I am wondering if it is possible to increase compression in early 70s 302 2V winsor with stock heads by slightly grinding off the block or head, and by how much? I am looking to get to 10-11:1, not more, to be able to use regular gas and possibly propane. Has someone done this? Did it work without porting the head (using stock valves)?? What was the increase in hp?
increasing compression in w302
- Thread starter pazur
- Start date
Tubo(2-bo)
Member
Sure, its possible, shaving the heads is probably the least expensive way.
A combination of of heads & pistons, would probably be best. Your question is rather generalized to accurately, determine out put increases.
Are you looking to optimize an engine for Propane use?? Or what goal do you have??
A combination of of heads & pistons, would probably be best. Your question is rather generalized to accurately, determine out put increases.
Are you looking to optimize an engine for Propane use?? Or what goal do you have??
By increasing the compression, my goal is obviously to maximize the hp, but I still want to be able to run the car on propane due to eg. gas prices, cleaner combusition and longer engine life, etc, especially when cruising and don't need high performance (otherwise switch back to gas).
I am not sure what do you mean "optimize the engine for propane", if any such thing can be done. Want to reach the compression at which neither pump gas or propane do not randomly detonate, which I believe should not happen at 10-11:1 (though not sure). I know buing $1500+ heads is the easiest way and no "shaving" or porting is neccessary, but I am curious about stock 2V heads.
Tubo(2-bo)
Member
Well it may take a little more research on your part to find out what optimum compression for a porpane powered engine is. I'd start with several googles.
Once you have the parameters, you want to use, then adapt your engine to that.
Most stock heads were not designed to support compression ratios like your asking for. Shaving a stock head wont give you more than a couple of points ratio gain, without doing much more than I feel your wanting to do.
If you really want more ratio, pistons is probably what you want.
You might be best served to just adapt your engine to propane as it sits, and/or be satisfied with minor mods.
For instance; I'm in the process of replacing a leaking headgasket, while I'm at it, I have done a little reshaping of the exhaust ports(& remove EGR bump) of my E7 heads. Nothing real extensive, & it only took about an hour to do both heads. This could give me 15-25 free HP. Possibly this is the type of thing you need to do.
First I'd find out more about Propane as fuel.
Once you have the parameters, you want to use, then adapt your engine to that.
Most stock heads were not designed to support compression ratios like your asking for. Shaving a stock head wont give you more than a couple of points ratio gain, without doing much more than I feel your wanting to do.
If you really want more ratio, pistons is probably what you want.
You might be best served to just adapt your engine to propane as it sits, and/or be satisfied with minor mods.
For instance; I'm in the process of replacing a leaking headgasket, while I'm at it, I have done a little reshaping of the exhaust ports(& remove EGR bump) of my E7 heads. Nothing real extensive, & it only took about an hour to do both heads. This could give me 15-25 free HP. Possibly this is the type of thing you need to do.
First I'd find out more about Propane as fuel.
jeffnoel
Founding Member
You could look for a set of used 65-67 289-2v heads. That would bump your CR to from 9.0 to 10.0, the cost to rebuild a good set of 289 heads would be comperable or cheaper than shaving the 302 heads since to achieve your goals with 302 heads you'd also have to shave some material from your intake.
65ShelbyClone
Founding Member
The octane ratings I have seen for propane vary somewhat, but most sources put it around the 108-112 range. You could probably get away with 13:1 compression running strictly propane.
You'll be limited by needing to run on pump gas with iron heads. I wouldn't shoot for much more than 10.5:1 in that case. Also keep in mind that propane is going to kill your volumetric efficiency by about 15% because it displaces much more of the intake air than gasoline.
You'll be limited by needing to run on pump gas with iron heads. I wouldn't shoot for much more than 10.5:1 in that case. Also keep in mind that propane is going to kill your volumetric efficiency by about 15% because it displaces much more of the intake air than gasoline.
ratio411
Founding Member
A few points and questions:
What year 302?
