EA81 cam grind choices - results

steptoe · Post by **steptoe** » Sun Oct 25, 2009 9:31 am

Just a little trivia for an old engine that very few of you would consider doing up now but....
I had a cam ground for mine a few years back, requesting 20/60 0.235" lift and got 16/56 0.235 lift. When asking why I not got what I wanted, the grinder told me he had complaints from some fitting bigger tyres and then losing their puff up Mt Ousley type roads (Wollongong) The next time around I got what i asked for and it is a great spirited little EA81 and the other day loaded her up with 400 or 500kg of crusher grit and went up a few small hills. Ian Watson was right. Change the tyres and/or give it a bit of a load and the engine loses its puff. The 16/56 would tear up hills with same sort of load on board as if it wasn't even there!

Moral of the story is 16/56 is good grind for all round performance

discopotato03 · Post by **discopotato03** » Sun Oct 25, 2009 10:33 am

Just to give a bit of an idea what the cam (valve actually) timing numbers mean .

Assumes the inlet and exhaust timing is the same ie 20-60 60-20 .
These numbers mean the inlet valve opens 20 crankshaft degres before top dead center (BTDC) and close 60 after bottom dead center (ABDC) . It means the total off the seat valve opening period is 20 deg (BTDC) + 180 deg (piston top dead center to bottom dead center) + the 60 degrees (ABDC) which works out to 260 degrees .
If you work the numbers for a similar profile (miror imaged) timing but at 16-56you get a duration of 252 degrees or 16 + 180 + 56 .
Now the duration at 252 vs 260 doesn't sound like a whole lot but the crucial bit is the overlap timing meaning where the inlet valves are beginning to open before the exhaust valves have finished closing .
To get the "overlap" phase if you like add the two smaller timing numbers together ie 20+20 with the warmer cam vs 16+16 for the milder one . Obviously this is 40 degrees vs 32 but it makes all the difference in a street driven motor thats intended to make torque at lowish revs .
Wider (longer) overlap timing is intended to help the engine scavange more completely in the higher rev ranges - which arguably EA81's don't have because they don't breathe well enough to turn high revs .
When you use wide overlap cams in a low rev engine that has a lowish CR you lose the cylinders trapping efficiency and because cylinder pressures are low torque output isn't the best . The usual way of getting the lost torque back is to increase the compression ratio but EA81/82's don't have real modern combustion chamber shapes so often detonation sets in - unless you use high octane fuel .
Most EA81's were carby and mechanical/vac distributor ignition systems so there were no electronic controls to ramp the timing in when the engine can use it and pull it back out with a knock sensor system when they can't .

You fare a bit better with EA82's because the MPFI heads breathe a bit better and you have more modern controls with the later MAF EFI system .
Also there is a wider choice of cam profiles from the very soft carby ones to the warmest NA spider MPFI ones - which are 20-60 60-20 .
For my rebuilt EA82T engine I chose to use the later NA L Series MPFI cam which is 16-60 60-16 , a good compromise for an 8:1 CR turbo engine thats slowly having its restrictions removed on the hot and cold sides . I originally was after 8.6 CR but that didn't work out for reasons beyond my control .
Anyway the durations work out at 256 degrees and the overlap is 32 degrees vs a std 28 degrees . Std spider turbo cams are 14-56 so I've gained 6 degrees duration and 4 degrees overlap - plus I'm up a small but usefull 0.3 of a CR so it all helps .
I believe the Grp A EA82T cams were something like 30-70 timing so they would have "idled" fast and had no torque at round town revs - particularly with 7.7-8.0 to 1 compression ratio and 60 degrees of overlap timing . I was told they had SFA under about 3500-4000 revs and probably ran out of lungs with the mandatory (homologated) std exhaust header and turbo though with the European spec slightly larger turbine housing . Thats what it took to make 190 strained and none too reliable horsepower with a rally legal EA82T . Had to use the garden variety MPFI manifold because the spider one was never homologated in an L RX Turbo .

Shuddup already ! Another essay but ya all got nothing beter to do than linger here on a Sunday ......

phillatdarwin · Post by **phillatdarwin** » Sun Oct 25, 2009 1:48 pm

we are all linger here on a Sunday or out fixing a car so it will run better on Monday .
That is good write up on cams .

rtcb65 · Post by **rtcb65** » Sun Oct 25, 2009 9:57 pm

I am running a 275 duration cam in my EA81 and found it to be a little much. I was told the same thing, if ya put the bigger tires on , the car will run out of puff. So i agreed to it but found it alittle much. I have had a 262 in a 307 chev before and didn't notice much difference from standard, other than the nice mileage i got from a tank of fuel.

