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Old 07-08-2012, 10:29 AM
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mods for a motor that's done some miles

I have a 400 sbc that has done some miles, not sure how many but it is still healthy.
I'm looking at getting some closed chambered rhs iron heads and torque cam.
I'm not wanting to rev it past 5000 rpm.
My question is do any of you think these mods will damage the motor seeing as it has racked up some miles?

Many thanks.

Rob.

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Old 07-08-2012, 10:45 AM
How fast is fast enough?
 
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If you feel its marginal then put your money into a rebuild. If its seen 100,000 miles and its carburated chances are its going to have significant bore wear and its rings are long worn out. Even with efi and good oil that many miles will still take a toll on cast rings.

While it may not be as exciting building a good short block has every bit as much effect on power as cylinder heads.
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Old 07-08-2012, 11:16 AM
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old engine

If you plan to freshen the engine in the future,then consider improving the exhaust system and maybe an intake.You didnt say what the vehicle is or application?
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Old 07-08-2012, 12:23 PM
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The cars a nissan patrol 4x4, I have replaced the cast manifold with a Edelbrock
Torker, and I will be doing something about the exhaust shortly.

I use it mainly for towing, and carrying fire wood so torque is the main objective.

I run it mostly on LPG, and know the Torker is not ideal for producing torque @ low rpm on petrol, but with LPG a single plan is the way to go.
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Old 07-08-2012, 12:43 PM
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propane

If its worth freshening the engine,propane will tolerate a lot of compression and timing can be bumped a little.Economy is likely an issue ?If you dont spring for pistons and the engine is good enough for a camshaft transplant then give all the details to a good cam manufacturer for your exact application.Ask them about a tighter intake lobe angle to take advantage of a higher cylinder pressure.Torker is fine on a 400.Put big exhaust on the truck.Dual 3 inch if you have room with x pipe for sound.Headers might be an issue though well worth looking into
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Old 07-08-2012, 12:44 PM
How fast is fast enough?
 
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Has it always ran lpg? If so those engines can easily go 300,000 miles. Exhaust will help a lot. The heads won't do too much at low rpm, a good valve job on what you have would likely be just as good. If you do go for new heads get the smallest port volume you can find and 1.94" valves.
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Old 07-09-2012, 08:08 AM
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Check the compression. If it is not close to factory specs, do a leakdown test.
I would suggest that if the rings are leaking more than about 10 percent, you need to refresh the rings. I know reringing an engine is not flashy, or impressive but why put effort into putting more air and fuel into the cylinder, if it is just blowing by the rings?
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Old 07-09-2012, 02:21 PM
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Pop the pan off and plastigauge a couple rod and main bearings.Do a compression test,if all is well I'd run it.
If you want to keep the rpm under 5000 I wouldn't spend money on heads.
I'd go with a mild cam Comp EX 262 comes to mind,some headers,a nice exhaust and an aluminum dual plane intake. Should be good for 300HP or a few more. Remeber to change the oil pump and T chain while the pan is off.
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Old 07-10-2012, 09:39 AM
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Thanks for all the replies..much appreciated.

Rob.
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Old 07-10-2012, 10:32 AM
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I see no reason you couldn't run an intake like an RPM Air Gap (no need for a heated plenum for LPG like there is for gasoline to promote vaporization), seeing as how the runners are fairly large and the center divider is notched (and could be notched more and/or an open spacer used).

The timing curve needs reworked for LPG, too.
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