300 6cyl swap

bubba22349

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I believe that the EFI heads combuston Chambers measure about the same CC's as a 240 carb head.
 

Frank

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There are pistons that look really close to that on Summit. Says it's a 3.22" dish, .3" deep. this calculates to a whopping 40 cc volume. It will be slightly less, since the sides are tapered. So whoever said 7.8:1 is close to the mark.
 

pmuller9

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The round dish pistons in your engine have a 32cc dish and yield an 7.8 compression ratio with the 1986 carburetor head.
The compression ratio will be a near 8.3 with the EFI head.
This is assuming the pistons are down .030" from the block deck at TDC
 

Mr. Bob

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The round dish pistons in your engine have a 32cc dish and yield an 7.8 compression ratio with the 1986 carburetor head.
The compression ratio will be a near 8.3 with the EFI head.
This is assuming the pistons are down .030" from the block deck at TDC
Okay this is pretty in-depth for me when you say block deck I assume you're talking about the top of the block where it meets the head, without the head on it how do I know it's at TDC and how do I find out if it's .030? Also is 8.3 good?
 
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Lazy JW

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You will lose the fast-burn characteristic of the combustion chamber if the proper pistons are not used. The EFI head has a distinct heart-shaped chamber and the piston dome matches this shape.

I used EFI pistons in my carbureted engine in order to reduce compression to go along with the extra-short duration camshaft that I chose. I still had to reduce the timing to control pinging.

I definitely would NOT use carby pistons in an EFI-controlled engine, and lacking a proper knock sensor is treading on very thin ice.

The EFI engine was designed as a complete system; in order for it to function properly it needs all of the correct components.
 

THE FRENCHTOWN FLYER

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Remember those shown are .040" oversized, if that is what you need. Also, they are hypereutectic design so the clearances will need to be "snug".
 

pmuller9

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Okay this is pretty in-depth for me when you say block deck I assume you're talking about the top of the block where it meets the head, without the head on it how do I know it's at TDC and how do I find out if it's .030? Also is 8.3 good?
Yes It is the the depth of the top of the piston from the top of the block deck.
Turn the crankshaft till the timing mark or notch on the balancer lines up with "0" on the timing tab on the passenger side.
That should bring the #1 piston to TDC.
You can turn the crank back and forth to rock the piston to see if it feels like it is at the top.
Place a straight edge across the top of the block over the piston and use a feeler gauge to see how far down the piston is.
 

Mr. Bob

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You will lose the fast-burn characteristic of the combustion chamber if the proper pistons are not used. The EFI head has a distinct heart-shaped chamber and the piston dome matches this shape.

I used EFI pistons in my carbureted engine in order to reduce compression to go along with the extra-short duration camshaft that I chose. I still had to reduce the timing to control pinging.

I definitely would NOT use carby pistons in an EFI-controlled engine, and lacking a proper knock sensor is treading on very thin ice.

The EFI engine was designed as a complete system; in order for it to function properly it needs all of the correct comp

Yes It is the the depth of the top of the piston from the top of the block deck.
Turn the crankshaft till the timing mark or notch on the balancer lines up with "0" on the timing tab on the passenger side.
That should bring the #1 piston to TDC.
You can turn the crank back and forth to rock the piston to see if it feels like it is at the top.
Place a straight edge across the top of the block over the piston and use a feeler gauge to see how far down the piston is.
Okay usually I've done the TDC with the head on stick a rag or piece of paper in the spark plug hole and when it blows it out you know you have it on the compression stroke and that's what I was wondering without the head on it how you would know it was on the compression stroke or does that matter?
 

pmuller9

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Okay usually I've done the TDC with the head on stick a rag or piece of paper in the spark plug hole and when it blows it out you know you have it on the compression stroke and that's what I was wondering without the head on it how you would know it was on the compression stroke or does that matter?
Doesn't matter. You are just trying to find out how far the piston is down in the bore.
 

Frank

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I thought the knock sensor threads were metric.
I thought the knock sensor threads were metric.
Oops, yes it may be metric. I've been saying 3/8. BUT, just checked the bolt I have plugging the hole for the KS and it's a short 3/8 that isn't threaded, held in with gasket sealant. (I just didn't like seeing the blank hole in the block.) It was years ago I converted to carb, should have done my homework before posting. Sorry guys. . Considering Mr Bob's conversion, I was wondering if the KS is position sensitive? It seems like it would need to be mounted in or very near the same location as the EFI blocks to receive the correct signal. ??
 

Mr. Bob

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Oops, yes it may be metric. I've been saying 3/8. BUT, just checked the bolt I have plugging the hole for the KS and it's a short 3/8 that isn't threaded, held in with gasket sealant. (I just didn't like seeing the blank hole in the block.) It was years ago I converted to carb, should have done my homework before posting. Sorry guys. . Considering Mr Bob's conversion, I was wondering if the KS is position sensitive? It seems like it would need to be mounted in or very near the same location as the EFI blocks to receive the correct signal
Would you post a picture of where yours was located on the Block then people like myself who know nothing about what a knock sensor is or where it's located since this is all new to me and I've primarily stuck with basic engine transmission and heater
 

Mr. Bob

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You will lose the fast-burn characteristic of the combustion chamber if the proper pistons are not used. The EFI head has a distinct heart-shaped chamber and the piston dome matches this shape.

I used EFI pistons in my carbureted engine in order to reduce compression to go along with the extra-short duration camshaft that I chose. I still had to reduce the timing to control pinging.

I definitely would NOT use carby pistons in an EFI-controlled engine, and lacking a proper knock sensor is treading on very thin ice.

The EFI engine was designed as a complete system; in order for it to function properly it needs all of the correct components.
I'm curious what is a extra short duration camshaft how does it affect why would you have to reduce compression and does that increase horsepower I would think the more compression you have the more horsepower you have
 

MechRick

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The 300, especially in EFI guise, is an odd design. The stock cam profile has an advertised duration of 268 degrees, and .050 duration of about 192 degrees. That is an extremely mild lobe. The result is compression bleed off at lower RPM, resulting in a very low dynamic compression ratio. The EFI static compression ratio is about 8.7:1. When adding performance cams the dynamic compression ratio increases dramatically, requiring high octane fuel. If you want to run pump gas with a performance cam, there are two choices. Lower the static compression or run a cam with a whole bunch of duration to lower the dynamic compression ratio.
 

sixtseventwo4d

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They are designed to only pick up a certain range of frequency. I have to wonder if all metal timing gears in an EFI engine would give interference with it's operation.
 
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