Poseidon

hey all i have been tossing around the idea to build a motor for my formula. i traded around a got a l31 truck 350 was told it spun a rod has 906 heads i will be tearing it down tomorrow. i was wondering if i could buy a 3.800 crankshaft use the rods from the 350 bore it .30 over and make a 412. then use scoggin dickey valve spring kit and run a big cam make a weekend warrior.

I've read the l31 cam is a upgrade from the 305 tbi cam would it be worth swapping to have more power while i build a new one i have to pull my 305 to swap the tranny anyway.

Thanks for any help given.

Night rider327

iTrader: (13)

If it spun a rod bearing then atleast 1 rod may not be usable. If it spun and ate into the bearing tang groove that rod is junk. Even if it did not eat the groove up, the rod big end may still need to be resized and if you do 1, you really need to do all. At this point aftermarket rods start to look better.

Then as far as the stroke goes, I do not think the rods will clear a 3.800" stroke, they would need a lot of grinding on the rod bolt shoulders.

Best bet would be scat I beam cap screw, stroker clearanced rods.

What block casting is your L31 engine? The 880 blocks MAY not be the best for a 3.800" stroke. The cylinder bores are shorter on the 880 blocks than all other GM 350 blocks. It's enough to make running even a 3.75" stroke a little scary IMHO.

Vortec L31 cam
10241264 casting number
Intake lift- .414"
Exhaust Lift- .428"
Intake duration @.050"- 191*
Exhaust Duration @ .050" - 196*
Lobe Centerline- 111

The 305 tbi cam #10088155*
Intake lift .350"
Exhaust lift .384"
Intake duration @ .050" 179*
Exhaust duration @ .050" 194*

So a little better but I don't think it would be worth my time to swap out for what little gain there is.

sofakingdom

iTrader: (1)

No...

That works out to 388 CID.

Not really...

You'll end up having to gratuitously grind on the block and use a small base circle cam at the very least, and grind on the rods (IMO about the stooooopidest way there is to deal with the problem) almost certainly anyway. Best to use aftermarket cap-screw rods for a stroker motor.

Sounds to me like you've never built a motor before. My advice in that case would be, learn to build a good reliable one at the stock dimensions first; pay attention as you build it, so you know and understand where the gotchas are; master the whole art and science of building; and after you've got some experience under your belt, THEN tackle an odd combo stroker.

dmccain

iTrader: (2)

No need to stroke it. Why bother. 350 is plenty enough.

Poseidon

ok i tore it down its a 880 block a few bearings had a little sliver on the end hanging very little metal in pan i was told it lost oil pressure then started knocking and locked up there might be minimal grooves on the crank. this will be my first problem build ive rebuilt a hand full of engines but just tear down replace with oe parts read out of the book and they have all ran and i assume still do. right now im thinking maybe 355 since the block has shorter bores all i really want is to use the vortec heads put Cranes cams p/n 10309-1 springs in and run a decent cam i got the odd stroker idea from a old issue of super chevy. I am no expert and like help so if i am just plain dumb on something tell me idc lol.

Night rider327

iTrader: (13)

Vortec 355 can easily cause you to have to throw your underwear away lol. Not hard to get 350, 375, even 400 HP out of them.

Strokers are fun but IMHO over rated for what they are most times. Like Sofa pointed out the 4.030" x 3.800" build would be a 388, not a 412... That is only a 33 cid gain over a common 355. In an engine making 1.2 HP per cube that's only a 40 HP gain. Most engines will only make around 1 HP per cube and that's a 33 HP gain... For the $800-1200 more that it's gonna cost to build the 383, I just don't see that small gain being worth it unless it's a max effort race engine.

I can not tell you what you can reuse out of that engine, cause I can't see and feel, or mic the parts.

You may be able to get away with reusing rods, even crank. Just keep in mind that a brand new scat 9000 crank is under $200 and turning your crank at machine shop may be $100-140.

If doing a 355 you will want flat top pistons. Something around 5-7 cc volume. Be sure to keep an eye on the piston compression height.. Std. is 1.56" With everything at spec this puts piston .025" in the bore at TDC. Also of the 'rebuilder' type pistons has a 1.54" or so compression height and you end up .040" to .060" in hole. This kills your quench height and some compression.

