Dual pattern cam makes up for poor exhaust port. Surely it won’t hurt. Oem heads are done by .440 lift. The comp 260 is another good grind. 212/212-.440
Cheap 318 performance mods.
- Thread starter Calhoun
- Start date
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Dale Davies
Well-Known Member
My experience of pulling wrenches for 30 years points not to the Magnum having less cylinder wear than the LA engines because of design. All manufacturers engines took a substantial leap in engine life with the introduction of EFI. The throttle body systems improved fuel atomization so wear was reduced due to less cylinder wall washing. Where the real jump ahead was going to sequential multiport EFI. This really tightened up fuel metering and distribution. The pressure the fuel is injected at went from 15PSI to around 50PSI which created much better atomization. If you put the SEFI from a Magnum on a rebuilt 273 or 318 LA, I see no reason they would not last 300k miles of daily driving. NOTE: DISCLAMER on that, not a race engine! Modern piston ring technology and materials with the current plateau honing cylinder finish is also a good start on the process.
Dale Davies
Well-Known Member
OK. I can accept that. Just my experience and the technology has come a long way.
Just my opinion is to build a torquey engine for the street first, keeping in mind the possibility of installing gears or/and converter later.
Just my opinion is to build a torquey engine for the street first, keeping in mind the possibility of installing gears or/and converter later.
Dale Davies
Well-Known Member
Look into David Vizard's videos. Dual pattern does compensate for a less than beneficial exhaust system. OEM iron manifolds definately fall into the less than beneficial category in most cases. There have been a few pretty good ones for performance engines. Cast manifolds for the OEM are inexpensive, easy to fit space wise and pretty reliable, with respect to warranty times.
Going to 40° exhaust seats aids low lift exhaust flow and thus blowdown even with a less than beneficial exhaust. This lets you use a camshaft with less duration split than commonly available on split pattern cams. Something like +2° to +4° more than the intake duration, or possibly a single pattern cam which tends to a slight bit more torque.
Exhaust lift is not as critical as intake lift. The intake on a NA engine is at best atmospheric pressure of 14.7 PSI. The exhaust at valve opening is 70PSI to 120PSI. A header designed for the intended operating RPM range makes use of the supersonic exhaust gas mass to definately improve the efficiency. Frequently dyno testing shows an improvement with exhaust rockers with .05 less ratio. Only on the dyno or track times can that be determined.
I can’t own it, yet I’ve experienced it.
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