dirty white boy
50 yr old Juvenal delinquent
should not have any eye brows if stock!
Comp cams xe268h for 318
- Thread starter dartfreak75
- Start date
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dirty white boy
50 yr old Juvenal delinquent
thats correct these factory roller cam 318s is close to 9 stock!
dartfreak75
Restore it, Dont part it!
Well if that is the case and I am right then I am not even worried about pistons the stock pistons will be higher in the bore than any aftermarket piston besides the Keith blacks of course. I had a set of kb167 pistons in that 67 318 in my barracuda. Kick myself for selling that car.
Clean out your in-box, I have a XR280HR-10 cam that I am not using.
inbox cleaned out and pm sent.
nm9stheham
Well-Known Member
There ya go... that's how it's done. With those numbers above, I get 8.6 SCR with a 1.755 CH (.067" below deck) and no eyebrows but adding 1 cc for the gap down to the rings, a .028" thick head gasket. So that is close to your 8.78 number.
For milling the smaller area of the 302 chamber means you will have to mill something like .007" for each cc taken off of the volume. So milling .020" would get about 3 cc's off and if the chamber start at 65 cc's then that 62 cc result would get you to about 8.9 for SCR. Getting better. I'd go at least .030" and also measure those head chamber volumes carefully, they may be smaller than you think. If you get the chamber down to an actual 60 cc's then you get to 9.1 per my numbers, again, using the .028" thick head gasket.
With that, you are at around 7.3 for DCR IF you advance the cam timing to an ICL of 104. That is a ton better than where things were heading before.
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nm9stheham
Well-Known Member
Just for info.
Early rods: 726 grams
Later rods: 758 grams
All numbers measured by 2-3 people, including me; I have both sets here. Magnum rods are another matter.
Yeah understood. I just was relating someone else's measured height below deck for some '68 318 pistons from a post here on FABO, in which they seemed very confident. It lined up with my '68 273 piston numbers, so I ran with it..... but now you have made me question that again.
dartfreak75
Restore it, Dont part it!
Ok thanks buddy I wasnt sure on those heads I looked it up and I found a list that had how much was need to remove 1cc for a bunch of different heads I didnt see 302 heads so I just went with la 318 heads it said .005 so that what I went with for 360 heads they had it listed at .0048. Either way if I'm above 8.5 I'm not going mill anything....yet ;).
nm9stheham
Well-Known Member
Yep, those numbers you list are for open chamber heads. The amount needed to mill for each cc reduction in chamber volume goes up when the chambers become closed.
BTW what kind of price are you getting for the Speed Pro's? The best I am seeing is on RockAuto at $22 each. Not too bad and half of the cost of KB167's.
I sincerely don't agree in the 8.5 number being adequate with the present cam. But the important thing is that you are becoming 'armed' with info and learning how it is done. You can make your own decisions and have a good idea of why things turn out like they will, and how to make things different. I.e, you are DESIGNING for a result, not just blindly following a formula. You can then fill in that framework of understanding with real data .... like don't slap 360 heads on a 318, or put a 300 duration cam in a 7.6 SCR Opel 1.9L engine and expect it have any low RPM torque LOL
Do yo have a favorite DCR computing tool yet?
All of this applies to the matter of low-mid RPM torque, for street/driver use. Things like peak HP for a different use goes into other matters.
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dartfreak75
Restore it, Dont part it!
136 on ebay
dartfreak75
Restore it, Dont part it!
That's with the pins no rings
dartfreak75
Restore it, Dont part it!
I found a set 273 rods on here floating pins are they good ones do they weight the same? I will get you part number
Also I found a set of 645 rods with fresh 318 pistons on them on Ebay I sent him a message for more info if they are not stock and are aftermarket I may buy them. Idk yet
Also I found a set of 645 rods with fresh 318 pistons on them on Ebay I sent him a message for more info if they are not stock and are aftermarket I may buy them. Idk yet
nm9stheham
Well-Known Member
BTW, I edited my last post with some more info/questions... we keep typing at the same time LOL
Those 273 rods should weigh the 726 grams. The rods you have in the '80's engine should weigh the 758 grams; that -645 PN looks right for the later, heavier rods. That is the one matter that may cause balance issues for using the early rods with the later crank. The heavier 273 pins should be able to be used to correct this but it is not a straight gram for gram change if the weight is added at the top end of the piston-rod assembly. Bobweight has to be computed for the original and new combination and the pin weight adjusted to make them match. The math is not hard!
