Need some camshaft guru advice on power loss from supercharger to nitrous

[TTSaleen]

The Question -
Why would my engine fall off power at higher rpms using nitrous but does not do that with a supercharger?

I have a 331 stroker engine (stock block) with a set of Ford Racing X302 heads (GT40 aluminum), Scat crank and I-beam rods, forged dome pistons and crank girdle.
* The camshaft is unknown but has a noticeable chop at idle.

On engine it runs very well for what it is and made - 315hp/359tq
I added a 125hp shot of nitrous (wet NX kit) and it made 440hp/530tq.
However you can see the nitrous trailing off and losing power as rpms build higher.

I replaced the nitrous with a vortech v2 supercharger kit at 15# boost.
Same engine just different power adder.
The power stays consistent and does not fall off at high rpms like the nitrous did.

I now have that engine in my other mustang and it does the exact same thing on nitrous. Literally makes within a few hp/tq numbers of the original test.
I replaced the nitrous solenoids and all my trigger wiring (relays, etc).

I think it is the overlap or something in the camshaft.
What do you think and what would you recommend for a replacement camshaft in this application?

Thanks,
Ryan

 

[AeroCoupe]

Fill out the custom camshaft data sheet here and that will solve it.

Cam Tech Form

flowtechinduction.com

 

[Noobz347]

Perhaps your valves/springs are floating.

 

[nickyb]

Ditch the nos and get another supercharger

 

[rednotch]

Exhaust timing of the cam for nitrous vs boost are two different animals, a cam designed for a nitrous combo is almost of always a dog on motor but I doubt that's the issue. What's the jetting and fuel pressue , Is a shark nozzle? a "100- 125" shot would be 52/33 on old fox body kits and where rich as hell. 52/31 is how I jetted those for years.

 

[AeroCoupe]

Perhaps your valves/springs are floating.

So it pulls and makes great power with the SC through the rpm range but falls off in the upper rpms with NOS so I don't think that would be valve float or would it? I am not busting balls here just asking as I would think it would do that under both circumstances. I am just thinking rpm and valve float doesn't care about a power adder.

 

[Noobz347]

So it pulls and makes great power with the SC through the rpm range but falls off in the upper rpms with NOS so I don't think that would be valve float or would it? I am not busting balls here just asking as I would think it would do that under both circumstances. I am just thinking rpm and valve float doesn't care about a power adder.

Because it hits harder. The PS and the I's are higher.

Similar to instances where there's no valve float N/A but it floats under boost. There are also instances where [more] boost has revealed valve float when upgrading or turning up a power adder.

It is not to say that this is the answer but it occurs to me that there are a [lot] of aftermarket assembled heads with crappy valve springs.

Other thoughts:

Ignition blowout: plug gap too big, coil/box marginal, and at 4500 with nitrous on it simply can’t light the mix. That’ll look like it hits a wall every time in the same spot.

Some kind of control/box behavior: nitrous window, rev limiter, or timing-retard function that’s misconfigured around that RPM.

Fuel/nitrous control issue that only shows up when the kit is active (fuel pressure droop on the fuel side of the kit, etc.) but @rednotch can cover this way better than I could.

 

[Bullitt347]

A centrifugal S/C makes more boost with rpm. Thus, HP rises with rpm.
Nitrous hits all at once at a lower rpm, and the Nitrous amount stays the same as rpm's rise, therefore, the HP will drop off with rpm because the amount of Nitrous per cyl gets less as rpm's rise.
I see nothing wrong with the dyno graphs.
It is to be expected.
But, if you did a progressive Nitrous system, the HP number would change.

 

[rednotch]

I'm still going with jetting. Over on corral he said its 73/42 jetting which is a super fat "175" jetting on old shark kits, not 125. I still use those but keep nozzles kits at 150 or below, otherwise something all ways ended up hurt eventually with distribution issues on efi intakes, prefer plates kits if what to go higher than that with the old efi upper & lower intakes.

 

[revhead347]

What are your spark plugs gapped at? I made that mistake before.

Kurt

 

[TTSaleen]

.032"

 

[rednotch]

The info is all over the place, and I would not be worried about the cam after watching this video if that's the combo being talked about, on corral you said its a .73 42 jet but said its a 125 shot?, in this video its 62 nitrous jet that made the most and so fat I'm not shocked it fell off as bad as it did, 10.7-11.0 on a efi single nozzle kits asking for trouble, nitrous and fat is not a good combo, your asking for a backfire with that set up on the bigger jets. Controlling timing is far more important on pump gas though, especially if it has a dome piston in it and tight quench and jetting will not be the same on e85 so comparing it to the old runs on that for data is dangerous. Didn't see any timing adjustments or controls in the video? if the set up likes 12.5 afr NA its going to be pretty much the same target afr for nitrous, but even your na run was just a see what it does pull. Look at the 50hp more it picked on the 62 jet when the af was still 11.5 on the second nitrous pull , can't really see the A/F graph in the video but it looks like it slopes to even richer with the Rpm curve. Did you ever run it again with a full bottle on the 73 jet?

