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Discussion Starter · #1 ·
I am building a 383 on a 1989 chevy k2500 with dart shp 200cc/72cc heads edelbrock man holley throttle body and eagle specality forged flat top 5cc pistons with 5.7 rods ...im needing to run pump gas as its a daily driver ... im needing to find what the cr is so i can chose a cam from comp cams but i need the cr and it changes depending on which website you go to please help
 

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Missing piece of data is whether or not the block has been decked and if so by how much?

Aluminum heads prefer a layered as in MLS or composite head gasket! These tend to be be thick ranging from .026 to .053 inch. This has a big effect on compression ratio and the squish/quench clearance.

The squish/quench clearance for a street motor should fall between .035 and .045 inch. The Chevy classic SBC uses a piston crown to head deck of .025 inch which with available thicknesses of MLS or composite head gaskets is not achievable with out either milling .020 to .025 inch off the head deck or using pistons with a additional compression height those available being .020 higher than ‘stock’. Not that there is anything ‘stock’ about building a 383 but unless otherwise stated the length build up of modified rod lengths including the 5.7 and the piston compression height will add up with 1/2 the stroke to 9 inches where the stock block height crank center to head deck is 9.025 inches.

Squish/quench are two functions of the piston closing at TDC with the chamber step of the head. Squish ejects the mixture with great force from the far side of the chamber to be violently mixed and set before the spark plug. This being the principle of “Fast Burn”. The next step is ‘Quench’; this uses the close clearance of the chamber step to piston crown to sink the extremely high end burn temperatures preventing the end burn mixture from exploding before the flame front gets there. When done with build accuracy these functions make the fuel used behave as if it’s octane is higher than its rating, this is called “mechanical octane”. It will make 91, E10 behave as if it’s 96 to 100 octane. Your choice of aluminum heads will favor the fuel reacting as if it were 100 octane, there is a bit of variation due to differing fuel brand blends.

So getting these dimensions right is quite important especially so the heavier the vehicle snd the higher the overall final drive ratio. That reduces to a light vehicle is less sensitive to detonation with high gearing than a heavy vehicle with high gearing. Any vehicle is less sensitive to detonation with stiff overall gearing.

As far as cam goes you need first to make some declaration as to the amount of power your hunting for and it’s purpose which is to get an idea of what operating RPM range you’re looking for.

Bogie
 

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Put the engine together with #1 piston only installed. If you have it together will all the pistons in that is OK. Measure how far down the piston is in the cylinder at TDC. This will give you a specific measurement to use in the compression calculations. CC one of the cylinder heads to get the exact cc of the head chamber. It is not necessary to do all the chambers for a street engine. With these measurements and with the cylinder head compressed gasket thickness you should be able to get a good compression ratio calculation. Go to wallace racing, They have many calculators. The only calculators that I have found different is Diamond piston which asks for the distance the top ring is down from the piston crown as this is a space to fill and calculates a slightly lower compression but a small difference.

My suggestion is to get as many exact measurements as you can to get a good result. Do not go with published information.
 

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Discussion Starter · #5 ·
This is my first engine build and block is stock havent picked out a gasket size yet but i will probably grab the bigger .053 and i called comp cams they wanted a pretty close cr to give me a suggestion
 

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Undecked stock block with piston down .025" @ TDC, 1.425" compression height piston(5.7" rod 3.75" stroke piston), and .041" thick x 4.166" bore head gasket (Fel-Pro) is 9.6:1. Quench is a not so good .066"
Zero decked block and same piston and gasket, 10.1:1. Quench is a nice tight .040"
Undecked block with the .026" thick x 4.125" bore #5746 Mahle Originals head gasket is 9.9:1. Quench is livable at .051"

I would definitely NOT be using an .053" gasket with the undecked block....ping city due to lack of quench.
 

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Discussion Starter · #8 ·
Undecked stock block with piston down .025" @ TDC, 1.425" compression height piston(5.7" rod 3.75" stroke piston), and .041" thick x 4.166" bore head gasket (Fel-Pro) is 9.6:1. Quench is a not so good .066"
Zero decked block and same piston and gasket, 10.1:1. Quench is a nice tight .040"
Undecked block with the .026" thick x 4.125" bore #5746 Mahle Originals head gasket is 9.9:1. Quench is livable at .051"

I would definitely NOT be using an .053" gasket with the undecked block....ping city due to lack of quench.
So zero the block
 

