My requirements... what to build?
So that narrows it down to 318 or 360. Not really interested in the 340's at this time.
What I am looking for is a nice driver with a little extra horses to boot. I would like to have some fun when I am on the street in town and still be able to take the car at 65mph with out having screaming RPMs. Most of my driving will be 0-65 maybe a few trips on the highway but not many. The car needs to run on pump gas, (does not need to be E85) and needs to be able to let the tires loose a little bit when I would like. Also the car needs to be reliable. The plan right now to do this rebuild once, and drive it for a decent many a years to follow. I do not put many miles on the Scamp per year. A few shows, a lot of ice cream runs, and a few trips to town. Thinking 300ish HP (maybe a tad more) to the wheel. The more the better but for my application I really do not see needing 400HP
You asked for opinions so here it comes.
Per your requirements,
With a 318, I think you will need;
>no more than 3.23s and tall tires, for 65=~2600.
>an A999 with a wide ratios and a loc-up.The ratios are 2.74-1.54-1.00. With 3.23s this gets you an 8.85 starter gear which is same as 3.61s with the A904.
> now you have to build an engine to pull that 8.85 starter gear, and to be able to pull it for as high up in the Rpm band as possible. This is a bit of a problem, so
lets switch to a 360/5.9
I think you will need;
>3.23s, and an A998 with the standard 2.45-1.45-1.00 ratios and a loc-up, for a starter gear of 7.91
Your 360 can pull this 7.91 to 60mph=6200 in first gear, @5% slip; problem solved. Cruising; 65 is still 2600
>So now you build your 360/5.9 to do that.
First hurdle. rpm at 32 mph is 1285 in Drive and cruising, but at WOT, it is 1960 in second,
3320 in First. So, when you are just cruising along in Drive, nobody can hear you, nobody even notices you. But when you floor it, and the trans kicks down into first, you want thunder and lightning, a roaring engine, and screaming tires. Well maybe you don't, but a hi-compression 360, has no problem doing it.
Second hurdle; 3320@32 mph, means the street stall is all used up, so you get not much help in the TC as regards Torque-Multiplication, so the engine is gonna have to do it on it's own.
Third hurdle: powerband. You need TORQUE at 3320. At this time you do not care about power yet. You want to power away from 3320 so the engine better have the goods.
Note1;
The hi-compression 360 can burn the tires from a standing start to the top of first gear, with almost any rear-gear, so we don't really need to spend a lotta concern about first gear.
And since 3.23s will get you 60@6200,we don't even care about second gear very much. This is what makes 3.23s so likeable.
Power
Keeping your introduction story in mind, IMO, you need to build torque down low, and power at 6000 be-darned. So lets pick a cam. I chose a power peak of 5000/48mph. Good heads will stretch that out to say 5500, and good springs will carry the revs to the required 6200@60 mph, when needed.
The 5000 power peak will put the Torque peak at about 3500, which will dovetail nicely with the 3320@32 mph.
Ok this is where it gets tricky.
You can take the easy road and install a hydraulic flat tappet. You set it and forget, and it runs forever. And in your application it would be fine.
But; lol, because of your story, I'd like to see you run a solid lifter flat tappet. It has several advantages, and in your case almost no disadvantage.
Solid lifters need periodic lash adjustments. But in your case, with the limited mileage you anticipate every year, this might only be every second or third year. The other thing about solids is that they tend to be a lil on the noisy side. But with modern tight-lash designs, I have heard, that it is a lot less noisy than it was in the past.
Now the advantages; With a solid, you can run the next bigger .050 cam, for similar advertised specs, so if you are compression limited, this is a big deal. But for you, flip that statement around; you can run the next smaller cam, have the same .050 specs, but it will run less advertised durations. This can be exploited in the EFFECTIVE compression ratio.
So let's talk about cylinder pressure. The more you got, the more efficient your engine will be ,right up to the point detonation sets in.Also the more cylinder pressure you have, the more power it will make, until detonation sets in. So the take-away is to build as much cylinder pressure as you can, consistent with staying out of detonation.
Ok so how do we marry these fine points?
Well, it just so happens, and this is why I would choose the 360, that it falls together pretty cheaply at ~10.7 scr. Just stick some tall flat-top pistons in there and some small-chamber heads and yur in business.
THIS IS NOT POSSIBLE WITH A 318; it's gonna cost you more money to make it happen, and you will not even come close to matching the 360 torque.
Do you need 360 torque?
Mostly no because mostly the 360 will piss it away in your body-style, spinning all the way to 60 mph. But 360 torque has other advantages; like lighting up the tires at 32 mph. Like powering thru the sound barrier. OK not that, but the 360 will fatten up your midrange. And KD at 55 mph to pass Grampa will get you ~ 3400@55mph; just about right at peak-torque. But the best part is you can run so much less starter gear, and that pays dividends at hiway cruising.
