Once the motor reaches 6800, it just seems to stop pulling. The HPTuners scanner graph just shows the RPM basically flatline once it hits 6800. The rev limiter is set to 7200 everywhere, and it's not bouncing off of it. I never logged it before, and the dyno pulls stopped by 6750. Not intentionally, that's just where the dyno operator let off. The dyno curve doesn't show anything unusual up to that point though. For now I've dropped the limiter to 6800.

My wideband sensor appears to have seen better days so I bought a new sensor and installed it this morning. It appears to be 10-15% rich at WOT all the way through the RPM band.

Motor is a 347 with stock crank, Wiseco pistons, Eagle H-beams, Clevite bearings, ARP rod bolts, 227/235 110+2 .645/.650 cam, LS1 rev-kit, TSP 5.3L heads, Platinum dual springs, 3/8" pushrods, stock rockers and LS6 intake. That's the basics for the longblock but I can give further specifics if needed.

The current motor was built last summer as a result of spinning a lifter. The old motor would pull to 7200 without a problem. This motor is using the crank and connecting rods from the previous motor

Any ideas on what would cause the flatlining RPM?

 

Out of cam maybe. 227 duration on a 110 pulling to 7200 rpms? would be my only guess

 

I would accept it being the cam if just the power fell off... here the RPM's basically refuse to spin higher than ~6800 at WOT with the rev limiter set to 7200.

 

valve springs maybe worn out? (using the same heads as before right?) or isnt getting air? sounds silly but hows the air filter?

 

New TSP assembled heads installed same time as new motor. Using a fram paper air filter, and I think it was slightly gray between the folds when I last checked it about a month ago.

 

damn, you've got an answer for everything I can think of. What about pushrod length?

valve float? can you post the graph, that might help someone. I cant think of anything else. New heads so there cant be build up, how did the intake look. I imagine if it had oil leaking out or a build up around the ports of it you would have noticed.

 

this sounds like the same problem i have with my other car so if you figure it could you please pm me i changed everything from heads to intake it was a carb'd 73 pontiac 350 couldnt figure it out

 

why do want to spin it to 7200 for ? shouldn't that combo peak much,much earlier than that and power would have fallen off alot by then. where does it peak at,6000-6200 or so ? anyways if it spun to 7200 before with that same cam and only thing changed is valvetrain i would look there.

 

what are you running for a fuel system? maybe you ran out of fuel at those levels?

 

Pushrod length was measured a couple of different times with a Crane pushrod checker during assembly. The heads were supposed to have been milled .020 from TSP, and the bolt boss indicated it had been done, but the chamber cc's indicated they were still 3cc too large, so I milled another .020 off them. Also, the pistons I bought were designed for a 6.125 rod instead of the 6.100's I was using, so they were in the hole ~.025, so I decked the block .020. When checking valve stem wipe, we ended up adding another a .020 shim to fix the wipe pattern, and then measure pushrod length multiple times. I've tried to confirm it since the build and it seems like it wanted something in the 7.2 range but since I was so far off from what was working I figured I was doing something wrong.

The intake was oily when we swapped it from the old motor, but I cleaned it out before re-installing it. I don't have a legitimate catch can, just a clear fuel filter inline. It does burn oil. We used lock-tite on all the rocker arm intake threads as sealant.

Fuel system is stock except for flow-matched 42lb Lucas injectors. Fuel pump or fuel pressure maybe?

The first dyno's on the motor, a few months back, are in this thread: https://ls1tech.com/forums/dynamometer-results-comparisons/815233-first-dyno-prc-5-3-s-patrick-g-cam.html.

