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Old 05-19-2019, 06:59 PM
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Cam timing

I'm about to take my engine to the machine shop to start getting built. I was wondering if anyone could run a simulation for me to try and figure if it would be better installing my camshaft straight up or retarded. Looking for peak HP right around 6000 RPM. I got great advice from an earlier post I made so I decided to give it another go. Build is a 383 sbc. 10.95 to 1 compression. Camshaft is 227/233 @ 50 with 560 lift on intake and exhaust. Howard's 180525-10. 180 brodix heads ported to 195. Head flow intake from 100 to 600 is:75,135,197,245,276,289. Exhaust flow from 100 to 600:55,112,159,189,204,210. Intake is an eldebrock rpm airgap portmatched to the heads. Will be running a 3000 stall convertor. Gears aren't decided yet. Will run between 3:55 to 4:10. I'm thinking the cam will be peaking around 5800. CSA of heads is 2.24. Thanks in advance.

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Old 05-19-2019, 07:22 PM
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By moving the cam retarded, what are you hoping to accomplish??

Retarding cam 4 will slightly increase HP above the torque peak, 4-8 HP or so, while at the same time hurting torque below the torque peak, 9-15 ft.lbs.

Give me a bit and I'll see if I can run it through the program I've got. and give you a more definite number.
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Old 05-19-2019, 07:25 PM
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Quote:
Originally Posted by ericnova72 View Post
By moving the cam retarded, what are you hoping to accomplish??

Retarding cam 4 will slightly increase HP above the torque peak, 4-8 HP or so, while at the same time hurting torque below the torque peak, 9-15 ft.lbs.

Give me a bit and I'll see if I can run it through the program I've got. and give you a more definite number.
Agree with Eric, retarding the cam 4-6 degrees will max out the top end at the expense of the bottom end. There ain't no free lunch.
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Old 05-19-2019, 08:18 PM
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The question that never seems to get asked around here is what are the intentions of the build? Looking for peak HP at about 6000 would tell me that is where you expect the engine RPM to be at a certain point on the track. Everybody knows that moving a cam around from it's base point changes the RPM characteristics. Retarding pushes the peaks to the upper range, advancing moves them to the lower range. Your selection of gear ratio indicates to me that you hope to overcome some of the lower end loss by getting the engine up on it's power curve quicker. The converter selection in my opinion does not help that intention as I believe it will be too tight but I have a bad preference for looser converters.


Other factors that could help with your question would be the final weight of the vehicle, fuel type and any power adders.
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Old 05-19-2019, 08:25 PM
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Numbers according to Desktop Dyno 2000, figured with 800 cfm carb/throttle body and 1-5/8" tube open headers...

Straight up cam timing:
2500 RPM - 211 HP / 442 TQ
3000 RPM - 258 HP / 451 TQ
3500 RPM - 311 HP / 467 TQ
4000 RPM - 366 HP / 480 TQ
4500 RPM - 418 HP / 483 TQ Peak torque rpm
5000 RPM - 454 HP / 477 TQ
5500 RPM - 478 HP / 456 TQ
6000 RPM - 489 HP / 428 TQ Peak Hp rpm
6500 RPM - 482 HP / 389 TQ
7000 RPM - 464 HP / 348 TQ

Retarded 4 cam timing:
2500 RPM - 207 HP / 434 TQ
3000 RPM - 249 HP / 437 TQ
3500 RPM - 302 HP / 453 TQ
4000 RPM - 355 HP / 466 TQ
4500 RPM - 406 HP / 474 TQ Peak torque rpm
5000 RPM - 446 HP / 469 TQ
5500 RPM - 476 HP / 454 TQ
6000 RPM - 486 HP / 426 TQ
6500 RPM - 489 HP / 394 TQ New peak Hp rpm
7000 RPM - 474 HP / 355 TQ
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Old 05-19-2019, 08:39 PM
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That answered my question exactly. Wasn't really sure where it would peak at being installed straight up. I was thinking it would have enough bottom end to be able to give a little to add to the top but I dont want to spin it higher than 6500RPM for sure. From the looks of your sim I'll be very happy with it running straight up. I appreciate the time taken out of everyone's day to help me out.
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Old 05-19-2019, 08:49 PM
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Same thought I had, you'd need to spin it to 7000 rpm all the time to really take any advantage or retarding it....in a street truck with 3.73 gears you'd end up slower.

Take the actual HP figures from DD2000 with a grain of salt, some of the part choices like intake manifold and exhaust can't be fine tailored close....figure it being 20 HP, maybe even a little more, overly optimistic....but it is good for spotting trends in how cam advance or retard changes things, or comparing different cam grinds quickly.
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Old 05-19-2019, 09:21 PM
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I'm sure it will be close enough for me. I'll actually be running 1.60 roller rockers on intake and 1.52 on exhaust so that might put it a little closer. Also looking into just a tad bigger headers. Either way it looks like its gonna do what I intended to do. My first engine blueprint and couldn't be closer to what I was wanting so I'm good with it.
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