Thread: 350 chev streetable engine build

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Yeh a set of 1 3/4's will be to big for that motor of course they'll bolt on but with that said dosent make them a good choice will give up alot of low and mid range power witch is were your going to live with this combo rpm wise. 1 5/8 will be just right

A good rule of thumb is to keep header pipe diameter as close to the exhaust valve diameter. Use the 1 5/8" unless you plan on over 500 hp.

Hey Tech. I have bought a set of rebuilt vortec heads from an engine rebuilder. I am now looking at cams and pistons. Which thumpr cam would you use or would you only use the one you suggested. Also, are the KB pistons the only ones you would use or are there any others to consider? And do you know how high a lift I can go with the vortec heads?
Thanks in advance, Brad.

Originally Posted by bad brad

I am looking to build this as economical as possible. I'm not trying to hit 500HP. I just want a good streetable engine that runs on pump gas that I can build with mainly the parts I have and a minimal investment.

OK, this is the hard way to do it, picking a cam and then setting the static compression ratio to fit the cam. There are way more cam choices than there are piston choices, but I'm trying to start with a Thumpr for you. Here is the cheapest 1.560" compression height piston I can find that has a reasonably wide, flat perimeter to make squish against the underside of the cylinder head and a properly sized dish to make the right static compression ratio with the Vortec heads.
http://www.summitracing.com/parts/STL-H670CP30/
Production cylinder heads will usually pour a little larger than the published chamber volume. Here's how these pistons work out with different chamber volumes:
64 9.77:1
65 9.66:1
66 9.56:1
What I was trying to do is get a static compression ratio that would work with the middle of the road Mutha-Thumpr, #12-601-4 and generate a dynamic compression ratio that would be compatible with pump gas.

You want to cut the block deck height to 9.010" and use a GM 10105117 head gasket. That will put the piston deck height at 0.010" and the squish at 0.038".

Cam: 12-601-4 flat tappet hydraulic Mutha-Thumpr. Intake centerline 102 degrees ATDC, Exhaust centerline 112 degrees BTDC, Lobe Separation Angle 107 degrees. Intake lift 0.489", exhaust lift 0.476". Intake opens 15.5 degrees BTDC, intake closes 39.5 degrees ABDC, exhaust opens 56.5 degrees BBDC, exhaust closes 12.5 degrees ATDC.
http://www.compcams.com/Cam_Specs/Ca...?csid=108&sb=0

Heads: Pin the rocker studs with this kit....
http://www.jegs.com/p/Mr-Gasket/Mr-G...49537/10002/-1
Must replace valve springs to use this cam. Can use conventional outer with spiral wound damper, but will probably have to cut the guide to a smaller diameter because the inner diameter of the damper will not clear the guide. Most popular would be to cut the guide to 0.530" for use with PC-type valve seals. Spring seats in the heads are cut to +/- 1.250".
Use these springs....(1.254" O.D.)
http://www.summitracing.com/parts/CCA-981-16/
And these 7 degree retainers....
http://www.summitracing.com/search/?...20742-16&dds=1
And these locks....
http://www.summitracing.com/parts/CCA-648-16/
Guide cutter....
http://www.summitracing.com/parts/CCA-4726/
Guide cutter arbor....
http://www.summitracing.com/parts/CCA-4732/

Heads, Plan B....
Use Comp beehive springs that require no cutting....
http://www.summitracing.com/parts/CCA-26981-16/
With these 7 degree retainers....
http://www.summitracing.com/parts/CCA-787-16/
And these locks....
http://www.summitracing.com/parts/CCA-648-16/

Rockers: Must use rail rockers unless you want to pull the pressed-in studs and machine the pads and tap the holes for screw-in studs and guide plates. You use one or the other, rail rockers with no guide plates or conventional rockers with guide plates. Using rail rockers with guide plates will break something. If you want to go with guide plates, forget the stud pinning kit I linked above. Wanna go cheap? Rescue stock 1.5 rail rockers from the boneyard. Ran this DynoSim with 600 carb and RPM intake....using a standard Performer will drop 38 hp....
RPM HP TQ
2000 139 362
2500 181 381
3000 230 402
3500 284 426
4000 335 439
4500 381 444
5000 415 436
5500 431 412
6000 419 367

Thanks Tech. How high a lift can I go with?

