Too much horsepower

[Pranav]

Got the car on the dyno (will post dyno sheet later today).

My usual, trustworthy dyno was booked up, so I went to a dyno I once went to a couple of years ago; back then with the LT1 I had issues with this dyno randomly reading high on torque, hp was definitely high; had me about 15/20hp/tq off once I visited my usual dyno later that season after I felt everyone was pulling on me hard.

Since then this "sketchy" dyno has moved locations but it's the same dynojet, so who knows.

Long story short initial un restricted run was 279hp/307tq. They did mention they were about 0.5 off on AFR with their wideband; according to it I was hovering around 12.0:1.

I shoved a restrictor donut inside my LT1 airbox outlet, took it from 3" ID to 2.25" ID, then made four more pulls; averaged roughly 275hp and 308tq roughly. Going from a 3" inlet to 2.25" inlet seemed to do nothing?

I'm going to visit my usual dyno this Friday.

I'm going to order a smaller series of intake donuts to be safe, but planning ahead in the worst case this dyno was indeed accurate, how do I take 15ish HP out of a motor without killing the torque too bad?

Sean has the same motor as me, runs 261/310ish; but he has a more restrictive exhaust with a restrictor insert.

It is very easy for me to modify my exhaust to accept a restrictor, but will likely visit the next dyno on Friday with just more intake restriction as I likely will not be able to modify the exhaust in time. There is time after that dyno before the next race if I still have a problem.

Worst case if I'm still high on hp on the next dyno, theories on intake vs exhaust restriction?

I'll post up the dyno sheet later today to see if you guys have any doubts over the dyno's accuracy, seeing that 0.75" of intake restriction seemed to do nothing, but being a first ever WOT run on this motor the ECU may have been learning and picking up HP at the same time...

Additional note, I usually run 75w90 gear oil, for this run I had 80w90, ran out of time to change it to my usual 75w90; was just running junk 80w90 to get any crap out from the rear end from the last failure/rebuild. Not sure if that makes a difference.

Additional note #2; forecast has a probably 30*F increase in ambient temp this Friday over today.

Additional note #3: dyno said it was 53*F ambient; out door temp was just barely crossing 40*F; not sure how these are supposed to be setup, didn't feel cold in the shop but had two big doors open.

Definitely don't want to start the season on the wrong foot, don't expect me to ask for a free pass unless I really have a real problem...

[Supercharged111]

Restrictors for me always impact hp more than torque. Since you only need to lose 15hp, I'd venture to guess torque will remain close to 300.

[GlennCMC70]

Power reduction is a result of restricting air flow. Since peak tq is very low in the rpm band, the airflow is in less demand as opposed to the rpm band where peak hp is. Thus hp is impacted more.
Changing valve lash will increase/decrease tq is I recall. I ran mine w/ about 1/4 turn pre-load.

[drwright]

Pranav,
What you have described is not surprising to me at all. The LS motors don't change much in horsepower until you start to get into the 46-52mm range of restrictors. In the Great Lakes region most of the 5.7's use 46-49mm restrictors. Most of the 5.3's use 48-51mm restrictors. At minimum when you go to the dyno again make sure you have 48-52mm restrictors in 1mm increments. A 1mm change in that range should change hp 2-4 hp. Once you get in the ballpark you may want to make restrictors every 1/2 to 1/4mm to fine tune the hp.
Derek

[Pranav]

Ah ha.

Derek that makes complete sense. My donut is 2.25" or 57mm, which would explain why I didn't see much of a loss/change.

I'm not sure if I can fab some inserts between now and Friday, but my off the shelf options are in 0.25" increments which will at least get me in the ball park. I'll try 1.75 and 2.0 if I can't figure out how to make a a series of inserts in mm increments.

Thanks guys for the comments; Dustin I would expect to be closer to 300tq all said and done, I believe 5.3s end up in that range.

Glenn I remember in the Lt I used to run 1/2, the machine shop set the LS to 1.5; not sure if it translates differently in roller rockers.

[GlennCMC70]

Forgot you are LS........
How did he set them @ 1.5? They are non-adjustable. Did you shim the pedestals?

[Pranav]

I don't think so? I found the 1.5 number odd too but he went off of what felt right and what his LS expert felt was right.

Mentioned this to the dyno shop and they said 1.5 is fine too. Seems way high than what I'm used to vs LT1 so not sure, wasn't too worried it

[GlennCMC70]

I quess you missed my point. LS rockers ate non-adjustable. You run the rocker bolt down and torque it. Unless you shim the pedestals, there is no "setting it".
1.5 seems like alot as well.

[mach1]

You can set the lifter preload with shims or different length pushrods, I wonder what they did.

[Pranav]

Ah gotcha, I'll call and ask.

This is the style of donut I insert from the inside of my air filter box:
http://www.intakehoses.com/mm5/merch...egory_Code=RIS

I'm thinking I will buy a bunch of these and have holes made in 1mm increments from 46-56mm:
http://www.ebay.com/itm/2-Pack-2-1-2...-/131875102074