000lb r/weight Cuda????
 
273 said:
I wouldn't get to caught up in light weight revability. A well built 440 revs quite well and those pistons are insanely heavy. But yes if you can lighten up a bit all the better.

As for the 394 hp I'd think you would need a little more. The recipe I've come understand for a 400 hp small block is 10:1 CR, 750 airgap, xe285hl or similar and 220 ish cfm heads.
With a little more head you probably can get away with xe275hl.
Click to expand...

Just for reference;KB 107s for a 360 are 502grams. At 11.3 Scr and with a 292/108 cam the revs were nasty fast, in my first iteration.
With the current 276/286/110 and now at 10.9Scr,it has quite a bit more torque at below 3000, and didn't seem to lose much up top.
It now pulls 4% less starter gear easy enough;11.44 vs 10.97 for the 276*.The 276* would be quite happy with a 9.98 starter;which would be 13% less than the 292.
And whereas the 292* liked 8.26 second,this 276* cam is fine with 6.78. That is 18% less second gear.
The 292* liked a third gear of 6.02, whereas the 276* is Ok with 4.97. That is 17.5% less gear.
4.30s cruise at 65=3472..Whereas 3.55s cruise 65=2867, which is 17.4% slower
My conclusion was;292 cam and 4.30s suck in a DD that travels at least an hour a day on the highway; 292 needs an overdrive. Having power at 5500 to 7000, which being 40mph to 50mph is great! Having to slip the clutch out to get moving is embarrassing, and not having reasonable torque until 2400rpm/17mph also sucks.Of course while i was in that mode it wasn't all that bad, cuz i didn't know any better. I'm sure a sharp teener couldda put a hurt on me at sub 3000rpm, in a roll-on.
But after the 270/280/110 cam went in, Well,then, that was when I knew I had made the right decision for me, and my application..and when that cam dropped two lobes, I got greedy and went to the current 276/286/110. I thought to myself, it's just 6 measly more degrees it will be alright, and I wouldn't mind a bit more steam at the top.So I thought. Wrong! This cam was a lot different than I anticipated. But in the end with a bunch of tuning, It is now fabulous."course I have an overdrive now,lol.
Long story short; gearing is almost critical. But as a streeter and a DD, I learned that a bigger engine can get to 60mph faster than the littler one, and can do it with less gear and less cam, leaving you with less rpm at 60mph, and sucking less gas per mile.
So yeah, a well matched teener combo can get to 60mph likkity-split. But it will take more cam and more gear, and if an automatic, it will take more stall, than a bigger engine.It will wear out sooner and cost more to maintain, and use more gas while cruising.
I think that is an excellent case for a stroker. It can use even less cam, and even less gear, to get to that 60 mph.
And once you hit 80mph or so and start to plow air,that is when the bigger engine starts to shine. And the faster you go,the more air you push, and the bigger engine keeps going long after the little one gives up, and gearing now won't help it, only more cubes or supercharging or a lower cd, or a lot less weight, but those are another thread.
A teener with 4.30s, an automatic,and too-big-really-for-street-cam, that peaks at 5800, is gonna begin the down slide at 103 mph. By 6300 it will be gasping it's last breath and going 112 mph. The torque peak on this engine will be at about 4400, and if it musters 1.2#/cid, it will make 380ftlbs. At 4400 this is 318hp
Whereas a 360 built to the same absolute power, will only need 3.73s to keep up to the teener with a cam that is probably 2 sizes smaller.At 103mph it still has plenty of revs left, probably spinning at just 5000 rpm. It's cam will run out probably around 5400, and will be wheezing at 6000, so it will make 124 mph,before running out of Rs.This engine will torque peak at about 4100, and it will only need to make 1.055#/cid to match the teener. At 4100, this is 298hp
The 318 of course, can only dream of making as much torque below it's peak as the 360 is casually delivering.
At the starting line;
the teener is looking good with a 10.54 starter gear, while the 360 is stuck with a 9.14 starter. The 360 will need to make 15% more torque at stall to keep pace with the teener.With it's 2 sizes smaller cam, and it's 13.2% size advantage,I'll go out on a limb and say with a street TC this is all 360 territory. With 4100TCs, I can see them taking off together.But I also see the 360 pulling ahead in a very short period of time.After that it gets too complicated to see what is going on in a moment by moment basis, but I still see the 360 ahead thru the traps.
Anyway that's arm-chairing again.
I guess I should add; at 32mph, the teener will be doing 4397 in first gear, just a tic below its torque peak.It is all set to go hammer down. Whereas the 360 is only doing 3800.If they launch together, and baring wheelspin, the teener will jump ahead. The teener will be done by 46mph and will have to shift. The Rs will fall to 3740, and the poor teener has nothing left.
Whereas the 360 will pull to 50. So the smart 360 owner will call 50mph the finish-line. Cuz if he has to shift, the Rs are gonna fall to 3550. But I still think the 360 has more torque at 3550 than the teener at 3740. So while the 360 has pulled ahead, it will just maintain the lead to the next shift.And by then it will be ahead by a bit more. And so on.Right thru the traps.
But most street blasts are done by 65 mph.This will be 5588 with the teener in 2nd, and 4600 in 2nd for the 360. Ima thinking the teener might be taking this one! Nah......probably not; the teener lost too much time,fighting up from 3740;it was practically drowning down there, for just too long.
And even if the teener manages to catch up, the teener is maxed out! Whereas in 75 minutes, 3.91s can be in the 360, and bye-bye teener,bye-bye.And the 360 still has 2 or 3 cams to plow thru and two more rear end ratios before it is similarly maxed out.
I won't say it...
Ok I will; 502 gm KB107 pistons rev quicker to 6000 than they do to 7000,lol. 1969 Factory 340 pistons were 719,and nobody ever called them slo-revers,lol. Teeners were 592 and 273s were 549.Everybody brags on their 273s being snappy revers. Also in 69, all rods are listed at 726 gms, and I put 318 rods into my 360 as they already had the bushed ends, whereas my 360s were pressed. As far as I could see, the 360rods were otherwise the same even down to the casting numbers. I did not weigh them. Yes, I know the earlier 273s and 318s had lighter rods and cranks........The point is, the 360 with the 502pistons, is no slouch when it come to reving quick.Especially if you put some decent compression in it. But if you like to buzz your engine up in neutral to see how quick it revs,and it just ain't quick enough for you? well then, you can always pitch the tank oem flywheel,lol.
 