Consider a warmed up 9/1 318, with 3.55s, a 904, and a 2800 stall TC. That's a typical pkg for a streeter.
Consider that at 2800, she might be able to put out 240ftlbs at WOT. Ignoring powertrain losses,and at zero mph, this ends up at the axles as
240x1.8x2.45x3.55=3760 ftlbs, enough to break traction and spin. About two car lengths out, the TC may have dropped to 1.2 ratio,from 1.8, so maybe it sustains the spin at 2500ftlbs, maybe not.The spin would probably go away, except the rpm has risen and the torque is climbing. But the 318 will torque peak very soon and so the tire-spinning is about to quit.
How about the 360 that I'm targeting here?
Well, lets give it a TC of just 2600, so it ain't smoking the oil at 65mph. And lets say that at zero mph and 2600 she is able to put out 340 ftlbs, then
340x1.8x2.45x3.23=4840 ftlbs, enough to annihilate the tires. Again, about 60ft out, the TC ratio has fallen, but with the larger torque differential , I'll guess the ratio to be still 1.3, and lets say the rpm ,because she is spinning, you control to 3500@peak torque, say 420ftlbs, so
420x1.3x2.45x3.23=4320, and still annihilating the tires. You can carry the smokey-business to 34 mph still at 4320 ftlbs, still smoking the tires. That is what the well-engineered 360 just does.
So leaving the 318 in the smoke lets continue.
Here on FABO,Some fellows have reported running 200 psi and a tickle more, on pump gas, with aluminum headed 408 strokers. Many of us run 180 to 190psi.
I myself have run over 185 on 87E10.
IIRC, Yellow Rose says he can run the high numbers with iron, I forget his number. And Rumblefish also states it can be done. I can't speak to that, but I can to the aluminums. I think you cannot hardly build too much cylinder pressure for pump gas in a street-type engine. Therefore; I highly recommend them.You just slam the motor together and do with it whatever you want.
Ok so, lets bring this puppy home.
1) we can run any Scr we need to
2) we (or I) want a 5000rpm power peak
3) I want mega torque , ok not mega exactly, put plenty of torque at 32mph/3320rpm.
4) and I throw in fuel economy cuz as soon as this Covids scare is over, the cost of fuel is gonna sky-rocket, probably well beyond what it used to be.
So, in the KB catalog you will find several pistons that will work. I used the KB-107 flat tops and she came in at .012 below the decks, with a quick pass over the decks. I later re-machined the decks for a .005 pop up. I used the indestructible FelPro head gaskets at .039, and I installed some 63cc aluminum heads. With 5cc eyebrows and .040 overbore this maths out to 10.95 Scr.
I ran this with a Hughes HE2430AL (no longer available)
flat-tappet hydraulic cam,Yes I took the easy road.
This is what the Wallace Calculator has to say;
Static compression ratio of 10.95:1.
Ica of 63/ 930 ft elevation.
Effective stroke is 2.81 inches.
Your dynamic compression ratio is 8.81:1 .
Your dynamic cranking pressure is .............
180.25 PSI.
V/P (Volume to Pressure Index) is
.............. 156
And I burn 87E10 in that monster 100% of the time.
Lets look at this cam.
In at 108*, it has;
270* intake,
117 measly degrees of compression, but
110 * of power extraction, and
276* of exhaust.
The overlap is 53* of which 52 are Effective,and
the Ica is 63*
Big deal you say! ; the numbers don't mean anything to you . Fair enough let me help you.
>Lets start with this;
V/P (Volume to Pressure Index) is
.............. 156
Read about VP here;
V/P Index Calculation
IIRC the 440 Magnum of 1969 had about this for VP.
VP is a ratio that attempts to define the low rpm performance of an engine. All engines with a VP of the same number, are gonna perform similarly to eachother below about 3000/3500 rpm. With 3.23 gears 3500 is 34 mph with 27" tires. So if you build a 360 like this, you can expect the bottom end to feel at least as strong as a factory stock 1969 440 Magnum, up to 34 mph, also with 3.23s. Well that is about say 80/90% of your city cars driving, right?
POW!!
And we haven't even mentioned power. Now I will. If your 360 makes 400ftlbs at 3500 rpm, that would be
400x3500/5250=267 hp. Wait, that's 267
measly horsepower, and it's cooking like a 440 Magnum? Hyup.
> next; the 270 intake *.
On this cam the net is
[email protected] and that points to a power peak right around 5000,perfect. IDK how much power it makes but it put my car into the 12s, shifting at 7000 .......... suffice it to say, it's lots enough for your application.
