MELVIN

WELL, MY 502 IS BROKEN IN, SO I DID A LITTLE HARD DRIVING TO COMPARE THE TWO. FIRST, A LITTLE HISTORY.

MY 68 L36 WAS 030 OVER, STOCK COMPRESSION, ALL STOCK EXCEPT A COMPS 270 CAM

A LITTLE AFTER REBUILD, I PLACED A L-68 TRI POWER SET UP ON IT

MY 505/502 WAS THE LONG BLOCK. I TOOK THE FOLLOWING OFF THE 427, AND USED THEM ON MY 502: TRI POWER SET UP, DISTRIBUTOR, WATER PUMP, STOCK EXH MANIFOLDS, VALVE COVERS.

IN OTHER WORDS, IM COMPARING BASICALLY THE SAME MOTORS AS FAR AS SET UP GOES BY USING THE SAME INTAKE/CARBS, EXH MANIFOLDS

WHEN I FIRST WENT OUT IN THE 502, MY STEERING SEEMED SQUIRRLEY. THATS A RESULT OF BEING ABOUT 80 PDS LIGHTER UP FRONT DUE TO ALUMINUM HEADS. THE FRONT END SITS UP HIGHER AS WELL

CAM IDLE FEELS ABOUT THE SAME. FROM 0- TO ABOUT 2000RPM, THE 427 SEEMED TO HAVE A FASTER ACCEL, BUT FROM 2000 RPM UP, THERE IS NO COMPARISON. THE 502 REALLY GETS IT IN THERE AND HIGHER. SO MUCH IN FACT, WHEN I ROMPED IT ON A SLIGHT CURVE, I ABOUT LOST IT BY SWAMPING OUT THE REAR END BY LOSING TRACTION

GAS MILEAGE SEEMS ABOUT THE SAME. MAYBE A TAD WORSE. THE 502 RUNS COOLER BY ABOUT 10-20 DEGREES OR SO, TRUSTING THE STOCK TEMP GAUGE

Garys '68

A 502 with with tri-power. God, I'm jealous.
Guess I'll have to go with the 540.
Gary

Flareside

Thanks MELVIN! I've been thinking about a similar swap, I just can't seem to part with the $$$. I'm suprised that the 502 has less low end than the 427. Are you referring to the 427 when it had the L36 cam or the Comp 270?

MELVIN

Flare,

Good point:

The comps cam 270 over the stick L36 cam was a bad choice for me. I like instant get up and go, which is what the l-36 cam had. The Comps 270 gave up that lower end, but really smacked in the mid range

je68

Also the tri-power is rectangler heads the zz502 is not . The zz502 also is not oval port kind of in between. So the port match is way off I wonder if that is why you have less low tq.

Tom454

MELVINS Tripower is the GM oval port version. There were two versions... oval & rectangular.


Edit: MELVIN-
Correct me if I am wrong about your intake... I've been doing so many of them lately that I can't always remember the facts.
I didn't put your intake casting number in the spreadsheet I gave you, so now I'm not sure.

Tom




[Modified by Tom454, 5:19 PM 11/20/2001]

Allan71

Oval intake on Rect heads is no problem; the other way around would have a flow restriction.

A couple years ago when the 502 first came out, one of the Mags took a 69 L71 and bought the new 502 short block. They used the stock L71 solid lifter cam and reinstalled the original tri-power and heads. The engine made a peak of 550hp running on pump gas and had lots of torque down low. Nice to have those cubes.

je68

But the zz502 are not oval port they are between oval and rectangular. The olly intake that fits right is the GM zz502 intake. If rectangular or oval port intake that doesnt match will work without a loss of HP I would like to know so I could run different intake.

Tahos

Melvin what was your temp running on your 427?I have a 454 that
runs around 210f in this cool weather and when it's hot it runs above 212f.Also what is it running on your new 502?Glad to hear you have
checked it out but don't get too carried away.I know about those
mountain roads around the Smokies.

MELVIN

IM NOT RUNNING THE ZZ 502, SO I COULDNT TELL WHAT TYPE HEADS ARE ON THAT MODEL. THE 505/502 I HAVE IS DEF. AN OVAL PORT. I HAD RESEARCHED THAT BEFORE PURCHASE, BECAUSE I DEFINITELY WANTED THE DRIVABILITY OF OVAL PORT HEADS. NOTHING AGAINST RECT PORT HEADS, ITS JUST IM A DAILY TYPE DRIVER

THE L68 (400HP) TRI POWER SET UP IS OVAL PORT. TOM454 IS CORRECT, AND ILL SEND HIM A COPY OF THE DATA SHEET HE GAVE ME BACK FOR HIS RECORDS

THE TEMP, AGAIN, GOING BY THE STOCK GAUGE, SHOWED EASILY 160-180 WITH A 160 THERMOSTAT, WHICH IS TOO COLD, I CHANGED TO A 190, AND IT CRUISES RIGHT AT THAT, NEVER ABOVE 200, EVEN AT LONG IDLES, OR AT 80 MPH DOEN THE FREEWAY

je68

Melvin your running a lot cooler then me. As soon as I went from 427 to 502 I started overheating. I had to go to Becool alum and now rum at 210 summer or winter no change even it 100 deg outside temp. Also my 502 does not seem to want to to run as good until at least 200deg.
John

GDaina

I retained my stock radiator, but added SPAL twin 11" fans. Runs at 180. needle between the first and 210 mark, actually closer to the first mark.