The jetting is off of what it wants and I'm betting so is the timing, and in the the bottle weight at the end and your going off bad data. Dropping down to 052 nitrous side jet will show about same peak increase and carry it better threw out the run when its matched with the right fuel jet as your best run on the 62 jet if your not going to dial in timing control or the jetting. I'd suggest starting with a .031 jet but have used as small as .028 on some cars depending on what the fuel flows. There base line jetting for fox body shark nozzle kits changed over the years but they where all ways on the fat side for those kits. They rated 52 at 100. 62 at 150. 73 was was 175 etc that jetting was stock fuel pressures and 19lbs injectors pretty much and its a really fat baseline, all those will make more power than the rating when jetted for what it wants if the rest of the system can flow it. https://www.nitrousexpress.com/images/allsinglenozzle.pdf.

As for pump gas I can show you local cars driving an hr to cecil with pump gas sbf's 10 years ago on wawa 93 and busting off 8 second passes and driving home, pump gas ain't an issue on a small shot efi nozzle kit on your typical efi 8.2 build. A lot of locals in my area went fast with pump gas nitrous stuff but you gotta know how tune it and its more than just throwing the basline jets in a kit and letting it ride like dyno video. I'd fill a couple bottles and dial in the timing and fuel jetting, and making sure there's no restrictions before the nozzle before messing with any thing else or placing blame on the cam.


View: https://www.youtube.com/watch?v=FblCUjIou2k

 

[JMG9350]

This is my Fordstrokers 347 on an NOS05115 dry kit, it ended up around 100hp increase. The jet combination is fairly odd since I have 36lb injectors, and when the kit comes on fuel pressure reaches 75psi. The bypass T is a 67, and the nitrous jet is a 63. The nitrous doesn't come on until 3300rpm. It made 416/404 at the wheels during the same tuning session.

 

[AeroCoupe]

416 on the juice or just motor?

 

[JMG9350]

416 on just motor, 505/527 on spray.

 

[revhead347]

.032"

That's pretty tight, and not likely the problem, but drop it down to .020" and see what happens. First time I went to a .057" jet it was blowing out the spark on the dyno at high rpm.

Kurt

 

[Qtrhrse23]

Yea, typical NOS wet shot dyno almost always peaks when the Nitrous starts flowing. Unless it it a dedicated 7000rpm motor. Only way it will start increasing at the end is dual stage it. Boosted will always make more HP ON THE SAME MOTOR. Double the motors HP? Add 15psi of boost.

Edit... After further review, that wasn't a full bottle. Right? Looks like she's was running low. A FULL bottle always makes more HP/runs the fastest.

 

[TTSaleen]

Problem resolved.
Had nothing to do with the engine/cam/etc.
Was simply a activation switch issue.
The switch was being pressed, but slowly pushing away from throttle body and causing system to turn off.
Took me a few times to figure this out. The dyno run not going rich had me rethinking why the car was back to N/A numbers at end of dyno pull.
But I also leaned it out and started reading plugs instead of a/f ratio and it runs great.
73N jet and 35F jet and 950 bottle pressure has the spark plugs looking great.

Appreciate all the feedback/insight.
Will dyno again in the future and get the final numbers.



Ryan

 

[revhead347]

Problem resolved.
Had nothing to do with the engine/cam/etc.
Was simply a activation switch issue.
The switch was being pressed, but slowly pushing away from throttle body and causing system to turn off.
Took me a few times to figure this out. The dyno run not going rich had me rethinking why the car was back to N/A numbers at end of dyno pull.
But I also leaned it out and started reading plugs instead of a/f ratio and it runs great.
73N jet and 35F jet and 950 bottle pressure has the spark plugs looking great.

Appreciate all the feedback/insight.
Will dyno again in the future and get the final numbers.



Ryan

I remember those crappy switches. Always was a problem. Glad you caught it. I switched to a Daytona Sensors ignition box years ago that uses the voltage signal from the TPS right off the factory wiring harness to activate the nitrous. That would be my advice to increase reliablity; ditch the physical switch and go to a voltage signal.

Kurt