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Discussion Starter · #1 ·
Interestingly, I was able to m

Interestingly, I was able to manipulate the event timing of the STOCK FI cams to give almost 300 hp on a 3.2 engine dyno sim by retarding both ignition and exhaust cams. While this would work well for those of you who already have EFI, if I can tweak these #s to avoid reversion, this should work with the Bosch stock Kjet. Will post the numbers when I'm home if anyone is interested. Imagine 20 - 30 or so hp increase for 3.0qv and 328 folks by re-indexing cams at your next belt change - wonder how close reality would be to the computer model? Anyone else try this?

I went and plugged 3.2 engine specs into my desktop dyno and the results are close based on my real world dyno numbers. When I simulated a stock 3.2 FI motor working from the stock lifts, durations, timing, bore x stroke, CR, etc, etc, - I found to achieve the stock rating of 260 SAE hp (pretty reliable average based on many dynos on this board) the stock Bosch K-jetronic should flow 900 CFM.
Simply substituting Pierce Manifold's spec of 500 CFM per 40 mm carb, as if all I did was replace the FI with the carbs, I got 290 hp from the sim which is within some error close to my dyno'd 288 (assuming 18% driveline loss). The mismatch occurs as I was using a 36 vs a 34 mm choke that Pierce's flow estimates are based on to achieve that number, but it is in the ballpark for comparison and development work...

Just for fun, I then kept everything constant and added Dema's new intake cam specs and retarded the exhaust cam 10 degrees: 320 SAE hp. How cool is that? It did lose a little bit of power down low but picked it back up above 4500 rpm. While I know this is NOT very accurate, it is pretty neat.

best
rt
 
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Discussion Starter · #2 ·
Hi Russ,

yes I'm very i


Hi Russ,

yes I'm very interested in this cam timing research you are doing so please post the info as you gather it.

Regards, JRV
 
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Discussion Starter · #3 ·
JRV
So far, the best Kjet twe


JRV
So far, the best Kjet tweak on the sim involves two main components (over the usual exhaust mods not accounted for in this sim):

1. Kermit's (www.durable1.com) bored out throttle body from 65 to 70mm: he documented a roughly 10+ % increase in CFM flow on the bench. Based on my calculations that would put airflow right at 1000 CFM. I think the prices may be lower than on the site, but not sure.

2. Retarding both intake and exhaust cams 6 - 8 degrees

Putting both of these conservative tweaks on the sim shows a 17 hp gain over stock on a 3.2 qv to 277 hp for the 6 degree cam (both) timing retard. For 8 degrees of cam retard there is a 20 hp gain to 280, but could be getting close to low rpm reversion as the intake closing is delayed: helps higher end flow, but reversion signals may begin to confuse the K-jet airmass sensor plate.

If a free flow exhaust is added would expect 5 - 8 more hp as well from flow improvements and perhaps a better scavenging pulse.

With K-jet, don't think you would have to reset the mixture much. Roughness in running, if any, would be in the low rpm range and clear as increased. Need to look at some Porsche K-jet numbers from 911SCs and 964s to compare.

Will keep tweaking the numbers - overall, looking at possible good 20 hp over stock using everything's that already there, if the computer modeling is close.

best
rt

 
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Discussion Starter · #4 ·
r turner,

What are you sayi


r turner,

What are you saying the settings would be? Is this retarding the intake and exhaust settings from the eurospec? Remember, the exhaust cams are set up differently for the us car.

Tim
 
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Discussion Starter · #5 ·
Tim
Thanks for the email -
W


Tim
Thanks for the email -
Was working off of the 328 specs, retarding both intake and exhaust 6 degrees:
I: 10/54
E: 48/16
best
rt
 
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Discussion Starter · #6 ·
Do you think the stock system

Do you think the stock system would be more inline with these numbers? The reason I ask is that the cam timing of 16 btdc(on a 308qv) is measured with a .5mm cam to bucket gap? with a tighter clearance, I would think it would bring it closer to your numbers...just a thought and thinking outloud.
 
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Discussion Starter · #7 ·
Tim,
There's a difference


Tim,
There's a difference between changing cam timing by retarding or advancing, versus using thinner shims. Moving the cams with the prescribed shim changes the time of the valve opening and closing event evenly, while using a thinner shim makes the duration between these events longer by keeping the valve open longer.
 
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