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Old 02-02-2013, 12:32 AM
67L 67L is offline
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Economy

If economy is important to you, I would recommend a dyno tune. Otherwise your timing could kill your mpgs. I've known people who gained 30% better mpg's by having the right timing.

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Old 02-02-2013, 12:49 AM
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64nailhead
could you show me the math? I dont even see a tire height?
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Old 02-02-2013, 01:07 AM
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looks like we will have similar results and yes thats perfect!
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Old 02-02-2013, 04:58 AM
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Quote:
Originally Posted by vinniekq2 View Post
64nailhead
could you show me the math? I dont even see a tire height?

ROAD SPEED vs ENGINE SPEED CALCULATOR

My math is in the road speed calculator I use. I use the one in the link above. I always confirm odd tire sizes by going to either Cooper Tire's website or tire rack.com and verify the size that comes up on the road speed calculator.

I've used this for several years and it has always been accurate. Also. you can see the formulas that are being used.

EDIT
Vinnie, I might have misunderstood you. Marques said he was using 265/35r22 tires on the previous page.

Last edited by 64nailhead; 02-02-2013 at 05:04 AM.
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Old 02-02-2013, 08:57 AM
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(Marques said he was using 265/35r22 tires on the previous page)

missed that part
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Old 02-02-2013, 09:04 AM
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3.73 x 2000 RPM @1:1 = 47 mph in my calculator

.7 O/drive nets = 67 mph in my calculator?
tire being 29.5 inches in diameter
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Old 02-02-2013, 12:54 PM
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demarques 191,
I've building a 383 too with rpm heads(70cc), air gap intake, & scat crank/6.0 rods, & 5cc pistons.
Just thought I'd mention that the 64cc heads are going to give you over 11:1 CR, and with that cam(XR270) it would put your dynamic compression over 9:1 if you have a zero piston to deck and 0.39 gasket. At least with the CR calculator I prefe to use( a good article IMO, and link at the bottom of the page-http://www.empirenet.com/pkelley2/DynamicCR.html).
Many different opinions on dynamic compression out there. Many say not to run over 8.5:1 DC on pump gas, others say it has no revalence on a running engine. Some say not to go over 180psi cranking compression, some say 200psi is ok? I know that just because you have only 160psi with a starter, doesn't mean much in a engine with 11:1CR and a big cam at higher rpm as it can still detonate/destroy itself.
I know it depends on the combination of parts, temp.,fuel quality,rpm,ect... I have a 350 that has less than 9:1 CR w/cast iron heads, HE260 cam, and 14* initial ign. adv.. Most of the time it runs great, but a couple of times when the ambeint temp got around 100*F, and a good heat soak on the engine/bay, it gets very sensitive to throttle input or it will detonate and have severe pre-ignition symptoms(bucking/surging/stalling). I believe a bigger cam would probably bleed off enough cylinder pressure to make it run better, or back off the timing, but I dont want to lose the low-end throttle response I have for the 99 percent of the time it runs great.
Just saying you might want to look at your CR a little harder because the quality of gas is only going to get worse.
FWIW
ssmonty
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Old 02-02-2013, 01:11 PM
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Vinnie,
What calculator are you using? Can you attach it to this thread? Is there one on this forum as a permanent link? I can say that I've used the one I attached for 2 different builds to figure out speedo drives and it has worked well. Also, both of the vehicles had multiple transmissions and rears and the calculator was accurate, for what it's worth.

If there isn't one in a permanent link/sticky here, then there probably ought to be. IMO
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Old 02-02-2013, 04:14 PM
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Scat Engine Rotating Assemblies 1-40605-1 - SummitRacing.com Here is the link to the bottom end i was considering buying and if i match it with the 64cc Performer RPM heads, then your saying the pistons and 64cc will put me over 11 compression?? I havent even figured out what size head gaskets just yet, maybe the ones Edelbrock would supply...
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Old 02-02-2013, 05:26 PM
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I'm saying the combination of a 5cc valve relief piston, 64cc chamber, 4.030 bore, 3.75" stroke, 0.039" thick gasket w/4.166 bore(Felpro pn 1010), and a "zero" decked block would equal over 11:1 CR.
If you don't deck the block at all the CR is around 10.5:1. The gasket is one of the thicker ones normaly used. Of coarse any thinner and the CR goes up.
You didn't say what type of gasket you were using. Edelbrock doesn't normally provide gaskets when buying heads alone. They may when you buy a top end kit.
Reguardless you stated in your 1st post that you wanted 9.5-10:1 CR and welcomed any opinions. I'm just saying your combination is going to have more than that.
Have you heard of quench/squish. That article I mentioned may shed some light on what could make a difference according to allot of folks.
Have you tried the CR calculator I mentioned? Just trying to help.
http://cochise.uia.net/pkelley2/dcrvb6.zip
FWIW
ssmonty

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Old 02-02-2013, 07:11 PM
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Quote:
Originally Posted by 64nailhead View Post
I think it depends on what kind of highway cruising your doing. If your highway cruising is 70-75, then the 3.73 would be fine, but if your highway cruising is 55-65 then 4.10 would be better for mileage and driveability.

