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Old 08-19-2012, 05:39 PM
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Have an L31 long block.....

I got my hands on an L31 long block (was pulled from a 1998 Van by the guy I got it from) that I intend to build up over time for my 84 TA. As may have been said before, I set myself a goal for 450 horses on pump gas spinning to at least 6000 rpms. That said, this should be easy. I know there are a billion ways to do it, but I just want something streetable as this is my fun car. I've brought this up before but at the time I had nothing to work with. Now however, I do have an engine to work with and now really need to see about the shopping list.

So far, the 84 has been built with a 97 Z28 spec T56, Konis and Eibach Pro Kit springs, UMI suspension for control arms and panhard bar. Rear brakes have been upgraded to PBR rears, fronts with LS1 fronts. 1LE prop valve. Rear is your standard 7.5 inch 10 bolt rear 3.73 gears. Moser axles.

What I had in mind here was to punch the L31 out to 383 cubes, an RPM performer intake, the heads need to be rebuilt anyway, so I'll get LS6 or LS1 beehive springs, 2.02/1.6 valves, looking at 1.6 roller rockers. I've read that should use at least the LT4 retainers if upping the lift. I'll get a 650 carb from a guy I know locally for this motor since I don't really need anything bigger than that for this motor.

The questions come up with this, the balancer on the front of the vortec is the 8 incher, can this be reused with your typical T56 flywheel? I never can seem to find anything about manual cars and balancing, its all flexplates and balancers.....what the hell?

What cam should I run with this? Roller cam naturally but which one?
I'm wondering about the comp 274 and LT4 Hot Cam among others.

What would be the best rod and piston combo for this setup? Need an opinion on using the stock rods (I believe they're 5.7 inches). Flat tops or dished pistons?

Finally what do I realistically need to do machine work wise on the heads? I know they would need port work and cut to use the bigger valves. What else?

I'm sure there will be other questions. I'm used to working with stock parts, this is the first time I'm truly trying to piece together several aftermarket compoents. I rebuilt a 350 TPI with success sofar, (that particular motor started on the first try literally) so the process of assembly is not new but piecing it together is.

I apologize for the novel, thanks for input. There are hundreds of ways to do this, I just want to narrow down my shopping list so I can buy parts and get moving on this build.

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Old 08-19-2012, 06:43 PM
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What you need to do is get one or two of David Vizards books (soft cover).Use that as a guide.....I wouldnt go with whats on here as gospel,even thou theirs some very good info.I would take anything that Daivd V. has to say as ”Build it like this”. And you will be internaly greatful.********************

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Old 08-19-2012, 07:53 PM
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There are two ways to stroke it to 383. You can get an internally balanced or externally balanced rotating assembly. If you use an OEM 400 crank it will be externally balanced and have a two piece rear main seal. This will require a flywheel that fits the 2 piece rear, with weights for the external balance. You can also get aftermarket cranks in this style too. GM used 8" balancers on 400's as well, and these also have external weights on them as well. Many after market balancers come neutral weighted (internal balance) and then you can add mallory weights to make them work with a 400 crank.

Then you have after market 400 cranks with a 1 piece rear main seal, which takes a different flywheel. These also tend to be internally balanced, so you can run a neutrally weighted balancer and flywheel.

So if you want to keep the T56 flywheel you need to find out if it was made for a 1 or 2 piece RMS.

As far as rods, you can google ideal rod/stroke ratio and benefits of a long rod engine and find out.

If would NOT recommend converting the L31 Vortec heads to 2.02/1.60" valves for two reasons:
1) They work great with the smaller valves because the intake charge velocity is fast, and opening them up will reduce intake velocity and hurt you (especially sub 6,000 RPM).
2) The L31's are a little crack prone due do the thinner casting from the tall intake runner port shape. Opening the valves is going to make this worse.

