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Old 07-30-2010, 08:04 PM
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New 350 sbc build

Hey all, I have a 1972 Chevy truck and I recently upgraded my 1974 350 sbc with a fresh paint job and some vortec heads and intake. I reused my long style tube headers and my Edelbrock 600 cfm card on it and added a 260 duration cam to the mix. It is set at about 15 deg initial timing and about 34-35 total timing. The engine sounds great except when accelerating. It is smooth and has power, but it doesn't sound the same as it used too with my old setup. Before it was just stock with a 4bbl intake and a 278 duration cam and the sound is alot different when driving it. I have 2-1/2 dual exhaust all the way back also. Could it be resonance or something to do with the turbo mufflers on it with this setup now? I thought possibly it might need an H pipe or something. Any ideas?

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Old 07-30-2010, 10:12 PM
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Add a H pipe and some resonators on the tips. Turbo mufflers have always had a drone at a certain RPM. You`ve made alot of changes to your combo, so now it`s getting more air and fuel, which means it`s creating more exhaust gasses plus the larger cam`s longer duration and it changes the exhaust note somewhat. If you just added headers when you did the upgrades headers cause the note to be different as well. When flow changes, so does the sound. A H pipe will balance the flow between the two banks which makes the sound blend as one. The resonators should eliminate the drone.
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Old 07-31-2010, 07:26 AM
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I forgot to mention that I have 3 or 4 inch tips on the back already. The long tube headers (Dynomax) I already had on there, but I freshened them up as well. My new cam is a 260 duration and the old cam was a 278 duration. Both cams are the Crane Energizer.
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Old 07-31-2010, 10:48 AM
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Do your tips have resonators? if so cool, just add a H pipe to balance the flow and sound and your there.
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Old 07-31-2010, 10:53 AM
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camshaft change

The new camshaft has more valve duration and thus more valve overlap than the previous cam. Longer valve duration and increased valve overlap will "blow down" (evacuate) the cylinders and a greater portion of the incoming fuel/air mixture wil flow out the exhaust system at lower engine speeds. That of course reduces low RPM power and torque and moves it to a higher RPM level. That will make the exhaust system sound quite differently a crusing speeds.

You should install a lower rear end gear ratio so the engine will get to cam range quicker. That is why the factory cams and valve train is different in cars with a manual transmission than those found in cars with a automatic transmission.
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Old 07-31-2010, 11:33 AM
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The tips don't have resonatore in it, just regular tips. Can they be added to the tips? Also, doesn't a 278 duration cam have more duration than a 260 one? My new cam is a 260 and the old one is a 278. The new cam is 1000rpm to 4600 recomedded with valve float at 6500. Cam is as follows:

Crane Energizer 260 H10, lift is 427 @ exhaust with 1.5 rockers. Cam timing @ .050 is duration of 204 deg.
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Old 07-31-2010, 11:43 AM
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Quote:
Originally Posted by MouseFink
The new camshaft has more valve duration...
The new cam has 18 LESS advertised duration than the old cam.
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Old 07-31-2010, 11:46 AM
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Quote:
Originally Posted by stfinney
Hey all, I have a 1972 Chevy truck and I recently upgraded my 1974 350 sbc with a fresh paint job and some vortec heads and intake. I reused my long style tube headers and my Edelbrock 600 cfm card on it and added a 260 duration cam to the mix. It is set at about 15 deg initial timing and about 34-35 total timing. The engine sounds great except when accelerating. It is smooth and has power, but it doesn't sound the same as it used too with my old setup. Before it was just stock with a 4bbl intake and a 278 duration cam and the sound is alot different when driving it. I have 2-1/2 dual exhaust all the way back also. Could it be resonance or something to do with the turbo mufflers on it with this setup now? I thought possibly it might need an H pipe or something. Any ideas?
If you had a Q-jet and you NOW have an Edelbrock carb, that alone changes the overall sound of the engine, mainly when under acceleration. The change in exhaust 'tone' is likely a result of the cam swap.
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Old 07-31-2010, 01:48 PM
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I am using the same Edelbrock 600cfm carb from before. I really don't like the sound of my truck when accelerating. It sounds worse than glasspacks, LOL. Sorry, no offense to anyone who likes them, I just never cared for glasspacks. Do you think flowmasters or just adding some resonators will help it? Summit has some h-pipe kits for about $40, so I will probably do that anyway. X pipe would be nice but can be expensive.
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Old 07-31-2010, 08:58 PM
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I read that within 3 feet of the collectors is best for the h-pipe. Is that about right or is there a better location?
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Old 07-31-2010, 09:29 PM
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Quote:
Originally Posted by stfinney
I read that within 3 feet of the collectors is best for the h-pipe. Is that about right or is there a better location?
That ought to be fine, shoot for an easily accessible spot after the collector and before the mufflers.
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Old 08-02-2010, 08:27 PM
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Ok, I have another question. Could the noise be from something else? When the engine was being put back together, I set all the valves and zero lash to the best of my ability, one at a time as I rotated the engine. The engine has a little light ticking but not much at all and idles great and sounds great. Could the valves be out of adjustment a little and not be loud or do you think they are ok? I'll try and get a sound clip of what I am talking about to see what you think.
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Old 08-02-2010, 10:17 PM
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what does it sound like?
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Old 08-03-2010, 05:49 AM
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Vortec heads generally don't want more than 32 of total timing,
Also, I bet if you took those big tips off and went to some 2.5" tips, it would help. I put a set of 4" tips on my S10, loved the way they looked, hated the way they made it sound, kinda like an echo.

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Old 08-05-2010, 09:14 AM
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your exhaust is too big for you cam. I would run a single 3" exhaust with a good muffler, forget the duals.
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