Hyper pistons are good for daily use and mild race..
Forged if you will be using nitrous or boost.

Why are you so set on the Cranes cams p/n 10309-1 springs? Seems like a very high dollar way of doing it to me. There is like 10 diff ways to set up vortec heads for higher lift and most cost under $100, a couple of ways are under $50.

Never pick your valve springs until you know what cam you will be using... Never pick your cam until you know the true compression of your engine.

Poseidon

thanks night rider and yeah im horrible at math and did the stroke bore in my head and thought hey 412 and the only reason i choose the cranes cam is its what ive been told works best so far like i said tell me im wrong idc lol it only makes me smarter to know im wrong here is a better way. what is the best way you know and cheapest i like those two combined lol. i am going to check all the parts over but ill just buy a crank to be safe but id probably be better off buying a stroker kit wouldn't I or could i save and only buy a crank and pistons? if the block wouldn't take a lot of grinding i thought about a 377 so i didn't have to bore the block but i think a 355 is more than enough for what i do A to B plus have the extra push to make the woman want to drive it lol.

Night rider327

iTrader: (13)

Yeah a 355 is more than enough to do what you need. Heck I'm still running a 355 in my camaro and making 500+ HP from it.

The stroker only gains you 20-40 HP over the same built 355.. A lot of time and money added to a stroker build that just don't make it worth it really. I would rather put that extra $500 or so towards better heads. You will get a better return (power gain)

You will have to have machine work no matter what. Boring the block is almost a needed thing with used engines. As the engine wears the bores turn from round circles to oval shaped holes. It will not be enough to see with the eye but when you measure it using snap gauges or dial bore gauge you can tell.

When that happens your ring seal is not as good as it should be and you loose cylinder pressure (compression) plus lets oil into the top of the bore.

So boring is a must for most rebuilds.

Common engine rebuild machine work is..
Hot tank clean the block and heads
Magnaflux (check for cracks) the block and heads
Bore and hone
press old pistons off rods and new ones on
Install cam bearings and freeze plugs

A common rebuild kit will come with pistons, rings, all bearings, all gaskets/seals, oil pump, freeze plugs.

You will also need a new timing chain set, cam, maybe pushrods, maybe lifters, maybe crankshaft, maybe connecting rods.

For the vortec heads...

I like howards brand valvetrain parts. They have 4 or 5 1.25" od springs from $28 to $65.. The ones you will need will run around $40 I would say

You can do the "ghetto grind" (goggle that, you will see alot of info from nastyz28.com) on the stock spring retainers. That's where you grind 3/32" off the bottom of all the retainers. That along with a good set of springs will have lift clearance to .525".... Free plus your $40 springs

Depending on cam lift (vortec heads are stock limited to around .470" or so) you may just need to install +.050" installed height valve locks and good springs to get the clearance you need. About $60 total

Or have machine shop machine down the valve guides, about $55 and install the $40 spring.. Total of $95

Buy the comp cam tool for $50 and cut down the guides your self, and install good springs $90

I did the ghetto grind on mine. 062 casting vortec heads, .484"/.512" lift cam, daily driver 355 in S10

Poseidon

Thanks again night rider I'll be looking.into that setup for the heads ways cheaper. I'm trying to find a machine shop to hotank and MagnaFlux my block I'm in the middle of nowhere lol. I know I'll have to bore at least .030 to make a 355 is there any point to go more

Poseidon

What do you think about these pistons with stock rods. Speed-Pro Digital Diamond Profile (DDP) Hypereutectic Pistons WH345DCP30

Night rider327

iTrader: (13)

Compression Distance (in):1.548 in.
Piston Head Volume (cc):+6.90cc

Like I said before look at the compression height.

"Std. is 1.56" With everything at spec this puts piston .025" in the bore at TDC. Also a lot of the 'rebuilder' type pistons has a 1.54" or so compression height and you end up .040" to .060" in hole. This kills your quench height and some compression."

Poseidon

Okay night rider what could you recommend instead of me selecting a few more.wrong ones lol

sofakingdom

iTrader: (1)

The Keith Black hypers supposedly have the factory deck clearance.

Some Mahle ones also are said to.

