Dynosim required data
- Rod Length
- Cylinder head flow, intake and exhaust 0.100" through 0.700" or whatever the mfg gives for range
- Intake valve diameter
- Exhaust valve diameter
- Static compression ratio
- CFM, type of induction (2-bbl, 4-bbl, TBI, TPI)
- Intake manifold type, mfg (single 4-bbl, two 4-bbl, one 2-bbl, three 2-bbl, individual runner Weber, mechanical fuel injection, low-rise, high-rise, tunnel ram, dual-plane, single-plane, part no. if you have it.
- Exhaust system (be specific, primary tube size if long-tube headers).
- Part number, grind number.
- Type (flat, roller, solid, hyddraulic).
- Intake valve lift, exhaust valve lift.
- Timing info and at what tappet lift the info is valid, i.e. 0.006", 0.050", etc.
 The following will show horsepower and torque results using different combinations of parts
OK, first things first. I have to agree that the DynoSim results sometimes seem optimistic, but consider this. The software is configured with the premise that the hard parts will be tweaked by the builder, the build dimensions will be blueprinted to the loose side and the final tuning will be spot-on. There's an old saying in hot rodderdom, "Loose is fast".
And when I run a sim, I change things around considerably to get to the final figures. It will take me an hour or better to do it properly on just one motor. You may have seen, sometimes I will include verbage like "tried 6 different cams, retarded 'em, advanced em', 3 different manifolds, 4 different static compression ratios, etc." Just changing the cam requires runnin it straight up, advancing 2 degrees, then 4 degrees, then retarding it 2 degrees, then 4 degrees. So I have 5 different sets of figures just for 1 cam. Do that with 6 different cams and you have 30 sets of numbers.....just for the cam.
Now, multiply that times different manifolds, different static compression ratios, etc. and you can see where it is a time-consuming task to sim a motor. But that's who I am. If I can't do it right, I won't do it at all. You can rest assured that when I post a sim, the motor has been tweaked to within an inch of its life. It's as good as it's gonna get with the parts used. Use different parts and you will get a lesser result. Anyway, that's probably why some fellows question my numbers, because they've never done what I've done with the software. Most people don't have the time or patience to do it the way I do, but I'm retired, have the time and patience and like nothing better than to start with a clean sheet of paper and "build" a motor.
I have checked the results I get against real dyno pulls and this DynoSim has shown to be within 2% of real. Not bad in my opinion. I'm seriously considering upgrading to DynoSim5 and an add-on cam file. I have 800 cam files now, but the add-on would give me 6000 files. I was dragged kicking and screaming into the computer age, but I'll tell you, there's nothing any more fun than dinkin' on this thing. Well.....there was that time in New Orleans, but that's a whole 'nuther story...
 355 SBC street motor, budget build
- Block: '68-'86 Chevy 350 Gen I bored +0.030". Check main bearing bore for round and parallel, align hone or align bore as necessary to correct the bores and insure they are round. Once the main bores are done, register the block from the main saddle and cut the block decks to square the block up and set the squish where you want it. Don't try to cut corners here, this lays the foundation for the work and parts to come.
- Crank is the stock 350, 3.48" stroke, 2.450" main journal diameter.
- Rebuilt rods are sufficient for this build. If using an existing set of stock rods, ARP hardware and resizing is recommended.
- Scat makes a decent set of 5.7" forged rods that are affordable.
- Pistons: Keith Black hypereutectic, p/n KB193, 12cc D-cup, 5/64,5/64,3/16 rings. 1.561" compression height. Gap top ring 0.026", second ring 0.018".
- RHS Pro Torquer Vortec heads, p/n 12410, 2.02" intake, 1.60" exhaust. These heads will accept either conventional or Vortec type intake manifolds, they are drilled and tapped for both types. More on using an early style intake on a Vortec style head can be seen here.
- Intake manifold: Dual plane, highrise such as the Edelbrock RPM p/n 7101, Weiand Stealth p/n 8016, Holley p/n 300-36 or Professional Products Typhoon. Check ebay and craigslist for used manifolds if your budget is tight.
- Carburetor: Vacuum secondaries 750 CFM.
- Headers: 1-5/8" primaries, long-tube. Install "X" pipe between collectors and mufflers. Run 2-1/2" pipe to the rear through mufflers of your choice.
- Camshaft: Comp Cams 260H flat tappet hydraulic, installed straight up.
- Rocker Arms: 1.6 ratio on both intake and exhaust.
- Static Compression Ratio: 9.6:1
- Dynamic Compression Ratio: 8.4:1
- Quench: 0.035" to 0.045". Zero piston deck height with 0.035" to 0.045" head gasket or 0.010" to 0.020" piston deck height with Victor Reinz p/n 5746 head gasket that compresses to 0.025".
- RPM HP TQ
- 1000 59 310
- 1500 103 361
- 2000 150 395
- 2500 192 402
- 3000 246 431
- 3500 306 459
- 4000 360 473
- 4500 407 475
- 5000 442 464
- 5500 453 433
- 6000 450 394
Stock converter and stock rear gear will work, but would be more fun with a converter that stalls at 2000 to 2200 rpm and a 3.73 rear gear.
 383 SBC stroker 485 hp/496 ft-lbs torque
Staying with RHS, using the Pro Action 180cc heads and reducing the advertised flow by 5% to get closer to real world results, the flow used for this build on a 383 will be as follows:
Lift Int. Exh.
.100 70 55
.200 143 96
.300 197 149
.400 231 168
.500 245 177
.600 250 181
.700 257 185
- This uses a 350 block bored to size, a 3.750" stroke crank and 5.7" rods. Scat makes a cast crank and capscrew I-beam rods that will work here. Have your machine shop sonic test the cylinder walls for thickness if the bores need to go more than 0.030" over. Smokey Yunick used to recommend a minimum cylinder wall thickness of 0.135" after boring and honing.
- Heads: Racing Head Service Pro Action 180, 72cc chambers, 2.02" intake, 1.60" exhaust.
- Pistons: Keith Black hypereutectic #KB134, 7cc flat-top, 5/64-5/64-3/16 rings, 1.433" compression height.
- Intake manifold: Dual plane, highrise such as the Edelbrock RPM, Weiand Stealth or Professional Products Typhoon.
- Carburetor: 850 cfm vacuum secondary.
- Headers: 1-5/8" to 1-3/4" primaries, long-tube. Install "X" pipe between collectors and mufflers. Run 2-1/2" to 2-3/4" pipe to the rear through mufflers of your choice.
- Camshaft: Comp cams 12-212-2 Comp Cams hydraulic flat tappet, installed 2 degrees retarded.
- Rocker arms: 1.6, lift at valve 0.512".
- Static compression ratio: 10:1.
- Dynamic compression ratio: 8.2:1.
- RPM HP TQ
- 2000 148 389
- 2500 188 395
- 3000 242 423
- 3500 307 461
- 4000 370 485
- 4500 425 496
- 5000 465 488
- 5500 485 462
- 6000 481 421
 383 SBC stoker 505 hp/500 ft-lbs torque
Same motor as above with Comp Cams solid lifter flat tappet cam, 1.5 rockers.
- RPM HP TQ
- 2000 145 382
- 2500 185 390
- 3000 239 418
- 3500 303 455
- 4000 370 485
- 4500 427 500
- 5000 466 490
- 5500 493 471
- 6000 505 441
- 6500 481 389
 350 SBC L31 heads
Flat tappet hydraulic cam, stock self aligning (SA) rockers, some head work for better springs.
In this build, a tight budget is called for. To that end, use stock self aligning rockers. Lift is under a half inch, so the SA rockers should be OK. Check to see if using a -0.050" lock will be needed to insure the valve tip sticks up far enough above the retainer so that the retainer top surface doesn't get loaded by the side rails of the rail rockers. More info on checking clearances, etc. under Resources.
- Bore the block 0.030", use these or similar 12cc dished pistons w/5.7 rods.
- Makes 9.6:1 static compression ratio. Cut block decks to zero and use a 0.040" head gasket.
- Use XE274H Comp cam (cam card), installed at straight up.
- Comp p/n 981 valve springs, p/n 750-16 retainers, p/n 630-16 keepers and stock 1.5 rail rockers. 1.250" springs should be OK because the cam is a moderate grind, hydraulic flat tappet.
- Machine the OD of the guide bosses to less than the I.D. of the damper spring and cut for PC-type positive seals.
- Cut top of guide for 0.550" play from bottom of retainer to top of guide seal. Pin the pressed-in rocker studs with this kit.
- Performance Distributors custom curved HEI distributor, p/n 12720, or build your own from a GM HEI.
- Edelbrock RPM Vortec intake mounting a 750 vacuum secondary carb of your choice. Edelbrock, Rochester 5 psi max at the inlet, Holley 6 psi max at the inlet.
- Performer RPM Vortec w/natural finish: p/n 7116, w/EnduraShine finish: p/n 71164, w/polished finish: p/n 71161, or look for a used manifold on craigslist to save a few shekels.
- Long-tube 1-5/8" headers with X or H pipe right after the collectors, 2-1/2" to 3" pipes to the rear through mufflers of your choice.
- Use 2500 stall converter, shorter rear gears.
- RPM HP TQ
- 2000 138 364
- 2500 176 369
- 3000 224 392
- 3500 281 421
- 4000 331 435
- 4500 370 432
- 5000 402 422
- 5500 405 386
- 6000 375 328
- Peak dynamic compression ratio 8.16:1 on KB's calculator.
- Peak volumetric efficiency 97.2% @5000
- Peak BMEP 184.5 @4000
 350 SBC dual four barrels
- Pistons: Keith Black flat-top, 7cc's, 1.561" CH p/n KB106-030.
- Heads: Edelbrock E-Street p/n 5073, 185cc intake runners, 70cc chambers, 9.53:1 SCR. Published flow was factored by 0.95 for this exercise.
- High leak-down rate flat tappet hydraulic lifters such as Crane p/n 99377-16 Hi Intensity Hydraulic Lifters because we are going to use "too much" cam for the SCR. These lifters will reduce duration by 6-10 degrees under 3000 rpm for better bottom end torque.
- Cam: Crane p/n 110591 Saturday Night Special flat tappet hydraulic, installed 2 degrees retarded.
- With pistons at 1.561", rods at 5.703" and crank radius at 1.740", the stack measures 9.004", so with a nominal 9.025" block deck height, you would need to make a cut of 0.021" to get to zero deck. A 0.040" compressed gasket would then put the squish at 0.040".
- 1-5/8" long tube headers.
- Edelbrock 2x4 RPM intake manifold mounting two 500cfm carbs.
- RPM HP TQ
- 2000 145 381
- 2500 184 387
- 3000 229 401
- 3500 284 427
- 4000 337 445
- 4500 378 441
- 5000 409 429
- 5500 420 402
- 6000 400 349
- Peak volumetric efficiency 92.1% @5000
- Peak BMEP 187.8 @4000
- This motor should be waaaaaay fun with a 4-speed or auto with a loose converter.
 400 SBC street/strip truck motor
- 400 block bored 0.030" and zero decked to the piston crowns, align honed main bearing bore.
- Scat p/n 9-400-3750-5700 cast steel Pro Comp crankshaft.
- Scat forged I-beam 5.7" rods.
- Keith Black p/n UEM-KB168-030 hypereutectic pistons with 22cc dish to make 9.8:1 static compression ratio with 64cc heads.
- Comp Cams p/n CCA-12-430-8 retro-fit hydraulic roller cam installed 2 degrees retarded.
- Howard's retro-fit hydraulic roller lifters.
- Comp Cams p/n CCA-200 thrust button.
- Comp Cams p/n CCA-201 wear plate.
- Edelbrock p/n EDL-7101 Performer RPM intake manifold.
- Dart Iron Eagle Platinum 215 cast iron heads, p/n DRT-10521123P (price shown is for one head).
- Barry Grant Speed Demon 750 (BG is now defunct, so a similar carb may be substituted).
- Hedman Elite headers, 1-3/4" primaries.
- RPM HP TQ
- 2000 154 405
- 2500 195 410
- 3000 250 438
- 3500 319 479
- 4000 386 507
- 4500 446 521
- 5000 486 511
- 5500 511 488
- 6000 515 451
- 6500 490 396
Note: L31 Vortec heads need work to use enough cam to make really good power. This can run into a lot of money. It may be cheaper to start off with an aftermarket head in the first place. That said, using production Vortec heads this 406 SBC combo did make an estimated 450 hp and 482 ft/lb of torque. But using a set of Dart heads the same combo made 515 hp and 521 ft/lb torque.
Use 16 degrees initial timing advance and 18 degrees of mechanical advance for a total of 34. If the motor needs a little more total, move the lead at the crank to 18 degrees. You will not need a high-dollar ignition system. A rebuilt GM HEI will work nicely. See Hot rodding the HEI distributor for more info.
 Fuel pressure
If you have too much fuel pressure, it will blow past the needle and seat in the bowl and into the intake manifold as raw fuel. This will cause you untold tuning nightmares, so get this under control first thing. Do not assume that published pressures are correct- you need to verify the pressure by using a gauge.
Run a nylon or copper line from the carburetor inlet back to the firewall and up past the hood lip to the cowl of the truck. On the cowl, temporarily mount a mechanical fuel pressure gauge (0-15 psi) so that you can view it through the windshield as you drive. Regulate fuel pressure down to 5 to 5-1/2 psi.
 Steam holes
The 400 block will require that you drill steam holes in the heads. Any manufacturer you buy from will drill them for you before they ship the heads to you. Install the heads with a head gasket that is designed for installation on a 400 block because the gaskets will also have steam holes in them from the manufacturer. Here is more info.
Use a composition gasket that compresses to 0.039" to 0.041". With the zero deck of the block, this will put the piston crown at 0.039" to 0.041" from the underside of the cylinder head with the piston at TDC. This establishes your "squish" dimension at 0.039" to 0.041", which will optimize the motor for detonation-free operation on pump gas.
 SBC pump gas street cruiser
- 375-400 horsepower, 425+ lbs/ft of torque with 9.0:1 static compression ratio.
- Stock converter
- Mild cam (204-212 degrees intake duration @ 0.050" lift, 110 LSA)
- Edelbrock Performer RPM intake
- 750cfm carb
- 1-5/8" long-tube headers
- Around 3.50:1 rear gear
- This build uses bare RHS heads. They're inexpensive and they work good. They're filled out with good quality valves, etc. Or they can be bought assembled.
- Here's the cam (installed retarded 2 degrees).
- Roller lifters.
- Use a Howards p/n 94402 composite distributor gear, it will outlast a bronze gear 3 to 1.
- RPM HP TQ
- 2000 148 390
- 2500 188 395
- 3000 238 417
- 3500 292 439
- 4000 342 449
- 4500 379 442
- 5000 401 421
- 5500 400 382
- 6000 355 310
 400 SBC with Vortec heads
This combo is best at building a lot of torque in the 3,500 rpm range. L31 heads on a 406 will not lend themselves to top end hp, so use them where they work the best. On a 400 ci engine that will be to make bottom end and midrange torque.
- Keith Black p/n KB168-030 hypereutectic pistons.
- Scat Pro Stock 5.7" rods. These rods are clearanced for the cam right out of the box. Minimum clearancing may be necessary at the pan rail for the big end of the rods.
6" rods can cause the wrist pin to get up into the oil ring land. This adds a little more complexity and more things to go wrong than if you were to use a 5.7" rod.
With nominal +/- 66cc heads (production head combustion chamber volumes are often larger than published data), these 22cc D-cup pistons will produce 9.6:1 static compression ratio. An added benefit is the tall 1.433" compression height, meaning less block deck to cut off to reach a target squish of 0.035" to 0.045".
Besides boring and honing, machine shop work will include align honing the main bearing bores and cutting the block decks square and to the proper deck height to work with the piston compression height and gasket thickness to set the squish.
Stock block deck height is +/- 9.025". The height of your stack of parts will be 1.875" for the crank throw radius, 5.700" for the connecting rod center to center and 1.433" for the piston compression height, for a total of 9.008". Using a gasket thickness of 0.039"/0.040", the block decks will have to be cut 0.017" to reach a zero deck. This will put the squish at 0.039" or 0.040", depending on the head gasket used. Decking the block will also insure that the block decks on all four corners of the block are the same distance from the main bearing centerline, meaning that static compression ratio will be closer to equal across all cylinders and will also contribute to the heads and intake manifold lining up and sealing the way they're supposed to.
Thinner shim head gaskets used to be available for the 400, but not any longer. If 350 shim gaskets are drilled for steam holes, they might have a large enough bore diameter to work on the 400 block, but this has to be carefully checked to be sure there's no overhang of the gasket into the bore. If the shim gasket intrudes into the cylinder/chamber, it could be a potential cause of pre-ignition/detonation. It's better to use a composition gasket that is engineered for the purpose and cut the decks accordingly. Speaking of steam holes, the heads will have to be drilled for them. Drilling steam holes in smallblock Chevy heads has info on this procedure.
