[Eric Z.]

Hello,

I’m building a 383 SBC for my 86 Pontiac Grand Prix. This engine will be 98% or more performance oriented street use, with only the rare trip to the drag strip. I don’t want it to have a crazy idle and I need enough vacuum to run my brakes and accessories. I’m more concerned with a fun motor than a specific hp#. I want to run it on 93 Octane pump gas. I am looking for input on my proposed build. The only thing I have purchased so far is the block so I’m open to any and all suggestions.
Block:

- 97 Vortec block set up for factory roller cam and one piece RMS. It’s been cleaned up, bored .030 over; and it has the stock deck height.

Here’s a build combo I'm contemplating:

- SCAT 1-91205BIE Rotating assembly (Forged flat top pistons, 6” forged I-beam rods, 3.75” cast crank)
- Comp Cams 08-305-08 (Hydraulic roller, Duration at 050 inch Lift: 220 int./230 exh., Lift: 0.510 int./0.510 exh., LSA: 114, Operating RPM Range 1,800-5,800)
- COMP Cams 900-16 Hydraulic Roller Lifters
- COMP Cams 1604-16 - Ultra Pro Magnum Rocker Arms 1.5 ratio
I’ll probably go with a head gasket in the .042-.045 compressed thickness;
- AFR 180cc SBC Eliminator Street Heads w/ 75cc chamber w/ the appropriate valve springs for the Hyd. Roller cam. (AFR recommended the 195cc version, but everything I have read says the 180cc would be better for the street. Thoughts?)
- Performer RPM intake #7101
- Holley 0-80670 Street Avenger 670CFM

The other way I was considering going with is basically the same engine with a dished piston and smaller chamber head like the Dart SHP 180cc intake runner / 64cc or 72cc chamber or the Brodix IK 180cc intake runner / 64cc or 70cc chamber. These heads are a little bit more budget friendly, but I’m not sure about the “Quench” with the needed dished piston.

Which Cylinder head / combustion chamber would be the most conducive to an efficient combustion?

Disclaimer: If any of the above makes no sense, its purely because of my lack of mechanical knowledge. I did use this compression calculator though:
United Engine & Machine Co. Incorporated

[vinniekq2]

I love it all except the little 670.It wont hurt you though.1 5/8s headers? 3 inch exhaust?I would use the afr heads as they work out of the box,fully cnc ported.My darts were cnc ported too,just not sure about 180 darts.

[ap72]

If you're realy after performance then you need a much better cam, larger ports in your heads, a larger carb, 1.6 rockers. What you have in mind is a good "daily driver" but doesn't have any pull up top.

195cc ports AT A MINIMUM.
230/235 ish cam on a 108ish lsa with .550"+ net lift
800cfm+ carb

Make those changes and you'll likely pick up 75hp or more.

For compression with good tuning and those AFR heads 10:1 will run on 87 octane with the rest of the matched combo in a reasonably well set up street car (no lugging).

[Silver Surfer]

I am not finding anything on the pistons that come with that SCAT kit, so we can only assume the pistons have a compression height of 1.125" (but probably less). Since the block is not decked we can assume it has the factory block height of 9.000"

This means your deck clearance is .025" (probably more considering the pistons). Which means your head gaskets are too thick. It will give you a squish of .067-.070" (probably more considering the pistons, almost all after market pistons have a reduced compression height to allow for block decking). You should aim for .040" and not over .050" at the most. Proper squish will reduce your need for advancing the timing, octane, reduces detonation, and gives more power.

[cdminter59]

Originally Posted by Silver Surfer

I am not finding anything on the pistons that come with that SCAT kit, so we can only assume the pistons have a compression height of 1.125" (but probably less). Since the block is not decked we can assume it has the factory block height of 9.000"

This means your deck clearance is .025" (probably more considering the pistons). Which means your head gaskets are too thick. It will give you a squish of .067-.070" (probably more considering the pistons, almost all after market pistons have a reduced compression height to allow for block decking). You should aim for .040" and not over .050" at the most. Proper squish will reduce your need for advancing the timing, octane, reduces detonation, and gives more power.

