bcarpman

As with most topics, I seem to get a variety of advice on this one.

I'm building a 490cuin BBC. Hopefully somewhere around 475-500HP. Idle is important.

Just calculating by VE, I come up with 750cfm as the perfect sized carb, but some have told me I should definately step up to an 850.

I'll be using a roller cam from a HP500. What size carb did the old carburated HP500 run?

ANyone run either an 850 or a 750 on a similar motor? What are the tradeoffs at that HP level.

Thanks again

BajaRunner

800 cfm carb

baja36ft

why use that cam when there are so many better ones!!!!!!!!

bcarpman

I guess I'll answer that question with another question. How do you define "better"? Higher lift (bad for valvetrain durability)? More overlap (bad for idle, reversion and driveability)? Or do you know something about the lobe profile that I don't know?

Hope that doesn't sound sarcastic, but your question was a little open ended. That cam is obviously capable of making 500HP (all I want), idles like a champ, and reportedly has no reversion problems.

BajaRunner

an hp525 vs an hp500. look at those cam specs.

Griff

That cam will revert. That is the reason that merc switched to a taller Gil riser.

SB

iTrader: (1)

Merc HP500 Carb
Crane Gen VI#169611 Grind#HR-284-2S-10IG
Adv 284, 292 at .004” Lift with 1.7 .576 / .598
At .050” 222, 230
ICL 105, ECL 115
LSA 110

Part Number: 169611 Grind Number: HR-284-2S-10 IG
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1996 Up CHEVROLET 8 HYD. ROLLER WITH CAST IRON DISTRIBUTOR DRIVE GEAR
Engine Size Configuration
454-502 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 339 @Valve 576 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 352 @Valve 598
Rocker Arm Ratio 1.70

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 33.0 BTDC 71.0 ABDC 284 °
Exhaust 77.0 BBDC 35.0 ATDC 292 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99896
Loads Closed 150 LBS @ 1.900 or 1 29/32
Open 441 LBS @ 1.330
Recommended RPM range with matching components
Minimum RPM 2500
Maximum RPM 6000
Valve Float 6500

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 6.0 BTDC 36.0 ABDC 105 222 °
Exhaust 50.0 BBDC 0.0 BTDC 115 230 °

Remarks:
CRANE 16535-16 LONG TRAVEL HYDRAULIC ROLLER- LIFTERS MUST BE USED WITH GREATER THAN .570 LIFT CAMSHAFTS TO PREVENT ALIGNMENT BAR DISENGAGEMENT.

bcarpman

Everyone seems to have different specs for that cam, or maybe it's the confusion over early model non-roller, or the confusion over HP500 vs. HP525, but I'm guessing it may also be because it seems like people make "relpacement" cams for the motor and some are quoting those specs. Not sure which, but the one I'm looking at is a Hyd roller with:
226/226 @.050 and 545/540 lift LSA114
Which seems like an excellent compromise from a lift vs. durability standpoint, and from what I've been able to decern, people seem to be very happy with the idle on cams of around 114LSA.

Anyone have any thoughts on the Carb?

blue thunder

If you go with the 800cfm and a dart single plane intake and run a pcv valve you can mimic the hp500 staggered jetting. That would eliminate a lot of tuning time. I run .060 over 454s with ex hp500 carbs and single plane intakes and really like the combo. The air gap style of the dart is good in a marine application due to keeping the engine cooler in the enclosed engine room.

BT

SB

iTrader: (1)

800 mechanical to 850 vac secondary carb should be used on a 500cid engine.
===================

It seems your a little purturbed (sp ?) .

Who's everyone ? Cam companies or just people ?

OSO is a blue motor website - if you know what I mean. A ton of knowledge here. I'd give people more credit. Other than me - I answer a bazillion questions a day all over the place so my head get's 'locked' or 'frozen' a few times each day.


The HP500 (blue carb'd motor )used the HR '721' grind from Crane. Gen V and Gen VI motors. Just different cam cores.

The Bulldog 540cid 500hp motor used a big flat tappet. Also from Crane I believe.
In fact the older 454cid's used a Crane flat tappet.
The 500EFI and 525EFI also used Crane cams, but HR's.

Here's the 500EFI cam.

Merc 500EFI
Gen VI #169621 Grind#HR-292-2S-14 IG
292,298 at .004” Lift with 1.7 rocker .598” , .610”
230, 236 at .050”
ICL 109 , ECL 119
LSA 114


Part Number: 169621 Grind Number: HR-292-2S-14 IG
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1996 Up CHEVROLET 8 HYD. ROLLER WITH CAST IRON DISTRIBUTOR DRIVE GEAR
Engine Size Configuration
454-502 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 352 @Valve 598 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 359 @Valve 610
Rocker Arm Ratio 1.70

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 33.0 BTDC 79.0 ABDC 292.0 °
Exhaust 84.0 BBDC 34.0 ATDC 298.0 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99896
Loads Closed 150 LBS @ 1.900 or 1 29/32
Open 454 LBS @ 1.310
Recommended RPM range with matching components
Minimum RPM 3000
Maximum RPM 6500
Valve Float 6800

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 6.0 BTDC 44.0 ABDC 109 230.0 °
Exhaust 57.0 BBDC (1.0) BTDC 119 236.0 °

Remarks:
CRANE 16535-16 LONG TRAVEL HYDRAULIC ROLLER- LIFTERS MUST BE USED WITH GREATER THAN .570 LIFT CAMSHAFTS TO PREVENT ALIGNMENT BAR DISENGAGEMENT.