What's the max bore and stroke a late model gm 350 can handle? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Big-Blue · 10-12-2009, 10:35 PM

A friend bought a 408 stroker from a reputable shop in NC about two years ago and hasn't found the time/funds to finish his build. It is sitting in its original wrapping. He wants to sell and the original cost was over $5k. I think he will sell it for about half of that. It dynoed around 500 hp/tq.

Question: How much bore and stroke is too much for that block?

My 71 K20 will be a truck driven for fun meaning occasional mud and hauling, but maybe some 100 mile trips here and there - in Texas. No track time obviously. I want the ponies but want it to be reliable at the same time.

Thanks for any thoughts as to clearance, overheating issues or anything else I should be wary of! (the warranty is up on it as well)

Here are the specs:

Bore and Stroke - 4.030 x 4.000 Inches
Compression Ratio - 10.5:1
Fuel - Premium pump gas
Crankshaft - 4340 Forged Steel (two piece rear seal)
Connecting Rods - 6.0 Inch Forged H Beam, bushed
Pistons - Forged
Rings - File fit plasma moly
Block - GM 350 late model roller, your choice of color, 4-bolt mains
Camshaft - Hydraulic roller
Lifters - OEM style hydraulic roller
Timing Set - Double roller chain
Timing Cover - Chrome
Harmonic Balancer - Professional Products
Oil Pump - Melling standard volume
Oil Pan - Stock style chrome
Heads - 200cc Dart Pro 1 Platinum, 72cc chamber
Head Bolts - ARP
Valves - Stainless steel 2.02 Intake 1.60 Exhaust
Springs - Dual with dampner
Rocker Studs - ARP 7/16 diameter screw in type
Rocker Arms - Aluminum full roller, 1.6 ratio
Pushrods - 5/16 Hardened steel with guide plates
Intake Manifold - Aluminum Edelbrock RPM Air Gap
Valve Covers - Chrome stamped
Spark Plugs - Autolite 3922
Oil Filter - Fram PH5 or comparable
Ignition Timing - 32 degrees at 4,000 RPM
Oil Type - Mineral based

Labor Details
All parts hand cleaned
Block sonic checked for thickness
Block pressure tested @ 40 psi
Block stroker clearanced
Block square decked with BHJ fixturing
Oil gallies tapped for screw in plugs
Aligned honed mains
Bored and honed with torque plates
All clearances checked to the nearest .0001"
Rotating assembly balanced
Engine blueprinted with specs sheet on file
Engine fully dressed to customer specifications
Dyno tested with actual results supplied to customer
1 year 12,000 mile warranty

JET4x4 · 10-12-2009, 11:20 PM

There was a pretty good article in Car Craft a few months ago about building a 408 from a 350. Maybe check out their website, just my .02

unclewatts · 10-12-2009, 11:51 PM

I'm drooling all over my keyboard. Nice engine! If you decide you don't want it, I can give it a good home!

Big-Blue · 10-14-2009, 09:05 PM

anyone else?

MudBug · 10-14-2009, 09:27 PM

The max overbore I would trust is .060 in any small block. For the stroke, I'm pretty sure a 4.00" stroke is the max. If you figure either machining the stock block or buy a Dart short block plus other neeeded parts,

you will probably come up even with or over the asking price for this engine.I would like to have this motor in a stockcar,Its close to what is being run now( IF IT WOULD STOP RAINING!!)

