turbocdubs

Okay so i swapped in a ly6 in my 95 chevy.. finally got it around to getting it dyno tuned and the dyno graph seems to hit a wall at 4700.

mods are a .598/.615 lift cam
vvt delete of course
full boltons
basically brand new rebuild
24x crank
411 pcm
if anyone has any questions on what else i did i can include it im just not real sure what is all relevant to be honest.

dyno chart seems to be making great power up until 4700

i did a few logs to see if it was knock retarding or anything and nothing on the scan tool ill post the log if i can figure out.

tuner said afr never dropped, im assuming its got good fuel?

anyone got any ideas.. i feel like im being robbed of like 70hp

03sierraslt

iTrader: (22)

What's the cam duration? Was it installed straight up?

turbocdubs

226/238, installed straight up

Gadgetized

iTrader: (9)

I am not the best dyno guy, but did you do a compression check? What valve springs are you running, and are you sure none are broken? What is your intake and exhaust system? Do you know what your final timing was? Are you running the original square port LY6 heads? If so, they should be flowing enough.

Vortec350ss

iTrader: (20)

Frankly with a cam that big I think you are seeing signs of it falling off far before 4700. Your peak tq shouldn't even be until after 4k. What valve springs?

For example look at this power curve


Heres the mod list:
-American Racing 1x7/8" headers
-Corsa 3" exhaust
-Stock L99 heads
-Stock L99 intake
-Vararam cold air intake
-Stock throttle body
-Tick Performance "Street Heat" Stage 1 for LS3(L76/L99/L92 intake lobe option for solid stem intake valve) 226/236 .605"/.578" 114+4

turbocdubs

havent done a compression check yet. pac racing dual valve springs, dont have the exact number handy. and havent checked for any broken springs

lycominghunter

iTrader: (2)

What is the intake and exhaust set up (tb size, intake, short or long headers and diameter)? Torque does look like its dropping off sooner than it should. What are the full specs on your cam? I know you didn't spin it very high, but on your dyno graph you barely get to the point where your hp and tq cross, not to mention that hp and tq intersect as both are on a downward trend - seems strange. Timing, afr, choked air/exhaust flow may be culprits based on the way the graph looks but idk how likely choked air/exhaust flow would be. Those valve springs should be fine but floating valves (if you had broken valve springs) would cause it fall off too soon as you got higher in the rpms. Were the valve springs installed to the correct height? Looks like it pulls hard down low though...

turbocdubs

tb is a 92mm
and longtube headers i believe 1 3/4
with full 3" exhaust.. i certainly think its timing or fuel related just not real sure on how to check that.

if a spring was broken would it make power down low??

Suburbazine

You have a flow issue, be in fuel, air or exhaust.

I'm no expert on cams, but I think the cam numbers are unusual, to the point where the gap in the durations and the difference in lift might be causing reverse scavenging and causing the intake air to have a pressure ripple. This would cause a loss of high RPM power.

lycominghunter

iTrader: (2)

if 1 of the coils of a dual spring was broken, the spring (in theory) could have enough force to still keep the valve open and closed at lower rpms. as rpms increased, however, the spring would not provide enough force to return the valve as quickly as required to the closed position - this could get to the point where the valve doesn't even fully close between between camshaft rotations and therefore a cylinder may not be building the compression it should be at higher rpms...

I've never had a broken spring, but I'd pop the valve covers off and see if theres any broken springs. Check and compare the spark plugs on all cylinders and see if one particular plug/cylinder is different than the others. You could also check to make sure youre getting spark from each plug - however if you weren't I think you're bottom end wouldn't be as strong as it is.

Timing on a ly6 should be mid 20's at WOT on 93. If you can, you could log the Throttle Position Sensor to make sure that its staying at 100% throughout the pull but Im sure your tuner checked that. Intake and exhaust system seem to be fine...

No other driveability/idle/tuning issues besides the lack of top end?