As far as getting to your HP goals, check out this awesome reference data of engine builds (there are over 100 of them to compare). I think these are all out of Hot Rod mags: Ryan's Small Block Chevy Stroker Engine Combo Page

Must use flat tops. Dished are low performance and don't give any good squish/quench. If you do not decide to use the 6.0" rods, Chevy OEM 5.7" rods are good for your power and RPM goals. Some guys like the powdered metal rods, some guys hate em and prefer cast. Either should be fine.

As far as the head/machine work, start reading: http://www.crankshaftcoalition.com/w..._cylinder_head

Many will tell you that you should use the largest balancer that will fit. GM made an 8". OEM balancers are just OK. The elastomer tends to slip which reduces damping quality and then makes it impossible to time the motor. Quality aftermarket units, while smaller in diameter, do provide better damping quality. Get an SFI damper for safety of people and your engine. ATI is noted for the best dampers. Their units are actually two in one. They have 2 inertia rings of differing diameter to cancel vibrations occurring at different frequencies.

A cam with 230-240 @ .050" is probably where you will want to be.

Hope this rambling helps.
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Old 08-19-2012, 07:59 PM
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heads that flow 260 cfm, 10: 1 or less CR, 750 cfm carb,dual plane manifold will work,good headers,roller cam that matches head flow
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Old 08-19-2012, 09:08 PM
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The engine is a one piece rear main seal, the T56 flywheel is also a one piece rear main seal. It came off an LT1 camaro.

The heads I have are the 906 casting if that means anything, I'm told it doesn't. I've seen the books mentioned here in the stores but I usually check out builds online to see what people are doing as well.

How does this sound to you guys...I've been doing some digging on the subject for awhile and sometimes due to conflicting info it still doesn't make much sense. But this is what I've come up with on my searching. I'll read the list of builds to compare it later on.

Do the heads with the stock valve size. 1.94/1.5 with the 3 angle job. LS6 beehive springs, Stock 1.5 rockers for now. Have the heads ported/matched, bowls blended smooth it all out. Its a roller block so maybe a XE282HR camshaft at .510/.520 lift and duration of 230/236 at .050 lift. The block bored .030 over, factory 5.7 rods to save the money, along with Sealed Power speedpro flat top with 4 valve relief pistons with a Eagle aftermarket 3.75 inch stroke crank. rod length is said to be 5.7 with that crank, says external balanced. The balancer is the stock 8 inch one which I could have checked at the machine shop to be sure its balanced right. Compression would be at 9.7 with 64cc chambers.

Top all that off with a RPM Performer intake manifold for Vortec heads and a 650 or if I find a deal 750 CFM carb. Headers and drop it in a car that had a shipping weight of 3205 lbs.....Go burn rubber.

Domed pistons would send the piston into the heads from what I read, unless they're inverted (dished).
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Old 08-19-2012, 09:51 PM
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Have an L31 long block.

FYI,those heads are only good up to a 0.450"lift cam. PERIOD! If you have a larger camshft,then have them upgraded with different springs and retainers, machine the guide down .080" too keep the retainer from coming down a crushing the seal. VORTEC heads rock, they work great on a carburated application,you can easly pick up 30hp! Some more info on vortec heads: L31 Vortec exhaust seats
Early on, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an oft-repeated, although incorrect statement made by a car magazine that said in essence the 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats.
The truth has been shown to be that there is virtually no difference in flow between the two, providing the seat is blended into the port. This is a common procedure that's often done in performance builds- regardless of whether the seats are inserts or induction hardened or unhardened. The manufacturing process leaves a lip where the seat and port pocket meet in many instances, and it's this lip that is carefully removed/blended when a head is prepped for performance use, again- regardless of whether there is an insert or not.
So both the c/n 906 and c/n 062 heads have virtually the exact same performance potential. In fact there are instances like for marine use where the hardened exhaust seat insert is actually preferred over the induction hardened seat.
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Old 08-19-2012, 10:37 PM
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Quote:
Originally Posted by cdminter59 View Post
FYI,those heads are only good up to a 0.450"lift cam. PERIOD! If you have a larger camshft,then have them upgraded with different springs and retainers, machine the guide down .080" too keep the retainer from coming down a crushing the seal. VORTEC heads rock, they work great on a carburated application,you can easly pick up 30hp!
Hence changing the springs and all to heavier springs and so on. No way in hell I'm keeping the heads stock arrangement for what I want. A friend of mine is pulling 477 horses at the flywheel with a set of vortec heads. He had to have all the machine work done and etc for the power he wanted. I'm basically doing the same thing, only with a 383 whereas he used a 406.
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Old 08-19-2012, 11:59 PM
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your power will be similar if you use the same parts,your engine will rev a little higher
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Old 08-20-2012, 05:52 AM
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Sell the used 906 vortec ehads to someone else and
start with NEW assembled GMPP large port Bowtie Vortec heads. #25534446
You will be much further ahead in all respects. This is a much much better vortec head.
A 650 is too small. Don't buy parts from your friends just cause they got them for sale.

