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Broken 454, options?
A scuffed piston in a .030 over 454 led to some knocking so I guess Im due for a rebuild. Currently has 088 rectangle heads and an unknown hyd flat tappet cam. Dual plane alum manifold, Q-jet and stainless marine exh. I'm thinking of building a 496 with this cam. What do you guys think?
http://i537.photobucket.com/albums/f...ps8f75b94a.jpg |
Just be careful and make sure you have an exhaust system that won't present reversion problems for you. I'm sure the cam will make fine power as if you ask ten different people you might get ten different answers. But your durations up in the 240's at .050 will definitely wreak havoc with many brands of manifold systems with short risers. Best regards
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Here is the exhaust, will it be problematic?
http://i537.photobucket.com/albums/f...ps82785163.jpg |
Rectangle port heads, cam with 240* @ .050, nearly .600 lift, and 110* LSA, and they are running what appears to be a stock Merc intake and a Q-jet? Just seems to be a lot of cam and heads for 750 cfm - unless the carb has been reworked considerably.
You will find that most of the pro engine builders on this forum recommend a hyd roller over a flat tappet, especially with that kind of lift. Yes, it's more expensive, but it will also run for the long haul if set up properly. Don't skimp on the valvetrain on a marine engine - buy the best springs, pushrods and lifters you can afford. Looks like Stainless Marine exhaust with long risers. Should be able to run a cam with pretty good overlap with those. Still, they can develop leaks. I would wait for the tear down to see what happened - that could affect the direction you take going forward. I have been told by people who should know their stuff that the longer stroke of a 496 could make an engine more prone to reversion. The piston is developing more speed on the downward stroke, so it tends to pull the intake and exhaust pulses back into the cylinder more easily. If you are on a limited budget, stay with the 4 inch stroke and concentrate on good heads and valvetrain. I learned the hard way - now I'm doing it for the second time in three years. |
Does that exhaust just have an outter tube welded onto the risers, without actually changing the point where water and gases mix? Looks like a owner modification to risors that are originally for silent choice.
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I have built several 496 strokers with great success.
Save yourself the headaches, have RMBUILDER Bob Mandra grind a custom roller for you, and your needs. You will not have to worry about reversion etc. Roller cam is the only way to go. A longer stroke has nothing to do with reversion. It caused by exhaust pulses. Ask Bob when you talk to him, he will explain it in simpler terms. |
i agree,call bob,im pretty sure he is going to say that cam with that exhaust system is going to create some reversion.
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Here is what I did and I talked to Bob also and I use Mercruiser 496 aluminum exhaust.
*1987, MIE/340 (7.4) 454 4 bolt main Big Block Dip it and hone the decks and cylinders cut .060 over Block was detailed with all casting debris removed *Scat 9000 Crank 4.25, 496 stroker *Scat 26385P - 6.385 in. Connecting Rods - Bushed -I Beam Forged 4340 steel Howards Cams 120255 - Max Torque Retrofit Hydraulic Roller Camshafts, Hydraulic Roller Tappet, Advertised Duration 288/294, Lift .585/.610, 112 L/S Howards Matching Valve Springs 98636 - 130# / 330# Cloyes Gear 9-203 - Cloyes Wear Plate, 031 in. Thick, Maxspeeding Hydraulic Retrofit Roller Lifters *Probe 496 Dome Top +18.0cc - SRS Piston Set Clevite 77 Cam Bearings Federal-Mogal 4400 M20 Main Bearings King Engine Rod Bearings CR849HP Cloyes true double roller timing chain Mahle - Plasma Moly Coated piston rings Melling 10778C (Anti-Cavitation) oil pump Melling HV oil pump shaft. New Harmonic Balancer Rotating Assembly Fully Balanced Comp Cams High-Tech pushrods #7954 Completely refreshed Chevy Heads 14096188 / 454 Open / 118cc / 3angle valve APR head bolt sets ARP 1.90 rocker studs Norris S/S 1.7 roller rockers Seal Power Gasket set EDELBROCK BBC R2 AIRGAP INTAKE Pro Comp 2752 Fuel Pump MSD Ignition Pro Comp distributor Super Stock coil 8mm Accel Hi performance wires New single wire alternator Mini (gear reduction and fully marine) starter Edelbrock 800 carburetor 12" aluminum, oval air cleaner (with K&N filter) Brass freeze plugs Stainless steel bolt set 4” Stainless steel "tall" risers 496 MerCruiser exhaust manifolds Sherwood motor mounted raw water pump |
Just out of curiosity, aren't those risers long enough to not have to worry about reversion?
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Originally Posted by Budman II
(Post 3921883)
Rectangle port heads, cam with 240* @ .050, nearly .600 lift, and 110* LSA, and they are running what appears to be a stock Merc intake and a Q-jet? Just seems to be a lot of cam and heads for 750 cfm - unless the carb has been reworked considerably.
You will find that most of the pro engine builders on this forum recommend a hyd roller over a flat tappet, especially with that kind of lift. Yes, it's more expensive, but it will also run for the long haul if set up properly. Don't skimp on the valvetrain on a marine engine - buy the best springs, pushrods and lifters you can afford. Looks like Stainless Marine exhaust with long risers. Should be able to run a cam with pretty good overlap with those. Still, they can develop leaks. I would wait for the tear down to see what happened - that could affect the direction you take going forward. I have been told by people who should know their stuff that the longer stroke of a 496 could make an engine more prone to reversion. The piston is developing more speed on the downward stroke, so it tends to pull the intake and exhaust pulses back into the cylinder more easily. If you are on a limited budget, stay with the 4 inch stroke and concentrate on good heads and valvetrain. I learned the hard way - now I'm doing it for the second time in three years. |
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