Max effort cam for low comp 318

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HardVG

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Looking for a bit of advice/feedback on other people's experience.

I have a track day car (circuit racing), it's actually a BMW E36 coupe, but fitted with a 318 Mopar engine. The engine was built maybe 30 years ago and is a pretty basic build of the day, stock replacement low comp pistons, factory heads which are supposed to be fitted with 360 valves and maybe bit of bowl work. It has a Weiand high rise dual plane intake, 650 Holley and shorty headers with twin 2.5" pipes. Running through a 4 speed manual box and 3.15 BMW rear end. The car is pretty light overall, say 2900 lbs with driver and runs around 96 mph in the 1/4 mile, so Wallace is saying I have around 200 HP.

It is pretty quick around the track, but my issue is that it lacks power and straight line performance. You can't really slam it up the inside under brakes at track day, so it needs to be able to pass cars in a straight line.

This is where it comes down to camshaft choice. The engine currently runs a 340 spec camshaft, so I want to know if I can make any significant gains with just a cam change. Lunati has suggested their 701 grind and I know there is the Hughes Whiplash cam that is supposed to work for low comp motors or am I wasting my time without bumping up the compression.

Can anybody give me some real world numbers of what some alternative cams will achieve for my application? The car tends to work in the 3500-6000 rpm range on the track, so that's where I need to make gains.

20200801220016-80a38dc6-me.jpg
 
Is it race only ??

what’s the maximum lift you can run ?

if it’s race only I’d run a lot more cam than a 701 but if dual purpose 701 would be better than you got.
 
It's track use only and I can potentially pull the heads and do some work on them if I have to. Thinking a bit of porting wouldn't hurt. The general idea is to keep it low budget and I know the low compression is a bit of an achilleas heal that will limit how much cam I can run.
 
Here is the next step up from the Mopar Performance 340 Cam that you have in now.

Lift, Duration and RPM Range numbers for comparison:

Screenshot_20200902-010040_Chrome.jpg


Your 340 cam now is:
Lift: 429/444
Duration: 268/276
Idle to 5800 rpm
As pictured below:

Screenshot_20200902-010853_Chrome.jpg
 
I would think of some Kind of solid cam

Lunati recommend seem off, for a 3500 - 6000 rpm, maybe a circle track cam some are design to work with low cr.
 
be money well spent to call a cam grinder and tell'um what you got and what you doing! jones or bullit or racer brown.... youll be happyer if ya do!
 
273 said:
I would think of some Kind of solid cam

Lunati recommend seem off, for a 3500 - 6000 rpm, maybe a circle track cam some are design to work with low cr.
Click to expand...

Lunati had issue with the low compression, refer below:

Looking it over i can't go where I need to because of the compression best i have for it is #10200701 1000-5500 454/475 213/220 112lsa
Click to expand...

Bit more lift and tighten up the duration to maybe build a bit more cylinder pressure. I guess the idea would be to close the intake earlier to help in this regard.

I read somewhere the 340 cam is 210/220 @ 0.050"

If I convert to adjustable rockers, a small solid might be an option.
 
You said you’d be willing to pull the heads so why not start there? Pull em and mill em and get the thinnest head gaskets you can. MLS comes to mind, they’ll make whatever you want. Seems you could get another point of compression doing so. Then mock up the valvetrain and measure piston to valve clearance, then pick your cam. I will also sugggest calling someone who will grind you a custom cam, Jones cams would be my first call.
 
HardVG said:
Lunati had issue with the low compression, refer below:



Bit more lift and tighten up the duration to maybe build a bit more cylinder pressure. I guess the idea would be to close the intake earlier to help in this regard.

I read somewhere the 340 cam is 210/220 @ 0.050"

If I convert to adjustable rockers, a small solid might be an option.
Click to expand...