See this link for Scat kit : http://www.summitracing.com/parts/SCA-1-91200/ The compression height on KB122 flat top 7cc pistons are 1.13" . The compression ratio with 72cc heads are 9.976. Check out Amazon for these RHS heads .560 lift max. with hyd roller springs.

Amazon

Amazon

Be sure and look under add to cart for More Buying Choices $567.24 each.

[farmwalker]

I really like your combo. I would go with a little bigger carb too. But... my only thing is, If you're going to go spend the kind of money to get forged pistons and "AFR's;" Why don't you go with a bigger cam, bigger carb, higher compression, and new gears. I'm not hating. I'm just saying you could probably get the same performance out of a hypertonic piston and some vortec's or world products sportsman II's or even some dart's. Just sayin... same performance for less money..

[PatM]

For a primary driver, I think I get what you want. I'd consider the AFR 195 heads vs. the 180 heads. Other opinions may vary. But, this is a 383.
PatM

[Eric Z.]

Thanks for the responses. A couple things I have realized are:

A) I suck at using the compression calculator I linked to in my original post. lol I keep coming up with different numbers than everyone else for some reason.

B) I know even less than I thought I did. lol

Originally Posted by vinniekq2

I love it all except the little 670.It wont hurt you though.

I chose it because the calculator I used suggested it, but judging from the responses, I may be better off with the 770 version.

Originally Posted by vinniekq2

1 5/8s headers? 3 inch exhaust?

Yeah, I had planned on using a set of 1 5/8 headers, probably a true dual 2.5"exhaust. I figured it would be more than enough for my build.

Originally Posted by ap72

If you're really after performance then you need a much better cam, larger ports in your heads, a larger carb, 1.6 rockers. What you have in mind is a good "daily driver" but doesn't have any pull up top.

195cc ports AT A MINIMUM.
230/235 ish cam on a 108ish lsa with .550"+ net lift
800cfm+ carb

Make those changes and you'll likely pick up 75hp or more.

For compression with good tuning and those AFR heads 10:1 will run on 87 octane with the rest of the matched combo in a reasonably well set up street car (no lugging).

I see what your saying, I guess "performance" is a pretty subjective word. I looked into something like what you have listed, but I MUST have enough vacuum to run my power brakes and accessories. From what Comp told me anything less than 114 LSA will compromise that. I have looked at several cams with 114 lsa, but with more lift, they might be a good compromise? It's nice to know I can go higher on the compression ratio if needed.

Originally Posted by Silver Surfer

I am not finding anything on the pistons that come with that SCAT kit, so we can only assume the pistons have a compression height of 1.125" (but probably less). Since the block is not decked we can assume it has the factory block height of 9.000"

This means your deck clearance is .025" (probably more considering the pistons). Which means your head gaskets are too thick. It will give you a squish of .067-.070" (probably more considering the pistons, almost all after market pistons have a reduced compression height to allow for block decking). You should aim for .040" and not over .050" at the most. Proper squish will reduce your need for advancing the timing, octane, reduces detonation, and gives more power.

So if I wanted to keep the same setup, but went with a thinner head gasket, say one with compressed thickness of .020. Would I be where I needed to be? Or should I do something different all together like a smaller chambered head?

Originally Posted by farmwalker

I really like your combo. I would go with a little bigger carb too. But... my only thing is, If you're going to go spend the kind of money to get forged pistons and "AFR's;" Why don't you go with a bigger cam, bigger carb, higher compression, and new gears. I'm not hating. I'm just saying you could probably get the same performance out of a hypertonic piston and some vortec's or world products sportsman II's or even some dart's. Just sayin... same performance for less money..

Yeah, the same thoughts have been going through my head. I'm just erring to the conservative side on the cam, carb and compression to keep drivability good. But hey, that's why I put my whole build up for review by people who like to geek out on car builds as much as I do. :-)

Originally Posted by PatM

For a primary driver, I think I get what you want. I'd consider the AFR 195 heads vs. the 180 heads. Other opinions may vary. But, this is a 383.
PatM

Well, its not a daily driver, it will see use on many Friday, Saturday and Sunday drives though. I'm planning on giving the "pro-touring" flavor throughout with an overdrive transmission, performance brakes, suspension and such. It will function as a backup vehicle for my daily driver though.

