therieldeal

iTrader: (2)

Alright... currently I'm running a stock GTR motor at ~23psi with the stock mazda BPT cams from the 323 GTX/GTR. Specs for these cams are:

Intake cam duration 233° @ 0.003"
Intake cam opening 2° BTDC
Intake cam closing 51° ABDC
Intake cam lobe height 44.094mm (1.7360")
Intake cam base circle 35.941mm (1.415")
Intake valve lift 8.1534mm (0.321")

Exhaust cam duration 247° @ 0.003"
Exhaust cam opening 59° BBDC
Exhaust cam closing 8° ATDC
Exhaust cam lobe height44.600mm (1.7560")
Exhaust cam base circle35.941mm (1.415")
Exhaust valve lift 8.6614mm (0.341")
Valve overlap 10°

I'm experiencing significant torque drop-off at high rpm - see dyno chart:


It is my hope that upgrading or adjusting my cams in some way might help with this issue. I picked up some fidanza adjustable cam gears, but now I can't decide what cams I should go with.

I may be able to get my hands on some Webcam 505 grinds for a reasonable price. Would these be a wise choice? I could also easily grab a spare N/A exhaust cam and install it on my intake side for the additional intake lift and duration.

Suggestions/experiences/specific settings please?

therieldeal

iTrader: (2)

38 views and no posts?

bueller?

sixshooter

iTrader: (12)

It is usually the intake manifold swap to aftermarket that cures the high rpm asthma from what I've read. Stock mani is designed to optimize midrange torque on a 130hp engine.

Cams are probably similarly optimized but you don't want to go huge because too much overlap is bad on a turbo engine. If you are going to change cams, a moderate increase would be better for a turbo engine than a cam that was designed for a naturally aspirated road race engine. If you go to a longer duration camshaft you will loose torque at lower rpms. You will shift the powerband up the rpm graph. If you want to see some fun engine parts look here

I've heard that the exhintake cam swap makes good power and it is cheap to accomplish, and doesn't ruin your low end torque. But you should look at the intake manifold, too.

Unrestrict your exhaust flow as much as possible through the exhaust manifold and downpipe for additional possible gains. Gasses don't like to turn corners.

Good luck.

therieldeal

iTrader: (2)

Lets see...

Theoretically I should have the best OE intake manifold available, since mazda optimized it for their Group A rally cars (323 GTR). At the very least it should be significantly better than a stock miata IM. A custom IM is currently too pricey for my budget, especially since I'm not sure how much it would help.

My exhaust is good to go... 3" from turbine housing to tailpipe w/ external wastegate. Manifold is stock GTR but it is a minature (cast) equal length ramhorn style.

I think I might just try an N/A exhaust cam on the intake side for now to see if it helps. If it does, maybe I'll invest in some "real cams". Just a matter of figuring out how to orient it I suppose...

JasonC SBB

Talk to Dema Elgin at elgincams.com
He's got software that will make suggestions.

I suspect you need an intake cam with more duration and closes later. Maybe open 5* earlier and close 10* later. This will improve your topend and also bring your flat portion of torque up to 5500 RPM.

Your exhaust cam is probably fine, it's got more duration than the intake; especially because your exhaust system is very open.

inferno94

iTrader: (2)

I'm pretty sure the exhintake mod doubles overlap. I tried it and found compared to how I had my stock intake cam setup I lost substantial low and mid range with a small gain in the top 2500rpm. Never tried it on my 323 before it was sold though.

Many have loved doing this mod but with your power curve I couldn't see the shift higher being something I'd want, I like mid range punch though.

If you're interested I have a cut exh cam with a gear drilled at 197.5* clockwise from "I", ~20000mi on it.

rrjwilson

Its very simple in terms of values but getting it is the pain.

The intake cam strangles every 5 engine because of its duration. The Exintake matches the duration of both cams by using two the same. This is a cheap and easy method however, if you feel you want better than standard duration you can get custom ones done. You might wish to make sure you specifiy forced induction use as cam profiles need to be altered rather a lot from NA to FI (if you go to the right tuning place).

therieldeal

iTrader: (2)

bump...

just picked up a set of web cams 505+2.5 grind for cheap. specs are:

.352" lift
225* duration
205* at 0.05"

i have adjustable cam gears... any suggestions for my initial settings? someone here must be running these cams...

miata2fast

iTrader: (2)

I am running a little bit bigger cam than yours, and have them straight up (no adjustment). I do not have pullys for my car currently, but had them on a previous car. The cams did make significant power gains.

Start with cams straight up, and make tuning adjustments with the intake cam first. If I recall correctly, that is where you will get the most gains. Start advancing the pully first, and see if you have a power increase or ET increase. If you are gaining power, keep going until you see a drop in power, and back it to the setting you gained the most power. After you are done with the intake, move to the exhaust side. If you get gains in power from the exhaust side, you may want to go to the intake side again and see if there is any power available with more adjustments.

Be patient. It takes time to do it right.

therieldeal

iTrader: (2)

Thanks for the advice/procedure! I'm glad to hear that similar cams gave you a good boost in power, I am mainly hoping that they will help with my high RPM torque drop off. I don’t reach my set boost until 3700 or so, and I launch off the revlimiter... so I'm not terribly worried about my low end torque.

