L31 Extreme Budget Build

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tayto

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This one is definitely not on a 112. Intake Lift maxed out on a 111 centerline and Exhaust on a 120 centerline.
i actually looked at my notes, it said 112.5*. I posted these on thirdgen.org a few years back. I guess GM has changed suppliers or something a few times? Either way for $100 i think it's still a good cam!

Are you going to be porting the stock intake base? any benefits for this powerlevel?
 

L31MaxExpress

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i actually looked at my notes, it said 112.5*. I posted these on thirdgen.org a few years back. I guess GM has changed suppliers or something a few times? Either way for $100 i think it's still a good cam!

Are you going to be porting the stock intake base? any benefits for this powerlevel?

You are not going to get a new steel core roller cam anywhere for $100, which makes it an excellent deal. I choose this cam over the the two perfect condition 395' cams I have in the shop because of the cylinder pressure the 395' makes was detonation happy even at 9.6:1.

No time for intake porting on this lower manifold and the one I did for the aluminum heads on the Express is opened up far past the ports on these heads. With a stock torque converter, TH400 and 3.08s I am not sure that it would benifit much. I think the TH400 shifts at like 4,500 rpm with your foot in it unless you manually shift it.
 

L31MaxExpress

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Those vortec heads are the best flowing smallblock chevy heads of all time, even better than the 2.02 valve Lt-1 heads of 70-71. That gm cam with the 115 deg lca will cost you 20-40 ft-lb though. Comp cams stuff is finally coming back in stock. I'm holding up my own L29 build for 2 more months to get one, even though I spent 200-something getting my stock one reground.
With headers and open exhaust, sure. With log manifolds, cats, a full exhaust and quiet muffler it will not. My Express with tri-ys and very free flowing exhaust loves a tight LSA. This cam has very little overlap so it should sound very stockish too and idle nice and low. I tried adding power to a 305 that was straddled to stock manifolds for a specific racing class. The only cam I found that worked decently had a 114 LSA. In a stock L69 the old L82 cam added 30 hp with minimal torque loss. Several aftermarket tighter LSA designs even small ones lost power everywhere, so there is more to power than LSA alone.

Also early IVC that is a byproduct of the way the cam manufacturers grind a tighter LSA would make this 10:1+ engine with iron heads have a bad tendency to detonate. Been there and done that with 9.6:1 using the OEM dished L31 pistons and a GM 395' cam that is 196/206 @ 0.050 on a 106 ICL with a 109 LSA. It would detonate with only 29° of timing at times on 91 octane. It LOVED E85 though.
 
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tayto

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You are not going to get a new steel core roller cam anywhere for $100, which makes it an excellent deal. I choose this cam over the the two perfect condition 395' cams I have in the shop because of the cylinder pressure the 395' makes was detonation happy even at 9.6:1.

No time for intake porting on this lower manifold and the one I did for the aluminum heads on the Express is opened up far past the ports on these heads. With a stock torque converter, TH400 and 3.08s I am not sure that it would benifit much. I think the TH400 shifts at like 4,500 rpm with your foot in it unless you manually shift it.
any idea what GM uses/used this cam for? is it a marine cam or a crate engine cam?
 

L31MaxExpress

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One is the Mercruiser Mag 350 MPI and they used them with the dual plane MPFI intake on them, so older serial numbers.
 

L31MaxExpress

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I simulated the cam and compression difference head-to-head. Stock piston 350 at 9.6:1 and LT1 piston 350 at 10.1:1. Both with 0.016" compressed head gaskets. Both modeled with stock Mexico 062 heads for the sake of comparison. Stock SFI with 650 cfm of flow. HP exhaust setup on both approximately replicates a higher performance factory style exhaust system.

The 9.6:1 395' cammed engine came out at 301 hp @ 4,500 and 399 tq @ 3,000. The 10.1:1 492' cammed engine 326 @ 5,000 and 410 tq @ 3,500. Remember too that this is going in front of a 3spd automatic without lockup. Even with the 3.08 gears it will be up in the 2,500-3,000 rpm range depending on the speed on the highway.

395' cam 9.6:1
RPM-----HP-----TQ
2,000---138---362
2,500---181---380
3,000---228---399
3,500---266---398
4,000---288---378
4,500---301---351
5,000---296---311
5,500---275---263

492' cam 10.1:1
RPM-----HP-----TQ
2,000---133---349
2,500---180---377
3,000---230---402
3,500---273---410
4,000---302---397
4,500---322---376
5,000---326---343
5,500---314---300
 

L31MaxExpress

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No progress today, but I did drive to Summit in Arlington. Spent a solid hour browsing their scratch and dent. Ended up with a cast aluminum TH400 pan, TCI SFI 168 tooth 1-piece rear seal flexplate, a nice set of Denso L31 plug wires, and another Cloyes L31 single roller chain setup for under $200. I also picked up a Holley aluminum timing cover, valve cover gaskets, rear main seal housing gasket, all the AN fuel fittings I need to plumb the fuel system and a flex fuel composition sensor. All said I am about $1,300 in new stuff for this build. Thats OK though, I got $3500 for the 6.0L I pulled out of it.
 

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I wish I had a Summit near me too :rolleyes:

Well, maybe not, I'd spend too much on stuff I probably don't need :deal:
My buddy already does. So far he has gotten a TKO 5spd and a LS Magnuson in the scratch and dent this year. They had so much there and super reasonable. I almost grabbed a set of coated Thorley Tri-ys for an early Chevy II Nova with rack & pinon conversion that looked like they would have fit this engine in the van for $200.

Then I also get too much on FB market place too. I was eye balling a pretty clean 72 C10 with a rebuilt 350/TH350 and newer tires for 4K today. Very little rust and a fairly straight body too.

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L31MaxExpress

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Put a little more work in this evening.

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Put the big block pump and milodon windage tray on. Used the 7qt bat wing pan I initially had on the 383, but decided to keep the OEM oil cooler instead on it. I put the $60 Summit scratch and dent TCI SFI flexplate on it. It is a really nice piece compared to the OEM and the ring gear welds are much more substantial.
New Holley timing cover, crank sensor with a new o'ring, the balancer and crank pulley are in place. I ended up RTVing the rear main seal housing to the block rather than using the paper gasket even though I bought a paper gasket.

I primed it for as long as the drill battery lasted, probably 5-7 minutes while I watched the rockers as they started oiling up from the lifters. All looks good there. Thats an old TBI distributor with the gear knocked off that I prime all SBC builds with.

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Upon priming it, I discovered an oil leak through an accessory bolt hole. It had been drilled and tapped clear into the oil drain back. I will put the alternator bracket stud there with some thread seal. I have had a couple of other engines leaking coolant or oil through the exhaust bolts that were drilled too deeply from the factory. It happens sometimes, but some thread sealer and it is rarely an issue. I have seen a few of these blocks also leak where the fuel pump pushrod should be as well even though a large number of them were not drilled, a short bolt with PTFE sealer on it fixes that too.

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I have a few things to grab at a wrecking yard if I can find a TBI or Vortec OBS. I need the studs that hold the metal bar behind the ps pump, some accessory bolts, the oil pressure pipe that the sending unit attaches to and finally I want the OEM spark plug wire looms. I also need a couple of the tin metal exhaust manifold heat shields for the driver side manifold.
 
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