Those 195's are getting some serious consideration. as well as many of the other suggestions.

[vinniekq2]

EricZ,good luck with the build.re 180 cc heads Vs 195 cc heads,yes 195s will or potentially can make more power. My 67 350 camaro back in the late 70s ran high 11s with GM angle plug heads,180s are a lot better and 195s can do better still.
currently Im using a 108 square cam and power brakes.If you used a bigger cam than what I have,maybe power brakes will be an issue.You can always bolt on a vacuum cannister. all the parts you mentioned will work,,,,,,how fast do you want to go?

[Silver Surfer]

Originally Posted by Eric Z.

So if I wanted to keep the same setup, but went with a thinner head gasket, say one with compressed thickness of .020. Would I be where I needed to be? Or should I do something different all together like a smaller chambered head?

Well first off I made a typo in my original post. The undecked block has a deck height of 9.025" (not 9.000").

The head gasket does play into the compression ratio calculations, but it also factors into your squish. Ideally you will get your shortblock back from the machine shop, then physically measure your deck clearance, then calculate what compressed thickness gasket you need, then find one that matches as closely as possible to achieve proper squish.

My guess is that when all is said and done you are going to end up with a cam around the 220º-230º intake duration for good street manners, vacuum, and power. That kinda cam is going to want to be around the 9.5 to 10.0:1 static compression ratio (more intake duration, actually the later the intake valve closes ABDC, needs more compression). So from there, you need to pick the combustion chamber size of the heads, piston dish/valve relief volume, and head gasket thickness to get that compression. So basically what I am saying is start with the cam, that is the heart of your non computer controlled engine, then design/part selection from there.

I would also avoid dished pistons. Get flat tops. They cause better squish, turbulence, atomization, flame front, yada yada. If those are out of the question you can get D-dish pistons, but they are more expensive, but you can really tailor your compression ratio by getting the exact volume you want. As you start getting more compression getting a good squish is a must. Aluminum conducts heat better than iron, so aluminum heads will allow you to achieve more compression with less chance of detonation (this means you can run lower octane gasoline). Detonation is the enemy. It will destroy your engine. You must avoid it.

[ap72]

Comp saying you need a 1114LSA is a load of crap, and for that reason alone I'd stop talking to them. Comp seems to have some decent lobe profiles but their tech department is absolutely terrible, I doubt many of them could even change their own oil.

For good tech and service call Mike Jones at Jones Cams. He has a lot of experience, very friendly, and know his ****. Tell him what you want your idle speed and vacuum to be along with what parts you are using in your combo (actually using, not "hope to use someday"), and he'll design you a better cam than anyone on this forum could. It will cost about $30 more, but it will be the best return on $30 in the entire engine.

If that sounds like too much for you the I would at least call Isky, again their tech is a lot better than Comp's.

A 180cc intake runner on a 383 is appropriate for a hp peak around 5300RPM, a 195cc runner on a 383 is appropriate for a hp peak around 5600RPM. These are just ballpark numbers but are a very good rule of thumb when picking head port size. For comparison a stock Vortec port is 165-170cc's and on a 350 usually peaks around 5300-5400. You can of course crutch that with a cam, but if everything matches you'll end up with a MUCH better combo overall.

If you're running good headers and exhaust with a good set of heads then I wouldn't even consider anything on a 114LSA, something around 108-110 would be much more appropriate with a slight lobe split (about 4 degrees more duration on the exhaust)

[Eric Z.]

Originally Posted by Silver Surfer

Well first off I made a typo in my original post. The undecked block has a deck height of 9.025" (not 9.000").

The head gasket does play into the compression ratio calculations, but it also factors into your squish. Ideally you will get your shortblock back from the machine shop, then physically measure your deck clearance, then calculate what compressed thickness gasket you need, then find one that matches as closely as possible to achieve proper squish.

My guess is that when all is said and done you are going to end up with a cam around the 220º-230º intake duration for good street manners, vacuum, and power. That kinda cam is going to want to be around the 9.5 to 10.0:1 static compression ratio (more intake duration, actually the later the intake valve closes ABDC, needs more compression). So from there, you need to pick the combustion chamber size of the heads, piston dish/valve relief volume, and head gasket thickness to get that compression. So basically what I am saying is start with the cam, that is the heart of your non computer controlled engine, then design/part selection from there.

