Nathan937

Just a quick question, I know larger cams and a log manifold don’t work well together. But I was wondering if this theory I have is plausible. Log manifold, running garret t3/t4 .63 .57. When vtec engages cars power falls flat on its face. Staying on the small lobes car runs out without issue, but as soon as vtec engages power drops off on the dyno. Is it creating a bottleneck effect that a log manifold just can’t flow for when the big lobes start to run things? Cams in question are the BC0012 (dur @.050 254int 248ex 11.99 lift)

I expected to leave some power on the table due to overlap, but I never expected the thing to just drop off like like it did. Thanks! And please excuse my ignorance in this.

Stopsign32v

iTrader: (1)

I'd say that is plausible

turboLScrx

I think the log would run out at a certain power level and not necessarily when vtec engagement. Gut feeling says timing or fuel

TheShodan

iTrader: (14)

This is timing and fuel related. the log manifold is not causing any backpressure.

Nathan937

Well, i do know I’m going to go ahead and put in some GSR cams because I know I’m not really benefiting from these crowers. Dealing with the tuner on this, he’s a pretty experienced local guy, and he showed me some graphs on previous customer cars that had similar issues (two prior customers) and one he tuned out on the primary lobes like mine, and the guy ended up changing cams and on the retune the issue was resolved. Not sure if the other car though. I do know on mine when the issue was going on, he was making several pulls with timing/fuel/vtec point adjustments and it was the same scenario every time. I’ll try to get ahold of some graphs, maybe that info could shed some light on what could be happening.


im a little stumped on this one. I think I’m going to verify the rockers lock when I put some air to the head, get some GSR cams in and see where we’re at.

Thanks for your input though guys, I do appreciate it.

Txdragon

High possibility you need to check mechanical timing.

Nathan937

the timing is “as good as I can get it”. And what I mean by that, is my head at some point was resurfaced, and I’m roughly 1/4-1/2 tooth off the crank mark at the gear. From everything I have read and those I talked too, said that usually is typical with a head mill such as that to line up the cam gears and once proper tension set to off a smidge down at the crank. Not ruling anything out at this point. Do you Think a 1/2-1/4 tooth at the crank gear would be able to cause such an issue?

Txdragon

Yup. Get some adjustable cam gears.. ESPECIALLY if you have larger cams and B-series. It doesn't *seem* like much but, well... Any head milling will throw it off at least slightly and where you're going to notice that fact is running larger cam(s).

turboLScrx

did you degree your cams? If not you pissing into the wind. Especially if you have had much mill work

Nathan937

no, I did not degree them.I didn’t have the degree kit I just kinda tossed them in there at 0,0 and ran them. Probably not my greatest choice, but I actually purchased the car off of here last year from a member who has let the car sit for over 10 years in storage boxes. I was trying to just run what I got and see what happens.

turboLScrx

factory set of cams might be best unless your willing to do the work

Nathan937

I’m going to order a degree wheel and grab a indicatior. Thanks for the advice!

turboLScrx

just get the cam card that goes with your cams. If you need help degreeing, I can assist with some details

Nathan937

this guy here? I think there’s more info on the other card I have.

turboLScrx

Yes you are on the right track, quick question......what springs / valves and retainers are you running? Large cams must have good springs or you will float valves

Nathan937

this head was from a prior NA build. It was sent to Endyn in 2008 for a resurface, port, Endyn springs, valves, and retainers. The receipt just says “Endyn” parts, although I thought the pervious owner told me it was a full Skunk2 head package including the skunk 2 tuner 2s that this head was originally running. I knew those wouldn’t serve me any purpose, so I traded the s2t2 for the crowers I have now due to the lower duration.

So my receipt says Endyn valves and springs, not sure if they are Skunk2 or if Endyn has their own line of products. It’s one or the other. It did run with the tuner2s in there for a couple thousand miles. So that’s why I’m assuming the head is ok to handle it.

turboLScrx

if your cams are close to the same lift as a Skunk2 pro1 you need springs 90lbs or above if your boosted. Every pound of boost will reduce the spring pressure by one pound. It’s why all motor cars can get away with lighter springs in the head than forced induction cars. If your staying under 10-15psi your probably ok

Nathan937

Ok that makes sense. So far we have stayed at 13-14. But I wanted to go to 20, I couldn’t tell you what the spring itself is rated at. I know the s2 cams were more aggressive in lift, but it wasn’t by much. I have a set of GSR cams, I think since I’ve got too many unknown variables I’m just gonna put those in and try my hand at degreeing. Because that still don’t help my timing mark misalignment from the work done to the block and head. I appreciate your advice though. I try to get on here and find some things out and so far it’s served me pretty well. It just stinks that many of the threads I find are old and the pictures are down.

turboLScrx

‘if I need to make a video on how to do your degree work I will

Nathan937

if it’s not too much trouble I would still be interested in learning how to do to it the right way. I’ve never tried, but I would imagine setting up the gsr cams wouldn’t be a bad idea either. Just to ensure everything is lined up right

turboLScrx

my cam gears did not line up after everything I did, degreeing is the only way to make sure things are correct. Proper measurements mean more than the lines on those gears

Nathan937

Yeah absolutely. I’ve watched a few videos on it. I do have a basic understand of how to do it. I get the principles, I guess I need to just get the stuff and get them dialed in.

Balor_Gr

Ive seen F20C loosing power on vtec with a log manifold. What psi this happens and what rpm you have the vtec engagement?

Nathan937

It was happening roughly 15-17psi, and vtec engagement we tried 5000, 5500, 6000, and 6500 with the same results

Txdragon

This REALLY sounds more boost pressure related; BOV leak, coupler, intercooler. You're losing boost pressure after 17psi consistent: check and/or replace above listed items.