20200902_091859.jpg
 
340 cam was not 228 at .050

They put that mention on that cam for some reason and it's not close to a factory stick
 
Yes there is something weird with the listing for that Mopar cam, some other sites have it as 228/235 advertised duration:

*P4452782 0.429"/0.444" Lift, 228/235 Adv. Duration

*P4452757 0.410"/0.425" Lift, 248/256 Adv. Duration

*P4452759 0.430"/0.450" Lift, 260/268 Adv. Duration

*P4452761 0.450"/0.455" Lift, 268/272 Adv. Duration

*P4452992 0.474"/0.474" Lift, 280/280 Adv. Duration

*P4120231 0.484"/0.484" Lift, 284/284 Adv. Duration

*P4120233 0.508"/0.508" Lift, 292/292 Adv. Duration
 
Here is a Melling SPD-22 real close to the Mopar 340 cam grind:

429/444 lift
279/289 duration
112/116 lobe centers

@..050:
209/220
 
Hard VG! Just bight the bullet and put some closed chamber alloy heads on it!After all it is only money and we can't take it with us when we die!
 
you cannot easily compare the duratons of the jegs cam and the stock or any mopar performance cam
above-- evevthough both say 268 the factory cam is longer especially on the close side
you can compare mp cams solid vs solid and hyd vs hyd but not solid vs hyd
that "real close" cam isn't
Road Race | Jones Cams if solid with edm lifters- that's also what we did but circle track
see what jones says if you have to keep hyd we can convert his numbers
but
price crower or Rhodes "lube saver" lifters or i can tell you how to DIY
what is your lowest off the corner rpm, how high is high- we limited to 7,200
 
I have no restrictions with regard to what cam I can run, so either solid or hydraulic is fine. I'm seeing 3,000-3500 out of corners and currently runs out of puff by 6,000, limited by valvetrain capability. Fast corners would be 3rd gear, dropping to 2nd on slow corners and rarely gets out of 3rd other than long straights.
 
were about the same out of the corners run to 7200 but very differemt heads, compression, alky so our cam specs would not help
estimate head flows and get that cam request card off
we used to run a similar lo compression motor in a stock class (no street driving)low rpm was higher as was top rpm
ran past peak with low gears at trans would take a different cam than yours and you would not like the frequent spring changes
open chamber heads "stock" we had to run stock rockers- the least of the problems just buy a bunch - make a sets and return the rest
 
closed chamber iron heads; maybe.But 1 full point of compression, with alloys, is not going to get you much more power.
But a fast-ramp,solid-lifter cam with a tighter LSA than that dinosaur that is in there now, that sounds promising.

But I think you have a problem with gearing, I would address first; namely 3000/3500 to 6000 with a normally aspirated 318 is asking a bit much. Without knowing much, I estimate 20% more gear. Jump down to the bottom to read my gearing theory.

If you install a bigger same manufacturer hydro in there,
with no other changes, it's gonna lose pressure at 3000/3500 and be slower down there. IMO, you would need to close up the LSA, to gain back some pressure, and or increase the Scr, to break even. That would strengthen the top end as well. But the powerband would be smaller, So it's a catch-22. I think you need to re-evaluate your gearing, and see if it's possible to pick up some rpm at the slower speeds. I'm kindof leaning towards a close-ratio 5-speed, but I haven't found one yet.
The standard A833 has ratios of 2.66-1.92-1.40-1.00, and
splits of .72-.73-.71.. Which means outshifting second at 5600, gets you 5600x.73=4100 in third.
That 340 cam is way past optimum at 5600, but you kindof have to go there to get some decent pulling power in third. Reving that 340 cam to 6000, is way outside it's best window, I'll guess 1100 rpm over peak, and 700 to 800 past a decent shift-rpm.
So to me, that looks like you need a cam about 3 sizes @.050 bigger to satisfy the top-end....... but that will kill the pulling power at 3000/3500.
It might be more prudent to sacrifice some of that top-end for more midrange. In this case going just two sizes on the .050, and increasing the breathing on the heads to pull a lil longer at the top, and still the other tricks for the bottom. And then,again, re-evaluating the gearing.


