Evo 3 with BIG cams???

[layzie12g]

I have an evo 3 16g with the FP1x cams. I have dual valve springs and retainers. I was wondering if anyone out there has dyno numbers or any information on using big cams with the evo 3 and a 2.0. The car is a DD and at 20 psi all the time. I raced an evo 8 a while back on the stock turbo with 280s and it hauled. the car had a good idle too. The 1xs have real strong mid range and im just curious how the car would respond to bigger cams. thanks for any input.

 

[Gstclipse69]

If you get bigger cams then your going to flow more air. More air=more hp. I have a set of fp2x but I havent put them on yet. With bigger cams on a 16g, say for instance you had 2xs, then the cams are going to outflow the turbo. Meaning that if you were running 20psi then at high rpms the boost is going to drop a little just because the cams are using all the air the turbo can provide to it. It will still pull hard but youll just be getting all the potential out of your turbo. Cant wait to get my springs.

 

[dsm-onster]

You can max out the evo3 16g with eve stock cams. So don't waste your money unless you want a bigger turbo. . .

 

[Mikael SS]

very nice numbers on that 16g. I'm running 272s on a ported head and E16g. Bigger cams wouldn't hurt anything, and will make the car ready for the next bigger turbo. It'll probably move the power band up in rpms a bit.

 

[layzie12g]

k i was thinking about doing a 50 trim in the future but im looking to make over 400 awhp on meth with the evo 3 before i do a bigger turbo. im still curious about that evo 8. it had a fuel pump stock injectors big front mount hard pipes 24 psi owner tuned and the 280s with dual valve springs and retainers. the car idled good too without the lumpiness you would expect from that big of cams. how big are those turbos compared to the evo 3?

 

[ScottH]

The FP1 and FP2 cams would be a good choice in cams for the Evo3 16g IMO.

 

[Calan]

Agreed.

I'm running an FP1/FP2 combo with ported Evo3 mani/16g/O2, and it runs very nicely all the way to 7200

 

[Jst4Cyl]

I would doubt he had cams unless it was either A) Idle'n high (1200 rpm or so) or B) They weren't that big. Check out a few EVO's with 280's and then report back. They have lump

My car starting and idling on sunday 11/18 - Video

06 evo ix with cosworth 280 cams at idle - Video

Walk around of my 05 Evo 8 MR at idle. 325hp 316tq on pump gas(93 octane) at 24psi. Buschur Pure Power package with 280 duration Comp Cams instead of HKS. - Video

Evo 8 idle with buschur racing turbo back and hks 280 cams and other mods... - Video

 

[gixrman]

The FP1 and FP2 cams would be a good choice in cams for the Evo3 16g IMO.

I will agree on that one, I'm flowing some good #'s on this setup and will be hitting the dyno soon.

 

[2gGSX]

Bigger cams on a small turbo like an Evo 3 will lead to even worse boost dropoff, and less power. The cams shift your power curve to the right, while the boost dropoff kills all top end--it sort of works against itself.

 

[layzie12g]

yeah i think he had his idle up because there was another evo 8 at the meet with a 35r and 272s and it idled like it had 280s it was was lumpy as hell for 272s. i think the 35r evo had a 3.5 or 4 inch exhaust also. If i were to compare the idle of these cars it would be like comparing my car with the 1xs(somewhat stock sounding) to a 2.0 dsm with 280s in it. The 35r car sounded mean. Im really happy with the 1x grind though im not saying they are a bad grind or anything i like i was just curious to what bigger cams would do. My car pulls like hell from 4-7 then falls off pretty good anything after that. I just cant wait for the meth and 25 or 26 psi.

 

[dsm-onster]

Bigger cams on a small turbo like an Evo 3 will lead to even worse boost dropoff, and less power. The cams shift your power curve to the right, while the boost dropoff kills all top end--it sort of works against itself.

Boost drop off is NOT indictative of power diminishing. It indicates that the engine is demanding more flow than what the compressor can deliver at that boost. The manifold pressure drops to a boost level where the compressor is capable of keeping up with the demand.

There is minimal difference in peak power with 272s or 264s with a compressor (like the evo3) that drops from 30 psi to 24 psi with 264s. The 264s will only encourage a flatter powerband versus the higher duration 272. You're correct in your suggestion but not in why. 264s will bleed down boost up top so why get more cam up top? Not that there will be less power up top with 272s, but there will be more power at 3000rpms with 264s.

 

[2gGSX]

Boost drop off is NOT indictative of power diminishing. It indicates that the engine is demanding more flow than what the compressor can deliver at that boost. The manifold pressure drops to a boost level where the compressor is capable of keeping up with the demand.

There is minimal difference in peak power with 272s or 264s with a compressor (like the evo3) that drops from 30 psi to 24 psi with 264s. The 264s will only encourage a flatter powerband versus the higher duration 272. You're correct in your suggestion but not in why. 264s will bleed down boost up top so why get more cam up top? Not that there will be less power up top with 272s, but there will be more power at 3000rpms with 264s.