Can you get access to a precise gram scale locally?
I think I see those pistons and rods on eBay. Look at the dish on the top of the piston; that is going to add something like 7 cc's + or - to the chamber volume and drop SCR and DCR by at least 0.5 points. Plus they are .040" over.... looks like non-starter to me.
Those 273 rods should weigh the 726 grams. The rods you have in the '80's engine should weigh the 758 grams; that -645 PN looks right for the later, heavier rods. That is the one matter that may cause balance issues for using the early rods with the later crank. The heavier 273 pins should be able to be used to correct this but it is not a straight gram for gram change if the weight is added at the top end of the piston-rod assembly. Bobweight has to be computed for the original and new combination and the pin weight adjusted to make them match. The math is not hard!
Can you get access to a precise gram scale locally?
I think I see those pistons and rods on eBay. Look at the dish on the top of the piston; that is going to add something like 7 cc's + or - to the chamber volume and drop SCR and DCR by at least 0.5 points. Plus they are .040" over.... looks like non-starter to me.
dartfreak75
Restore it, Dont part it!
Those are different ones the ones I'm talking about didnt have a pic of the pistons he sent me a message with more pics they are factory 318 pistons no eyebrows. According to my book 645 is the same thing my engine already has so those are probably identical rods and pistons that is in mine lol I will just stick to what I have its not the extra money to me. Especially if I'm at 8.5 cr that is ok for street use. I would rather be above 9:1 but I can always tackle that later. I read a post on here where a guy milled 302 heads to 57ccs according to my numbers it would only have to remove less than 5 ccs to get to 9:1! Give or take
dartfreak75
Restore it, Dont part it!
dartfreak75
Restore it, Dont part it!
According to this it says .0053 to remove 1cc does this sound about right?
Wyrmrider
Well-Known Member
learning a bunch
op
you mentioned comp 256 and 262 a few pages bak
the comp 256 closes the valve about 54 ABDC which is ok but it will not have the power of a 256 voodoo or howards (with 15 footnote)- look at the difference in lift which equals more area under the curve
cheers
op
you mentioned comp 256 and 262 a few pages bak
the comp 256 closes the valve about 54 ABDC which is ok but it will not have the power of a 256 voodoo or howards (with 15 footnote)- look at the difference in lift which equals more area under the curve
cheers
nm9stheham
Well-Known Member
Mmmmm.... I stuck my neck out and made an educated guess at the .007" number.. so, well OK, maybe .006" for 302 chambers. .0053 just computes out too small, even for the early 273 head chambers, which is what they are talking about with that .0053" number. If you milled off .030", then the difference is only 1-1.5 cc's anyway. So, let's compromise on .006" milling per cc and you'll be darned close. If you over do it with milling, it is only going to make it better. I can't imagine much price difference if any to mill .020" vs .030".
IMHO, I don't think I;'d bother with those eBay rods and pistons. There are better ways to spend those $$.
nm9stheham
Well-Known Member
Mmmmmm...... Backwards logic..... 8.5 is (marginally) OK for casual drag racing since you will rev the crap out of it everytime you launch and can use a high stall TC to get past any low RPM 'dead zone'. Low CR on street/driver use is only OK for grandma going for groceries, or hauling logs. 8.5 is 8.5, nothing better and DCR will be the mid 6's which is below the DCR of a stock 318.
Edit to add: You mention getting down to 57 cc's; that would be an interesting approach..... put the $$ in milling and save $$ on pistons. Assuming pistons .075" down in the bore, flat tops, and .028" thick head gaskets, you're around 9.25 SCR, and DCR is now back up to around 7.3-7.4 with that cam. Keep in mind that when you mill that much, then milling the intake side of the heads may become necessary (more cost), AND you are going to possibly push the heads down far enough that the pushrods might be a bit too long. With some tricks, you may be able to get past the pushrods (IF it indeed any issue, which it may or may not be; it's a case-by-case thing, and completey dependent on the individual parts). That may be your lowest cost approach and forget any piston/rod changes.
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dartfreak75
Restore it, Dont part it!
Yea I agree with you I'm gonna pass that the same thing that is in I now. And as far as the milling numbers go I wasnt trying to prove you wrong or anything I believe you that's just the info I had found and was going off of before you commented on that subject. Furthermore milling of the heads is not a top priority right now that will be a later project if I am not happy with the performance when I'm done
dartfreak75
Restore it, Dont part it!
