tbird31

iTrader: (22)

After completing the current setup I put 1000 miles on it with a brief tune in it to break it it, then it hit the dyno. Made good power, but hit a freaking WALL at 6400rpm and then the power dies. The tuner said it just wouldn't pull past it.

When I did the swap I put all new plugs/wires, rebuilt MSD Billet Opti, the coil was relocated to the back of the intake, so I had to make a wire but it works just fine at all other RPM.

Here's the dyno graph:



I'm at a loss. I'm frustrated because both myself and the tune thinks it has a good bit more left on the table, but neither of us can figure out this issue. Opti was the first choice but, 1) it's brand new and 2) it doesn't present a problem at any other RPM. Same with the thought process of the coil...

Any thoughts/suggestions?

trilkb

iTrader: (4)

no idea man, nice numbers tho, wish my car had 408RWPH lol

tbird31

iTrader: (22)

haha I appreciate it. When I got it dynoed it still had the original plugs from the break in period and the MAF was filthy. Since then I've put in a fresh set of plugs and cleaned the MAF. I am getting the car re-tuned at the end of the month and I hope to have a new intake setup by then too. With the new intake, cleaned MAF, new plugs and hopefully this issue figured out, I honestly think it should see a decent gain in HP and TQ; not to mention when I got it tuned initially it was like 100* out, compared to it being ~70* when re-tuned.

speed_demon24

iTrader: (6)

Whats your valvetrain setup?

Wicked94Z

iTrader: (26)

yep....

and what makes you think you'll see more power with plugs, wires, cleaner maf, and cooler temperatures. they have a correction factor for a reason, and the a/f looks spot on

MattSapp95_T/A

iTrader: (35)

yea I am thinking springs here too.....
Give us some info on your valve train...

Air Fuel looks good....So you can rule that out

The stock opti will rev higher than that....was it busting up or anything or just fall off???

And yea its already corrected so the weather shouldn't matter......But good numbers regardless...

trilkb

iTrader: (4)

guessing you guys are leaning towards valve float?

tbird31

iTrader: (22)

Quite true. However the car does feel quite a bit more crisp since I cleaned the MAF and changed the plugs.

Valve train setup is 918 springs, Scorpion 1.6 RR and stainless Ferra valves. New valve seals also when I had the heads redone. Everything was installed with the new cam specs in mind...

tbird31

iTrader: (22)

I forget exactly what length pushrods I have. Would a source of the problem be spawning from the incorrect length pushrod? I'd assume no, but I'm getting tired of this problem and will accept any guidance I can. haha.

Wicked94Z

iTrader: (26)

what's the installed height on those springs? they shouldn't be any higher than 1.74. valve sizes?

AChotrod

iTrader: (17)

I had a bad MAF during a tune. Got a new one and didnt pick up any peak HP, although the car did drive better and needed a retune for midrange AFR

JAKEJR

My view: Unrealistic Expectations. You're expecting too much from your setup.

Time for a solid roller and all the associated valve train parts.

Jake

speed_demon24

iTrader: (6)

Yep it's very difficult to rev a hydraulic roller setup past 6k let alone make any power...

MattSapp95_T/A

iTrader: (35)

there are TONS of LT1s on here reving to 6700-7000 with hydraulic rollers....especially with AI and LE cams...

Maw they may peak around 6200-6400 but they carry the power to 6700-7000 no prob....

to the op... How old are the 918s and what is the install height...May want to look into some Patriot extremes installed between 1.780 - 1.800..... I have some comp shims if you need them....


Matt

tbird31

iTrader: (22)

I will have to check the spec sheet I got back with the heads to give you an accurate number and valve size. I believe 2.00 and 1.56 are what's popping into my head for sizes though.


I don't agree with that at all. My CC503 had a smooth curve and didn't stumble at all. Revved it to 6700rpm+ on the dyno. I understand that my power expectations might be somewhat high but as far as camshaft size and dyno curve, it should continue well into the 6800rpm mark, this is quite a top end camshaft.


Exactly. I did the initial LT1/T56 swap Jan 2007. So they're 3 years old...(holy crap I didn't think it's been that long). At the time the springs were good to .600 lift and I honestly haven't heard of any problems from them. The Lunati camshaft I have 60122 with 1.6 RRs specs to 231/239 .575/.585 on a 110LSA. So, I assumed the lift at .600 would be ok.

tbird31

iTrader: (22)

I agree, my idle and midrange definitely need to be tinkered with a bit. At idle it smells quite rich, and the midrange has become sluggish...it's all quite frustrating.

MattSapp95_T/A

iTrader: (35)

I would buy a set of patriot extreme springs and put them in and shim them.... I think it could very well be a valve float issue....with the springs being old its good insurance anyway

you can order them through Lloyd Elliot at a good price and he has awesome customer service...He steered me away from beehives on my setup..



Matt

1redta

its probably the springs, I went thru the spring change because of the beehive springs being to weak for the cam I have. I installed some patriot dual extremes and it has been good since. The old springs looked like this and messed up some of the lifters when the spider gave up the ghost

JAKEJR

Could be your 231/239 cam (that's what I saw in your sig) just isn't up t it and or their lobes are just too aggressive to continue to make more power up top. The more aggressive the lobes the harder it is to control the valves up top. Comp cautions that either better springs are called for or the rpms lowered when running an aggressive lobed cam.

AirFlow Research has written about this. GMHIGHTECHPERFORMANCE magazine's cylinder head shoot-out showed much the same thing at about the same RPM 6200-6400 (both are on their sites). GMHTP was running a 230/236 HR, close to what you're running.

Popular HotRodding had the same experience at about the same rpm point. I'll try to find the link to see if they ever solved it - I usually save links to things like this.

Could be cam, springs, valve train dynamics, harmonics setting in, ignition or something else entirely. I still feel you're expecting too much from your combination. Just getting the engine to rev higher doesn't mean the power hasn't taken a nose dive up there.

I'm sure the cam card shows the tested rpm power range of your cam. What does it say?

Taking a HR above what you're now seeing isn't the norm. Heavy lifters, more aggressive lobe ramps, limited spring pressures, pushrods, etc., all conspire to work against rpms higher than what you're now seeing. Especially rpms where the engine is still making more power.

One series of dyno tests I read about in one of the better known mags said something to the effect "It was like the engine hit a brick wall. Repeated tests and it wouldn't even go 25 rpm higher".

So my thinking is that if you're really determined to make more power at rpms higher than you're now seeing, you're looking at changing some valve train parts. If it were me, I'd immediately go with a solid roller. Starting in the mid 240 @ .050 range with the required springs, etc.

Jake

JAKEJR

According to dyno tests done by Popular HotRodding, 6500 rpm was the highest they could take their 383 test engine before the valve train came unglued. (Their word) They were hoping for 7000.

That rpm brick wall was EVEN with AirFlow Research's stud girdle installed.

The full test is on their website. The article even includes the 20 rpm brick wall the engine hit.

Jake