Camaroholic

iTrader: (1)

I have a friend who dyno'd 402 rwhp after installing GTP Stage II LS1 heads & a pig cam (I think the pig is something like 227/227 .581 or so). M6, 3.73 gears in a stock 10-bolt. Car has never seen the spray and has under 20k miles on it. Cometic head gaskets were installed (.054", I believe), and 7.35" pushrods were ordered (we have not pulled them out to remeasure). Hooker longtubes, no-cat Y-pipe, Corsa exhaust.

In theory, this combo should yield at least 420-430 rwhp, if not more.

We did a compression check at full preload - 135-140 psi in each cylinder. We loosened the rocker arms to zero lash. Compression went up to 170-ish psi. So obviously, preload on the valve is hurting compression. We think this missing compression is the missing power. We still think 170-ish is a little low, but can't do a leakdown because we don't have a tester.

I'm thinking we have 3 options at this point:

1) Adjustable rockers (with valve cover spacers) - $$$$
2) Different pushrods (would need to really check length)
3) Shim the rockers

Or are we missing something?

GTP suggested going with the adjustable rockers. However, another grand isn't really in the budget - but if it's the only way to get the extra 20-30 hp, then it may happen.

Thanks for any thoughts or suggestions...

Andrew

Fireball

iTrader: (21)

when tightening down the rockers, once you achieve zero lash, how many turns did it take until you reached 22 ft-lb?

My compression checks always read alot higher than 170

A local guy (Moose) has that combo and I recall needing 7.300 pushrods to get his lash right

<small>[ April 08, 2003, 03:43 PM: Message edited by: Fireball ]</small>

Chicago Crew UnderBoss

iTrader: (1)

One real basic and simple but very IMPORTANT question is have you had the car professionally tuned via ls1 edit on a wide band dyno?

If not, DO IT, as TUNING as i am sure you are aware IS ALWAYS HUGE!

MTI 427 C5 Roadster

Pro Stock John

iTrader: (34)

How much lifter preload did you have initially? Did the dyno HP flatten out really early like in the 5500 range? If so you might have too much lifter preload.

Zero lash with stock lifters must be nice and chattery, I'd do 25 thou preload, stock is about 50 thou.

170'ish is okay but it should be at least 170 if those heads are milled.

Formula 1

iTrader: (5)

The car was tuned on a wide band dyno via AMS & Chris Marsh.
The dyno chart flattens out at 6000-6500 at 402hp
I'm thinking about trying a set of 7.30's to see if we can get the preload out. This is my car by the way.
Andrew, the pig cam is 226/226 591/591. Do you see pewter tail lights in your sleep? <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" /> <img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" /> <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" />

Camaroholic

iTrader: (1)

Thanks for the replies, guys. I think Travis covered it, except that the heads are milled .030.

We'll give the 7.30 pushrods a try. If that doesn't work, well, looks like old pewter will have to go back to stock. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" />

-Andrew (ain't seen no pewter tail lights yet)

Brian98

there is a method to determining lifter preload...
I just did this last week.......
In my comp cam instructions......
If i remeber correctly. put in 2 pushrods...make sure your on the lowest point on the base circle((no lift) i used a dial indicator but you can just make a mark on the pushrod where it sits (no rocker on) use the edge on the head as a guide point. put both rockers on tighten them down to 22 ft lbs. rotate the engine 360 degrees. wait for about 5 minutes and let the lifters bleed down. then unbolt the rocker arms and remove,,,,,the pushrod will then rise..mark again with a marker/pencil/etc in the same location where you marked from before. take pushrod out and measure between the line.....you should only have about .030-.060 if you have more a shorter pushrod is a needed. i did this and came up with .100-.110 so i went with the 7.350's,,,i probably could have went with the 7.300's but would have had to shim,,,alittle

Pro Stock John

iTrader: (34)

It's not unusual for folks to shim the rockers to get the correct lifter preload. We fugged up an install a few years ago because we were advised into getting too long a pushrod and we ended up with .120 lifter preload.

Zero lash can make more power if you can tolerate the significant increase in valvetrain noise.

Camaroholic

iTrader: (1)

Travis just called me from the shop.

They pulled a pushrod. For his install, he had ordered "735 pushrods" from Scoggin-Dickey. They interpreted this as the part number that ends in 735, and not a "7.35 inch pushrod"... And that part number is a 7.40" Pushrod!!!!

The 7.35" pushrod ends in 751. Talk about wacky.

Apparently the installer of the h/c didn't measure the pushrod length either. Ah well.

We'll get some other pushrods in there and see what happens. He's <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" /> right now tho. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

-Andrew

Formula 1

iTrader: (5)

Well this changes everything. I'm talking w/ SDPC as we speak to see how fast I can recieve the correct push rods (7.35's) It looks like they will pay to overnight them. We should have some new results tomorrow night. Thanks to all of you that posted with ideas! I'll keep you posted! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
-Travis

F8L Z71

Well, did it get fixed??? <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Camaroholic

iTrader: (1)

Yes. Some 7.35" pushrods were installed, and the compression check was much better this time around. Travis 'feels' like the car is stronger. Haven't done any data logging or dyno pulls yet tho.

Now if he'd just replace that POS factory rear end, he could take it to the track. <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" />

-Andrew

Argon Z

not all dyno put the same numbers out. Before i do anything i would get it tuned and go to a different dyo to compare numbers.
Also i do not think thoes numbers are all bad.

FYI i got my car dynoed and put down 360, a viper GTS put down 365 on the same dyno. OF course it was a mustang dyno, but even for a mustang dyno that is low.

Tim 98z

iTrader: (1)

HM let us know after you dyno. I have Stage II heads and a 224/.581 cam and just dyno'd 407. But i just said Oh we it runs mid 11's so nothing wrong with that. I also have 7.4 pushrods and milled 30tho.

F8L Z71

Cool!

I am having a similar problem I think and we are going to a smaller pushrod also and see if it helps fix the problem.

Good luck on the dyno <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />