Thread: 400 hp sbc 350

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So im wanting to make at least 400 horsepower without nitrous on a stock bottom end and stock heads...i was thinking about putting in a big cam, springs, rocker arms, intake, and carb. What do yall think will be the outcome, maybe some help on which parts to use? Thanks everyone

try this.

edelbrock.com

Installing a long cam on an otherwise stock motor with very low static compression ratio will result in the motor producing less power than it did before the cam swap. This scenario has been played out in all areas of the world by people who don't understand that it takes a COMBINATION of the correct parts to make a good motor. The mistake was made yesterday, it is being made today and it will be made tomorrow.

Well said Tech., theres a couple good rebuilding books you can get from places like Summit. They usually have proven combos. Dont get discouraged though by anybodys words here they just dont want you to make a mistake. Tech had a great link to proven combos I wish I would not of lost, hint.

Originally Posted by BigTruckDriver

Well said Tech., theres a couple good rebuilding books you can get from places like Summit. They usually have proven combos. Dont get discouraged though by anybodys words here they just dont want you to make a mistake. Tech had a great link to proven combos I wish I would not of lost, hint.

http://www.ryanscarpage.50megs.com/combos1.html

Thats the one, thanks tech. , I like reading over the info. bookmarking now

Found out tonight that the motor was rebuilt not to long ago, so its a 355 with i think flat top pistons and the stock heads with apparently a valve job...and i knew about the combination stuff, i was asking what kind of combo could i use without dropping a grand into buying some new heads? Like cam springs pushrods rockers lifters intake and carb

Ok found out tonight that the motor has a rebuilt bottom end, bored 30 over with i think stock crank and rods, just bigger pistons...the heads apparently have had a valve job, i dont know exactly what...and i already knew about the combo thing working best but without dropping a ton of money on heads what kind of cam springs lifters pushrods rockers intake and carb should i use to get hopefully a little over 400 at the flywheel? Thanks for all the future help

need a ton more info than your giving.

I was going to stay out of this, but it’s just too hard not to throw in my two cents.

First off, welcome to CHR. We’re really a good bunch of hot rodders and you’ll find a lot of valuable information on this site. You’ll also find that there are a lot of opinions as to how things should be done. One of the areas where you’ll get very strong opinions is in the engine build section with SBC probably getting the most attention. Don’t know if that’s because there are more SBC “experts” or if there’s just so many small blocks out there that everyone has become a “self-proclaimed” expert.

Your post reveals your desire to, “make at least 400 horsepower without nitrous on a stock bottom end and stock heads.” I could write a book on that statement alone, but here’s a few pointers to you started:

1. Get us the casting numbers on your engine and your heads. The venerable 350 will make 400HP easily with the right components – but we need to know what foundation you’re building on. If you tell me you have GM 12558062 Vortec heads I’ll get real excited. They typically flow 225 to 230 cfm at 0.450- to 0.500- inch lift and are one of the best factory heads on the planet. If you’ve got 3998991 low compression smog heads – 1.72 intake and 1.5 exhaust valves with 75cc combustion chambers I’m not so excited.

2. Bored .030 over is good if you’ve got flat top pistons. Rebuilders typically install cast, dished, low-compression pistons unless they’re directed otherwise. As such, compression is in the 8-8.5:1. Not enough to make good horsepower.

3. In my opinion, static compression ratio needs to be 9.8:1 or higher to make good HP. Others will differ, but most will agree that without knowing your SCR, you’ll be spinning your wheels and wasting your hard earned dollars. To calculate SCR you need to know:
• Bore-- The diameter of the cylinder bore
• Stroke-- The distance the piston travels in the cylinder
• Deck Height-- The distance between the top of the cylinder bore and the top of the piston, when the piston is at TDC (Top Dead Center, or at its highest position
• Compressed thickness of the head gasket-- varies with gasket manufacturer and application
• Piston top volume-- If the piston is dished, domed, or flat it affects the compression ratio.
• Combustion chamber volume-- How much open space (in cc’s) is in the head above the cylinder
Once you have the above information, use this handy little calculator and fill in the blanks - http://www.rbracing-rsr.com/compstaticcalc.html.

The easy variables to change are the head gasket thickness, head (combustion chamber volume) and piston style - in that order.

4. Regardless of your heads, the Edelbrock Performer RPM and a 650CFM combination is a good value. Yes there are others (Victor for one) – but this combo is a great bang for your buck.

5. Cam – lots of variables here – transmission, rear-end ratio, stall speed of converter (if automatic), weight of car, what operating range do you want? A very safe bet is Edelbrock Performer-Plus cam and lifter kit - $124.95 Summit Racing Part Number EDL-2102. It’s a hydraulic flat tappet with an idle-5,500RPM range. Intake duration at 050 inch is 204 degrees; exhaust duration at 050 inch is 214. Advertised intake duration is 278 degrees and exhaust duration 288 degrees. Valve lift with stock 1.5:1 rocker arms is 0.420 int./0.442 exh. Very safe.

6. Headers and 40 series Flow Masters and you’ll have some nice sound too.

To recap:
• Get your SCR to 9.8:1 or higher
• Heads that flow well (Vortecs are winners)
• Flat top pistons
• Thin head gaskets
• Moderate cam
• Edelbrock Performer RPM and 650/750 vacuum secondary carb
• Headers (1-5/8, four into one)
You’ll have 400+ horsepower and 425+ f/lb torque

Good Luck,
Glenn

Originally Posted by bigtruckdriver

need a ton more info than your giving.

what more info do you need?? Ill try to figure it out

I looked at the casting numbers, the ones on the block are gm 3970010 and the heads are gm 333882...hopefully that helps, what would you suggest i do to the heads?

Well – there’s some good news and some “not-so-good” news. Your block was produced from 1969 to 1979 and used in cars, trucks and even in a few Corvettes. It came in 2 and 4 bolt with advertised horsepower ratings from 185 to 370. Not bad. The heads - another story.

The 882's have hardened seats and that tends to make them prone to cracks. They were one of the first factory hardened seats and it took GM a few years to get this right. Some would tell you that 882's are the "best" of the worst heads.

There are two good “versions” of this head:

L48 (1970 – 1980, cars, trucks and some Corvettes) w/1.94 intake/1.50 exhaust, 76 CC Chambers - flow is not-so-good, i.e., intake +/-137cfm, exhaust is a measly 95cfm. These are the early series used in the low output (believe it or not, 1973 Corvette used this and was rated at 190HP!). These are the most crack prone!

L82 heads (1973 – 1977 Corvettes and some Impalas - 210 – 250 horse,) had 2.02/1.60 valves, guide plates, 76cc chambers, 151cc intake runners and flow increased to 206 cfm on the intake and 145 cfm on the exhaust. With some “gasket matching” porting you can squeeze another 10cfm on both intake and exhaust. With “serious” work, the L82’s can get into the 226/158 cfm range but you need a real head pro machinist and be prepared to part with a paycheck - $750 plus – but why would you rework a tired old smog head when you could get a set of Vortecs or go aftermarket.

There were actually three series of these castings. The third is a “red-headed step child” that uses 1.72 intake and 1.50 exhaust - that was used on 2 barrel truck/passenger car applications. They look deceptively like the L48, but trust me – they different (use a .3750 [3/8”]” stem as opposed to the .3414”).

See if you can find a set of used 96-00 Vortec 350 truck heads they flow 229/162 cfm stock and don’t seem to be as prone to the cracks. Some on ebay for $500 w/free shipping. Another set of 12558060, brand new for $585.

Hope this helps,
Glenn

thanks, what kind of cam intake and carb would you run with a set of vortec heads? and when i put a big cam in it would i need to swap out springs or anything in the heads

Okay – so we know you have a 350 +.030 over (bore = 4.030) with flat top pistons with no valve reliefs. We know the stroke is 3.48. We know Vortec combustion chambers are 64cc. Don’t know the deck height yet, but you’ll get that when you remove the heads – but let’s say it’s .020. Use a .028 head gasket and you should have a static compression of 10.47. Not bad at all…

When you get the heads off and if you something different, go to http://www.rbracing-rsr.com/compstaticcalc.html and recalculate.

Vortec heads perform best with asymmetrical cams because their design focuses on a significant intake flow (hence the name "Vortec" [from VORtex TECnology]) however; they have similar exhaust flow characteristics as any other stock head. As such, to move more air through the head one needs to make the openings flow more, or hold the valve open longer. If we consider this to be a mathematical equation and we’re drawing more air in, we need to move equal volume out and since the exhaust port flows less than the intake; you hold the valve open wider and longer to compensate for the difference.

On the Vortec head, the maximum lift before the spring retainer hits the valve guide seal is 0.530 inches (see picture below). Generally accepted practice dictates that 0.060 inches of clearance should be maintained between the retainer and seal (0.530 - 0.060 = 0.470 maximum valve lift). As such Vortec heads, in their stock form are capable of accepting a camshaft with a maximum valve lift of 0.470 inches. The valve guide seal will be pinched between the retainer and guide if valve lift exceeds 0.470 inches. Some will say, “I’m running .480 on my stock Vortecs with no problems!” That may be true – for a while, but what they won’t tell you is they are also seeing a “bit o’ smoke” on start up as the valve seals become compromised.

With stock Vortec heads, a good bet would be a COMP Cams CL12-238-2 (“aka” EX-262), Summit Racing kit (with lifters) is $185.95. This cam gives you:
Advertised Duration - 262 intake/270 exhaust
Valve Lift with Factory Rocker Arm Ratio - 0.462 intake/0.469 exhaust
Lobe Separation – 110 degrees
RPM Range – 1300 - 5600
Note – a bit more duration and lift on the exhaust site to compensate (as per the above)

You could also use the Summit Racing SUM-K1102 at $100.95, a bit less money and notice with this profile the power curve drops – however – many street machines rarely see above 4800RPM. Specifications:
Advertised Duration - 262 intake/272 exhaust
Valve Lift with Factory Rocker Arm Ratio - 0.420 intake/0.442 exhaust
Lobe Separation – 112 degrees
RPM Range - 1200 - 4800

If you have heads machined to accept a higher lift, the COMP Cams CL12-242-2 is a tough one to beat:
Advertised Duration - 268 intake/280 exhaust
Valve Lift with Factory Rocker Arm Ratio - 0.477 intake/0.480 exhaust
Lobe Separation – 110 degrees
RPM Range - 1600-5800

Good Luck,
Glenn