Here's what I found with your setup :
3.73 at 60 mph = 1800 rpms
4.10 at 60 mph = 2000 rpms

3.73 at 70 mph = 2100 rpms
4.10 at 70 mph = 2300 rpms

If fuel economy is the concern and cruising speeds are closer to 70, then the 3.73 are fine. Personally, though, the 4.10 will be more fun at all rpm ranges and shouldn't kill your fuel economy too much because your running relatively tall tires.

Now, if fuel economy isn't a concern, and your going to change the gears anyway, which you should, and you want it more snotty, then 4.56's would be even better yet and it would still be driveable at low speeds :
4.56 at 60 mph = 2200 rpms
4.56 at 70 mph = 2550 rpms

Just my opinion, for what its worth. Have fun.
I think to use fuel economy with a carbed 383 in the same sentence is a mistake.

Alot depends on which hat you want to wear.When you want a hot rod or when you want to have fuel economy.It's certainly a balancing point in parts choices.

What compounds this is 29.5 tires and O/D.

But to go to 4.56's or even 4.10's is I think a mistake.3.73's is a good around gear.Then to wire in switch to lock up or not T/C might be a better solution.Your trying for a cake and eat it too is something everyone wants.That is the main reason behind TCI's 6 speed auto and Gearvendor's spit O/D.Both very expensive and hard to justify on a return of investment giving the gas savings.

Guys talk about better gas mileage with these 383,but what exactly does that mean??.12 mpg vs 14 mpg??.383's are not known for gas mileage that have carbs.So the leads me to EFI systems.SFI's being a better choice.Certainly a EFI have a better spark curve and better fuel curve if tuned properly.Edelbrock with it's Pro-flow system is there again very expensive.

So which hat and when??. Hot rod or D.D'er. Get the TCI lock-out switch kit which is going to help you make that choice in conjunction with 3.73's.Make sure the cruise control is working.Right foot active control is going to directly effect the gas mileage. Start a research for a EFI system.
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Old 02-02-2013, 09:18 PM
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i'm still a newbie to the engine building process as well as understanding it. Well, honestly i just want enough compression for power but i was always told you really dont need to go over 10.1 compression for a street engine, im not too familiar with the detonation etc and how it works knowing there are many factors that could be the culprit to detonation....i'm trying to use this site you posted now.... What would you recommend to get me right at 10.1 or less? and i know it can be done and still have great power ... after reading this website where they compared a 355 vs 383 355 & 383 Chevy Engine Performance Gain - Super Chevy Magazine
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Old 02-04-2013, 10:03 PM
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hey thank you for your advice, what do you think if i moved it to a 70cc head? Would that bring it down then?
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Old 02-04-2013, 11:21 PM
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Quote:
Originally Posted by demarques_191 View Post
i'm still a newbie to the engine building process as well as understanding it. Well, honestly i just want enough compression for power but i was always told you really dont need to go over 10.1 compression for a street engine, im not too familiar with the detonation etc and how it works knowing there are many factors that could be the culprit to detonation....i'm trying to use this site you posted now.... What would you recommend to get me right at 10.1 or less? and i know it can be done and still have great power ... after reading this website where they compared a 355 vs 383 355 & 383 Chevy Engine Performance Gain - Super Chevy Magazine

When you use magazine articles as references you can never forget they are in business to sell parts.The deal is you can throw out haft of it and wonder why the other haft has so many gaps in the story.One of the better sources is sites like this one.
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Old 02-05-2013, 12:56 AM
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building the right street setup for a 383 chevy

If you want to stay 10.1 or under static compression ratio you will need to get a rotating assembly like this Scat Engine Rotating Assemblies 1-40805 - SummitRacing.com The static compression ratio will be 9.474 with 64 cc heads, 0 deck, and .040 compressed gasket thickness. With .025 deck clearance and a .015 compressed thickness gasket for .040 quench the C.R. would be 9.507 with 64cc heads.
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