MPFI NA cams in EA82T ?

discopotato03 · Post by **discopotato03** » Thu May 22, 2008 6:44 pm

Hi all , given that Ellie has shorter legs because of its close ratio gearset I'm reconsidering using NA MPFI cams it its almost finished fresh EA82T engine .

What I'm finding is that the closer spaced gears tend to make me drive it slightly further up the rev range than I did with the turbo (wider/taller) gear ratios . I end up floating around 26-2800 rather than 23-2500 and this makes me wonder if the NA cams would work better with the NA gearing .
There is not a huge difference in the profiles like 256 deg instead of 250 deg but I guess it all helps .
My 87 WSM shows the 9.5:1 CR NA EA82 cams as having one group of 1 ring and the second group having 2 rings ie A 1 2 markings .

Can anyone confirm these are the Aus spec NA cams ?

Cheers A .

Gannon · Post by **Gannon** » Thu May 22, 2008 7:40 pm

I end up floating around 26-2800 rather than 23-2500

I assume you are talking about when you are cruising on the highway?

I thought turbo cams would be ideal as their peak torque is at 2800 compared to NA cams that have their peak torque between 3200 and 3600rpm

As far as interchanging cams go, Id be more concerned with the overlap of the valves.

NA cams overlap to create a small vacuum in the cylinder just after TDC to increase air velocity and ram more air in the cylinder, which is great for increasing torque when not under boost, but it will reduce airflow when the turbo is trying to push air in.

If you wanna change your torque curve, you'd be much better off with a custom cam regrind to suit you requirements.`

Subafury · Post by **Subafury** » Thu May 22, 2008 9:01 pm

on the topic ive also heard of the US guys using Delta cams in their ea82t's, but i think this helps more in the higher rev range which isnt what you're lookin for.

Suby Wan Kenobi · Post by **Suby Wan Kenobi** » Thu May 22, 2008 9:50 pm

Suparoo wrote:I assume you are talking about when you are cruising on the highway?

I thought turbo cams would be ideal as their peak torque is at 2800 compared to NA cams that have their peak torque between 3200 and 3600rpm

As far as interchanging cams go, Id be more concerned with the overlap of the valves.

NA cams overlap to create a small vacuum in the cylinder just after TDC to increase air velocity and ram more air in the cylinder, which is great for increasing torque when not under boost, but it will reduce airflow when the turbo is trying to push air in.

If you wanna change your torque curve, you'd be much better off with a custom cam regrind to suit you requirements.`

I could go on but what he said....

discopotato03 · Post by **discopotato03** » Fri May 23, 2008 9:30 am

Long post Alert - you have been warned .

Production cam profiles are really all about trapping efficiency in the cylinders and dynamic or effective compression ratio . I'll try and keep this down to 1 volume ...

Production turbo engines tend to get short duration (valve open period) cams because their static or measured compression ratio is low , very low (7.7 to 1) if its an EA82T . These engines are very restrictive in their ports/headers/turbo/cat etc so they need short cams to make adequate torque off boost in std trim .
The gearing in an RX Turbo is made to suite their std power producing characteristics but I aim to change most of those in my engine , the gearing in my car is really the NA type but with the taller MPFI 3.7 final drives .

I chose to have a static CR of 8.6 to 1 (edit - ended up being 8:1) but the engine will only develop a decent effective compression ratio if it can breathe well enough - basically if the inlet manifold/ports/valves are less restrictive they allow the cylinders to be charged (filled) more completely so there is more air in the cylinders for the pistons to compress (effective compression pressure) .

Also we aim to have a lot less restriction on the exhaust side of the engine by using a far less agricultural header , slightly larger turbo , much less restrictive dump/cat/exhaust .

When you do all these things the cams that were designed to work with all the inefficiencies are no longer suitable .
Because exhaust manifold pressure is lower at low revs the short cams are too short and restrict breathing in the mid range . Also the short cams with their reduced overlap means that the engine cant scavenge as well off boost .
The way Subaru went about shorter closer gearbox ratios was to have the same 1st ratio (3.545) and the other 4 lower and closer together in the NA vs turbo gear sets . They would have done this because the NA engines develop their mid range torque higher up the rev range than a turbo one - so the NA gearing places the revs where they need to be in relation to road speed for the NA MPFI EA82's power characteristics . The thing is that the percentage difference in the NA vs turbo gear sets is almost 12% for 4th and 5th , 12% lower . This equates to approx 3360 vs 3000 rpm at 100 km/h and 3470 vs 3100 at 110 km/h . Even at 80km/h it's (by calculations) 2690 revs vs 2400 in 5th .

Back to Ellie , it now has miss matched gearing and power curve - plus some butchers added major exhaust restriction .
When the next engine is all together in final form I expect it to make more torque everywhere than a std one , turbo engines usually work better against a load so with lowish gearing its state of tune needs to rise in the rev range so that it matches the gearing .

Anyway as I mentioned the right NA cams are a whole 6 degrees longer than the turbo ones at 256 vs 250 degrees duration so not a massive difference .
The interesting ones would have been the USDM NA spider Vortex's 260 degree cams but I don't think they were used here .

