C30-350 cam & manifold for torque/mileage? - Chevelle Tech
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post #1 of 24 (permalink) Old Jan 12th, 20, 11:55 PM Thread Starter
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Richard
 
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Question C30-350 cam & manifold for torque/mileage?

Got tired of 8-10 MPG out of the "Good-wrench" 350 in my '81 C30 one-ton dually flat-bed.
It's my support truck, hauls the smaller cars and all the junk, does my towing, NOT a speed-performance vehicle.
Seems to me it used to get better mileage but lately it's been pretty bad, around 10 MPG.

I have to replace the flywheel ring gear, and a fender.
So now seems like a good time to upgrade the engine with a new timing chain, improved cam, lifters, and intake.
It's got an almost new Q-Jet on it and it seems everyone insist they are great so I should keep it.
My prior flat-bed Chevy had a "Stock" crate engine, with a Performer cam and manifold added.
It got much better mileage, but I do not remember what carb it had.
Back then I was also running at much lower elevation, and it was all thirty years ago.

So what would be the suggested "Best" cam and manifold for this truck?
Currently it struggles to get over the Sierra's and as said mileage is not great even on level ground.
And no, not intere$ted in an F.I. conversion.

Performer idle to 5000 cam still the best, or has technology improved for flat-tappet 350 truck engines too?
I bought a new Perform RPM Q-Jet intake at a good price but it seems that is the wrong manifold to use. (1500-6500 RPM)
Regular Performer still good, or has real progress been made in the past thirty years?
Like I said, not looking for a lot of "performance", but I do want to be able to cruise with traffic.
So that means 75 or so with 4.27 gears, no OD, 16" truck tires.

I know someone is going to say I'm trying to have my cake and eat it too.
But I've done this in the past so it should still be possible, and easier with all the new tech "Improvements".

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #2 of 24 (permalink) Old Jan 13th, 20, 10:02 AM
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Mr Bill
 
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Re: C30-350 cam & manifold for torque/mileage?

Quote:
Originally Posted by Richard/SIA View Post
Got tired of 8-10 MPG out of the "Good-wrench" 350 in my '81 C30 one-ton dually flat-bed..

Richard,
To be honest with you I am surprised that it even gets that. I don't think you are going to get much better. I think it is asking too much for that little engine. You might pick up a mile or two with a freshen up but at what cost ? I don't know that a cam is going to help anything.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


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post #3 of 24 (permalink) Old Jan 13th, 20, 10:12 AM
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Gene
 
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Re: C30-350 cam & manifold for torque/mileage?

LS conversion candidate!

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post #4 of 24 (permalink) Old Jan 13th, 20, 10:19 AM
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Re: C30-350 cam & manifold for torque/mileage?

I'm going thru the same kind of issue with my 71 C30 Longhorn. I've removed the 402 that's work out. I'm installing a 454 from a motorhome. I've got a 700R4 in it. I'm replacing the 4:10 rear end with a Dana 60 with 3:54 gears. When I bought the truck, 24 years ago, it had a 4 speed in it. I got 10 miles to the gallon. Put in a 700R4 to improve that. May have gained 1 mpg. It'll just be nice to get the truck back to running strong again, and hopefully the new rear will help some. I pull a 5500 lb trailer load with it every week, and it's been having trouble pulling hills any more.

66 Malibu

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post #5 of 24 (permalink) Old Jan 13th, 20, 11:27 PM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

OK, new plan.

Truck is a real PITA to work on, the engine is nearly unreachable over the fenders and under the hood.
I have a very nice engine test stand and an S.E.A. engine analyzer.
So I'm going to put the engine on the stand where I can get to it for tuning/diagnoses.
Once sorted I will put it back in the truck.
I've seen some odd readings on the scope before now, so I hope this will let me get to the bottom of the issues.
Old manifold is coming off for certain, and a direct look at the cam.
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At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #6 of 24 (permalink) Old Jan 29th, 20, 2:30 AM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

Making decent part-time progress on getting the engine out.
Lots of vacuum hoses, air injection plumbing, and stock exhaust manifolds are going away.
Bought a Performer cam kit and latest version used manifold.
They may not be as effective as I hope for but certainly will not hurt.
If nothing else I can add another 100 Lb. to my carrying capacity.
Also bought a book on tuning the Quadra-Puke, maybe with the engine on the test stand I will be able to make it work better for me.
If some pending additional funds come through I may opt to replace the heads too.
Resealing the crank and pan seals while I am at it.
Just hope I do not find anything alarming when I have the pan off, oil pressure has always been excellent.
No idea of the actual mileage on this Good-Wrench engine except that it is not original to the truck.

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #7 of 24 (permalink) Old Jan 29th, 20, 9:21 AM
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8-10 MPG is fine for a one ton
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post #8 of 24 (permalink) Old Jan 29th, 20, 11:09 AM
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Tim
 
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Re: C30-350 cam & manifold for torque/mileage?