This build uses a low-cost hydraulic flat tappet cam and the stock L31 valve springs and retainers. The rpm limit with this motor will be 5000, so there's no need to make any changes to the heads except maybe replacing the seals, unless there's a need for new springs. If you want to keep some safety margin (total of at least 0.050" between the 5 coils, and a safety margin for retainer-to-seal clearance), then you should limit valve lift to 0.420- 0.450". There's no need for 1.6 ratio rockers for this build, either.
Crane has a cam that uses easy ramps and will fall right into the static compression ratio range we will use in this motor. #10017 has an operating range of 1800-5400. Here's the p/n 100172 kit which includes lifters. Always buy quality lifters. Get them with the cam if possible.
Crane's description says this cam needs a 2500 converter, but with the amount of torque the engine will make down low a stock converter and a 3.50 gear will suffice. The lobe separation angle of 106 degrees will help make the bottom end torque that's needed for a stock converter and 3.5:1 range rear gears. The 0.450" lift will work with the stock springs and retainers. Be sure to use feeler gauges between the spring coils at full valve lift to insure that the springs don't stack solid. In theory, they shouldn't, but they have to be checked to be sure. Use 16-18 degrees of initial advance with an additional amount of mechanical advance to bring the total initial and mechanical to 34 degrees. That's all you need with these heads. You need more at the crank than you would with a stock cam though, for the motor to idle properly. We need to bring the idle down for use with a stock converter so we don't have to stand on the brake pedal at stoplights. See Hot rodding the HEI distributor for details on this and for using a vacuum advance.
To the long block, add an Edelbrock Performer RPM intake manifold and top it off with a rebuilt Edelbrock Thunder series AVS 650 CFM manual choke carburetor, p/n 1805. Also get the Edelbrock choke cable p/n 8013.
Mount a 14" x 4" air filter on top. Stack two 14 x 2's if you can't find a 4" thick element. This (and any) motor needs to breathe. Bolt on a pair of long-tube 1-5/8" to 1-3/4" headers and connect the two sides of the exhaust system by using either an X or an H pipe right after the collectors. Use the mufflers of your choice.
- RPM HP TQ
- 1500 122 426
- 2000 174 457
- 2500 217 457
- 3000 268 470
- 3500 315 475
- 4000 354 465
- 4500 380 441
- 5000 373 392
- 5500 326 311
There you have it boys and girls, a tire-shredding motor with a "flat-as-a-table" torque curve and a cam that will have a slightly rough idle so the OP can pose cool down at the Sonic Drive-In.
When using a flat tappet cam, break in is uber important. Read up on what to do and how to do it here.
 350 SBC- Cheap to build/regular fuel street motor
- These pistons
- This cam
- Vortec L31 heads from a boneyard, casting number 12558062 or 10239906. Magnaflux for cracks. Fit new stock or equivalent 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 will work. Same casting, both styles flow the same. Give them a three angle valve job and backcut the valves if they're not already done. Use the self aligning stock rockers that came on the heads.
- 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 a vacuum leak. Use GM head gasket #10105117 or equivalent.
- Static compression ratio will be 9.1:1 and squish will be 0.042". Use Edelbrock p/n 7116 Performer RPM intake manifold. A 600cfm carb is all that's needed.
- Makes 365 hp @ 5000 rpm with a double torque peak of 420 ft/lbs @ 3500 and 4000 rpm. Should make this power on regular pump gas without detonation and make for a real nice daily driver motor.
- The cam begins making power at 1200 rpm, so there's little need for a looser converter. A 2000 stall converter would be all that wouold be needed to keep the car from creeping at stoplights and also to get up into the 1500 rpm bottom range of the intake manifold at the hit of the throttle.
 Comp Cams free simulation program
- Camquest, Comp Cams engine simulation program
- Valve spring tech
- Valve train geometry
- Valve train points to check
- Hot rodding the HEI distributor
- Drilling steam holes in smallblock Chevy heads
- Camshaft install tips and tricks
- Computer dyno simulation and engine building software
Return to 350 SBC L31 heads