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This is probably more reasonable concidering i live in the middle of nowhere and this guy builds them but gotta drive 2 hrs to get it decked then 2 hrs back ect ect ect
Building a 383 requires clearancing the pan rail on both sides for each rod. Further if you’re using a rods that employ bolt and nut retention of the rob cap then the rods on 1-2-5-6 need to have the bolt head and perhaps some of the upper bolt boss ground away to gain clearance for the cam lobes at those points. This is not an exercise in buying parts and just bolting them together. Needs less to say there is scant space to get this wrong. There is some mitigation for example rods that use cap screws where the bolt enters from the cap and screws into the upper shank often allows one to get clearance on the cam lobes with little to no grinding on the upper part of the rod. At tge pan rail and sometimes on the roof of the crankcase and where the cylinder bore meets the crankcase some relief needs to be done here as well. Not all Chevy block castings are dimensionally identical

Given the block needs to be bored unless you buy a pre prepped block it’s hard to escape going to a machine shop? .

The head gasket issue can be worked without decking by using a .026/.028 inch thick gasket, not ideal as it nets a total squish/quench of .051 to .053 which is a bit wide but aluminum offers more toleration of detonation than cast iron. Using a .053 thick gasket makes a very poor squish/quench of .078. Chevy actually did this on some aluminum headed engines but it really kills the compression ratio on a 350 with a 64 cc chamber and some of those heads used 60 cc or less chambers. Plus these thick gaskets cut the squish/quench to little to nothing.

Your 89 came with Rochester Throttle Body Injection (TBI) you mention Holley as a replacement which brings the question as to a stand alone Holley or a large bore factory style TBI?

The cam will need to be compatible with the injection system among other things, even self-learning systems struggle with big cams. Some guys build combinations that give the aftermarket injection builders fits.

For a regular daily driver it shouldn't take much cam on a 383 to hit around 400 ft pounds and 400 horsepower which keeping the cam more conservative is a big help in getting the EFI to dial in.

So hopefully we’re giving you enough data to appreciate the trip wires built into performance builds in general and 383 builds in particular.

Bogie
 

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Discussion Starter · #12 ·
Building a 383 requires clearancing the pan rail on both sides for each rod. Further if you’re using a rods that employ bolt and nut retention of the rob cap then the rods on 1-2-5-6 need to have the bolt head and perhaps some of the upper bolt boss ground away to gain clearance for the cam lobes at those points. This is not an exercise in buying parts and just bolting them together. Needs less to say there is scant space to get this wrong. There is some mitigation for example rods that use cap screws where the bolt enters from the cap and screws into the upper shank often allows one to get clearance on the cam lobes with little to no grinding on the upper part of the rod. At tge pan rail and sometimes on the roof of the crankcase and where the cylinder bore meets the crankcase some relief needs to be done here as well. Not all Chevy block castings are dimensionally identical

Given the block needs to be bored unless you buy a pre prepped block it’s hard to escape going to a machine shop? .

The head gasket issue can be worked without decking by using a .026/.028 inch thick gasket, not ideal as it nets a total squish/quench of .051 to .053 which is a bit wide but aluminum offers more toleration of detonation than cast iron. Using a .053 thick gasket makes a very poor squish/quench of .078. Chevy actually did this on some aluminum headed engines but it really kills the compression ratio on a 350 with a 64 cc chamber and some of those heads used 60 cc or less chambers. Plus these thick gaskets cut the squish/quench to little to nothing.

Your 89 came with Rochester Throttle Body Injection (TBI) you mention Holley as a replacement which brings the question as to a stand alone Holley or a large bore factory style TBI?

The cam will need to be compatible with the injection system among other things, even self-learning systems struggle with big cams. Some guys build combinations that give the aftermarket injection builders fits.

For a regular daily driver it shouldn't take much cam on a 383 to hit around 400 ft pounds and 400 horsepower which keeping the cam more conservative is a big help in getting the EFI to dial in.

So hopefully we’re giving you enough data to appreciate the trip wires built into performance builds in general and 383 builds in particular.

Bogie
To be honest i dont know near enough about engines but that is y im doing this and all i know about the holley 670 cfm tbi is i need it for more ait because the stock will choke it out thats y im here to lear more before i actually get into it and mess a bunch of stuff up ...also good point about the machine shop
 

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A 670 will require a custom programmed chip in the GM computer.

TBI as GM does it is mapped. That is for a given engine size with a factory cam, TBI capacity, exhaust and intake system the engine was put on a dyno and run through expected operating scenarios. There are three controlling functions that are treated for each performance station of the test. This is values for the throttle position to intake manifold pressure or as we think of it manifold vacuum, and RPM. These are the three primary relationships that are mapped for each expected operating condition.