I would also avoid dished pistons. Get flat tops. They cause better squish, turbulence, atomization, flame front, yada yada. If those are out of the question you can get D-dish pistons, but they are more expensive, but you can really tailor your compression ratio by getting the exact volume you want. As you start getting more compression getting a good squish is a must. Aluminum conducts heat better than iron, so aluminum heads will allow you to achieve more compression with less chance of detonation (this means you can run lower octane gasoline). Detonation is the enemy. It will destroy your engine. You must avoid it.

So I contacted Scat and they told me the piston included in that rotating assembly had a Kieth black part # of 9935fhr, Summit is either sold out on these or doesn't carry them any more, but has a substitute ICON (Same Mfgr) part with similar #. Here it is: ICON Performance Pistons IC9932-030 - ICON FHR Series Pistons - Overview - SummitRacing.com . The compression height does indeed look to be 1.113 and +3.5 cc on volume. So if the stock piston is .025 in hole, this piston will be .037 in the hole. (Assuming stock deck height.) So I'm almost @ the magic # of .040 with no head gasket. I'm wondering if I might be looking at decking my block or getting a different piston all together. If decking the block is the answer, I'd rather do that while the machinist has the engine for boring. Am I making sense, or talking out my arse? :-)

Originally Posted by ap72

For good tech and service call Mike Jones at Jones Cams. He has a lot of experience, very friendly, and know his ****. Tell him what you want your idle speed and vacuum to be along with what parts you are using in your combo (actually using, not "hope to use someday"), and he'll design you a better cam than anyone on this forum could. It will cost about $30 more, but it will be the best return on $30 in the entire engine.

I will definitely give Mr Jones a call. The right cam is worth an extra $30.

[Eric Z.]

Originally Posted by Eric Z.

The compression height does indeed look to be 1.113 and +3.5 cc on volume. So if the stock piston is .025 in hole, this piston will be .037 in the hole. (Assuming stock deck height.) So I'm almost @ the magic # of .040 with no head gasket. I'm wondering if I might be looking at decking my block or getting a different piston all together. If decking the block is the answer, I'd rather do that while the machinist has the engine for boring. Am I making sense, or talking out my arse? :-)

It looks like I was talking out my arse, the compression height is 1.33 and + 3.7cc on the volume, so that changes things completely. With stock deck height it would be 0.017 in the hole. Correct? then I would only be a 0.023 compressed gasket away from perfect?

[cdminter59]

Eric Z, The Icon forged piston IC718 is a flat top piston for a 383 chevy with 6" rods. The effective head volume is 4.9cc, the compression height is 1.13. The Icon FHR series pistons are the first made of the Icon Forged Pistons. The FHR piston has 5/64,5/64 rings and 3/16 oil rings much like a stock piston. The Icon Forged Pistons have 1/16,1/16 rings and 3/16 oil rings like most high performance pistons. BTW you can call CNC Motorsports at 1-800-341-1528 and order the Scat kit you want SCAT 1-91205 with the Icon718 pistons or whatever brand you want at no extra cost. Also the 383 engine needs to breath and in my opinion these heads by Comp Cams would be more suitable for that engine. The part# includes HYD roller springs up to .600 lift. Check them out.

RHS 12044-02 Pro Action 23° Aluminum Assembled Cylinder Head with 200cc Runner/72cc Chamber for Small Block Chevy : Amazon.com : Automotive

RHS 12044-02 Pro Action 23° Aluminum Assembled Cylinder Head with 200cc Runner/72cc Chamber for Small Block Chevy : Amazon.com : Automotive

. To calculate how much the piston is suppose to be in the hole: Stroke*2 + rod length + compression height= 3.750x.05+6.0+1.13=9.005. 9025-9005= .020. Best way to check it is install the crank, install one piston (with no rings) bring it up to TDC. Use a bridge and a dial indicator to measure how far in the hole. You will have to the hold piston in the center of the hole or shim it. Good luck with your build.

[cdminter59]

Eric, check your PM's.