Last edited by F-BIRD'88; 08-20-2012 at 06:06 AM.
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Old 08-20-2012, 10:17 AM
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F-Bird, I may wind up doing just that. I really needed a basis for the motor which is why I picked up this one. You got all the stupid things like lifters, dogbones, spiderplate, rear seal housing etc. It was better than starting with just a bare summit block. The same guy I mentioned with the carb is a local forum club member. I run into him now and then. He pulled a Vortec out of his Suburban and is putting it into his S-10 or his Camaro. He and I were discussing the heads and he said hes had all kinds of machine work done and said in hindsight he wishes he had sold the heads and gotten the GMPP ones after I sent him a link to them. I'll talk to the machinist and see what he says. For all I know he can get them to what the GMPP heads are, or close to them for lil more than the cost of just one head at Summit. But I do hear you there. If the machinist agrees that I may be better off, I'll put the heads on craigslist and get the GMPP heads. Either way I didn't do bad picking up that engine for 250, especially if I sell the heads for 150 because I got all the little stuff you never get with getting just a block.
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Old 08-20-2012, 10:53 AM
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I've had 4 sets of the vortec heads. My present 2.02x1.60 ported 062's work real good but if I had to do this again I would buy the GMPP big port Bowties. Miles ahead. Big power,way way better castings. I have never and will never bother with a worn out take off vortec head. My vortec stuff all started with new 062 (Canadian) castings .
At the time when I built mine, there were no GMPP Bowtie Vortecs. The OEM L-31 heads are yesterdays lunch, now.
You will see many offered for sale. Cause the owner is upgrading.

The big port bowties are a rocking big big power head with just simple port clean up.
Some shops that prep these like to do their own valve job.

There are three versions of this GMPP head Make sure you get the latest design revision head
casting number ends in "C"

Last edited by F-BIRD'88; 08-20-2012 at 11:01 AM.
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Old 08-20-2012, 10:56 AM
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Look at the Comp XR280R-10 mechanical street roller cam K12-771-8 "K Kit"
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Old 08-20-2012, 11:01 AM
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f bird:re XR280R-10
whats the intake centerline on that cam?
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Old 08-20-2012, 11:05 AM
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Quote:
Originally Posted by vinniekq2 View Post
f bird:re XR280R-10
whats the intake centerline on that cam?
You can install it any way you want.
But the cam card C/L's are 106 IN and 114EX 110LSA.

If you want some other LSA just call comp.
Special orders don't up set them.
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Old 08-20-2012, 11:10 AM
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Sounds like you did the same thing the forum guy I know did, did the heads then realized if could do it again would have just bought them assembled already.

The other option I'm looking at is the Scoggin Dickey heads that are already modified for .600 lift for 399 each. Already assembled with 1.94/1.5 valves. Slightly less open than the Bow Tie ones but I'm sure they'll make just as much power for what I want, which is simply a fast street car. Lemme see what the machinist says. He may say just get the heads, or he will say I can beat the prices....we'll see. I've got a feeling it will be the former.

Just a note for those who are wondering about the car's purpose, its not a pure drag car. I built it to corner and stop. If I wanted a drag car I would have built one.
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