The map establishes for each condition the related air and fuel flow snd ignition timing. For each condition this becomes the data population at an address assigned to that condition. In operation the sensors supply data to the computer, the computer compiles thst information into an address. The address is opened and the functional timing of injector duty cycle and ignition timing is opened and delivered to the TBI and distributor module.

Changing the engine size, cam timing, TBI air flow and injector flow capacity now also changes the relationship of the actual operating conditions into something that isn’t mapped in the addresses. So calculated addresses are either false where it is essentially trying to deliver mail to an address that doesn’t exist or it develops an address that does exist but has the wrong family of settings for the conditions. So to get around this a new program needs to be put on the existing chip or a new chip with new program installed.

The original computer does have a little learn capability that is there for wear compensation which might eventually cover some of your changes. An example is with the stock 400 something cfm TBI it will pick up a cam change to about 200 degrees intake and 210 exhaust usually without problem but that’s about the upper limit to changes on a fresh long block that it can do.

Short of reprogramming for significant mods is to convert to a carb. For an 89 with a manual trans or a 700R4 automatic this is a fair amount of electrical work but doable for the average guy with a decent wiring diagram. The 87 through 92 trucks aren’t too bad to convert, the 93 through 95 V8 trucks a little more complicated, 96 up brings OBD2 and from there on there is more and more Rocket Science driving modifications to higher levels of complexity and cost for hot rod changes.

I’m a really big proponent of not buying trucks younger than 1986 if your not well versed in electronics, electrical and modern systems integration because with the advent of OBD 1 which for Chevy/GMC pickups is the 1987 model year, Ford a little earlier and Chrysler about the same you bet into the computer running everything and it gets increasingly complicated as time goes on from there. I say this as a old man that is a life long hot rodder and biker and a degreed engineer with 54 years in aerospace, so it isn’t like I don’t know of what I speak.

Bogie
 

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Discussion Starter · #14 ·
A 670 will require a custom programmed chip in the GM computer.

TBI as GM does it is mapped. That is for a given engine size with a factory cam, TBI capacity, exhaust and intake system the engine was put on a dyno and run through expected operating scenarios. There are three controlling functions that are treated for each performance station of the test. This is values for the throttle position to intake manifold pressure or as we think of it manifold vacuum, and RPM. These are the three primary relationships that are mapped for each expected operating condition.

The map establishes for each condition the related air and fuel flow snd ignition timing. For each condition this becomes the data population at an address assigned to that condition. In operation the sensors supply data to the computer, the computer compiles thst information into an address. The address is opened and the functional timing of injector duty cycle and ignition timing is opened and delivered to the TBI and distributor module.

Changing the engine size, cam timing, TBI air flow and injector flow capacity now also changes the relationship of the actual operating conditions into something that isn’t mapped in the addresses. So calculated addresses are either false where it is essentially trying to deliver mail to an address that doesn’t exist or it develops an address that does exist but has the wrong family of settings for the conditions. So to get around this a new program needs to be put on the existing chip or a new chip with new program installed.

The original computer does have a little learn capability that is there for wear compensation which might eventually cover some of your changes. An example is with the stock 400 something cfm TBI it will pick up a cam change to about 200 degrees intake and 210 exhaust usually without problem but that’s about the upper limit to changes on a fresh long block that it can do.

Short of reprogramming for significant mods is to convert to a carb. For an 89 with a manual trans or a 700R4 automatic this is a fair amount of electrical work but doable for the average guy with a decent wiring diagram. The 87 through 92 trucks aren’t too bad to convert, the 93 through 95 V8 trucks a little more complicated, 96 up brings OBD2 and from there on there is more and more Rocket Science driving modifications to higher levels of complexity and cost for hot rod changes.

I’m a really big proponent of not buying trucks younger than 1986 if your not well versed in electronics, electrical and modern systems integration because with the advent of OBD 1 which for Chevy/GMC pickups is the 1987 model year, Ford a little earlier and Chrysler about the same you bet into the computer running everything and it gets increasingly complicated as time goes on from there. I say this as a old man that is a life long hot rodder and biker and a degreed engineer with 54 years in aerospace, so it isn’t like I don’t know of what I speak.

Bogie
Do you have any carb convertion advice ... i have thought about this just havent got too it wanted to find the main components but this is turning into one more and more .... after this one i have an 86 that im planning ... but one then the other or neither get done
 

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Since your converting to Edelbrock heads the simple approach is to use their Performer RPM intake.

