Looking for feedback on new build... - Page 2 - Chevelle Tech
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post #16 of 27 (permalink) Old Apr 3rd, 19, 3:34 PM Thread Starter
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Jim
 
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Re: Looking for feedback on new build...

Hi Tom/Bill -

Thanks for both your responses - I do have an email out to Brandon with some questions. Their SP03 block has 12.3cc dish pistons, and per their specs would be 9.7:1 with 64cc Vortecs. I don't see any other short blocks they're selling that would spec lower than that. My current engine is dated 1973 - not sure what piston/compression ratio I'm currently running, but I only get a hint of a ping on rare occasions. Sounds like you're both saying that 9.7 is still too high?

jim
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post #17 of 27 (permalink) Old Apr 3rd, 19, 3:37 PM
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Quote:
Originally Posted by Jim's69Ragtop View Post
Hi Tom/Bill -

Thanks for both your responses - I do have an email out to Brandon with some questions. Their SP03 block has 12.3cc dish pistons, and per their specs would be 9.7:1 with 64cc Vortecs. I don't see any other short blocks they're selling that would spec lower than that. My current engine is dated 1973 - not sure what piston/compression ratio I'm currently running, but I only get a hint of a ping on rare occasions. Sounds like you're both saying that 9.7 is still too high?

jim
In 73 the compression ratio is in the 8s somewhere most likely

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post #18 of 27 (permalink) Old Apr 3rd, 19, 3:53 PM Thread Starter
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Re: Looking for feedback on new build...

Hi Justin -

Agree that was typical for that era, but would that still be the case with the 64cc vortecs I'm currently running?

jim
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post #19 of 27 (permalink) Old Apr 3rd, 19, 7:40 PM
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Tom Terrific II
 
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Re: Looking for feedback on new build...

if it has flattops and 76cc heads it's going be around 9:1. if it has flattops and 64cc heads it's likely around 10:1, maybe 10.25 depending on how things stacked up with the build. if it has 12cc dish and 64cc heads it will be down around 9:1, maybe 8.8 or so. It can easily get down in the 8.5 range if the stack-up is bad.

Anyway, if your heads are really 64cc and all the other parts involved are within the "normal" range, you'll be at 10:1 which is "supposed" to be OK. Personally, I'd be a lot more comfortable at 9-9.5. Sometimes there's old gas in the tanks at the station you're at, occasionally the owner will fill the Premium tanks with Regular just to make a few extra bucks. I don't want to be on the edge. I'd rather have 9:1 and be able to tune for max performance and mileage with worrying about things like a few degrees timing or or a couple octane points. My cars are drivers, not trailer queens.

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post #20 of 27 (permalink) Old Apr 4th, 19, 7:21 PM Thread Starter
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Re: Looking for feedback on new build...

How reliable are the Static/Dynamic CR calculators? I calculated both using this one @ gofastmath.com

Using the following values: Bore = 4.04, Stroke = 3.480, Cylinder Head Chamber Volume = 64, Piston Dish = 12, Head Gasket Thickness .050, Head Gasket Bore = 4.06, Deck Clearance = .02, Connecting Rod Length = 5.7, IVC @ .050" = 33.

Note - I took their default for the Deck Clearance as I don't have that number and tried a couple variations on the head gasket values. Based on that, it calculated 9.05:1 Static and 8.06:1 Dynamic.

I realize the DCR is more important and per this calculator they state that 8:1 is the max for iron heads and pump gas. The SP04 with the flat tops are too high, but the SP03 with the 12cc disk pistons seems more reasonable.

Anyone see anything wrong with these calculations? I tried a 2nd site (uempistons.com) and got similar results, so the calculators are at least consistent. Note - tried a couple more sites which calculated the DCR as high as 8.5:1 - not sure why the difference.

Thanks -

jim
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post #21 of 27 (permalink) Old Apr 5th, 19, 8:05 PM Thread Starter
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Jim
 
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Re: Looking for feedback on new build...