10-12-2009, 10:35 PM	#1
Big-Blue Registered User Join Date: Dec 2008 Location: highland village, TX Posts: 309	What's the max bore and stroke a late model gm 350 can handle? A friend bought a 408 stroker from a reputable shop in NC about two years ago and hasn't found the time/funds to finish his build. It is sitting in its original wrapping. He wants to sell and the original cost was over $5k. I think he will sell it for about half of that. It dynoed around 500 hp/tq. Question: How much bore and stroke is too much for that block? My 71 K20 will be a truck driven for fun meaning occasional mud and hauling, but maybe some 100 mile trips here and there - in Texas. No track time obviously. I want the ponies but want it to be reliable at the same time. Thanks for any thoughts as to clearance, overheating issues or anything else I should be wary of! (the warranty is up on it as well) Here are the specs: Bore and Stroke - 4.030 x 4.000 Inches Compression Ratio - 10.5:1 Fuel - Premium pump gas Crankshaft - 4340 Forged Steel (two piece rear seal) Connecting Rods - 6.0 Inch Forged H Beam, bushed Pistons - Forged Rings - File fit plasma moly Block - GM 350 late model roller, your choice of color, 4-bolt mains Camshaft - Hydraulic roller Lifters - OEM style hydraulic roller Timing Set - Double roller chain Timing Cover - Chrome Harmonic Balancer - Professional Products Oil Pump - Melling standard volume Oil Pan - Stock style chrome Heads - 200cc Dart Pro 1 Platinum, 72cc chamber Head Bolts - ARP Valves - Stainless steel 2.02 Intake 1.60 Exhaust Springs - Dual with dampner Rocker Studs - ARP 7/16 diameter screw in type Rocker Arms - Aluminum full roller, 1.6 ratio Pushrods - 5/16 Hardened steel with guide plates Intake Manifold - Aluminum Edelbrock RPM Air Gap Valve Covers - Chrome stamped Spark Plugs - Autolite 3922 Oil Filter - Fram PH5 or comparable Ignition Timing - 32 degrees at 4,000 RPM Oil Type - Mineral based Labor Details All parts hand cleaned Block sonic checked for thickness Block pressure tested @ 40 psi Block stroker clearanced Block square decked with BHJ fixturing Oil gallies tapped for screw in plugs Aligned honed mains Bored and honed with torque plates All clearances checked to the nearest .0001" Rotating assembly balanced Engine blueprinted with specs sheet on file Engine fully dressed to customer specifications Dyno tested with actual results supplied to customer 1 year 12,000 mile warranty

10-12-2009, 11:20 PM	#2
JET4x4 Registered User Join Date: Jun 2009 Location: Birdsboro, Pa Posts: 135	Re: What's the max bore and stroke a late model gm 350 can handle? There was a pretty good article in Car Craft a few months ago about building a 408 from a 350. Maybe check out their website, just my .02 __________________ 67 Chevy K20 LWB Fleetside project 85 GMC K10 High Sierra LWB, 37's, 8 lug rears, 4.10's project 86 m1009 blazer, 6 in lift, 35's, driver 69 c10, 307, long bed, 3 speed, driver 07 Dodge 2500, cc, lb, cummins turbo diesel 00 z28 camaro, ls1, 6 speed, rarely leaves the garage

10-12-2009, 11:51 PM	#3
unclewatts 70 Chevrolet=Obsession Join Date: Jun 2009 Location: nice ca Posts: 1,067	Re: What's the max bore and stroke a late model gm 350 can handle? I'm drooling all over my keyboard. Nice engine! If you decide you don't want it, I can give it a good home! __________________ I'm Just like my truck. Old, Ugly and Grouchy. Except my truck starts easily in the morning and doesn't smoke! IT'S NOT EASY BEING GREEN! -Kermit the frog 1970 Chevrolet C-10 Longbed Stepside : 350, Muncie M20, 3.08 GM corp. positraction Forest green exterior/light green interior(Where all my money goes) 1996 Toyota Corolla (Parts runner)

10-14-2009, 09:05 PM	#4
Big-Blue Registered User Join Date: Dec 2008 Location: highland village, TX Posts: 309	Re: What's the max bore and stroke a late model gm 350 can handle? anyone else?

10-14-2009, 09:27 PM	#5
MudBug Registered User Join Date: Jan 2007 Location: tennessee Posts: 159	Re: What's the max bore and stroke a late model gm 350 can handle? The max overbore I would trust is .060 in any small block. For the stroke, I'm pretty sure a 4.00" stroke is the max. If you figure either machining the stock block or buy a Dart short block plus other neeeded parts,you will probably come up even with or over the asking price for this engine.I would like to have this motor in a stockcar,Its close to what is being run now( IF IT WOULD STOP RAINING!!)

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