kmcn47

looking at building a stockish rebuilt vortec 350 with some better heads (bigger chamber, larger runner, bigger valves) and topping it off with one. i have a partslist I've put together if anyone wants to give me their thoughts on it or what i should/could do differently or better.

Street Lethal

iTrader: (16)

It's been awhile since someone went this route. If this is really happening, definitely looking forward to seeing this build being documented. Throw up the parts list so we can all compare...

- Rob

kmcn47

yeah the pro street look is just too cool lol.

starting with junkyard l31 out of a 96-2000 silverado/tahoe/suburban
swapping heads for a cheap brand i found, power products aluminum heads, 205cc intake 72cc chamber 2.02 intake 1.60 exh
comp cams "nitrous cam and lifter kit)
comp ultra gold 1.5 rocker arms.
pretty stock rebuild kit with chromoly rings and dish pistons
some ebay special longtubes (the chinesium stainless ones)
arp head/rod bolts and main bolts for peace of mind
milodon "diamond stripper" windage tray
holley 130gph mechanical pump regulated to 7-8 psi
holley 750 blower carb
keeping the 700r4 with an overhaul to handle more power and torque and either beefing up the 10 bolt (83 z28 no idea about the rear end) or thinking about the tnt fabrication 8.8 rear end.

mostly just want to daily drive this car but i'd also like to track it for atleast a few weeks out of the season (it rains so much here)
i have no idea what heat range plugs i'd need, i've read about a few guyus running R44lts plugs and i know blower motors like 112-115* LSA and alot of initial timing and not alot of advance.

again i'm a total newb when it comes to FI and any criticism is welcome.

kmcn47

Correction to those heads.
PROMAXX freedom series heads. 225cc intake runner 62cc exh, 2.08 intake valves 1.60 exh. 72cc chambers. max lift .575. bronze valve guides, 3/8 rocker arm studs, not crazy about that but they're not a huge problem with lower rpms.

https://www.summitracing.com/parts/pmx-2122/overview/

Confuzed1

iTrader: (4)

I'm not really familiar with the 177 blowers, but I am familiar with running small blowers and have been running a MP122H Magnacharger on my car for 6 years or so. Sounds like you've done some research. I would always recommend forged rods, pistons and crank - BUT - you can get away with stockish internals if you tune it right - and that's important. As you said, they do need a lot of advance at idle with a short advance curve. I've also heard of others just locking the advance out all together and setting the timing at around 28 degrees at idle.

Mine seems to like about 21 degrees of advance at idle, and I have a short timing curve that maxes out at 36 degrees all in by 2800 RPM. I also run a boost retard that takes out anywhere from 1-3 degrees of timing per pound of boost depending on where I have my dial set. I actually have a MSD boost retard sitting in my garage doing nothing that I intend to sell. I switched to a (I think) MSD 6BTM box that not only retards boost, but has the multi spark to help clean things up at idle. Tuning will take a lot of trial and error until you get it dialed in. Every setup will need different amounts of timing advance, rate of timing increase and carb jetting requirements. If you're going to stick to a carb, I'd recommend getting a MSD box. It'll help clean it up at idle quite a bit. You need to keep it on the rich side to be safe, lean it out too much and bad things happen quickly. I ran a carb for quite a while, and switched up to a FItech unit, so I can set cruising A/F ratios and different ratios while under boost. Keep in mind, that when you get a lean backfire with these roots blowers, it sounds like a shotgun going off and it can damage things. Always give the throttle a good shot of gas prior to starting to make sure you don't get a lean backfire when the engine is cold....

kmcn47

anyone know how much of a dish i need to get the L31 down to around 8:1 8.5:1? the 72 cc heads will help i know but idk how much they'll change compression. i honestly don't know how to calculate it that well

QwkTrip

iTrader: (22)

Calculating static compression ratio is pretty straight forward. It is the total volume of the air space inside the cylinder and combustion chamber with piston at bottom dead center, divided by the volume with piston at top dead center. The hard part is getting the data you need to make the calculation. You need to know,

* Cylinder bore diameter.
* Crankshaft stroke length.
* Height of piston above or below deck with piston at top dead center.
* Piston dish or dome volume.
* Head gasket bore diameter and compressed thickness.
* Cylinder head chamber volume.

This will give you a reasonable estimate without going to the gnats *** with other fine details. I can help you with the calcs if you get the data.

kmcn47

stock 96-00 L31. the heads i mentioned. 72cc chamber. anyone recommend a head gasket? stock copressed for a l31 is 0.28 thickness. i know most fel pro replacements are .38 or .41 compressed thickness. that should help with CR. anyone know the stock dish on the l31 pistons? how much more to get it to around 8, 8.5:1? stock l31 CR is 9.1-9.4:1 from what ive read. hard to get straight answers.

QwkTrip

iTrader: (22)

Earlier you mentioned rebuilding the engine. That could change bore diameter and deck height too.

You can fiddle with gasket thickness to alter compression ratio but really the gasket thickness should be more focused on minimizing quench.

QwkTrip

iTrader: (22)

If you can find a copy of the engine service manual it will have all the specs in it.

kmcn47

i was planning to rebuild yeah but not overbore or undersize the rods. there are alot of low miles 90s chevy trucks in pick n pull here (wa state) so i was hoping to find a good low miles example. stock specs 9.4:1 CR from GM, bore x stroke: 101.60 x 88.39 mm, stock vortecs are 64 cc chamber. my heasd are 72cc chamber. stock gasket is 0.28 compressed. stock dish on pistons is 11cc from what i can find.

QwkTrip

iTrader: (22)

Still missing some info. Walk down the list I gave you.

anesthes

iTrader: (12)

8:1 ???

It won't get out of it's own way!

-- Joe

Orr89RocZ

iTrader: (20)

QwkTrip

iTrader: (22)

Not sure if this is entirely correct but this info is what I found in a few minutes on Google.

L31 engine
Bore: 4.00 inch
Stroke: 3.48 inch
Compression Ratio: 9.4
Head chamber: 64 cc
Piston: -12 cc
Deck height above piston: 0.025 - 0.030 inch
Gasket diameter: 4.10 inch
Gasket thickness: 0.028 inch

These numbers give about 9.2 compression ratio but it goes up to 9.4 if you tweak the deck height to 0.015 inch. Close enough for government work. Looks like a 72cc head would deliver somewhere around 8.7 or 8.5 compression ratio.

kmcn47

thats BEFORE the blower goes on haha

thanks for the assist everyone. i'm doin my best to look things up but on the ship the internet is spotty at best and about as fast as it was in 1991 when it does work haha. awesome to hear the heads help so much i may not have to go crazy with the pistons when i rebuild afterall if i keep boost low. also thanks whoever said anything about the plugs, info like that was what i was having a real hard time finding.

anesthes

iTrader: (12)

It still won't get out of it's own way. A 177 is a little blower.

-- Joe