Carb is your choice, my personal 350 powered S15 uses an 800 CFM AVS 1, Thunder carb.

You can use a bypass regulator to cut the TBI pressure down to what a carb will accept and use the existing bypass system to keep fuel flowing through the pump as it does now for cooling the pump and stabilizing pressure against variable consumption rates which is necessary for fuel injection and a nicety with a carb. The carb brings a lot of rehiring to remove the computer and wiring harnesses. You can steal the switched B+ to the computer for other functions such as fuel pump circuit and ignition.

Fuel pump should include an analog oil pressure switch which will go where the electronic switch is now. The trade is upon cranking the computer starts a count down where if it doesn’t see oil pressure in 7 to 10 seconds it shuts off the ignition. For a no computer situation you use a manual or analog three pin oil pump switch that when energized starts to warm a thermal switch, if oil pressure is not seen is 5 to 10 seconds it cuts ignition power. The point here is in case of roll over or engine stall the electric fuel pump is shut off. To clean things up and trace out circuits you will need a manual with good wiring schematics.

You will need a conventional HEI for ignition as the current ignition gets its advance from the computer. If you run a roller cam the distributor needs a Melonized gear which will also run with a flat tappet cam.

If you want to go ahead with the 670 Holley TBI here’s a link to one of the chip burners still out there. Modding TBI was once popular but these vehicles have become pretty rare any more so a lot of companies no longer cover these old systems.

Bogie
 

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Discussion Starter · #16 ·
Since your converting to Edelbrock heads the simple approach is to use their Performer RPM intake.

Carb is your choice, my personal 350 powered S15 uses an 800 CFM AVS 1, Thunder carb.

You can use a bypass regulator to cut the TBI pressure down to what a carb will accept and use the existing bypass system to keep fuel flowing through the pump as it does now for cooling the pump and stabilizing pressure against variable consumption rates which is necessary for fuel injection and a nicety with a carb. The carb brings a lot of rehiring to remove the computer and wiring harnesses. You can steal the switched B+ to the computer for other functions such as fuel pump circuit and ignition.

Fuel pump should include an analog oil pressure switch which will go where the electronic switch is now. The trade is upon cranking the computer starts a count down where if it doesn’t see oil pressure in 7 to 10 seconds it shuts off the ignition. For a no computer situation you use a manual or analog three pin oil pump switch that when energized starts to warm a thermal switch, if oil pressure is not seen is 5 to 10 seconds it cuts ignition power. The point here is in case of roll over or engine stall the electric fuel pump is shut off. To clean things up and trace out circuits you will need a manual with good wiring schematics.

You will need a conventional HEI for ignition as the current ignition gets its advance from the computer. If you run a roller cam the distributor needs a Melonized gear which will also run with a flat tappet cam.

If you want to go ahead with the 670 Holley TBI here’s a link to one of the chip burners still out there. Modding TBI was once popular but these vehicles have become pretty rare any more so a lot of companies no longer cover these old systems.

Bogie
It seems easier to carb it it is hard as heck to fine specific stuff for what im trying to do. Now that im learning more about this stuff i might go the preformer instead of the rpm in order to keep the powerband down lower in the rpms and i believe please let me know ... i should be able to just get an edelbrock intake and a carb .. pluss the other stuff but that should bolt up correct
 

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The RPM gives up little to nothing against the Performer and hangs with you above 4500 revs. For mass produced intake manifolds at affordable cost it is the go-to intake. If you drive year around and you have cool to cold winters I‘d strongly suggest against the air gap model whether in the end you go with a carb or the 670 cfm Holley TBI.

Bogie
 

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Discussion Starter · #19 ·
The RPM gives up little to nothing against the Performer and hangs with you above 4500 revs. For mass produced intake manifolds at affordable cost it is the go-to intake. If you drive year around and you have cool to cold winters I‘d strongly suggest against the air gap model whether in the end you go with a carb or the 670 cfm Holley TBI.

Bogie
Im thinkin carb and iv been looking at the rpms all day and also thinking about a 750 4 bbl from edelbrock ... glad you said that about the airgap .. i was gunna get the nascar edition with the airgap .. i live in texas btw so ... whats winter haha
The RPM gives up little to nothing against the Performer and hangs with you above 4500 revs. For mass produced intake manifolds at affordable cost it is the go-to intake. If you drive year around and you have cool to cold winters I‘d strongly suggest against the air gap model whether in the end you go with a carb or the 670 cfm Holley TBI.

Bogie
Question now is will the rpms fit with the dart pro 180/72 heads iv been looking at and can i put all that on before it gets stroked
 
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