Didn't look up the specs. But the intake still won't let it pull to 7500. The cam itself should, but you'd still have to have the heads and intake.Originally Posted by blindsquirrel
Didn't look up the specs. But the intake still won't let it pull to 7500. The cam itself should, but you'd still have to have the heads and intake.
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Explain how this is an intake manifold:
screenshot.12-05-2024 10.54.01.png
MAP also increases right when it starts doing whatever is happening.
I'm going to be moving soon so I am not planning on taking it back apart immediately. I am going to keep poking around some easier stuff to make sure I don't have some other issue going on. Here is a log with my wideband working. Made 2 pulls, first one was uphill on a bridge and I held it at 6500 for a little longer to get some data. You can see it begins to lean out so now I'm really unsure of what's happening. I feel like valve float should make it read rich but maybe I'm thinking backwards.
I have the Lingenfelter drop in C6 fuel pump that should be plenty sufficient at my power level.
https://www.summitracing.com/parts/l...ette/year/2003
MAF, Inj PW, Cyl Air all drop off.
I thought maybe the MAF was getting pegged because it is still in the stock tube, ran the car in SD and it did the exact same thing, I did not save that log though.
27DEG PULLS BRIDGE AND FLAT.hpl
JAMES C5 V0045 05.12.2024 CURRENT 27 DEG.hpt
Misfires read lean at the O2 sensors. O2s do not measure unburned fuel, they measure oxygen.
Did you ever answer if it sounds like a rev limiter when it stops pulling? Sounds funny, goes flat, maybe some popping/banging? Or it just hangs at that RPM and sounds normal?
Yeah it's hard to tell. Looks like a normal shift except for MAF falling off. I'm leaning valve float. What's the P/N on the springs?
Sure, some component of the intake tract can't keep up with airflow requirements, but that's not going to make MAF airflow decrease at WOT. Something to address later.
Usually when there is insufficient airlfow capability, it is accompanied by map decreasing. Maybe not all the time, but most of the time.
Springs are .660 dual platinum BTR springs.
No weird popping noises when its happening. Just a sudden decrease in acceleration and you can hear the engine just sounds like it doesn't want to rev anymore.
I am beginning to think I set the adjustable rockers wrong. I set .050" preload on the lifters about 1-3/8 turns after zero lash. Someone before told me to ditch the adjustable rockers and of course I didn't listen.
Do you know what lifters they are? Wouldn't hurt to set valves again by doing overlap.
Aftermarket rockers will need more spring to go to the same RPM as stock rockers. Heavier aftermarket valves will need more spring to go to the same RPM. There is no one-size-fits-all when there are so many variables and so many things changed from what works with everything stock but the camshaft.
What rockers are they? Stud mount adjustable or pushrod seat adjustable? What's the thread pitch? 1-3/8 turns is a lot, depending on the pitch.
I always did hydraulic Gen 1 SBCs with only 1/2 turn past zero lash. Some folks (weird folks) prefer going with the plunger 1/2 turn upwards from bottoming in the lifter, something about lifters collapsing from aerated oil. I think not having aerated oil is the better solution.
Pushrod adjustable. I don't know the brand. I don't remember seeing part number on the lifters but the appeared to be the Delphi LS7 lifters. Threads were 10x1.25.
Right. MAP is decreasing. That tells me and edcmat that something in the the intake can't keep up. The decreasing MAF part points toward valve control.
You really need to be careful. Coil bind, burnt valves, etc. There's obviously a hardware problem. Don't do any more running until you've pulled the valve covers and checked everything with actual measurement tools like calipers and dial indicator. That's a very expensive, and really nice, build you've got there. Take your time.
Save that adjustable garbage for the Harley folks. Use a pushrod length checker then order the correct length pushrods.
I'm assuming the pushrods aren't adjustable. Never seen that on a car engine before lol. Definitely nothing wrong with adjustable rockers, not needed for a hyd lifter though.
MAP falls as expected with a not-up-to-par intake system right up until 6300, then when MAF/cylair take the nosedive MAP goes back up. Almost like something was being burped back up the intake ports.
Assuming you know how to check for proper push rod length and can order the proper push rods, I think the easiest test will be to put a stock set of rocker arms on it and test it. Those rocker arms, among the other pieces already mentioned are much heavier than stock. The other option as already mentioned, is to add spring psi as a test.
I didn't say this looks like an intake manifold. My statement was in general. Stock plastic intakes aren't going to pull to 7500 rpm. That's just fact. Even an LS7 won't pull much beyond 7000 on a stock intake.
Yes I noticed the bump in MAP right when it noses over and even commented on it.
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I agree. The MAP bump indicates the airflow slammed on the brakes.
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An intake manifold or other restriction won't do that though. Not even an elbow collapsing or something will make MAP higher. Pressure would continue to fall off with a restriction as engine speed climbs. Nothing in the air intake system can make the pressure go back up unless there's a big hole that opens up and vents to atmosphere. Though why it wouldn't leak more at low speed/high vacuum doesn't make sense. Know what does make sense of all these various oddities? Valve float.
You could always call or email BTR. "Hey, I have these heads with these valves and these rockers and these springs at this installed height, it hits a wall at 6300-6400. We're trying to rule out a valve float issue; what springs would you recommend for it to go to 7500 with these parts?" If they then ask you about an intake manifold or what kind of floormats you have, remind them "Springs. Tell me what springs this combo needs please. Once the spring issue is settled I'll move on to other things."
(probably nothing less than a PAC 1208X or 1209X, but what do I know...)
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