Virtually ALL cast, MOST hypers, and MANY forged especially TRW/SpeedPro, add the extra deck clearance.

Best thing to do is, ASK the mfr what the ACTUAL MEASURED compression height is (distance from center of wrist pin to top surface); ignore "designed to fit", "for engines with", and similar mealy-mouth non-specs. If you have one in your hand you can measure it; pins in the SBC are .927", so if you take half of that (.4635") and subtract it from 1.560", which is 1.0965", that's what the piston should mic from the pin bore surface to the top surface. If it mics 1.1165", throw it back; it's not a keeper.

True actual RACING pistons such as JE, Diamond, Arias, etc. typically are correct. You can even order em with LESS than stock if you want to pay the coupla extra coins for "custom", to come closer to zero-decking without having to do machine work.

Night rider327

iTrader: (13)

Here you go.. Same brand you was looking at... Just the correct specs

http://www.summitracing.com/parts/sl...make/chevrolet

All of these would work as well
http://www.summitracing.com/search/d...0%2B4294879698

http://www.summitracing.com/search/d...2%2B4294882365

http://www.summitracing.com/search/d...3%2B4294880206

Poseidon

ok so far i have these bookmarked
Pistons http://www.summitracing.com/parts/su...make/chevrolet

Valve springs http://www.summitracing.com/parts/hrs-98214/overview/

Cam http://www.summitracing.com/parts/cc...02-8/overview/

Crank http://www.summitracing.com/parts/es...3480/overview/

Night rider327

iTrader: (13)

I recommend the Scat crank over the eagle. I have seen way too many eagle cranks with finished machined journals off.

http://www.summitracing.com/parts/sca-910526/overview/

BTW sometimes being out in middle of nowhere is better for machine shops, performance shops, etc.

I'm really in middle of no where (6 miles just to closest store of any type, 18 miles to nearest wal mart) and we have 3 machine shops in a 30 mile radius of me lol.

-=Z28=-

iTrader: (3)

Keith black or sped pro is the way to go for hypereutectic pistons IMO.

+1 for Night

Poseidon

night rider i wish it was like that here i drive 4 miles to get to a carryout store 6 to a gas station 10 to Walmart and there isn't a machine shop within 100 miles there's a speed shop but they only do bolt ons. I looked at the scat cranks ive heard bad on the quality of them never hear much about eagle tho.

novaderrik

get the 3" stroke crank and 5.9" rods out of a 94-96 Caprice L99, bore it .030 over, and build the 305 that GM should have built. cam it right and it would rev to the moon.. just make sure you put really steep gears in it and set your shift point at somewhere around 8000 rpm...

Night rider327

iTrader: (13)

I played with short stroke engines. In fact I cut my teeth on 302 and 327 chevys.. I love the short strokes but they are not the best way to go.

The 3.48" stroke is a good balance of middle ground. I can do anything with a 3.48 stroke, that you can do with a 3.00 stroke and do it better.

I make peak power at 7200 rpm and shift around 7400 rpm in my camaro with a 355 (3.48" stroke)

I make peak power at 5600 rpm in my S10 with a 355 (3.48" stroke)

Night rider327

iTrader: (13)

Hmmm, that's odd. I have never seen any probs with the scat cranks and only heard of a hand full of issues... I myself was sending cases of eagle rods back and crank after crank back cause of bad journals/machine work.

For budget rods/cranks I know only use Scat in mine and my customer's engines.

Heck I have a Scat 9000 cast crank in both of my 355's right now. The one in my camaro I bought in 2004. It has been through 2 "rebuilds" and many changes. Best time on the old engine combo was 11.40's @ 118 mph. Shifting at 6400 rpm. It was a daily driver then too. During that time I would say I put atleast 500 1/4 mile passes on it.

Then I upgraded heads, pistons, cam, converter, gear, etc. Crank still looked good and mic'ed good so it stayed.

New combo has maybe 10K street miles on it but no track time yet but should run in the low to mid 10's shifting at 7400 rpm

Poseidon

ok night rider its not a big price difference so ill look into a scatt crank whats the stock crank suppose to mic at i may just look at the stock crank and rods they look like new i dont feel or see grooves i believe the previos owner ran it out of oil and it just got hot and seized it.