Last year I dyno'ed my 71. The result was a best of 250 rwhp @5000rpm and 295 ft. lbs @3500rpm with the following combo:

355 ci
Approx 9.2:1 c/r
S/R Torquer heads
generic hyd. cam (.480" lift, 292 advertised dur/ 230 @.05, 109 LSA)
Torker II intake
Holley 650 mech. secondaries
Hooker competition headers
2-1/2" exhaust

That first run was pretty good, but lost 20hp by the third run. To make a long story short, I traced the problem to crappy hyd lifters that were bleading down as the oil thinned out from temperature.

To remedy that problem, I replace the hyd cam with a Comp 282S (solid flat tappet .495" lift, 236 dur @.05",110 LSA). I also increased C/R to approx 10.0:1 through the use of steel shim gasket, added comp cams 1.52 roller tip rockers, and did some minor port matching to the intake. Theoretically, this should have improved HP to 275 rwhp at the very least, right?

Wrong!! Todays runs were even more disappointing than last time. I actually lost power and pulled a best of 237 rwhp@5000 rpm and 293 ft. lbs @3200 rpm. How is this possible. :confused: :confused: A/F was fairly consistent from 3000-6000rpm at 12:1 - 13:1. There was no valve float,no fuel starvation, cam was degreed when I installed it, total timing of 36* all in by 2500 rpm, and no detectable miss. Everything appears good and the engine runs smooth. In fact, it feels stronger and pulls much harder to redline than the old cam. What am I missing? Any suggestions?

Tom




[Modified by tsw71, 10:36 AM 5/26/2002]

 

Kind of dumb of me to ask this now, but did you check your throttle actuation before you put the car up on the dyno?.
-Steve

 

no points i assume? new wires? cap? 12v to coil?
what size runners in the torquer II?
Have u checked back pressure ahead of muffler?
carb checked and is WOT?
valves not too tight?
was the cam degreed?
valve springs at least 105# seat?
plugs clean?
compression at least 175?
30psi in tires?





[Modified by drives61, 6:58 AM 5/26/2002]

 

Most articles I've read including the manual I received when I installed my Holley heads/cam/intake state to run no more than 34* total advance on todays premium fuel. Also if I read your posting right you went from a 230 degree cam @ .050 (hydraulic) to a 234 degree cam @ .050 (solid)...you ended up actually going DOWN in cam size. It takes on the average of a ten degree increase in duration to remain the same when going from a hydraulic to a solid cam, in other words you lose ten degrees in timing in valve lash on your solid cam. Deen

 

Tom,

I still think it the problem will turn out to be something simple. It sure looked good doing it and sounded very strong!

Chuck

 

Drives61, Thanks for the input. Here's what i've got so far.


no points i assume? new wires? cap? 12v to coil?

Unilite distributor, new taylor wires, new cap and rotor, voltage to coil is good.

what size runners in the torquer II?

I have no idea :D This intake uses stock size gaskets, so runner size is on the small side compared to other single planes.Since the S/R torquer has 170cc runners, I thought this intake would compliment these heads well. Both the intake and heads use somewhat narrow runners to boost port velocity and low end torque, while being large enough to run well up to 6000-6500. I have been discussing this intake with Ganey recently as well as reading mountainmotor's writings about these intakes and am considering switching to Stealth or old style Torker in the future.

Have u checked back pressure ahead of muffler?

No. Please elaborate on this

carb checked and is WOT?

yes

valves not too tight?

Lash is correct. Valvetrain looks good.

was the cam degreed?

I installed it strait up and degreed it to verify both .004" and .05" numbers. All numbers were within 1-2* as is the mfgs expected variation.

valve springs at least 105# seat?

I stuck with the installed S/R Torquer springs which are 100# seat pressure. Should be close enough, right?

plugs clean?

looks good and I have low miles on this set of plugs

compression at least 175?

Last time I checked after cam install, they all ran at about 185

30psi in tires?

38psi (44 is max for these Firestones)

DeenHylton,

Very interesting. This is something I never considered. Time for me to do some reading on this.

Chuck, I sure hope so.

Thanks guys. :cheers: Keep the suggestions coming.

 

If you are looking for HP don't waste your time with an old rotten block. Always start with a new GM short block or a complete GM HO engine. Can't build HP by slapping parts toghter.

 

i know how you feel. everything i have done to my car in the last two years has made it slower :crazy: Im so ready to give up. :smash:

 

tsw71
sounds good.
i am not familiar with the torquerII. My 72 had a holley intake that was too small, that's why i ask. Weiand 8004 plenty big on my 72 now.

Use a vacuum/fuel pump gauge to check exhaust back pressure. Drill a small hole ahead of the muffler (cover later with a hose clamp) Work a length of 3/16 or 1/8 tubing about an inch in. 3-5 feet or more switch to rubber hose, tape gauge to windshield for a quick test on an open road. Need rev-limiter or co-pilot; easy to over rev or hit pole while looking at gauge :yesnod:
2 PSI or less is ideal. 2-4 not so hot, over 5 is awful. Are mufflers new? Any kinked pipes? Any jealous people shove a potato in your tailpipe?

That cam is excellent; the previous cam is too big, for SRT's IMO. Recheck springs; stick a scrap of wood on each one, lean your weight into it; not scientific, but you could find a weak/broken spring that way.

2.02" valves?

Does it pull, on the dyno to 7000? Where does power level off/decline?

I assume a good air filter with a drop base?

What is the plug gap? Try .030"

EDIT: i looked up the 5001, seems it should be OK.


[Modified by drives61, 2:02 PM 5/26/2002]

 

drives61, Thanks for the quick reply. The mufflers are only a few years old. They are stock type turbos with 2-1/2" inlet and 2" outlet. The pipes are also 2-1/2" factory style replacement for LT-1 and have no tight turns or kinks.

