Vortec 350 Questions

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Gashog
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Vortec 350 Questions

Post by Gashog »

I'm freshening up an engine for my 2 door Tahoe.
Untouched 350 with cylinder crosshatching intact.
Pistons are Speed Pro Digital Diamond flat tops +6.9cc
Cam is a stock LT1 grind .447" 201 .459" 208 Center-112
I have 1.6:1 rockers but I'm on the fence with those.
Exhaust would be .490" with 1.6
Stainless shorties into stock exhaust.
The trans is a 4L60E with 13 vane pump, hardened sun shell, 2012+ pressure plates, extra steels and clutches, Kevlar brake and Vette servo.
Torque converter is Kevlar clutch. I think 2200 stall.

I measured my new pistons with new rod bearings and they sit .036" down.
I measured the same rod and piston at 4 corners and the block is square.
With a .015" head gasket, I'm getting 9.78:1 compression ratio.
I'd like to run 87 E10 with my black box PCM and stock tune for now.
Do I need to deck my block? Sealed Power says that tight quench engines should run less then .060" squish and the internet says that the sweet spot is .040"
Also I haven't touched the heads but was planning to install LS springs and Summit retainers. There are cheap blue takeouts on ebay all the time.
I'll maybe bowl blend the valve seats but that's all.
Should I use the 1.6 rockers I have..or is that dumb?
This is my personal beat around truck and I just want it to be fun to drive. I think it weighs about 4800lb and I drive around at between 420' and 700' above sea level up here in 'dem 'dere upstate NY where it's very humid.
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Re: Vortec 350 Questions

Post by Keith Morganstein »

Gashog wrote: Wed Mar 21, 2018 7:20 pm I'm freshening up an engine for my 2 door Tahoe.
Untouched 350 with cylinder crosshatching intact.
Pistons are Speed Pro Digital Diamond flat tops +6.9cc
.

I measured my new pistons with new rod bearings and they sit .036" down.
I measured the same rod and piston at 4 corners and the block is square.
With a .015" head gasket, I'm getting 9.78:1 compression ratio.

For what your doing, a mild overhaul build, it will be OK.
The issue is that you bought rebuilder Pistons that have a .020” reduced compression height to compensate for decking the block. So now you either deck the block, get different pistons, or run it.
Automotive Machining, cylinder head rebuilding, engine building. Can't seem to quit #-o
Gashog
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Re: Vortec 350 Questions

Post by Gashog »

That's exactly right.
I chose them cuz $96 and standard ring end gap.
I saved $50 over the KB hypers but cost myself $150 in machining.
I think I'll run it and see.
I'm building another one as soon as this is finished and I'll be able to nickel and dime it over the summer.
It'll need an overbore and undersized so I'll be milking it all summer. Spare engine for one of the three trucks with L35 engines .
If the Tahoe engine sucks, it'll be the spare.
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Re: Vortec 350 Questions

Post by Gashog »

1.6 rockers?
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Re: Vortec 350 Questions

Post by CGT »

Gashog wrote: Wed Mar 21, 2018 8:58 pm1.6 rockers?
Self aligning I assume? Ive fought the same quench issues as you on a couple vortecs. That stupid 1.540 comp height!
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Re: Vortec 350 Questions

Post by ProPower engines »

Gashog wrote: Wed Mar 21, 2018 8:58 pm1.6 rockers?
You better add an extra .030 for spring clearance if you are using 1.6 rockers. But a word of caution. We tested all the name brand entry level and better rockers and a few of the generic brands for ratio and found they were generous on ratio. The rockers tested were both 1.5 and 1.6 ratios and we found that the 1.5 in a perfect geometry yielded 1.59 and the 1.6 were 1.69 respectively. At almost a full ratio above advertised ratios this has caused more valve train issues cause guys never check that stuff and because it says what ever the advertised ratio is that is what is calculated.
Vortec heads can be a PITA with the guide boss that is taller then needed and FYI I recently had 2 engines in here they were both brand new GM crates and the vortec heads were untouched with 1.6 Scorpion tip guided rockers they suffered coil bind bad enough to bend the stock short length push rods. and the stoch PR was too long and they were almost rolling off the tip of the valve. We did see some failures because of the push rod length causing the rocker to roll off the outer edge of the valve tip in new marine engines.
But as for your current deck heights I would cut them regardless of you may have pinging issues with the tall quench.

