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Old 11-28-2018, 02:33 PM   #1 (permalink)
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SBC gurus, advice needed.

Nearing completion of my SBC powered DJ5 build and after some advice for motor goodies.

Motor is originally out of an 80s truck, (TBI non vortec) 350. Looking for cam advice. Currently have a set of Votec heads with Beehive springs and retainers Summit 1.5 roller rockers and oversized valves. Intake is an air gap style. Will be running propane and flat top pistons, ideally Iíd like to be in the 350ish HP range.

Looking for the proper cam setup to give a decent lopey idle and a broad power band. Cam selection is overwhelming to say the least and I donít want to have to buy shit twice. Advice is appreciated.
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Old 11-28-2018, 04:30 PM   #2 (permalink)
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Generally speaking, the better the lope in the idle sounds, the higher up in the rev range the power is going to be due to the valve overlap timing and such. I guess a good general question would be "What would be an RPM range you would be comfortable driving the truck in?"
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Old 11-28-2018, 07:56 PM   #3 (permalink)
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Ok, well if the meat is in the 2000-up range that would be ideal, but I’d also like it to not be a dog off idle up to 2000-2500. I may be asking for something that isn’t attainable.

This will be an east coast rig, I want some crawlability for some slow technical rock sections and also have the mid/high power for loose hill climbs that require some wheel speed, if that helps.

I will also admit this is my first SBC build, so I’m in unfamiliar territory.
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Old 11-29-2018, 06:38 AM   #4 (permalink)
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Comp ratio on that motor is about 8.5:1 IIRC...Vortecs had 64cc chambers same as the 193's that you most likely removed so comp ratio should be about the same. Propane has a higher "octane" so you could choose a cam and go tighter on the lobe sep and duration to build cylinder press and use more lift or even 1.6 rockers (trial on Int or Exh...OR both). Generally lopey cams have a lot of overlap/duration which "bleeds off" cylinder press (power) at low revs. There are some street cams that offer that "lope" but I am not too familiar with them...I see them as a band-aid.

EDIT: Oops just saw you're going w/flat tops.....so around 10:1...depending on piston selection, machining (block decked or not, etc...). So the above may no longer apply. I'd still look into the milder "RV " style cams. Do you have a preference between hyd. tappet vs. solid lifter, vs. roller? The best advice is to call 3 different cam tech lines and tell them what you have and want the outcome to be.

Last edited by cj8scrambld; 11-29-2018 at 06:51 AM.
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Old 11-29-2018, 07:19 AM   #5 (permalink)
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This: In my opinion, anymore cam than this will require a compression increase.

https://www.jegs.com/i/Comp-Cams/249...0aAlMFEALw_wcB
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Old 11-29-2018, 07:51 AM   #6 (permalink)
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Originally Posted by cj8scrambld View Post

EDIT: Oops just saw you're going w/flat tops.....so around 10:1...depending on piston selection, machining (block decked or not, etc...). So the above may no longer apply. I'd still look into the milder "RV " style cams. Do you have a preference between hyd. tappet vs. solid lifter, vs. roller? The best advice is to call 3 different cam tech lines and tell them what you have and want the outcome to be.
Stock deck height, flat tops with 2 valve reliefs.

I was leaning towards hydraulic lifters to take some of the guess work out.

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This: In my opinion, anymore cam than this will require a compression increase.

https://www.jegs.com/i/Comp-Cams/249...0aAlMFEALw_wcB
Too much lift. I need to be .470 max, other wise Iíll be into retainer/seal clearance issues.
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Old 11-29-2018, 02:47 PM   #7 (permalink)
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What LPG mixer are you using? It might be the choke point making your heads and cam kind of irrelevant.
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Old 11-29-2018, 03:01 PM   #8 (permalink)
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.480 lift on a small block really isn't all that much in a 350ci if you want to push 350hp. That is unless you want to step up the cubes to a 383
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Old 11-29-2018, 03:12 PM   #9 (permalink)
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Quote:
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What LPG mixer are you using? It might be the choke point making your heads and cam kind of irrelevant.
This.
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Old 11-29-2018, 06:58 PM   #10 (permalink)
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Too much lift. I need to be .470 max, other wise I’ll be into retainer/seal clearance issues.
That limit is with stock springs.....You have beehive springs and I am pretty sure that allows up to .550 lift without machining....going of memory, it's been a while

Edit....found this article.....is this your set-up? https://www.hotrod.com/articles/vort...pring-upgrade/

Last edited by cj8scrambld; 11-29-2018 at 07:00 PM.
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Old 11-29-2018, 08:42 PM   #11 (permalink)
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Years ago I ran Rhodes lifters that bled down the high lift at low rpms so it pulled better at lower rpms. They stayed pumped up at higher rpms and used all the lift. My engine had a much wider powerband, about 1800/2000 to 6000.
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Old 11-30-2018, 07:56 AM   #12 (permalink)
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What LPG mixer are you using? It might be the choke point making your heads and cam kind of irrelevant.
I have to check again, itís not an Impco, it is a 4 barrel base plate and has the standard 5 1/8Ē air cleaner diameter.

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Originally Posted by cj8scrambld View Post
That limit is with stock springs.....You have beehive springs and I am pretty sure that allows up to .550 lift without machining....going of memory, it's been a while

Edit....found this article.....is this your set-up? https://www.hotrod.com/articles/vort...pring-upgrade/
Iíve came across some conflicting information myself, hence the thread.

But yes. That is what I currently have.

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Years ago I ran Rhodes lifters that bled down the high lift at low rpms so it pulled better at lower rpms. They stayed pumped up at higher rpms and used all the lift. My engine had a much wider powerband, about 1800/2000 to 6000.
This sounds exactly like what Iím after.
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Old 11-30-2018, 03:35 PM   #13 (permalink)
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Iíve came across some conflicting information myself, hence the thread.

But yes. That is what I currently have.

Then you're good to go with more lift.
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Old 11-30-2018, 08:27 PM   #14 (permalink)
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Xe262h from comp cams

In the middle of building pretty much the same motor. 4.060 pistons 6cc flat tops, vortec heads, performer intake, ls6 valve springs and comp 787 retainers to allow the lift of the cam with the vortec heads.


http://www.compcams.com/v002/Pages/387/XE262H-10.aspx

The static compression ratio is right at 10:1 but more importantly the dynamic is right at 7.53:1 so safe with vortec heads.

Keep your squish/quench in check also. Has alot to do with keeping detonation under control
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Last edited by RSWORDS; 12-01-2018 at 06:57 AM.
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Old 12-01-2018, 11:34 AM   #15 (permalink)
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Also dont forget to put a coolant bypass hose from the pump to the intake
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Old 12-04-2018, 09:26 AM   #16 (permalink)
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Also dont forget to put a coolant bypass hose from the pump to the intake
Was going to run out the pump, to propane regulator, out to intake.

Get two birds stoned at once.
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Old 12-04-2018, 10:46 AM   #17 (permalink)
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Was going to run out the pump, to propane regulator, out to intake.

Get two birds stoned at once.
That should work
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