After typing some spiel, I just realized we're essentially arguing the same point. Would you mind expounding your first argument though? It seems counter intuitive that while engine demand is rising, a drop in compressor speed/pressure would allow for the turbo to meet this increased demand. Given the Evo 3's flow map:

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dropping from ~26 to 20 psi by redline would reduce airflow, assuming healthy/increasing engine VE throughout the pull wouldn't it?

Furthermore, if you look through the Evo 3 dyno sheet thread (http://www.dsmtuners.com/forums/turbo-system-tech/156794-evoiii-16g-dyno-sheets.html) you can see that they all suffer from torque drop off up top, which coincides with their boost drop off, and gives them a flat power curve (not necessarily a bad thing).

 

[dsm-onster]

Well, first, horsepower is torque over time. There can be a drop off in torque but the hp can increase in such a way that more is seen over a period in rpms. Hence, a flat powerband that still puts out a useful energy increase per rpm increase.

As for my first arguement. Yes it is very counter intuitive. . . But,

26 psi = 2.77 PR
20 psi = 2.36 PR



PR*(Displacement*RPMs*VE)/2

--------------------------------------- = n

RT​

Where,
n = number of molecules of the gas per minute (proportional to mass/min)
R = Avgodro's number, a constant
T = Degrees K in the intake manifold. The lower the boost the lower this number(adabiatic proccess)

The above is a derivative of the Ideal Gas Law.

Lets assume T is a constant and boost just starts to drop slightly at 5000rpms and reaches 20 psi by 7500 rpms. . .



2.77 (2.0L * 5000rpms * 100%VE)

-------------------------------------------- = n

RT​

13,850/RT = n



2.36 (2.0L * 7500rpms * 100%VE)

-------------------------------------------- = n

RT​

17,700/RT = n


​

Since R and T are constant, n or massflow increases by 28% {17700/13850}, though boost dropped from 2.77PR to 2.36PR.

T is NOT constant. Temperature goes down as boost goes down. So the 7500rpm massflow is in fact at a higher percentage larger than the 5000rpm massflow. Massflow is directly proportional to horsepower.

 

[2gGSX]

You are right that T is not constant, but the assumption that simply going to a lower boost pressure results in lower intake charge temps is incorrect. Given equal intake tract volume between the two situations, a higher mass airflow would indicate more molecules per given unit of area, and more collisions, etc. From a kinetic-molecular standpoint, that wouldn't make sense.

Furthermore, if you look at the flow map posted, even though you drop from 2.77 PR to 2.36 PR you aren't actually shifting efficiency islands more than likely (given the same airflow) since islands are basically vertical. If you do in fact have increased mass air flow (which I haven't seen either based on ShapeGSX's logs from a long time ago), you would actually be shifted further right on the map, meaning a lower efficiency island.

I agree with you on the horsepower/torque argument, but a flat powerband is not conducive to drag/street racing--assumed to be the OP's purpose for the car.

 

[dsm-onster]

You are right that T is not constant, but the assumption that simply going to a lower boost pressure results in lower intake charge temps is incorrect. Given equal intake tract volume between the two situations, a higher mass airflow would indicate more molecules per given unit of area, and more collisions, etc. From a kinetic-molecular standpoint, that wouldn't make sense.

The adiabatic process (process of compressing air increases the heat of the air) is independent of mass and density. See Adiabatic Processes. And, more massflow does not necessarily indicate more density. That is why at the same pressure and temperature, a higher rpm can achieve more lbs/min airflow than a lower rpm.

A compressor increses the heat of the aircharge by compressing it. At the limits of the compressor map, the increase in volume over time lowers the pressure because the compressor rpms cannot keep up with that volume displacement increase. So pressure drops. Unless the compressor can spin faster, pressure drops and temperature goes down. Because the temperature increase by the adiabatic process is not mass or density dependent. See Turbo Outlet Temperature Calculator.

See here. This is a good explanation that air pressure from a turbo does not affect the speed of sound and thus intake runner design. But more importantly it describes air density.

Density of air (air density) ρ = air pressure p / (gas constant R × temperature in Kelvin)​

ρ = p / R × T​

If pressure goes down and temperature stays the same, then the density goes down. If pressure goes down and temperature goes up, then even lower density is achieved. Temperature has to go down for the density, ρ, to go up.

Thus lbs/min on a compressor map is an expression of air velocity, not density.


And,

I agree with you on the horsepower/torque argument, but a flat powerband is not conducive to drag/street racing--assumed to be the OP's purpose for the car.

The car is a DD and at 20 psi all the time.

There is no significant gain in peak power by running 272s over 264s. Why not have more power down low to do work and the same up top to do work. Givng up power down low, with no gain up top doesn't win races .

 

[dsm-onster]

In short, we're all saying that 264s/fp1s are good for an evo3 16g, even if you're running 26psi that falls to 20 psi.