Any feedback from the engine builders on my question above?

Thanks!

jim
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post #22 of 27 (permalink) Old Apr 9th, 19, 2:33 PM Thread Starter
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Re: Looking for feedback on new build...

OK, I found another CR calculator by Pat Kelly that seems to be well respected on several sites. Running the numbers on this calculator yields a static CR of 9:1 and a Dynamic CR of 8.6:1. This is using a .050 head gasket and a deck of .015 (Per ATK) for a quench of .065. I realize this is on the higher side, but if I go thinner on the head gasket that will bring the CR up. Is it better to get the quench closer to .045 or keep the DCR down? A .030 head gasket would raise the DCR to 9:1 - everything I've read, that's too high for pump gas. Maybe I'm over thinking this, but don't want to end up with a combination that doesn't work. It's my understanding the Vortecs are less prone to detonation, so am I safe to go with a DCR of 8.6:1 and 91 octane.

Thanks -

jim
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post #23 of 27 (permalink) Old Apr 9th, 19, 3:20 PM
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Re: Looking for feedback on new build...

Doesn't altitude also play into all of this?? I would think that closer to sea level, you would have less of a tendency to ping.

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post #24 of 27 (permalink) Old Apr 10th, 19, 3:01 AM
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Re: Looking for feedback on new build...

>> I would think that closer to sea level, you would have less of a tendency to ping.

oops, other way around.

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post #25 of 27 (permalink) Old Apr 10th, 19, 3:45 PM Thread Starter
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Jim
 
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Re: Looking for feedback on new build...

That was my thinking as well...(I'm basically at sea level)

Back to my question above on quench - am I better off with a .045 quench and a DCR of 9.1 or a .065 quench and a a DCR of 8.6. Or are neither of these good choices and I should look at heads with larger chambers or a cam that would bleed off more DCR? These are Vortecs which are apparently less prone to detonation than earlier style heads.

Thanks -

jim
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post #26 of 27 (permalink) Old Apr 10th, 19, 4:37 PM
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Re: Looking for feedback on new build...

I run a 10 to 1 358 at the track from time to time and it runs great on 91 octane. Not sure what the dynamic compression is on it. I do know that in the past I had built a SBC that pinged a lot, changed the cam to one on a 114į LCA and it never pinged after that.
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post #27 of 27 (permalink) Old Apr 10th, 19, 11:02 PM
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Re: Looking for feedback on new build...

I ran 13:1 on 91 octane pump gas. Did not build it to do that and wouldn't recommend it. I built a 357 many years ago for nitrous with a 268/274 @ 0.050" roller cam with 108ICL and 112LSA with 0.630" lift. I built it for race gas. After I had it running for a while I did a compression check. It cranked 195-205. The engine I ran before this one had 10.9:1 compression and cranked 215-230 because the cam had a 102ICL and 106LSA and a few degrees less @ 0.050". I ran the 10.9:1 engine as my daily on pump gas for 6 years. It had more cylinder pressure than the 13:1 engine so I started running it on pump gas on the street. Still ran race gas at the track because it was on nitrous.

I didn't build the 13:1 engine to run on pump gas. I was more than happy to run race gas. With the cylinder pressure, gearing, converter and car weight it worked fine. That same engine in a tall geared stick car might rattle itself to death. There's more to it than just static compression ratio. The pic is of the pistons used in the 13:1 357. Ross #91461 with 15.2CC domes, zero deck with 64CC heads and 0.041" gaskets.
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'69 Camaro - 429 SBC Dart Iron Eagle 9.325" block, Crower crank, Crower 6" Billet rods, Ross pistons (10:1), Total Seal S/S rings, AFR 245 heads, T&D steel rockers, Cloyes Timing Set, 4-7 swap solid roller 274/286 @ .050", .704" lift, Dart single plane, Dominator EFI, Stef's #1705R pan, F2 Procharger on E85
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