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Re: Vortec 350 Questions

Post by Keith Morganstein »

For inexpensive SBC replacement pistons, I can often find a Silvolite in standard compression height. Usually for mercruiser applications.
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MadBill
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Re: Vortec 350 Questions

Post by MadBill »

Decking to the 0.040" P/V range would be best, but 0.036 + 0.015 is 0.051", still less than the often-quoted 0.060"-0.080" cliff and if the previous gaskets were composite, probably no worse than stock. I'd run them as-is.
Re rockers, I've seen 10-12 HP for stock 350s with them just on the intake, virtually nothing on the exhaust. As mentioned, you'd have to verify P/V and guide clearance.
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Re: Vortec 350 Questions

Post by Gashog »

Edit: L31 I'm an idiot
Also I'm in no rush to get the truck up and running.
I can assemble the engine and if there's a problem with clearances, I can rethink it.
When I tore it down, I measured the stock piston at .022 down.
The head gaskets were Mr Gasket graphite/composite with copper spray and not the steel GM ones.
Not sure what the story is with this engine. It's in pretty good nick though.
I'll get it decked I guess.
What's the most I can go without intake leaks?
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Re: Vortec 350 Questions

Post by travis »

I think the LT1 cam is on a 117 lsa, versus the stock L31 at 111 lsa.

If you haven’t already, using the GM upgraded injector/spider assembly is a worthwhile upgrade. A little porting in the intake also helps as they are really rough internally. They do tend to get too lean really easily
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Re: Vortec 350 Questions

Post by pdq67 »

Seems to me that you are at .050" quench now with the 1094 shims. Not all that bad.. Or to heck with quench and go for a CR up at 10 to 10.25 to 1 by planning your heads some.. CC them and figure out how much of a cut will need to come off?

Anyway, you might install no more than the good old CC 268HE hy-cam. It should be powerful in your engine. It or an old Isky 264 Mega..

pdq67
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Re: Vortec 350 Questions

Post by Gashog »

Thanks to everyone for your input.
I'm still mulling it all over since I was out all night plowing.
I'm gonna sleep on it and think it over again.
This is the cam I have:
12551705 Hyd. Roller – 201/208 – .447/.459 – 112 – 95-96 Gen II, LT1, w center dowel pin
I'm hoping the flat tops and Vette cam will make the L31 run like it should have out of the box. Nice smooth powah!
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Re: Vortec 350 Questions

Post by rfoll »

Vortec engines came with .028" composition head gaskets. The stock dished piston produced just over 9:1, I measured it. The engine in my 79 impala is very similar to what you propose, including the cam spec. I have 1.6 full roller rockers and it produces a fairly nasty idle for something that small. Excellent torque and mpg.
So much to do, so little time...
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Re: Vortec 350 Questions

Post by Gashog »

rfoll wrote: Thu Mar 22, 2018 8:18 pm Vortec engines came with .028" composition head gaskets. The stock dished piston produced just over 9:1, I measured it. The engine in my 79 impala is very similar to what you propose, including the cam spec. I have 1.6 full roller rockers and it produces a fairly nasty idle for something that small. Excellent torque and mpg.
Saweet!
Did you deck it? Head gaskets?
I was confused about the gaskets I pulled out. I was expecting shims.
I've made up my mind to get the block cleaned off 10 or 15thou. Machine shop will make the final call.
I like the guy (actually his cat) and I want to give him another $150.
I ran it by him a couple weeks ago and he said after decking, no need to lap for the steel gaskets to seal.
Also I put a Scooby together for a friend of mine and I liked it a lot. I took the time and a couple more dollars to get him a decent squish and I think it made a difference.
It was easier for him to tune then I predicted.
I hope mine runs like that.
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Re: Vortec 350 Questions

Post by groberts101 »

I highly doubt L31's came with .028" stock. More like .041" and one of the main reasons I used to hunt down Victor Reinz .035" gaskets during head ports/swaps and rebuilds.
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