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Jaiden2010 06-20-2011 04:03 PM

350 build questions, looking for 300-350 hp
Hi. I have a tired 350 out of a 1991 3/4 ton truck block casting 10243880, heads 14102193. Since this is out of a 3/4 ton truck. I was thinking the heads are probably not the best flowing. I am replacing a dead 283 that I had in my 89 S-10 Blazer 2wd. I installed 3.73 gears. I have a set of V8 swap S-10 headers, Performer RPM intake, and a new VooDoo cam, these are just some new parts I have that were for purcased for a project I sold. I'd like to utilize them, any thoughts on the best route to go. Possibly what heads I should pickup from the boneyard? The block was inspected at the machine shop and does not to be bored, but should I have it punched out? I also have access to a 400 crank. I am not sure what way to go lol. I have a $1500 budget on building this motor. I will assemble it myself. I am shooting for 300-350 hp.

eric32 06-20-2011 04:27 PM

Well first thing that would help out a lot is what are your cam specs and there are a lot of guys on here who know there stuff on chevy factory heads.

If your wanting to save money and I know your looking towards that you could just keep it the 350 cubic inch for now and if your able to get a set of vortec heads for dirt cheap paired up with your cam and if its not too big on the lift specs and your can get the proper springs to be put on your vortec heads you could make 300 very easy if not more.

I just had my flattop 350 topped out with a set of rhs pro action 180cc heads and a zz4 roller cam and it runs very strong and still drives through town with a 350 turbo and 3.42 gears and my s10 is a 96.

I am sure someone on here will post some way better info that I just did. Vortec heads are very good and easy to make 300-350 horsepower no problem with a mild cam. Only thing is the springs to be matched to your cam.

Jaiden2010 06-20-2011 04:55 PM

I should have been more specific. The Lunati Voodoo cam I have is part #60103
Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 227/233
Gross Valve Lift (Int/Exh): .489/.504

I have a fresh built Turbo 350, with shift kit. I have not purchased a torque converter yet. I have a new 670 Holley Avenger carb, I also have a 650 double pumper, and a 750 vacuum secondaries. I was thinking maybe I should get Vortec heads, but I'd like to use the Performer RPM intake I already have. I am assuming I will need different valve springs? of course 400HP would be better ! It's not my daily driver. I have a Ford Exploder 8.8 posi rear for it.

eric32 06-20-2011 05:15 PM

That's a pretty good size voodoo cam and I don't mean big like not street able but its not a mild type cam like the one I have in my 96 s10. Your gearing is just fine at 3.73 and building your turbo 350 with a shift kit will work well. You will need a good stall converter to get the most out of your cam. I have a 231/239 voodoo hydraulic roller in my 86 s10 and they are very good cams.

If you want to keep your current intake and I am assuming its the 86 and earlier intake bolt pattern? Vortec heads will not bolt up too the old style intake correctly and trying to make them do so is asking for trouble. I don't know how your current heads flow as I don't know much about the older heads and no some about vortec heads but just from reading on them from others on here.

For vortec heads to work with that cam you will have to most likely have the heads machined for the correct springs cause voodoo cams have very fast ramp rates and with high pressure springs they can rip pressed in studs out.

If you want to use your current heads you might look into a kit that allows you to have screw in rocker studs in place of your pressed ones and maybe someone on here can post I know there are some stock size springs that will allow over 500 plus lift and no machining will need to be done to your heads.

You might be able to make around 300 but with better flowing heads it will be much easier.

Jaiden2010 06-20-2011 06:09 PM

I will buy a Vortec intake if need be, I have no problem with that. I also thought maybe I should spend the cash for aftermarket iron heads. I want the most bang for the buck. I could always downsize on the cam, they aren't very expensive. I plan on a stall converter. I am most concerned with what heads, and valve springs I will need but maybe I can avoid that with a little smaller cam.

techinspector1 06-20-2011 06:57 PM

These pistons
This cam
L31 heads from a boneyard, casting # 12558062 or 10239906. Magnflux 'em for cracks. Fit new STOCK springs and seals. Make certain seals are fully seated on the guide boss by tapping them with a socket and small hammer. The stock springs will work well with the mild cam and will not pull the rocker studs out of the heads. Doesn't matter whether the heads have hard inserts in the exhaust or induction hardened seats, either way will work. Same casting, both styles flow the same. Give 'em a good valve job and otherwise leave 'em alone. Use the rail rockers that came on the heads stock.

Align-hone the main bearing bores in the block and cut the block decks for 9.015" block deck height, referenced off the main bearing bore so that you know the block deck height is equal on all four corners. This will insure that the heads sit level and flat on the deck and that the intake manifold will sit square to the heads with no gaps to cause an internal or external vacuum leak. Use GM head gasket #10105117. Static compression ratio will be 9.1:1 and squish will be 0.042". Use Edelbrock #7116 Performer RPM intake manifold. 600 carb is all you'll need.

Makes 365 hp @ 5000 rpm's with a double torque peak of 420 ft/lbs @3500 and 4000. Should make this power on crummy cat-pea pump gas without detonation.

