Greg Fell

iTrader: (9)

Has anyone had 'problems' or unexplicable loss of hp up top, when using 1.8 RR's, or more specifically, the yella terra 1.8's? My dyno curve noses over pretty good up top, and I was told that it may be due to the YT 1.8's.

Thanks!

XTrooper

It's specifically due to harmonics and the resulting valve float which sometimes occurs with an incompatible roller rocker/valve spring combination and this can happen with any ratio roller rocker and any make of them. I've seen it with the Comps and my Crane Golds as well.

I had the same big dip in power starting at ~5900 rpm when I first installed my 1.80 roller rockers. They just didn't like my PRC dual springs and when I swapped in a set of Crane duals, the dip disappeared and I picked up 10 extra rwhp over the SLP 1.85's I previously had installed.

vettenuts

iTrader: (4)

I dynoed today and have the dip at about 5,900 RPM. Makes great power then rolls over. Wondering if the advance in the cam is acentuated somehow by the bigger rocker ratio. Car pulls hard, but then dips. At 6,300 it starts coming up again so it might be KR but tuner says no. It is about a 25 HP dip before it recovers. I don't think it is valve float as it would recover at higher RPM.

XTrooper

Mine was valve float caused by valvetrain harmonics @ 5900 rpm and it did recover (though not fully) at around 6200-6300 rpm. I'd suggest a valve spring swap and hope for the best.

Are you using the Crane duals now? If so, maybe a set of the Comp beehives would do the trick for you? I'm pretty darn sure it's valve float that your motor is experiencing and not something else. If it's KR, that's easy enough to check for.

Good luck!

Greg Fell

iTrader: (9)

Usually, you get KR at peak tq, unless the timing/fuel curve is wacked out.

I have a set of stock rockers I'm putting on this weekend and will re-dyno.

vettenuts

iTrader: (4)

Greg,

Interested in your results. Not sure what I am going to do yet but I did spend some time speaking with Crane this morning and they have been helpful. I would like to see how you make out, but I am not willing to give up on my 1.8 rockers yet.

vettenuts

iTrader: (4)

Crane is coming out with a new spring in about a month. That may be the solution. Discussions still continue though.

What sucks is I love this setup and the car is very very strong Just have to figure out the quirk and correct it.

Greg Fell

iTrader: (9)

Yes, I don't necessarily think its all 1.8's...maybe just the YT 1.8's. Not sure, I'll find out this weekend hopefully, and post up.

vettenuts

iTrader: (4)

Greg,

Did you see this post? Turns out it was his cats, but the tuner thought it was the rockers. Curve looks similar to yours, but at a lower RPM.

Dyno Thread

quickneSS

I have the comp pro magnums( 1.85 ) and I was experiencing the same loss of power up top like you guys. I thought a quick fix would be to swap in some 05 LS6 springs that were available. Well it seemed to fix it, but then I realized it only moved the problem a little more up the curve. It was major valve float with my stock springs!( .541 lift on stock 98' springs= ) Now not so bad, but I'm still not that happy! I don't know whether to get some 1.7's or new springs. I don't want to give them up yet! It still does'nt shift at WOT without letting off this is valve float right?

TIA
Jon

vettenuts

iTrader: (4)

LS6 springs don't have much seat pressure nor are they very stiff. You might want to upgrade your springs yet again. Also, over on Z06Vette.com there seems to have been a rash of valve spring failures on stock cars. They are still trying to sort it out.

Greg Fell

iTrader: (9)

I do not have cats on my car.

vettenuts

iTrader: (4)

Whoops

Greg Fell

iTrader: (9)

I dont think your shifting woes are related to valve float, unless you cant turn enough RPMS to shift.

I have Patriot Golds, which are about the stiffest spring you can use with a hydraulic lifter.

vettenuts

iTrader: (4)

Greg,

What happened with the stock rockers? I am looking at shimming mine to get the issue above where I want to set my rev limiter. Looking for shims now and a new way to turn over the motor. I had a special tool made for when I had the stock balancer and bolt, but now with the ATI balancer and ARP bolt it doesn't work and I have to figure this out as well

Greg Fell

iTrader: (9)

Attached is the results. Good news/bad news.

I did 484/459 at speed inc in may.

I have sinced added FAST 90, 1.7 stock rockers, stock TI zo6 exhaust, and dyno'ed 484/459!?!?! But the curve is most def better. I guess losing the lift and changing the exhaust negated the FAST 90.

I ran the car last night, and ran 10.85 @ 129.6 with a 1.55 60' bumping the rev limitter in 3rd. May have been a 130 mph trap speed

vettenuts

iTrader: (4)

Interesting results. What springs are you running and are they shimmed? Curves looks a lot like mine, but I would like to keep the 1.8 rockers as I think I get some additional power from them.

Greg Fell

iTrader: (9)

I am running the patriot golds. I do not know if they are shimmed, I believe they are installed at 1.800. Not sure.

I think I lost some power from less lift, but I have already bent valves from the valve float, and I think they extra revs will benefit me as I can stay in a deeper gear and get some mechanical advantage there. My traps went from 126ish to 129.6 last night, granted the weather was nice.

I'm switching to the LS7 stuff anyway, so I'll just be happy with the stockers for now.

vettenuts

iTrader: (4)

You bent valves? Do you know how and when that happened?

Dan_the_C5_Man

Looks like more "issues" with the 1.8 rockers..