The valves are 2.02/1.60. Not long ago, there was discussion here on the forum about poor quality springs and dampers on the World Product heads. Many were finding that the dampers were breaking with fairly low miles. What effect would broken spring dampers have on performance and what would be the likely symptoms? As I said before, there is no hint of valve float, so I'm hopefull these springs and dampers are still good enough.

On the street, this motor pulls strong to 5800-6000 through the first 4 gears. I have not wound out 5th(1:1) on the street for obvious reasons. On the dyno, it pulled to 6000 easily, but not quickly. On the second pull, I ran to 6100. More is possible, but not enough confidence in con rods of motor to find out. :eek: Besides, peek appears to be at 5500, so there seem little point in trying. If you have a chance, download the file for my car that Steve(pacinCA) posted here on the C3 forum last night and let me know what you think.

Plug gap was/is .035". Air cleaner is LT-1 drop base with K&N filter.

My 0-60 G-Tech times were disappointing @5.8 sec. I dump the clutch at 3000 and feather to hook up. Low gears and close ratio of tranny should have produced better times IMO. I thought it might be traction causing the slow 0-60 times, but now.............

The dyno's accuracy did come to mind yesterday, but Chucks Z06 ran after me and ran exactly as expected, so that theory went down in flames with my performance numbers :D

Thanks again, Tom

 

tsw71
"crappy lifters" lost 20hp? i don't buy it. This incorrect diagnosis is the key to the problem.
What oil? 20w50 is a must.
More likely a faulty coil or dist. that degrades with heat. You won't notice a 20% misfire rate; plugs will look fine. :cheers:

 

You may be right on the diagnosis. I run sae 30wt with the high volume pump. The 20-50 that i used to run upto a few years ago always took a long time to thin out enough to bring the press guage down from 70# at cruising speed durring warm up. It made me nervous, so I strated using the 30wt.

My diagnosis of the lifters was based on a couple factors. These were anti-pump-ups that I installed many, many years ago when I was young and dumb. I had no idea that they were to be set at zero lash, so they had always been set with 1/4-1/2 turn preload. In the months leading up the last years dyno day, I noticed the valvetrain making lots of noise like that of a solid cam setup. While quiet when cold, it got louder as oil warmed up. I assumed that the thining oil combined with many years of running the lifters improperly caused damage to the valving of the lifters since there was no one bad lifter, but just simply noise coming from the entire valvetrain. Perhaps a thicker oil would have solved the lifter noise, but I have never been satisfied with any setup for too long and it was time for a change, so I made the switch to solids.

I also have since replaced the blue streak coil that was run last time with the MSD blaster that I now run. Your theory could be valid, but thyankfully, that coil is long gone.

 

Tom
my 2nd choice is springs.
i built my SRT's from bare heads, but the valve job was pre-done.
i had to add .060 shims because the height was wrong, and seat psi was too low.
did you check seat psi, or are you going by the specs?
Dampers eliminate float/ could be the problem if a coil/dist swap does not help. :seeya

 

is there different symtoms of valve float. I have experience valve float years ago and in that case it killed top end power and simply would not rev. Is it possible to experience valve float and not know it?

And yes, I'm going by the specs listed by World Products




[Modified by tsw71, 11:55 AM 5/26/2002]

 

Tom
float will show up often with a pointy peak on the dyno chart, when the springs give up power spikes down. You could just shim the springs for a quick test with a g-tech. .060" shims ok as long a there is no coil bind.

Your combo should be good for 285-315hp on a dynojet.
Last year there was a c5 guy that got, i think, 240 hp, dealer changed coils, modules, cleaned carbon, etc, then months later they found the problem: Spark plugs!
...............

Better, if you are going to hang out at the dyno, get some AFR or trick flow heads, and sell the SRT's. i spent 30 hours porting mine.

 

If his motor is an L46, it already has a forged crank, pink rods, and forged pistons. Why would you downgrade to a cast crank, and hypereutectic pistons?

AC

 

Tom
years ago i met CC at the Circle Track Trade Show.
They suggested the 282S for my 61. They gave me a catalog, which i dug up just now, and i had written in 115-120 seat and 300 open, their advice.
Your springs are junk. :cry

 

drives61, I was wrong on the coil voltage. :bb I was running a ballast resistor in series with the factory resistor wire. The result was 7 volts to the + side of coil at an idle and about 9 at higher rpm. I bypassed the additional ballast and now run 9.5v at an idle and 11-11.5v at higher rpm. The Unilite instructions say to run a ballast if voltage at an idle is within 1v of batt voltage. I am substantially lower than that, but would have to eliminate the resistor wire to gain any voltage. Test drive showed no difference. Your thoughts?


Now on to the next test. :smash: stay tuned

 

tom
i had to bypass the resistor wire on my 72 and use a ballast resistor. Run near the max they allow.
Did you g-tech it? Years ago at the drags i had some ignition problems; i could not tell SOTP a 14.0 from a 15.0 :eek: i had to close the plug gap down to .022(turbocharged 22psi boost 6cyl)

Regardless, those valve springs need to be upgraded. i want 300 RWHP :yesnod:

 

Sounds good. I will play with the voltage today. I also am going to follow a hunch and do a leakdown test on the cyliders. I just remembered that I was a little surprised at the amount of slop in the bore. Last time the heads were off, It appeared that there was more movement up and down than there was side to side. Perhaps it's nothing but my imagination, or maybe the cyliders are no longer round. It's hard to tell with forged pistons when they ere cold, and I regret not taking the time to verify the bore with an inside mic. I will also see about getting some shims for the springs. It may be next weekend before I get to that though. I appreciate your advice and hope you will continue to follow this thread for updates.

Thanks, Tom