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04-24-2019, 07:43 AM | #26 |
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Re: Rebuilt 350 - detonation --> Cam swap?
Interesting read. I guess the OP has some timing to back off.
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04-24-2019, 07:45 PM | #27 | ||||
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Re: Rebuilt 350 - detonation --> Cam swap?
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It sounds like some motors like less advance, I guess. Quote:
Quote:
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I was ALWAYS taught that Small block Chevys like [Need] between 32 and 36 degrees total timing or you're giving up power. I will play with the timing and see what happens. I'll keep this post updated. |
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04-27-2019, 10:38 PM | #28 |
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Re: Rebuilt 350 - detonation --> Cam swap?
Isn't your .061 quench in the detonation danger zone? Need .035-.045.
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05-26-2019, 06:11 PM | #29 |
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Re: Rebuilt 350 - detonation --> Cam swap?
So, I finally got back around to working on my truck.
Here's what I learned; I reinstalled a brand new MSD street fire dizzy. I set the initial timing to 4* without vac-adv mechanical came in at 25* set the vacuum advance for an extra 10* and my timing at idle jumped to 15* with vac-adv attached Seems happy, idles smooth, decent torque, starts easy. Probably not 100% dialed in, but it is a solid starting point.My truck runs great with the original cam and heads, No parts swapping required This has been a learning experience, and I have had to admit that I might not understand timing and combustion quite as well as I thought I did. (I know a little more now though ) Seriously, thanks for all the help and suggestions. |
05-26-2019, 07:23 PM | #30 |
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Re: Rebuilt 350 - detonation --> Cam swap?
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05-26-2019, 08:01 PM | #31 |
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Re: Rebuilt 350 - detonation --> Cam swap?
geezer is right on the link.....I run 16 deg initial with 20 deg mechanical advance in the distributor for a total of 36 deg mechanical timing all inby 2500 rpm. At idle with 10 degrees of vacuum advance it idles at 26 degrees. Fires up at a touch of the key and shuts down without dieseling using the full manifold vacuum port on the carb.
This method works great just takes a bit of time and patience. |
05-26-2019, 10:16 PM | #32 |
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Re: Rebuilt 350 - detonation --> Cam swap?
If your running that much compression with iron heads you should of decked your block to zero deck and went with a .039 head gasket.
Your cam is also too small for that much compression. You need to bleed some off. A ran I to all of this last winter with my build. I built a 350 bored .040 over. 9.9 compression with iron heads. Dart iron eagles. 7cc 2 valve relief pistons, zero deck, my quench is .039. My cam is .221-.221 duration @.50 lift is .470-. 470 4 barrel holly with performer intake, headers. My compression test was 190psi - 192psi per cylinder. 16 degrees of Initial timing with 20 degrees built in. 36 total. No detination on 89 octane. The key is to have your quench on the money if your going to try to have that much compression. Needs to be around .035-.045. I didn't loose any botton end tourqe with my cam. I have 30in tall rear tires and can break them loose at a 25mph roll. I do have a 2000 rpm stall with a th400 tranny. |
06-15-2019, 07:38 PM | #33 |
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Re: Rebuilt 350 - detonation --> Cam swap?
Are we talking ally heads here? Just checking. Cos If steel heads should be looking for 9-1 surely
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06-15-2019, 07:54 PM | #34 |
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Re: Rebuilt 350 - detonation --> Cam swap?
185 cranking pressure is perfect for a performance aluminium headed motor on pump gas. If you have iron heads that’s surely your problem. Backing the timing off is a way round it but the consequences are a big loss in performance and economy. Total timing should be 34-36 as previously stated. If you haven’t milled the block. 76 cc heads and flat tops puts you around 9-1 compression which would be perfect with a small ish torque cam. Good luck hope you get it dialled
Last edited by Sparky dave; 06-15-2019 at 08:08 PM. |
12-10-2020, 11:03 PM | #35 |
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Re: Rebuilt 350 - detonation --> Cam swap?
THREAD RESURECTION:
I got tired of the mediocre power of this motor with 28* total timing. I decided to tear it down and do an exploratory surgery. This is what I found. SPOILER ALERT, some of my previous calculations were off. Actual numbers: Pistons---------------8cc, Flat top with 4 valve reliefs, Measured with a syringe Head-----------------65cc, Advertised, also measured with a syringe Piston to deck------.020, Measured with a Mitotoyo caliper Gasket thickness---.041, advertised Bore:----------------4.06", bored.060 over Stroke:--------------3.48, stock My new calculations: This yields a compression ratio of 9.68 with a quench of .061 and intake duration @ .050 is 204 I think I have solved my detonation mystery. -Russ Summit racing compression calculator https://www.summitracing.com/newsand...ion-calculator
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12-11-2020, 12:47 AM | #36 |
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Re: Rebuilt 350 - detonation --> Cam swap?