I sent an email over to Derrick at Corksport yesterday as well. As it turns out, they run these very same cams in a GTR motor just like mine in one of their drag cars. He's going to check the settings for me today. Very helpful guy!

therieldeal

iTrader: (2)

put the cams in this weekend. breaking in the new clutch (again) so i am taking it easy for a few days.

still hoping for some recommendations on initial settings for my cam gears. the drag strip is about 2 hours away, and i'll probably only get to go once or twice this year (they close the end of the month). i'd rather set it up as best i can and tune it at home, and then go to the track and race... rather than spending all day at the track tuning.

JasonC SBB

You can tune it on the street by logging AFR's. Better breathing will raise AFR's ...and also tend to lower boost pressures, unless you have solid boost control.

therieldeal

iTrader: (2)

I got a hold of webcams, they gave me the following specs:

Web 505+2.5
Intake open: 8.5* ATDC
Intake close: 33.5* ABDC
Exhaust open: 33.5 BBDC
Exhaust close: 8.5* BTDC
Lobe centers are at both at 111*

Stock BP05:
Intake open: 5 ATDC
Intake close: 48 ABDC
Exhaust open: 56 BBDC
Exhaust close: 14 BTDC
Intake lobe center: 111.5*
Exhaust lobe center: 111*

BPT BP26
Intake open: 2 ATDC
Intake close: 51 ABDC
Exhaust open: 59 BBDC
Exhaust close: 8 BTDC
Intake lobe center: 114.5*
Exhaust lobe center: 115.5*

The problem is the lack of a standardized method for measuring the initial open/close. Webcams list a duration of 225* for both cams, while mazda lists 233* for intake cams and 247-250* for the exhaust cams. The webcams grind has a duration of 205* at a lift of 0.050", which is more duration than the stock cams at the same lift.

I think I may just adjust things to make the LSA the same as the BP26 cams, and leave it at that for now. Thoughts?

miata2fast

iTrader: (2)

The duration that you need to worry about is at 0.050" Advertized duration is meaningless. There are variations in the way cams are measured, but at 0.050", what you see is what you get, regardless of manufacturer.

Keep in mind, that Webcam is grinding the cam with the assumption that the cam will be run straight up. They have done the adjustments for you. There may be some benefit to running them with some adjustment, but you should not try adjusting it initially.

therieldeal

iTrader: (2)

i realize the issue with duration numbers, in fact i already covered that a couple posts up.

the grind is designed for a "bolt in performance gain" on a n/a car. i'm running pretty high boost, so i need to tune out at least some of the overlap

i just realized that i could probably calculate overlap at 0.050" and go from there, too. for now it seems to be running well though, i'll worry about it more in the spring

therieldeal

iTrader: (2)

OK so:

NA at 0.05 (http://www.solomiata.com/cams.html):
190 intake
202 exhaust

Divide by two and subtract from lobe center angles:
111.5 - 95 = 16.5
111 - 101 = 10
10 + 16.5 = 26.5
Subtract the "actual overlap" of 19* and there are 7.5* where the cams are both under 0.05" lift.

Doing the same for the 505+2.5, using the lobe center angles from the BP26 cams since this is how I have it set right now:
115.5 - 102.5 = 13
114.5 - 102.5 = 12
12 + 13 = 25

I'm not sure where to go from here, its too early and I have to go to a meeting lol.

sixshooter

iTrader: (12)

miata2fast is right.
The .050 numbers are the only important numbers because that is usually accepted as the point at which the valvetrain clearances are eliminated and the valve actually begins to open.

Those cams are designed for a naturally aspirated engine but will probably still benefit you quite a bit. You will, however, need to adjust them on a dyno to get them to perform best. Forced induction engines do not like overlap and tend to put raw fuel in the exhaust manifold which can cause very high EGTs. This can also cause your wideband to read erroneously.

You may find on the dyno that advancing the exhaust cam and retarding the intake cam may improve your power by reducing overlap, but it is all speculation until you try it.
You will absolutely need to retune your MS2 for fuel and spark because of the changes in volumetric efficiency, but I'm sure you knew that.
Good luck.

miata2fast

iTrader: (2)

That makes sense.

Some people are not aware of the 0.050" issue, and I was not sure if you were either.

therieldeal

iTrader: (2)

a dyno tune will come in the spring... for now i'm just ball parking it so i can run it for a couple of weeks. i just wish i had an EGT gauge so that i could make sure it's safe :/

therieldeal

iTrader: (2)

Thinking more and more on this...

ALL of the overlap in the stock cams is under 0.050" lift, which must mean that there is some significant airflow down there... otherwise why would we be worried about it?

Stock BP05 cams have 26.5* separating the intake and exhaust points at 0.05", yet they have 19* overlap

Stock BP26 cams have ~35* at the same point, yet they have 10* overlap

Now with the 505+2.5 cams set with the same LSA as the BP26 cams I only have 24.5* separating the 0.05" points... which would likely mean significant overlap of 20*+

So, I guess I need to open up the LSA even farther... I'll probably leave the exhaust cam where it is and retard the intake. IIRC, retarding the intake shifts the powerband up in the RPM range, which will hopefully increase my 6000+rpm VE. It falls off HARD, I'm down to like 84% VE by 7k at 23 psi. At 5k, same boost level, it is at about 112% VE.