1992Vortec

Hey guys so i cant turn anymore than 4800 rpm shes all out of steam. Is this normal or am i asking for too much? I have a 60 over 350 at 9.5 to 1 with HSR Vortec intake, chevy vortec bowtie 185 runners, gt45 single turbo 5lbs of boost, 3 inch exhaust into a single chamber with a turn down, 3 inch intercooler piping, comp cams 08-305-8 camshaft. I am not expecting anything crazy for rpms but the car almost lunges forward letting the rpm go any higher. I'm wondering if my cam is the cause or my valves are floating or maybe my stock throttle body is being restrictive? Maybe timing and or spark is weak? No MSD and before the turbo was installed it did the same exact thing... Any ideas would be great help.

Thank you,
Matt

tom3

Need more description on the lunges forward. Normally I'd suspect valve springs, but lunging is often a fuel supply problem.

project89

iTrader: (1)

for starters get rid of the crap chambered muffler , flowmasters and all there chambered knockoffs are the worst thing u can use on a turbo car.

does it pop and bang or does the motor stay smooth , willing to bet on valve springs/fueling issue or the rev limiter is set way to low

1992Vortec

So when making a pull it sounds good and strong then right around 4500 to 4800 you can her the tone change and if i stay in it the rpm just sorta hang at 4800. The car is making a ton of power at 4500 then just nothing not a slow tapper off like what i thought a normal power band felt like leaving. Sound alone makes you want to shift engine screaming with no/ very slow movement of the tach. No lean back fires fuel pressure is up at 45psi afr is at 12 or so. I ran the car a while with just down pipe till my neighbors called got pissy after a late night run same deal but i will for sure get rid of the chambered muffler. Checked the rev it maxed on the EBL iv put some thought into the timing just because 4800 is when the table changes to the extended SA. Tried many different sa changes in the area with no change in performance. But by no means have i mastered tuning yet... my thought is springs but i have had stock vortec heads run the same as these bowties just sorta exact. What is typical for valve float for a stock small block vortec?

project89

iTrader: (1)

post up a data log u will prolly have to zip the file up first

anesthes

iTrader: (12)

Is this on a dyno?

Valve float will feel like you hit a brick wall.

What's the air cleaner situation like? I've sucked intake tubes closed before.

The combo should spin to 6000 rpm.

Springs should be at lest 120lbs closed, 360 open. What did you use?

Like he said, post a log. MAP will go nuts if you have valve float, we will see it right away. It's probably the tune.

-- Joe

1992Vortec

This is not on a dyno and the air cleaner is a filter on the turbo. It has also been ran with no filter to check this issue with same problem. the spring pressure is at " installed height IS 101# @ 1.78" with 332# the average rate of pounds per inch" Low spring pressure causing valve float? I will try and get the log loaded after work tonight.

1992Vortec

Sorry i posted the incorrect cam part number... It is a comp cams 12-268-4

project89

iTrader: (1)

im really thinking valve float as this point , it has all the symptoms of it.
should be real easy to spot in the data log

1992Vortec

From what ive found out about the springs they are stock LT4 spring and the come in the zz4 engine... specs show a larger lift cam than my running and making power about 1000 more than me. But valve float is what it feels like to me to. be off in a few hour ill try and load a log.

anesthes

iTrader: (12)

I was about to say not enough spring, but then you posted a different cam part # which is a flat tappet. The first came you posted was hydraulic roller.

-- Joe

1992Vortec

ya just a bit of a difference between flat tappet and roller lol sorry about that. Im going to have to wait till this weekend to get a full pull on a log too much traffic in Colorado these days..

Drac0nic

backpressure can cause float! open the dp and see if it improves. 3" is not a huge dp for a gt45 esp with a chambered muff.

shawnc16

I had an issue similar to that. It ended up being a junk msd ignition module.