Here's what you need to see;
Without regard to the .050 numbers,
you need to see the big picture.
The OEM 340 stick is listed as a 268/276/114cam, in at split overlap, here is the big picture;
268int/114 comp/106power/276exht/44 effective o/lap
Notice that the comp degrees are just 114, that's not very much. From the factory your 318 might have made 140 psi cylinder pressure with the factory cam. but with just 114* , now, it might make 120psi, and that is killing your power especially at the lower rpms.
Ok lets go to a bigger cam ,say the Mopar 284/484/114
284int/106comp/102pwr/284exh/52* E-overlap
So now, the comp is down to 106degrees and cylinder pressure may have dropped to 110psi cranking. This is not good for low-rpm.
So lets put a solid lifter cam in there with about the same .050 as the 284 hydro. I'll GUESS, a 278intake, and with your X-heads lets make it a split pattern and lets tighten it up to 110LSA. I get
278int/112comp/107power/284exh/60*E-overlap.. The climbing 112 comp, may have increased the pressure back up to 115psi, which is closing in on the 120 that you may now have.
Ok so lets shelf the X-heads and install some OOTB iron Magnum replacements of 59cc, versus the 72cc or so you may now have. This will reduce your total chamber volume from ~93cc to 80cc, and your Scr goes from 8.0 to 9.15; and the pressure sky-rockets to 136psi.. Well. How do you like that!
So now, your top-end has increased by virtue of the 10* more intake duration, and your bottom-end has increased by virtue of the increased cylinder pressure. And the 110LSA has tightened up the powerband some. You may now be coming out of the corners at 3800, and powering down the straights at 6600. I'm just guessing. So you may need to change the gearing.... cuz when you shift at 6000 into 4th, the Rs are gonna plummet to 4260
However, those shortie headers are costing you some bottom end, and they are reducing the effectiveness of the now 61* of overlap.
So say 20% more rear gear, might put your engine at 4500 in the slow corners, and 5100 in 4th on the long straight. Waitaminute, 5100? I know that number! That is just over peak power on the 268 Mopar cam....... But now in 4th gear instead of 3rd.
Remember in the beginning I mentioned gearing?
Well, the 268 running at peak power in 4th, is gonna make nearly as much power as the theoretical 278/110 running 400 below peak........ Without the powerloss at low-rpm, that we had to spend so much money on, to get back!

So what if we just plugged in a 268 solid lifter cam, and ran 20% more gear? I get 125psi and
268int/120comp/112power/276exh/56E-overlap/108LSA
So the 20%more gearing will get you 3600/4200 at the slow spots and 4400 in 4th before the power increase due to the greater .050 of the now solid-lifter design.... so maybe 4600/4800.... which is about right on the power peak of this cam.
So 3.15x1.2=3.78s;
I'm just guessing, tho, based on your statement of only rarely getting into 4th, and the rpms you so nicely detailed.

My gearing theory
The difference in the Mopar box from 3rd to 4th is 1/.73=37% more, so, a half gear would be 18%, or 1.18x3.15=3.72s
With NO OTHER changes to the current combo, except gearing, at 3.72s over 3.15s, your rpm in the now average 3250 corners would jump to 3840, plus whatever the increased power would bring. AND
where you are now doing 6000 in third, the 3.72s would get you 5030 in 4th; plus you are now on or close to the power peak of the 268 cam, instead of 1100 rpm down the far side of it, so that is gonna push the rpm up a bit, so let me estimate 5300;
I dearly love figuring, but I gotta work in the morning so
Happy Gear Hunting.
 
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I knew AJ would blow it up. Lots of good info.
 
HardVG said:
Looking for a bit of advice/feedback on other people's experience.

I have a track day car (circuit racing), it's actually a BMW E36 coupe, but fitted with a 318 Mopar engine. The engine was built maybe 30 years ago and is a pretty basic build of the day, stock replacement low comp pistons, factory heads which are supposed to be fitted with 360 valves and maybe bit of bowl work. It has a Weiand high rise dual plane intake, 650 Holley and shorty headers with twin 2.5" pipes. Running through a 4 speed manual box and 3.15 BMW rear end. The car is pretty light overall, say 2900 lbs with driver and runs around 96 mph in the 1/4 mile, so Wallace is saying I have around 200 HP.