The last dyno's (just pictures of the sheets, post #8) are in this thread after new headers: https://ls1tech.com/forums/generation-iii-external-engine/843960-norris-motorsports-installed-my-arh-headers-today.html

Regarding the cam and RPM, it appears to peak around 6300 and carries nicely to at least 6700. It doesn't look peaky at all, and shifting at 7200 was dictated in the cam request so I could take advantage of mechanical gearing and not shift as much. Again, this new motor received a new cam, new heads, new pushrods, new injectors, new oil pump, new pistons, new Caddy lifters (forgot to list those earlier) and the rev-kit instead of the lifter trays. A lot different than the old motor. I tried to build this motor to easily handle 7300RPM's and I'm irritated it can't get there.

 

I would check the fuel pressure. On my bone stock 346 with just a cam and other minor bolt ons, my car was running out of fuel at about 6400 rpm and falling flat on its face. When I added the nitrous to it, it really leaned out at higher rpm's. I have a fuel pressure gauge that I can attach to the fuel rail and put inside the car so that I can see what its doing under WOT. Sure enough, the car started out with 55 psi at idle and when I nailed it, it dropped dramatically to 30 psi. I changed the fuel pump and went with a set of 60 lb injectors (found a really good deal), and now it stays at 60 psi no matter what I throw at it. Hope this helps.

 

Know where I can find a good deal on a fuel pressure gauge system where I can monitor from the cabin? When you are saying falling on it's face, do you mean the power just dropped off or did the RPM's effectively stop climbing prematurely?

 

Just get a fuel pressure gauge (remote type with hose) and hook into your shraeder valve and tape it to the windshield. Seems to me if you dyno'd it, you'd be leaning out big time up top. Quite a few people turn stock engines with Trex cams and the like to 7100, so something isn't right. Have you checked the timing as well?

 

x2 on the fuel pressure check.

 

Jim, your power curve is absolutely beautiful. I can't tell from the graphs, but it does not appear to fall off on the posted dyno sheets. For its size, you have excellent power down low and up high. However, with an intake valve closing point of 41.5 degrees ABDC at .050", your ICL is probably a little too far forward and your duration is a little too small to give you big power at 7200 rpm. You would need more like a 46 degree IVC, more duration and more overlap to enjoy extended power in that area. And that's the rub. Cams are about compromises. For a road race/autocross application, power under the curve rules and your combination has it in spades. It appears to be very well matched for all your components. Remember, that few combinations have as broad a power curve as the one you have. The ones that are stellar upstairs really suck down low. Because you're running a long runner EFI intake manifold, you're going to be somewhat rpm limited by the cross-sectional area and runner length. The manifold, by design, will force a torque peak of 4800 rpm and a power peak of 6300.

As long as you've exhausted all potential valve control issues (springs shimmed to within .050" of coil bind, proper wipe pattern on valve tips, precise plunger depth on hydraulic lifters), you could retard your cam 2-3 degrees and this would help your top-end. But expect to take a hit in the low and mid-range as a result of decreased dynamic compression. Again, it's a compromise.

Check all the valvetrain issues mentioned above first.

 

I'm happy with the power curve, I just want to know why the RPM's take so long to climb above 6800. Here's the HPT log, starting at frame 31350. You'll see that it's obviously fat because my old WBO2 sensor needed replacement. I just replaced it yesterday and hadn't fixed the fueling yet.

Something else I noticed is that my MAP gradually climbed instead of immediately hitting 100kPa. It behaved this way earlier in the log at frame 27140 but there it reached 100kPa before 4000RPM. I removed most of the PID's not necessary for VE tuning so it's hard to determine what I was doing with the throttle, etc. When I'm VE tuning and I mash the throttle it goes immediately to 100kPa so I'm confused why it didn't do it when I wasn't watching the laptop

 

You'll get lots more feedback if you limit the log to just the frame you want us to see. I don't have time to sit through 9 minutes of logging. Show us what counts or better yet, put it in a spreadsheet so we can read it.

 

Stewart Warner #114218. Summit has them.

 

I was having the same problem and it was the valve springs worn out, less than a year,put new spring in, and now i can crank it to 7600 rpms ,but with the old spring i could only clime to 6800.

 

Next time log injector pulsewidth too.