Also the dirty countries that didn't spec cat equipt cars have the longer NA cam timing on their exhaust lobes and advanced (in relation to Top Dead Center) 250 degree inlet lobes .

To make it easy to visualise EA82 cam specs :

Inlet Duration ..... Exhaust duration .. Std Application .

260 .................. 260 .................. USDM NA Spider Vortex .
256 .................. 256 .................. ADM NA L MPFI .
250 .................. 256 .................. No Cat EA82T spec .
250 .................. 250 .................. Aus/Euro EA82T spec .

I think the NA cams and gearing would work better together with the exhaust restrictions removed and the more even flowing Spider inlet manifold should tie it all together .

Sorry so long , cheers A .

YouTube · Post by **El_Freddo** » Sun May 25, 2008 10:45 pm

Hey adrian,

First off Never be sorry about a long post, you have good information and insight. Keep it up (not that you seem to have trouble with that).

Second, with all that info and your ideas, wouldn't it be easier to get a set of cams ground to your personal specifications? I realise that may cost some $$$ but you'd be getting what you want... well, in theory you would be.

An interesting read - are you saying that the AWD L gearbox your running has the standard NA 3.7 gearset for 1st to 5th and not the turbo variation?

Cheers

Bennie

YouTube · Post by **El_Freddo** » Mon Aug 01, 2011 3:00 pm

Ok I know I'm digging up an old post - sorry for using the search function! Expect more as I keep looking for some info, I'm a sucker for old threads!

Disco I'm keen to know how these cams went in the EA82T - worth the effort and did you get what you were wanting from them??

Cheers

Bennie

steptoe · Post by **steptoe** » Sun Feb 23, 2014 11:54 am

I'm digging up an old post too !

Jay might find it handy, might not. There must be more details on Discos little adventure to get these NA mpfi cams as I recall a little behind the scenes biff going on at the time between a few members. Not sure if Disco ever got these cams, or maybe not from someone who had them on offer first. SCOOBIDOO, where are YOO ?

I am running EA82T cams in EA82T heads - so, mpfi twin ports

on my EA82Mongrel, as NA . Chose them as thought was gonna strap a turbo on this NA comp block but been advised against it for longevity. The turbo profile and NA LPG profiles can be similar, so justify at least trying them out. Got a real power band above 4000rpm, and will spin out to 6000 in second sometimes, depending on the load, flat or slight incline up. Bit hard to tell while has a noisy clutch fan on, but mostly sounds happy at 6000. Wondering if say an NA mpfi cam from 1989 will shove my power band down a bit lower to a more useful rev range. Need to find and identify them first.

Gannon · Post by **Gannon** » Sun Feb 23, 2014 2:06 pm

I sold a set of 88 MPFI cams to Adrian at some stage, not sure if he got around to using them

FujiFan · Post by **FujiFan** » Sun Feb 23, 2014 3:03 pm

Hmm, this is interesting information that has come to light. I think though that I will stick to using the turbo cams that I have had ground to a "stage 1" profile. I have a spare set of carby cams that I've considered trying out for shits n giggles or even 89' NA touring wagon cams.

Now my head hurts after considering all the options

J.

YouTube · Post by **El_Freddo** » Sun Feb 23, 2014 7:18 pm

Steptoe, I remember my MPFI EA82 having a "power band" at 4000rpm onwards. I think this is the ECU opening the injectors up to give everything and ensure the engine doesn't lean out as well. So I don't think it's got much to do with the turbo cams... Unless they're the same cam.

Cheers

Bennie

steptoe · Post by **steptoe** » Sun Feb 23, 2014 9:50 pm

Hmmm, interesting .... might have to speak to my cam guru at Watsons and get a 16/56 or something - for each side .....

What year NA mpfi was yours Cheers Bennie ? Disco was chasing later '89 cams and I have a pair somewhere....out of Touring Wagon #2

steptoe · Post by **steptoe** » Sun Feb 23, 2014 9:56 pm

FujiFan wrote:Hmm, this is interesting information that has come to light. I think though that I will stick to using the turbo cams that I have had ground to a "stage 1" profile. I have a spare set of carby cams that I've considered trying out for shits n giggles or even 89' NA touring wagon cams.

Now my head hurts after considering all the options

J.

Can only tell you from recent experience Jay, that your head is gonna kep hurting until you turn the key and drive it. The EA82M sat on my floor something like 3 1/2 years before I found out in last month .

Even now am a little undecided.. have a favourite intersection that if I step on it, in first sees 45k, 2nd sees me through the two lane roundabout and into third at about 80 whicjh I think was about 6000 rpm . Almost goes like my turbo if I hold foot to floor, just no noise, no turbo shove, and I always leave traffic behind, except that one time when an R32 FLOGged me on the inside lane of the roundabout like I was sitting still !

YouTube · Post by **El_Freddo** » Mon Feb 24, 2014 5:16 pm

steptoe wrote:What year NA mpfi was yours Cheers Bennie ? Disco was chasing later '89 cams and I have a pair somewhere....out of Touring Wagon #2

I think it was a 1989 model - can't be sure though as we purchased the original engine from ebay but the second MPFI (that ran with the same characteristics) came from an '89 unit - the electrics came from the same car.

Cheers

"Cheers Bennie"