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cudaracer said:
I ran camquest6 from comp cams, using the following parameters:

3.97" x 3.31"
XE268 cam (1600 to 5800)
DP high flow intake
600 carb
Large tube headers
9.5 CR
308 head flow numbers (max CFM 207) with 1.88 / 1.60 valves

HP seemed just a bit high at 364
Torque was at 394

I then replaced the cam with a retro roller, XR268 (1400 to 5500)
HP jumped 30 to 394
Torque also jumped 23 to 417

And not just the peaks, but much higher averages and sooner with that roller cam. I was not aware it impacts torque so much. And yes, I know the program is a bit optimistic, but I think the difference between roller and not is much more realistic.

Fun program. I played around and increased bore and watched only torque go up. Same thing happens with increasing stroke, just torque.
Click to expand...
Do you have large tube headers and a high flow intake? I've found honesty in the dyno programs will produce a more accurate number
 
lomchivok said:
Do you have large tube headers and a high flow intake? I've found honesty in the dyno programs will produce a more accurate number
Click to expand...

No I don't. I assume that would be 1-7/8" tubes? I actually have Dakota manifolds. When I select those, I lose a lot of hp, like over 40. But most people run headers, so I just base lined it with headers for reference, and then know that I am leaving plenty of power on the table.
 
cudaracer said:
No I don't. I assume that would be 1-7/8" tubes? I actually have Dakota manifolds. When I select those, I lose a lot of hp, like over 40. But most people run headers, so I just base lined it with headers for reference, and then know that I am leaving plenty of power on the table.
Click to expand...

If you don't see over six grand very often stay with the small diameter header.
It will have better low end torque. Big tube headers are great if you are running mostly high(4500 to 8500)rpm but are generally a waste on the street. been there,done that, got the shirt.

If you're building a badass big cam high revving motor, go with big tubes....and if you have the big headers already, that's a perfect excuse to build that kind of motor for it...Most people oversize their headers because they believe bigger is better. While your peak HP number may be down with the smaller headers, you'll actually make more usable power.
 
cudaracer said:
I then replaced the cam with a retro roller, XR268 (1400 to 5500)
HP jumped 30 to 394
Torque also jumped 23 to 417

And not just the peaks, but much higher averages and sooner with that roller cam. I was not aware it impacts torque so much. And yes, I know the program is a bit optimistic, but I think the difference between roller and not is much more realistic.
Click to expand...
As to be expected... the roller has steeper ramps. Better lift to duration ratios will help torque all over.
 
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