83 Crossfire TA

iTrader: (2)

Could be lots of things, but I wouldn't have even tried those springs with that cam (either one, especially the hr you posted the first time, but even with the flat tappet xe cam) + boost + the restrictive downpipe/muffler.

like everyone has already said, a datalog will show valve float, but barring that ditching the muffler will make a big difference in power even if it isn't your problem (a bigger downpipe woudn't hurt but 3" should be enough to go well past 4800rpm). I'd be planning on replacing those springs even if they weren't your problem either. Unless timing is doing something really weird or you have a problem with the ignition hardware that shouldn't be it. If you really suspect it the fast way to check for an ignition issue is tightening up the plug gaps to something in the .024" range and see if that changes the RPM that it will pull to. Fueling could do it, but if you've been running out of fuel up there and hitting it repeatedly I would be surprised that you haven't blown it up yet.

project89

iTrader: (1)

good point i didnt even think of asking him what his plug gaps are, they should be in the .024-.026 range anyways.

though if that was the issue he would getting poping out the ex at higher rpm

1992Vortec

I cant for sure recall what the exact gap is set at but know they are set larger than .024- .026 range. My ignition system inst really upgraded at all just have a MSD billet dis, MSD coil, and MSD wires. Will check the gap ASAP

junkcltr

iTrader: (1)

Are you 100% sure the spark limit and fuel limit is set right? It seems odd that it is being limited to the stock ecm 4800 rpm settings.

I don't see the mechanical parts limiting it to that low of an rpm.

If it was breaking up then I would think ignition problems if ecm isn't limiting it. A healthy stock ignition at 4800 rpm and 5 psi should have no problem igniting.

jimw67

What do you guys consider safe plug gap for a properly functioning stock ignition with quality parts, basically, no MSD box or other ignition add ons? A recommendation at different boost levels would be greatly appreciated. I.e. at what point will .035", .030", etc. be an issue?

1992Vortec

I triple checked all spark/ fuel cuts because I was thinking the same thing you are. I checked my plug gaps and they we huge .045... Installed some fresh plugs and gapped them at .025 will test this weekend when I can do a full pass and get the log loaded. Thanks guys

project89

iTrader: (1)

ive seen spark blowout with a good stock ignition system @ 4k rpms 6psi with a .032 plug gap , every engine will be different , if ur running a boosted motor start at .030 gap and if u have issues tighten it up from there

being ur plugs were at at .045 i belive u found ur issue , and u should be pretty good to go now for the most part , prolly still need to adress the valve springs at somepoint though

1992Vortec

new plugs gaped to .025 and a bit of tweaking on timing brought me up to 5500 rpm with no issues! thanks for the help now i can turn up the boost lol

83 Crossfire TA

iTrader: (2)

Good.

Now fix the other things I also mentioned and you'll be much happier with it in the long run ;-)

junkcltr

iTrader: (1)

That is good news. Every time I have come across too big of a gap the engine would break up up top (pop/misfire). If that is a stock GM module, 1990+ TBI/TPI coil, good wires it should be capable of more PSI. If it is a large coil-in-cap setup, then it is already maxed out.

Ah, just noticed you posted msd dizzy and coil. Got the specs on it? What is the L & R of the coil? Some aftermarket stuff is worse that stock 1990+ GM parts.

anesthes

iTrader: (12)

Could also be having coil dwell issues as well. One of the reasons I went DIS.

-- Joe

junkcltr

iTrader: (1)

I was interested in DIS also. I had some time to mess with coils last year. I found the 1996+ vortec truck coil and module rivaled most aftermarket manufacturer coils and modules. The vortec setup was designed so that the module sits external to the dizzy and has a heat sink to dissipated all the extra heat it makes from being high power.

Any module that sits inside the dizzy can't produce the same power reliably. So even a great coil is limited by the module.

With a little voltage translator ckt, the stock dizzy coil fire (gnd) output can be converted to a 5v output to signal the vortec module/coil pair.

DIS is nice but the same ignition power up to about 6500 RPM can be had with the stock ECM and a $20 JY/ebay vortec pair.