Yes absolutely agree. But I do kinda drive like a grandma soo.....Mmmmmm...... Backwards logic..... 8.5 is (marginally) OK for casual drag racing since you will rev the crap out of it everytime you launch and can use a high stall TC to get past any low RPM 'dead zone'. Low CR on street/driver use is only OK for grandma going for groceries, or hauling logs. 8.5 is 8.5, nothing better and DCR will be the mid 6's which is below the DCR of a stock 318.
Edit to add: You mention getting down to 57 cc's; that would be an interesting approach..... put the $$ in milling and save $$ on pistons. Assuming pistons .075" down in the bore, flat tops, and .028" thick head gaskets, you're around 9.25 SCR, and DCR is now back up to around 7.3-7.4 with that cam. Keep in mind that when you mill that much, then milling the intake side of the heads may become necessary (more cost), AND you are going to possibly push the heads down far enough that the pushrods might be a bit too long. With some tricks, you may be able to get past the pushrods (IF it indeed any issue, which it may or may not be; it's a case-by-case thing, and completey dependent on the individual parts). That may be your lowest cost approach and forget any piston/rod changes.
Haha I just read that on here idk if its possible like i said in my previous comment that will be a later project if I'm not satisfied. Once the car is running and driving and the interior is done the body is painted and I want more power i will start things like swapping and milling heads maybe even save up and get an aluminum intake new carb etc
dartfreak75
Restore it, Dont part it!
Let me ask you (yall) this stop light to stop light will a cam like the xe256h or xe262h or luniti voodoo. Be a huge noticeable difference in the cam I have now? Like what are we talking here half a sec difference 0-60 or a couple secs lol
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Oh yeah big time!
here is something that illustrates cam characteristics pretty good.
Consider three different cam sizes B,A,and C each just one size bigger than the last. Imagine the lowest is a 256 and then a 262 and finally the 268. Notice the huge amount of bottom-end power given up to get a relatively small amount of power at the top. This stems from the pressure loss down there, as each larger cam losses progressively more low-rpm efficiency, ......... to get that higher rpm efficiency.
The trick is to choose the right cam for the combo..... and if the Scr is already in the basement to start with, then there is just no getting around that low-rpm performance loss, with a streeter.
The E and D curves are representative of the shape of the power peaks using wide and narrow LSAs, not on the same cam tho.Just consider the shapes
The thing you want to notice is where the B line crosses the C line. I'm gonna guess that is about 4200rpm(see note#1). If I'm right, that would be 47mph with 2.76s. Now just let that sink in for a bit.................................................................. The speed limit on most city streets is 30/35 mph.
Note#1,
how I got 4200. I assumed the bottom of the graph to be 3000 and the highest point of the C-curve to be 5400, so that is a range of 2400rpm. The crossover point appears to be at about 50% of the range so. .50x2400 plus 3000=4200rpm....Ok but say the low end of the graph is 2500, then .5x2900 plus 2500 is 3950@44mph, still speeding ,mostly.
Now look what that C cam is doing to your power. Nothing but a total power loss under 47mph.And not just a little bit, but a huge bit. You can never make that up in just the engine, no matter how much compression you throw at it. You can see that, without tirespin, the B-cam will be way quicker to 47 mph than the C-cam.......... because it is putting down more power during that time.
So suppose you had that B-cam which might peak at say 4400, and by the shape of it you can carry it out to 5000. So then for low ET, you could run 4.30s to get 4900rpm@35mph. And you will outrun any C-cammed 318 with any like-sized convertor and 2.76s; no matter what it's Scr.
This is why I love a stock 318 with nothing more than 4series gears and the 2800. A freeflowing exhaust is a must and a 4bbl will get you a little more wheel spin in second.
There is another option, a new TC that eliminates all the rpm or maybe just most of it; below the crossover point,which I guesses to be 4200. Now your rpm will blast up to where the power of the C-cam is and rocket you off the line with mega-wheelspin
EDIT; This part was added later:
Now lets talk about the D and E curves.
If you have two cams with the same specs except they are ground on different centerlines, this affects the power delivery, as the curves are trying to demonstrate. Imagine the D-curve is on a 114 LSA, and the E-curve is on a 108LSA. Notice how the E-curve builds to the power peak and then falls off rapidly. This is a nice shape for a drag-race engine, with tight transmission ratios or a high-stall TC .A cam with this shape usually makes a little more power over the narrow rpm range that a drag-race engine uses.