New plan;
Lunati Voodoo cam 10120702 Intake Duration at 050 inch Lift:219 Exhaust Duration at 050 inch Lift:227 Duration at 050 inch Lift:219 int./227 exh. Advertised Intake Duration:262 Advertised Exhaust Duration:268 Advertised Duration:262 int./268 exh. Intake Valve Lift with Factory Rocker Arm Ratio:0.468 in. Exhaust Valve Lift with Factory Rocker Arm Ratio:0.489 in. Valve Lift with Factory Rocker Arm Ratio:0.468 int./0.489 exh. Lobe Separation (degrees):112 Fel-Pro 1142-026 PermaTorque Multi-Layer Steel Head Gasket .026 installed thickness Should yield .046 quench 10.02:1 compression 219 Intake Duration at 050 inch Lift Hopefully this will wake the old truck up. It will certainly sound cooler. I did limit the mechanical advance in the distributor to +16°, I will likely need to adjust that to around +20°-22° with the new configuration. We'll see
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12-13-2020, 02:58 PM | #37 |
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Re: Rebuilt 350 - detonation --> Cam swap?
If it were me, I'd be saving for cylinder heads. I've had detonation issues with TBI heads in anything but stock builds.
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12-15-2020, 08:48 PM | #38 | |
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Re: Rebuilt 350 - detonation --> Cam swap?
Quote:
Will I regret that decision? possibly, but I didn't hate the way it ran with the smaller cam, It was just kind of anemic. This should be an improvement. It's just an old truck.
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12-15-2020, 10:05 PM | #39 |
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Re: Rebuilt 350 - detonation --> Cam swap?
Have you been using 87 octane ? If so tune it a little rich and run E15/88 in if it still detonates - it's cheaper than 87. Probably have to play with timing again but your getting a good hang of it
(edit; I like thread updates and here's "how it's doing now" )
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Tim K. 84 K30 srw Silverado 454 auto 85 C20 350 C6P auto flatbed 94 K1500 lifted shortbed 350 4 bbl NV4500 Last edited by 68post; 12-15-2020 at 10:08 PM. Reason: yes |
12-15-2020, 10:23 PM | #40 |
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Re: Rebuilt 350 - detonation --> Cam swap?
I've been running 91 octane, 10% ethanol.
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12-15-2020, 10:30 PM | #41 |
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Re: Rebuilt 350 - detonation --> Cam swap?
Is that locally your highest available ? Notice a diff between different brands ?
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Tim K. 84 K30 srw Silverado 454 auto 85 C20 350 C6P auto flatbed 94 K1500 lifted shortbed 350 4 bbl NV4500 |
12-15-2020, 10:43 PM | #42 | |
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Re: Rebuilt 350 - detonation --> Cam swap?
Quote:
I think my quench was a big part of the problem. A tighter quench coupled with a longer intake duration should make it less susceptible to detonation. I hope
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12-15-2020, 11:12 PM | #43 |
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Re: Rebuilt 350 - detonation --> Cam swap?
It will help. But also you definitely cannot always hear detonation. I consider .046 on the very edge of wide.
I'd love to have a spark-knock retard type ignition such as a J&S, not cheap but good I believe. I'd really prefer electronic fuel injection and timing control together and run high compression much easier with better octane tolerance, but that's thousands of dollars to just replace a cheap carb & hei setup (and more time and trouble than I want to spend).
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Tim K. 84 K30 srw Silverado 454 auto 85 C20 350 C6P auto flatbed 94 K1500 lifted shortbed 350 4 bbl NV4500 |
12-16-2020, 12:00 PM | #44 | |
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Re: Rebuilt 350 - detonation --> Cam swap?
Quote:
.020 is the deepest hole. My quench will actually range from .038 to .046. The shallowest piston is .014, otherwise I would have used a .015" steel gasket, I just wasn't comfortable with .029 clearance on a couple cyls, so I compromised with a .026 head gasket. Is .006 a lot? I don't know and it really doesn't matter at this point, The motor is going back in. I need my truck. No matter what, too much clearance is better than not enough. Piston----><----Head
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