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I was going to update the header thread, but this is just so incredible and such a large leap forward for the NA guys that I had to give it it's own thread.
Let me explain.
Our 350 is making 315whp with headers, exhaust, nismo cams, injen intake, tilton clutch etc. You can read more about it in the roadster / headers thread. The engine however is bone stock, sealed from nissan. Stock crank, rods, pistons, heads, no porting, no balancing nothing. This is a different engine than what I was using before which was balanced.
I've been seeing 0.7-0.8psi of vacuum in the intake manifold, which translates to about 10-15whp from my small experience with tuning turbo 350s - typically 1psi equals about 15-20whp.
My goal was to see how much power the engine would make if we let the runners breathe fresh air, from no real collector. Just like ITBs. The ECU does not use a MAF and is tuned strictly by throttle position, so as long as the throttle body is still plugged in, it doesn't matter if there is a huge vac.
The engine isn't choked up for air until around 4500-5000rpm, so I figured the fueling would be the same below that and we could lift the plenum after the dyno pull started at 3500rpm. When I say lift the plenum I literally had two guys standing at either side of the car, holding the plenum down entirely un-bolted so the car would idle, and then once the car was loaded up at 100% throttle on the dyno, they would lift the plenum and let the runners breathe fresh open air. Once the dyno held maximum RPM at it's stop point they would slam the plenum back down, allowing the engine to build vacuum. The fueling is all controlled through my foot, so there was no chance of a dangerous over-rev - leaving the plenum up simply acts like a fuel-cut rev-limiter.
Well I was expecting 5, maybe 10hp if anything. I half expected the test to backfire and either lose a ton of hp or do absolutely nothing. Well the first signs of success came when the motor went dangerously lean at 4700rpm and I had to abort the first run and add 8% fuel everywhere above said speed. After a few pulls and fine tuning the fueling (not even touching cam timing yet), we saw a jump from 315whp to 336WHP!!!!
I know you can't believe it, frankly I can't believe it either. But we did run after run and the results were the same. An interesting hole in the torque appeared at 5700rpm, most likely what the factory plenum was tuned, no longer able to revert high pressure pulses to opposing cylinders as the runners are essentially in open atmosphere.
This has been the most incredible test I've ever done. I'm still smiling ear to ear realizing that not only do we have the highest HP stock block/stock head VQ35 in the world (please correct me if I'm wrong), but more-so at discovering HOW MUCH is left on the table with this intake.
This image compares a pull made 10 min earlier with the plenum sealed, vs the power we saw after only fuel tuning with the plenum raised as pictured below.
What we're looking at here is an engine that can develop 100-130whp MORE than factory with only a cam, intake and exhaust tuning. This is no surprise however because the factory heads really are fantastic, the valves are big, the bore is big, the stroke it small... i mean it really is an awesome engine.
Here are a few photos of the test we did, you can see that lifting the plenum up allows the runners to suck as much air as they want, but also eliminates the plenum tuning effect that comes with a sealed manifold.
Chris lifting one end the of the plenum, constrained by none other than motordyne's longest M6 bolts supplied with their spacer.
Hi little runners, do you want to breathe?
Now I can't drive the car like this obviously, but I'm going to try and develop some sort of way to free up this power, be it by testing a cosworth intake manifold, modifying the stock manifold, building a new intake or something along those lines. So good!!!
Cool stuff albeit that it lacks any real world application.......does go to show how well the stock block will flow with just an adequate quantity of air. It's pretty impressive how much volume the stock heads can flow even with "smallish" cams. Like I said, it's a cool test.
P.S put your headers in production lol.
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"Racing makes Heroin addiction look like a vague wish for something salty." -- Peter Egan
That's very cool scientific experimenting. Legendary stuff. Nice work!
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"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us." - Calvin
wow that is amazing, and a really cool experiment. what was the baseline of that car on ur dyno in stock form? and when are those headers coming out lol
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base 08 Nogaro Red tp/s-tune exhaust, no tune 13.184@106.54mph 2.006 60ft
that's a pretty sweet experiement, now if you could find some way at higher rpms of lifting the manifold with a small quick motor or some servos that would be sweet
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With spring comes the mod bug....
Pretty sick experiment, and goes to show how much we dont know about these motors yet. Im assuming once someone finishes a ITB setup they should see these types of massive gains? WIth a properly tuned plenum couldnt you even see more gains?
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MY350Z.COM just got a little bit better with big uncle TX gone
I would say easiest way would be retrofitting the hr upper plenum. I have thought about this numerous times but more in the if only this car had a multi stage intake manifold ala gt3 or even bmw 330i where you can run a huge throttle body with no downside.
Jeremy noticed the same vacuum on my NA motor when he first tuned it. I have been trying to open up the intake system to eliminate the vacuum and improve performance, but with not much luck so far... You bypassed my designs by a wide margin...
You certainly get an A+ for thinking outside the box.
Very, very creative. Thanks for posting this.
-jb
__________________ Florida G Club, President 2k5 LR G35 Coupe 6MT
Cosworth Plenum | Crawford Headers, HFC | HKS Ti | Carbonetics LSD | 4.083 FD
Osiris Pro Tune | JE 11.7:1, Eagle Rods, JWT C8R Cams, ARP L19 | ACT Fly | JWT Clutch
Jeremy noticed the same vacuum on my NA motor when he first tuned it. I have been trying to open up the intake system to eliminate the vacuum and improve performance, but with not much luck so far... You bypassed my designs by a wide margin...
You certainly get an A+ for thinking outside the box.
Very, very creative. Thanks for posting this.
-jb
+1, but there is only so much you can do when still using a maf set-up. It must be nice to tune via tps.
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"Racing makes Heroin addiction look like a vague wish for something salty." -- Peter Egan
336whp!?!?!!? Well sortof.... Crazy Plenum Test