It is pretty quick around the track, but my issue is that it lacks power and straight line performance. You can't really slam it up the inside under brakes at track day, so it needs to be able to pass cars in a straight line.

This is where it comes down to camshaft choice. The engine currently runs a 340 spec camshaft, so I want to know if I can make any significant gains with just a cam change. Lunati has suggested their 701 grind and I know there is the Hughes Whiplash cam that is supposed to work for low comp motors or am I wasting my time without bumping up the compression.

Can anybody give me some real world numbers of what some alternative cams will achieve for my application? The car tends to work in the 3500-6000 rpm range on the track, so that's where I need to make gains.

View attachment 1715588446
Click to expand...

I know an engine similar to yours that shows a genuine 400 hp on the Moroso for the weight that it runs. Stock bottom end except for 1 3/4 inch pipes and 1.6 rockers. Oh its only got a performer manifold as it was looking to breakout of the the class they ran the car in so they took the airgap off.

The camshaft is a solid 256 @ 0.050 and around 490 lift on a 108 lsa 320 adv . Once lash is factored in its 10 degrees smaller to an equivalent hydraulic and the beautiful thing is they only spin it 6000 rpm to make that 400 hp. The idle is rough for the cubes. If it were me I'd pony up for some cheap rockers and go a solid in the 240's on a 108.
 
Thanks for the detailed post AJ, I will take a bit of time to digest everything, but I like that there is some science in what you are saying.

FWIW, I have an Aussie made 4 speed with ratios 3.32, 2.00, 1.43, 1.00, which might make things marginally worse, fortunately 1st gear isn't needed on the track other than off the line. I actually had 3.45 gears in the car to start with, but changed to the 3.15 gears because it seemed to suit the track better and be a bit more user friendly, sounds like I should be going back the other way. Although on the track I normally run, I am in third for most of the lap because there are mostly short straights between the corners and only a couple of low speed corners where you get back into second, so by the time you wind it up to max RPM in third, you are back on the brakes again. They have recently changed the layout of the track and the current gearing doesn't suit the new bits of the track as well

I understand where you are coming from with regard to a bigger cam killing cylinder pressure and from memory around 120 psi with the current setup is pretty much on the money. That's pretty much the main point of this thread, to work out if I can make a worthwhile gain with a cam change or if I really need to throw in some higher compression pistons like the KB167s for instance.

Hysteric, that seems like an insane amount of cam for a stock bottom end 318, what sort of heads is he running? Closing the intake valve earlier is going to help with cylinder pressure, so I guess that's where the 108 LSA comes into it.
 
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HardVG said:
Thanks for the detailed post AJ, I will take a bit of time to digest everything, but I like that there is some science in what you are saying.

FWIW, I have an Aussie made 4 speed with ratios 3.32, 2.00, 1.43, 1.00, which might make things marginally worse, fortunately 1st gear isn't needed on the track other than off the line. I actually had 3.45 gears in the car to start with, but changed to the 3.15 gears because it seemed to suit the track better and be a bit more user friendly, sounds like I should be going back the other way. Although on the track I normally run, I am in third for most of the lap because there are mostly short straights between the corners and only a couple of low speed corners where you get back into second, so by the time you wind it up to max RPM in third, you are back on the brakes again. They have recently changed the layout of the track and the current gearing doesn't suit the new bits of the track as well

I understand where you are coming from with regard to a bigger cam killing cylinder pressure and from memory around 120 psi with the current setup is pretty much on the money. That's pretty much the main point of this thread, to work out if I can make a worthwhile gain with a cam change or if I really need to throw in some higher compression pistons like the KB167s for instance.

Hysteric, that seems like an insane amount of cam for a stock bottom end 318, what sort of heads is he running? Closing the intake valve earlier is going to help with cylinder pressure, so I guess that's where the 108 LSA comes into it.
Click to expand...
Can you change heads? Are there restrictions at you track or can you do whatever you want? Just curious. You probably have open chambered heads. A closed chamber head will raise your compression a bit but not by much. Maybe a half a point. With a higher rpm cam, a different rear gear to compliment it and some heads with more flow you may be surprised at how much power you could make.
 
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