Originally Posted by bad brad

Thanks Tech. How high a lift can I go with?

Beehives install at 1.700". Max valve lift 0.525" @ 1.175". Coil bind at 1.115".
981's install at 1.700". Max valve lift 0.490" @ 1.210". Coil bind at 1.150".

Hey Tech. I need some more help please. I have talked to a couple of local engine builders. I do value your advice though! I have purchased a comp cams H270 (PART #12-211-2) First, do you think I will have to modify the heads for this lift? Second, the one builder recommends Mahle hypereutectic pistons over the KBs. What do you think of them? Third, the other builder (builds stock car motors) says to use the pistons that are in the engine. He figues they are 10.5 to 1 as they have .100 domes. Is there a way to use a thicker head gasket with these pistons with the vortec heads to bring down the ratio?
Thanks
Brad

OK, first, let's bring everyone up to speed on this cam....
http://www.compcams.com/Cam_Specs/Ca...x?csid=78&sb=0

Any competent cam grinder will tell you that you need a minimum of 0.050" clearance to prevent coil bind on the valve springs at max valve lift. That means that you should be able to insert a 0.010" feeler gauge blade between each of the 5 coil spaces in the spring with the valve at full lift. If you can do that with a valve lift of 0.470", go fo it. If not, you'll have to change springs. The other thing you need to check (and this is the most frequently given limit on Vortec heads) is the clearance between the bottom of the valve retainer and the top of the valve seal. Most cam grinders will suggest 1/16" to 1/8" clearance with the valve at full lift. If you have that much clearance with the 0.470" lift cam, go for it. If not, you'll need to change springs or do a ghetto grind on the bottoms of the retainers. Even at that, using the stock Vortec springs isn't gonna do much for you in a performance format. Seems I remember the "over the nose" pressure is something like 240 lbs, so they're gonna float the valves pretty easily if you wind the motor very tight.

Comp calls for spring numbers 981 or 983 with that cam, so heed what they are suggesting or wing it yourself. It's up to you. I gave you all the tool numbers earlier in this thread.

A 350 Chevy with 0.100" dome pistons and 64cc heads will make 11.80:1 static compression ratio. Better send that machinist back to school.

Thanks Tech. I will do an assembly of it and check out the clearances. I also was doubtful of the comp ratio of those pistons. Thanks for the input.
Brad

Originally Posted by bad brad

Hey all. I have been lurking around this site for a couple years and I am amazed by the vast amount of knowledge here. I would like to ask you pros for your opinions on the best way to build my engine?
First off I will tell you what I am putting it in.
I am building a Steel bodied T bucket. I have a turbo 350 trans and plan on a 2800 stall converter. I have a 3.50 ratio rear end and 29 x 15.5 M/T Sportsman Pro tires.
The engine I am starting with is a 350 my brother ( he passed away 4 years ago so I don't have much info on it ) was building. He was building a race motor out of it so it has I am guessing 11:1 pistons. The bottom end is all done, so I was hoping to just re-assemble it with about 9.5 to 1 pistons so I can run it on pump gas.
Head options I have:
-1.94 camel hump heads- need hardened seats and rebuild.
-882 heads that need rebuild.
-heads on a '71 chev truck engine I have for rebuild.
-looking at buying a set of ProComp alluminum heads.(Probably a couple hundred more than rebuilding the camel humps)
The other engine parts I have to work with are:
-Edelbrock 600 carb
-Edelbrock performer Air Gap intake
-Electronic ignition (would buy an MSD box)
-I was thinking about a Thumper Cam (they sound cool!)
-1 5/8" sprint car headers
I am looking to build this as economical as possible. I'm not trying to hit 500HP. I just want a good streetable engine that runs on pump gas that I can build with mainly the parts I have and a minimal investment.
Thanks for your help in advance.
Brad.

11:1 is pump gas friendly, just make sure its premium.

Hey guys. A new development here! Today I picked up a 1998 vortec 350 that has 2 new 906 heads( 1 hour run time !!!) with 2 slapping pistons for $500. Crank has some wear but will clean up. I have heard of some good things about building these engines. Should I be building this engine or continuing with the origional plan?
Thanks
Brad