The D-shape is generally preferred for a streeter because the power delivery is smoother and spread over more rpm, so you always know what to expect when you gas it. Unlike the E-shape which generally explodes and then pukes; Like a pipey 2-stroke motocross bike.
Off the shelf cams are usually mostly 110s now, so you don't have much choice in the choosing.
But if you did, and you also had appropriate gears, remember that a streeter is basically a two-gear race-car that traps at 65 mph....... so why put a granny 114* cam into your engine?
For low-ET with a streeter,and an automatic;
probably every last streeter in the country,is stuck with the same problem; how to trap at 65 mph. Will he use one gear or two, then you have just two or maybe three ratios to choose from, to go with your choice. Small engine will usually choose 2 gears, while bigger will use just one. 318s need two gears.
So then your trap ratio is solely dependent on your tire size and trap rpm. And the rpm range might be from 5200 to 6200 depending mostly on the cam. Lets chose a 27" tire with an 85" roll-out. So;say with 5% slip in the TC, 5200 will require a 6.13Final Drive ratio, while 6200 will require 7.31FD. Probably every streeter in the country is stuck trying to fit into this range.
Now if you have a TorqueFlite with a 1.45 second ratio, then your rear gear choice is gonna be between 4.23 and 5.04 which choices are; 4.30,4.56,4.88.
Now all you gotta do is choose one of those ratios and build your engine to hit peak power at the rpm associated with one of those gears, tune it, and go win.
This now takes us back to the D and E curves.. Since you no longer care about power after the peak, ( because you will be running plenty of gear and plenty of TC, and you don't care about power after the trap;just like a drag-racer), there is no reason to run a wide LSA. In fact, run as tight as you dare, or as you have convertor for.
Let's say you choose 4.30s which hit 65@5300
or 4.56s, which hit 65@5600.
Or say you wanna be a lil quicker and go with 4.88s. Now she hits 65@5900
For a tight LSA108 cam, you might want the powerpeak to be 200rpm lower, to spend a lil more time at or near peak power. In this way you can be in the slightly higher power part of the curve that a 108LSA cam makes. (If you had a flat-line power delivery like a 114LSA cam makes, you might be able to use any of the three rear gears,and the same TC,with a corresponding loss of low-ET)
Now comes the secret; each of these cams will peak about 300 rpm higher than the last one, and so will require a bigger cam to stay in the efficiency window......... And what does the bigger cam do? It loses low-rpm efficiency. So along with the cam change, the combo may need a TC change .
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nm9stheham
Well-Known Member
I want to hear what others have experienced, but here is what I have found when having low DCR with a low stall TC (or too high gear with a manual):
- When 'off the curve', you can push the throttle 1/4 of the way and then all the way down and it makes hardly ANY difference; it accelerates slowing at the same pace regardless of throttle positions of 1/4 or 100%. In other words, throttle response is non-existent. Have you ever driven a loaded truck and picked too high a gear, and put the throttle to the floor and the acceleration did not change? It's just like that.
- When you get 'up on the curve', the thing takes off. You end up with a light switch-like behavior: off, then on. If you ever have ridden 2 stroke motorcycles, you will know how this feels: get the RPM too low and the thing just falls on it's face. My overcammed low CR Opel was (seriously) like a light switch. You have more cubes to weight, and not as bad a DCR if in the low 6's but it will still have an off-on character. That on-off character, plus the non-responsive throttle at low RPM's, tends to suck when trying to accelerate out of corners on back roads.
- As far as 0-60 times... I can't say a number with total confidence. But several seconds improvement would not surprise me with the cam change you mention. The guy with a 7.4 DCR and the XE256/262 valve lift of .447"/.462"will be far ahead of the guy with a 6.7 DCR and the .421" lift of the present cam. And with the added lift, the advantage will continue past 60 MPH; the performance will be better past the mid RPM's 'til the heads' flow stall out.
Wyrmrider
Well-Known Member
We used the term "come up on the cam"
makes a big deal in sports cars where you can get below the curve and maybe have to shift down where with a little more torque you would not
and with a boat if you are below the curve you can't get up on a plane and can never go fast- been there- done that
makes a big deal in sports cars where you can get below the curve and maybe have to shift down where with a little more torque you would not
and with a boat if you are below the curve you can't get up on a plane and can never go fast- been there- done that
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