The0nlyon3

I have a dart Ls next block, 427ci with TFS Gen x 260 LS7 heads. 11.5:1 compression with a BTR LS7 NA stage 3 cam, comp shaft rockers, manton 3/8 pushrods and Johnson tiebar lifters.


im running a Holley mid rise single plane intake manifold with a Wilson manifolds 4150 throttle body.

for exhaust I have 1.75” Hooker blackheart long tubes and a full 3” dual exhaust from Hooker

it’s backed by a summit twin disc clutch, t56 magnum transmission, 3.5” steel drive shaft and a moser 9” with 4.11 gears and 35 spline axles.

im running Holley terminator X

It’s currently tuned on e85.

power output was 510rwhp at 6200rpm and 500ftlbs at 4300rpm.


I was hoping for more RPM and more power but I’m not sure if it’s parasitic loss through drivetrain or something else.

anyone running a similar setup with power numbers?

thanks for your time

theunderlord

Was the car dyno tuned by someone well experience at Holly EFI?

old motorhead

iTrader: (10)

Those 1.75" headers are probably hurting your efforts. I'd want 2" primaries on that bad girl.

The0nlyon3

He mainly uses hp tuners but has gotten into Holley. I’d imagine Holley would be a walk in the park if you’re a pro with hp tuners

The0nlyon3

I’ll have to see if someone makes 2” primary headers that’ll fit a Ls swapped 67 A body :/

Mickyinks

Who built your engine? Is the cam degreed? Your torque comes in way early

fastlt1

iTrader: (4)

Whats the cams specs

99 Black Bird T/A

iTrader: (4)

This cam?
BTR CAMSHAFT - LS7 - N/A STAGE 3 - 33750133Specs: 237/250 .646"/.632" 113+3

******

That's stock LS7 w/bolt on's peak numbers.
Something seems wrong to me. Peaks early etc.

1 7/8 headers would help hp on the top but i doubt the headers are costing the missing ~100 whp

FWIW - my peanut cam'd (237/245 ~.620 ish lift) 416 w/Fast LSXR, 1 7/8 headers & Hooker Blackheat true dual 2.5 inch exhaust, Magnum transmission, Hawk's 8.8 rear, 4.11 gears made 517 whp on 93 gas. Based on my research and pretty sure my 416 is down ~15 whp vs a 3 inch true dual exhaust- but it has good ground clearance .

The0nlyon3

yup that’s the cam.

im going to do a leak down test. I’m having crank case pressure issues (there is another thread for that) so im wondering if that has something to do with it.

The0nlyon3

precision machine engine in Sacramento. He does excellent work, pretty much builds LS and LT engines mainly. Yes the cam is degreed

The0nlyon3

BTR CAMSHAFT - LS7 - N/A STAGE 3 - 33750133Specs: 237/250 .646"/.632" 113+3

Z28SteveA4

iTrader: (16)

Can you post a dyno graph? Sure stepping up to 2” headers would help but that’s not what’s causing low numbers and rpm right now for you. Crankcase could be part of it. Does it seem to be floating the valves?

The0nlyon3

im thinking crank case issue… I’ll post a dyno graph as soon as I get it from my tuner.


valve float would be springs correct?



Valve spring specs from TFS. I’m running non roller rockers

Onbusy

iTrader: (4)

Valve float could be an issue, and it would explain the low power at higher RPM

I have a Dart LSNext 427 that's on the backburner, with the Dart Pro1 LS3 heads. I had Nick at BTR spec out my cam and springs, and my cam came in at .614/.614 242/254, supposed to peak around 7600RPM, and through the traps at 8200. Unless you have Titanium Valves, your valves are heavier than mine. I'm using the BTR Ultimate RPM Spring Kit with titanium retainers. These are stiffer springs than either of the options listed for the trick flows. 200 lbs closed, 500 lbs open. I was told the .650 springs that came with my Dart Heads would float, and BTR's .660 Platinum Spring kit wasn't enough.

Food for thought.

Mickyinks

Your max hp is early and I bet it shows power and torque crossing over early on you dyno sheet.
either there’s something wrong with the cam or it’s not degreed correctly
hp should equal torque at 5252rpm
so it doesn’t
your torque 500ftlb at 4300rpm
Your hp. 510hp at 6200rpm
took you 1900rpm to make 10hp
Your dyno graph will look very sad if the hp and torque figures are correct
i think the cam has been retarded...
need to see dyno graph

The0nlyon3

maybe the torque is at higher rpm, I can’t recall exactly and will post the graph once I get it from my tuner (doesn’t work weekends)

Mickyinks

even if your torque does crossover at 5252 , it still only pick up 10hp to 6200, so not lookin good

The0nlyon3

Okay, conducted a cylinder leak down test on a cold engine. Here are the results

#1 17%
#2 17%
#3 14%
#4 16%
#5 17%
#6 15%
#7 14%
#8 17%

also I should mention the piston rings are gapped for nitrous.

I would imagine on a warm/hot engine the 17% would be closer to 10-12%.

I should also add that I had to run a shorter (lengthwise) windage tray for clearance in the Holley Ls Swap oil pan.

Can crankcase windage cause excessive pressure that would essentially push against the pistons as they come down during combustion? I have heard this could be an issue.

another reason I slightly suspect this is my tuner turned my rev limiter up beyond 7k and the engine seemed to not want to spin up past 6800. I will get verification from the tuner if it was just stopping the rpm increase or if it was hitting rev limiter..

The0nlyon3

Red line is Holley mid rise single plane and 4150 TB Blue line is stock ls7 manifold and NW 92mm TB

The0nlyon3

For what it’s worth and for anyone still checking in on this thread, I believe I have narrowed down the loss of top end power.

tuner said when he turned up the rev limiter in the Holley pcm it wouldn’t rev beyond 6700. He asked if I had my 2 step plugged in still (was using that as a rev limiter prior to Holley) because it sounded it it was bouncing off of it.

this coupled with peak power being made at 6k and dropping off as rpm increases

and the TFS springs having a 400lb open pressure, me running .646” lift with stainless valves (vs titanium)

valve float is my issue.

I called cam motion and they recommended a spring kit that I’ll order and install, and report back to this thread for anyone that cares.