phillatdarwin · Post by **phillatdarwin** » Sun Oct 25, 2009 10:04 pm

so what is the best cam for all round go with good HP upgrade in a cam .
and all so what is a good cam if u are running boost as i are going to build a engine up soon and i wood like to get a cam grinned soon .

discopotato03 · Post by **discopotato03** » Mon Oct 26, 2009 7:44 am

Cam choice will depend on the specifications of the engine , the important things are how well it breathes and with turbos how restrictive the exhaust manifold/turbo/exhaust system is .
I think it's pointless using longer period cams with std EA82T headers and turbos for the street , you may get the head to breathe a bit better but if the header and turbo are restrictive you don't gain as much as you should .
As I said I used the later L Series NA cams because they were affordable and I'm doing other things to make my engine breathe . If I'd have got my static compression ratio higher I probably would have chased up a set of NA Spider Vortex 20-60 cams from the US .
In another thread I posted details of the warmest factory (road) EA82T cams and they had the 20-60 exhaust timing with the usual shorter turbo inlet timing and the inlet lobes were rephased to close the overlap timing back to I think 28 degrees .

You need to realise that as the cams increase in duration the CR needs to rise to keep the dynamic or effective (throttled) compression ratio high enough to have adequate torque at lowish revs .
With turbo engines you also have to make sure that you reduce the restrictions on the hot side or detonation and therefore retarded ignition timing to control it kill your combustion efficiency and pressure .

With my beastie a lot will ride on how well the custom header and turbo perform on an EA82 , the emphasis is on header tubing size that isn't that much larger than the largest sections of the std one ie 1 3/4 vs 1 5/8 and a free spinning BB turbo with the best turbine in its series .
I want my engine to make power from better gasflow paths than high boost pressure so that torque delivery is not brutal but it makes adequate torque over a wide rev range because thats whats easy AND nice to drive .

Along the way my car grew a closer (than std RX Turbo) gearset so it doesn't fall off the power range it has now , if it makes more everywhere than it does now and revs more freely should be a nice drive .

A .

rtcb65 · Post by **rtcb65** » Mon Oct 26, 2009 8:12 am

discopotato03 wrote:Cam choice will depend on the specifications of the engine , the important things are how well it breathes and with turbos how restrictive the exhaust manifold/turbo/exhaust system is .
I think it's pointless using longer period cams with std EA82T headers and turbos for the street , you may get the head to breathe a bit better but if the header and turbo are restrictive you don't gain as much as you should .
As I said I used the later L Series NA cams because they were affordable and I'm doing other things to make my engine breathe . If I'd have got my static compression ratio higher I probably would have chased up a set of NA Spider Vortex 20-60 cams from the US .
In another thread I posted details of the warmest factory (road) EA82T cams and they had the 20-60 exhaust timing with the usual shorter turbo inlet timing and the inlet lobes were rephased to close the overlap timing back to I think 28 degrees .

You need to realise that as the cams increase in duration the CR needs to rise to keep the dynamic or effective (throttled) compression ratio high enough to have adequate torque at lowish revs .
With turbo engines you also have to make sure that you reduce the restrictions on the hot side or detonation and therefore retarded ignition timing to control it kill your combustion efficiency and pressure .

With my beastie a lot will ride on how well the custom header and turbo perform on an EA82 , the emphasis is on header tubing size that isn't that much larger than the largest sections of the std one ie 1 3/4 vs 1 5/8 and a free spinning BB turbo with the best turbine in its series .
I want my engine to make power from better gasflow paths than high boost pressure so that torque delivery is not brutal but it makes adequate torque over a wide rev range because thats whats easy AND nice to drive .

Along the way my car grew a closer (than std RX Turbo) gearset so it doesn't fall off the power range it has now , if it makes more everywhere than it does now and revs more freely should be a nice drive .

A .

To understand what you wrote, you just cant pick a can size and just put it in and hope for the best. You need to pick the cam that suits the rest of the engine set up. Eg, intake , head flow ability, exhaust flow , etc. Is that right

steptoe · Post by **steptoe** » Mon Oct 26, 2009 8:29 am

I specd the 20/60 and got it, advising cam grinder I was intending LPG which I've now got, and possibly turbo said engine (why'd i say that?). Was told this would suit my request and LPG and turbo. I told that I run standard wheels. What I fogot to to add was that sometimes I shove half a tonne on the back (or more) and still expect same purrformance

. I also run a throttle body same DIA as EA82T so there is no over riding air valve like the Hitachi carbs use. The Brumby with EA81G20/60 is a good all rounder but can't expect all its attrbutes to reach extremes of each. It is a ute, it is 4WD with lo ratio, on LPG it is cheap to drive (500km $32) small enough to park, goes harder than the old EA81, sounds throaty and ultimately is result my handiwork.