> next; the 117* compression.
This is normally thought of as a small amount of degrees. But a "normal engine" will not have 10.95 Scr. The goal of these degrees is to build enough squeeze to make decent power, so it doesn't matter if this number is small, if the pressure is large. And in the above example we see
Your dynamic cranking pressure is .............
180.25 PSI.
So again, this number is lots enough for your application.
> Next; the 110* of extraction.
This is actually quite a lot for a performance engine. I chose this cam for this reason,because it offers the potential to get your car into the 20s mpg,point to point on the hiway. It has the potential for more, but that will be up to you to glean. In any case;this number is lots enough for your application.
> Next,the 276* exhaust duration.
With good heads,and headers, this is a good number for the 270* intake duration. Certainly, this number is lots enough for your application,lol.
> finally the 53* of overlap.
With a good working exhaust, this will put a little bulge in the power curve throughout the midrange, but it is not hard to tune the carb with just 53*.
I like this cam; it has just enough idle lope to know it ain't a stock 340. But if you install the 340 exhaust system (and I'm not recommending it); especially the factory tips, it will sound very much like a 340. As for exhaust, I ran full length 3" duals, right to the bumper, with just turn-downs. IMO, there is no such thing as too big, until you can't fit it under the car anymore. There is only one downside, well two,lol, the dual 3 system is stinking heavy, and the volume level at the back, from the curb, tends to be "loud". But that is very dependent on the mufflers and tips you use.
This combo will like a dual-plane intake, and a 750carb, but for you, I would recommend a 650DP, or a spreadbore, even down to a 500, which will be adequate to 5000rpm, or most of your driving situations. I just really really like the 750DP on mine.
Do you need this much cam?
No!
But it won't cost you anything to run it! Because at 10.95Scr or even 10.7 where it is likely to fall together with no deck machining, this build has adequate pressure to handle it. So;
I heard that you don't need 400hp, but if it falls in your lap with no downside, then ........ WTH, why not!
Well there are actually a couple of downsides;
1) Your wife will give you heck every time you return from the grocery store having been gone for hours and hours, and you completely forgot to bring milk; cuz you were having so much fun, that you lost track of the time. And
2) It burns a lotta gas. It takes gas to make the fun, and you like the fun, so bring cash.
3) after you have given all your friends a ride, none of them come back for seconds. Well maybe one.
4) before you take your wife out for a spin;install a throttle-stop,a rev-limiter, and DO NOT make any promises that you cannot keep.The couch is a very cold,lonely, and uncomfortable place.
So, to recap;
What I would do is
build a hi-compression aluminum headed 360 with a modest hi-torque cam, a small carb on a dualplane, headers, a free-flowing exhaust, a 904, 3.23s and just about any old TC, you happen to already have.
Be warned
If you install fat sticky tires, you will need at least an 8.75 rearend to put up with the 440-Magnum type low-rpm torque. I kid you not, this build broke a lot of stuff for me in the 4 short years I had it. When you have to build a driveshaft, make sure it has at least 7290 U-joints on both ends, and install a front driveshaft loop.
Do you need a 360?
Probably not; you said it's a cruiser, an ice-cream getter.
But it costs nearly same to build either combo; actually more to build the 318 to high compression; exclusive of the aluminum heads.
You can get away with less money on the 318, by using the factory rocker gear, too. But I get the sense that a grand or two is not gonna affect your budget.
Plus; if you talk to Yellow Rose or Rumble, they might tell you how to marry hi-pressure and iron heads, maybe saving you some coin there; nothing wrong with iron on your combo.
But I just gotta say one more thing;
the 340 was always a performance engine, but it doesn't have to be that way. I mean guys try get them to 500hp all the time, and some even succeed. But that is not the type of engine you want;you would want the 340 to be de-tuned for torque.
IMO, and for your application
the 318 does not have the capacity to make both low-rpm grunt and hi-rpm power, and stuck with 3.23s, I am fairly certain that you will be disappointed.
The 360 will have a preponderance of low-speed torque, a powerful midrange (with that 2430cam), and a reasonably good top end, all with 3.23s, and no disappointment.
The 340, could fly right up the middle, giving up some of that 360 copious torque, and still nearly match the 360 the rest of the time. You just can't slam it together like you do a 360. So if you have one........ I sure would think it over.
And I hate to say it but this is how it goes; with your hood up, every knuckle-dragger at the carshow will blast your 360, telling you that you shouldda built a 340. They will say "everybody knows the 360s were junk". I finally painted my 360 Orange, and when asked, I called it a stroked 340, after all it was 4.04x3.58. That was the end of it. Very few people noticed the Orange painted Eddies.
Happy Hotrodding.