Cam begins making power at 1200, so it's your call whether or not you need a looser converter. If I did anything at all with this combo, it would be a mild 2000 stall unit just so I didn't have to contend with the car creeping at stoplights.

ap72 06-20-2011 07:28 PM

with machine work and a good basic rebuild kit your budget is gone, also you will need the springs recomended for the cam. The parts you have will get you over 300hp, BUT those heads are pretty bad. If you can afford getting something better it would help but a good set of heads will probably run you about a grand on top of your $1500 budget. Proper machine work and good pistons, bearings, gaskets, etc are NOT cheap.

Also, most s10 swap headers are 1.5" primary size, those cant support much more than about 350hp, good 1 3/4" headers run about $500, and they'll support a little over 500hp.

eric32 06-21-2011 04:21 PM

If your looking to replace your heads does as tech inspector said above and it may cost less then getting a set of new heads assembled but don't quote me on that as some machine shops prices vary.

The best route if your buying a complete new set of heads you can go RHS pro action 180cc intake runner heads and they come in 64 or 72cc combustion chamber and I just put a set on my engine with a gm zz4 roller cam and they are very nice heads and worth more then my old world heads ever where. Search all your options and do with what will work best but don't jump the gun and say well this for now you will only spend more in the wrong run.

Reason I say that is I have done the quick route and then regret not doing more and then ended up spending more then what I should have and would of been less if I did it right the first time. In short terms use your budget wisely and make it match good and you should be very happy with it.

Have fun with your build.

techinspector1 06-21-2011 05:43 PM

eric32 asked me to run a sim on his motor on a PM. I thought I may as well post it on here for everyone to see. This is a very mild 355 with 9.1:1 static compression ratio, low-rise intake manifold, 600 carb, ZZ4 cam installed straight up. He didn't tell me about the exhaust system, but I'm assuming 1 5/8" long-tube headers. Heads are RHS 180's which I factored down to 95%.
1500 109 382
2000 155 406
2500 193 405
3000 230 402
3500 275 412
4000 302 396
4500 316 369
5000 313 329
5500 290 276
Peak volumetric efficiency 86.3% @3500
Peak BMEP 174.8 @ 3500
Motor makes 400+ ft/lbs of torque from 1800 to 3800, right in the street driving range and should operate detonation-free on cat pea pump gas. Low-rise intake is a power killer. A change to a high-rise, dual-plane intake would add 51 horsepower and 24 ft/lbs of torque according to the DynoSim software.

There's just no getting around it, you have to get the carburetor up off the motor in order to make power. The over and under runner system on a low-rise, dual-plane intake just doesn't work well. On some motors, like the big 472 and 500 Cadillac, the runners were so screwed up that the mixture went uphill to get to the head ports. You can get around it with a single plane intake, but then you are stepping into another rev range for the motor (4000-8000), whereas the dual-plane works well from idle to 6000.

Jaiden2010 06-22-2011 05:43 PM

3 Attachment(s)
I found this today for $125 I pull. Not sure if it's a 305 or 350, I can't see the casting numbers on the block. The heads are 10125320. I have no idea if it runs, it's a as is deal. I am going to build a fresh motor, as long is not junk inside maybe this is a better bet. I found it under the hood of a 60's chevy. I don't plan on running any fuel injection/computer in my S-10. I am going to run a carb. I am not skilled in playing with wiring etc. The engine harness and computer is there however. The transmission is gone. The motor is just sitting in the engine bay. Here are some pics I took with my phone and emailed to myself so excuse the quality.
Somebody did a lot of work to this Suburban it has a late model instrument cluster, late model 5 lug disc brakes, late model tilt, ABS module/setup. Looks like they just never finished the engine install. all the wiring is unplugged as with some of the fuel rails/injectors are out. Unless it happened at the yard?

eric32 06-22-2011 05:45 PM

Hey thanks Tehcinspector much appreciated. I went with a different intake for time being to help see if the minor issue I had before was caused by intake leak and it was not after all so its on there for now might step up to a bigger high rise next year but I am done for now. Just got the motor and everything else back in last week and after 6 weeks am a little burnt out for now. That gives a good idea for this guy on a decent street motor. What does it make on the dyno sim if its not to much with high rise dual plane by chance with everything else the same? Thanks guys. Hope this guy figures out what to do within his budget.

Jaiden2010 06-22-2011 05:49 PM

I have another $1000 from our taxes maybe can squeeze another $500. Ill bug the wife enough and she will want to shut me up. :spank:

eric32 06-22-2011 06:34 PM

From what I found out on those head numbers if the source is right they are a Chevy LT 1 350 which is a gen 2 small block chevy with reverse cooling. LT 1-4 heads and top end stuff will not work on gen 1 style block. There is some differences in parts mainly the top half and water pump etc. LT's are good and there heads are similar to a vortec head and if I read right vortec heads was designed after the LT head design minus the reverse cooling. Maybe others will post some more info.

techinspector1 06-22-2011 06:39 PM


Originally Posted by Jaiden2010
The heads are 10125320.

techinspector1 06-22-2011 06:52 PM

Hello Tech thanks for your help much appreciated. If you got time can you show me the numbers with a highrise dual plane non air gap design.

1500 105 368
2000 150 394
2500 188 395
3000 237 415
3500 287 430
4000 325 427
4500 354 414
5000 367 386
5500 340 325
Peak volumetric efficiency 89.5% @4000
Peak BMEP 182.4 @ 3500

Keep in mind that this is a 9.1:1 motor with a very short cam.

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