I've had many one ton trucks over the last 35 yrs, best mileage was always with a quadrajet carb and a manual trans and at least a set of headers with great free flowing exhaust.
Last older truck with daily use was an '83 K30 1-1/4 ton with a 350 & I got to 12 mpg (loaded, & not babied at all).
With; 4.56 gears, 32.5" tires, 4spd, small cam (in it when bought) (if you can tell it has a bigger cam on cold starts only - it's as large as you need !), performer intake (on it when bought), modified Q-jet, quicker ignition advance springs (careful here - be moderate).All synthetic fluids (using 0W-30 Mobil One engine oil).

The newer design Performer EPS intake is an upgrade over the original design, but I'd be hesitant to recommend an intake upgrade on a ton trk, a stock intake may be best - at least with an auto.

But I would use either '88-'95 TBI vortecs or '96 & up vortec heads for better tq off idle and to raise compression (either of these need their own intake), with headers at the least. If the cam needs changed because of wear then upgrade it from stock - nothing larger than a single pattern like a Comp 260HE (212* @ .050) or Isky 264 Mega (214* @ .050), or smaller, less duration if using a split pattern cam.

T K
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post #9 of 24 (permalink) Old Jan 30th, 20, 10:29 AM
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Bob
 
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Re: C30-350 cam & manifold for torque/mileage?

I would use one of those driver adjustable ignitions to find out exactly how much timing could be used when cruising and how much under load, after you know, you can tailor your standard ignition so you don't have to remember to adjust while driving, also depending on your altitude maybe advance the cam on installation
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post #10 of 24 (permalink) Old Feb 2nd, 20, 12:24 AM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

Engine is out at last.
On a stand, flywheel off.
Even with most of the front clip removed it was a PITA to work on.
Really makes me miss my old '57 one-ton.

I'm going to pull the cam covers and do cylinder leak-down test.
Then pull the intake and heads.
Looking into the exhaust ports I'm unsure if it's been running too rich or sucking oil past the valve guides.
In any case there is a fairly thick crust on the valves and in the ports.

Considering an upgrade for the heads, despite not really wanting to spend another $700.
The new heads have smaller chambers, so would push compression from 8.5 to around 8.8.
It's possible I may end up rebuilding the entire engine.
If so, is 9-1 comp a good idea, or too much?
Iron heads, home elevation around 4,000'.

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #11 of 24 (permalink) Old Feb 2nd, 20, 1:42 AM
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Gary
 
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Re: C30-350 cam & manifold for torque/mileage?

Vortec heads 260 single pattern cam on 108. Guarantee it will be a different truck
427L88 and novadude like this.
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post #12 of 24 (permalink) Old Feb 2nd, 20, 2:04 AM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

Compression limit to keep it a Truck running on the cheapest gas?

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #13 of 24 (permalink) Old Feb 2nd, 20, 4:54 AM
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Re: C30-350 cam & manifold for torque/mileage?

Hi
vortec heads
vortec performer manifold
Q jet carb
camshaft duration ???
cam roller or flat tappet ??? A roller has aggressive ramps on lobe = better performance
compression will be 9:1 thru 9.5 :1 measured no guessing,,, depending on camshaft
1 5/8 headers into a single 3 inch system

Programable ignition
probably a fairly lazy curve and take a while to be fully advanced This is to prevent pre-ignition when under load .
Programmable allows u to tune for a lot of timing quickly without going to far .

A well tuned carby will get almost the same fuel economy as TBI throttle body injection =electronic carby .
This was often the case in the 80`s and early 90`s when injection came to the mass population .
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post #14 of 24 (permalink) Old Feb 2nd, 20, 10:09 PM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

Well, now I know why it's a dog.
Leaking #2 exhaust valve, and 40% to 70% leakage past the rings for every cylinder!
Never overheated while I owned it, but I do know it sat for while under the former owners care.

So it's going to be a full rebuild.
Hoping I can re-use the pistons.
Goodwrench crate engine so "Should" be Std. bore and crank.
I will find out when I get it further apart.

Looking at these heads, https://www.summitracing.com/parts/sum-152123/overview/
Supposed to be a decent upgrade to stock heads at a price comparable to rebuilding the originals.
Chambers for these heads are a little smaller for a mild bump in compression.

I've already bought a Performer cam and manifold, plus headers, so Vortecs are out of the picture.
Vortecs also seem to have a reputation for cracks.

If the pistons do have to be replaced I will build for 9-1, and balance the lower end.
Even a truck deserves a decently balanced lower.
427L88 and Smoothdawg like this.

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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post #15 of 24 (permalink) Old Feb 3rd, 20, 5:55 PM Thread Starter
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Richard
 
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Re: C30-350 cam & manifold for torque/mileage?

Anyone know what the factory spec is for "Down the hole" on a stock GW 350?

Trying to keep this "Budget".
Summit Racing engine kit is about $350 with Moly rings.
Compressed gasket is .039.
Heads I am looking at are 72cc chambers (Stock are 76cc).
More expensive than the lower rebuild kit and still iron.

Trying to figure out how much I would need to deck the block to arrive at 9-1 compression.
From what I've been able to determine so far it looks like I end up with .052" quench.
As I recall that is not a great number, correct?

At these gas prices I want it 100+ octane, leaded, and my windshield washed!
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