I have a stock internal engine with typical boltons and had it dyno'd about a week ago. Peak RWHP was 316 and TQ 342. However near the peaks at approximately 5700 rpm the cruves drop sharply by about 40hp and the torque curve drops just as much if not more. The power returns around 6200 RPM.

The motor also has random missfires across all of the cylinders at idle but disappears when throttle is applied.

A cylinder preassure test was also done and values were all around 170.

Would this most likely be a valve spring / float issue? Could it be a lifter crapping out? Please give me some advice.

 

How many dyno runs?

 

Well, if it has random misfires, you need to get that take care of first. It may or may not be related, but obviously its a problem. Knock retard can cause strange fluctuations in power output. That drop at 5700 rpm is an infamous LS1 anomoly, but can't remember what the cause was.

 

After plugs and wires and fuel pressure test, top end cleaner, cylinder pressure test and dyno we were basically out of ideas about the random misfire at idle. If there are any more I'd be willing to try them.

As far as dyno pulls, I saw it reproduced 4 times on back to back dynos. These were the first time I know of that the car has been on the dyno.

I believe knock retard was not an issue at the time of testing. The noise when the drop occured was a VERY fast almost click noise.

 

Most of the time its valve springs...

Install comp 918's make sure they have blue stripes.. Fairly cheap..

 

Can 918's or Manley's be run with a stock cam? I was told that it was a bad idea due to increased spring pressure. They were going to do LS6 springs for the time being. I had wanted to do the Manely Springs, Retainers, Pushrods all at once so that if i do a cam later i can run it safely and not waste money on the LS6 option. Please clarify.

 

haha, no the 918 and the manley will be fine with the stock cams..the actualy seat load isnt really that high with either. And Ls6 springs would be wasting money..

 

It could be weak stock springs. I've seen it before, but again that wouldnt account for your random misfires at idle. Is your car a stick or auto? Any bent pusrods or valves from mis-shifts possible?

 

Its an A4 C5, tpis headers, random cats w/ xpipe, o2 sims, 160 tstat, SS3600, transcooler, 3.42 gears, and basic tune for the mods (not a dyno tune).

The misfires were occuring well before the SS3600 went into the car. I dont know how a pushrod could have been bent on it but I did buy it used with 10k miles on it.

 

From the posts I've read, many a dip in the dyno at that rpm range is due to a bent pushrod.

 

Ahhh crap.. Okay so going the route of manley springs, titanium retainers, and new pushrods would probably be a good idea. can someone please confirm the earlier post about a stock cam being okay with these until I upgrade in a few months to a beefier cam (TR230ish)?

 

I spoke to a few people and wont be doing the upgraded springs with stock cam because they may actually reduce power by running too much/little pressure.

Here is a really bad picture of the suspect dyno. =(

 

Thats total BS. Using stiffer springs DOES NOT cause an appreciable power loss. Whoever told you that was wrong. A stock cam with upgraded springs is perfectly fine. If you plan on staying stock for a while, just order the '02 LS6 springs and check the pushrods. Pull the valve covers off and remove all of the pushrods and roll them on a flat surface.

 

This came from both MTI and LG ???

Regardless, if I wanted to change my springs are there any good sites I can read up on. And what tools would I need? I've poped my valve cover on the passenger side before but never attempted a spring and pushrod change.
How do I make sure I set proper spring pressure and lash?

Are there any specific tips you can please give me?

Thanks!

 

you sure the dyno didn't lose pickup of rpm? whats the a/f ratio when that happens?

the injectors aren't going static to 10:1? That would cause that for sheezy if you flood the **** out of the (blow out spark/misfire)

 

www.ls1howto.com

http://www.ls1howto.com/index.php?ar...7697841d8fa990

 

Well, its still incorrct. I'm sure you got it from some guy other than the owners...I respect MTI, but I've called there before and was given mis-information by a sales guy. Now if Jayson told you that, i'd take it more seriously. It's been discussed many times around here at great lenghts. Heres the basics of it...as one valve is opening, requiring power to open it, another valve is closing "returning" power back to the system, basically equalizing everything. Sure, some energy is lost due to friction, but its a negligible amount. Now if you used Top Fuel Dragster springs, you may notice the difference, but a 918 spring is still a pretty weak spring in the scheme of things.

 

I'm not sure what the a/f ratio was. I do know there was an audible valvetrain sound when that happened for a slight instant. Can you explain your theory on the injectors a little more clearly (laymans terms)? The dyno itself was done by Jayson @ MTI himself. I'm just trying to cover all possible bases and plan if this turns out not to be a spring issue.

thanks

 

I doubt the injectors went static on a stock motor

 

how does the car idle / drive around town . I saw something similar (though not as severe) and it turned out to be my O2 sensors. the other thing I was experiencing was bogging at low rpm or after sustaining rpms for a while and a hunting idle.