They dropped compression about a half a point per year from 71 to 73.
Was 9.0:1 in 71, then 8.0:1 by 73!
That will affect an accurate answer to what you are looking for.
I don't quite understand your rationale, but understand your basic questions.
With iron heads, you will be limited to about 9.5:1 on pump gas.
They detonate much easier than aluminum heads. You could squeek out 10.5:1 with aluminum.
The 9.5:1 is probably too low for propane.
Remember that too much octane is a bad thing if you don't need it!
You should never run more octane than what you truely need.
It makes your engine less effiecient, lowers MPG, and can carbon up the works.
Higher octane is less volitile, and if you don't have the compression, it won't burn as completely. So it's a big waste. The big secret that the gas station commercials don't want you to know when they talk about using premium fuel with fancy names like 'techron' and such. Most cars do not need premium. I'll get of the soapbox now and back to the subject....
Depending on the year of the engine, I would think you have 58cc heads.
The only way to do better than that is get some earlier 289 heads as proposed in another post.
You can gain by shaving your heads a little and seeking out the thinnest head gasket you can find.
You can also shave the block if you have it apart.
The thing about shaving either the block or the heads is that you also need to shave the intake if you do either one, or a total of more than .010".
Another thing you can do is use a cam with 'pressure building' characteristics.
Most RV cams are pressure builders. They use valve timing to increase the dynamic compression seen by the engine.
If you get a cam with alot of overlap, it will bleed off your static compression, effectively lowering what the engine actually sees when running.
What year 302?
They dropped compression about a half a point per year from 71 to 73.
Was 9.0:1 in 71, then 8.0:1 by 73!
That will affect an accurate answer to what you are looking for.
I don't quite understand your rationale, but understand your basic questions.
With iron heads, you will be limited to about 9.5:1 on pump gas.
They detonate much easier than aluminum heads. You could squeek out 10.5:1 with aluminum.
The 9.5:1 is probably too low for propane.
Remember that too much octane is a bad thing if you don't need it!
You should never run more octane than what you truely need.
It makes your engine less effiecient, lowers MPG, and can carbon up the works.
Higher octane is less volitile, and if you don't have the compression, it won't burn as completely. So it's a big waste. The big secret that the gas station commercials don't want you to know when they talk about using premium fuel with fancy names like 'techron' and such. Most cars do not need premium. I'll get of the soapbox now and back to the subject....
Depending on the year of the engine, I would think you have 58cc heads.
The only way to do better than that is get some earlier 289 heads as proposed in another post.
You can gain by shaving your heads a little and seeking out the thinnest head gasket you can find.
You can also shave the block if you have it apart.
The thing about shaving either the block or the heads is that you also need to shave the intake if you do either one, or a total of more than .010".
Another thing you can do is use a cam with 'pressure building' characteristics.
Most RV cams are pressure builders. They use valve timing to increase the dynamic compression seen by the engine.
If you get a cam with alot of overlap, it will bleed off your static compression, effectively lowering what the engine actually sees when running.
I see nobody's asked him yet what pistons and year he's got. 
The 70-71's had a slight dish, the 72-76 motors got pistons with huge dished tops(8 to 1 ratio). With these, you'll never get anywhere close to a 10 to 1 ratio. The easiest way, is to use flattops with a 1.610 comp height, and combine that with 54 cc heads (66-67 289) That will yeild a 10.5 or better ratio. Even with the 70-71 pistons the only way to 10 to 1 is to use the 289 heads. If you're shooting for 12 or better, the only route is the old 12.5 to 1 pop up pistons, I think these are still made. I don't see the reasoning in using Propane, unless you haul it and get it free. 
It cost's nearly the same as gasoline, but it yeilds less BTU's so you lose MPG.
The 70-71's had a slight dish, the 72-76 motors got pistons with huge dished tops(8 to 1 ratio). With these, you'll never get anywhere close to a 10 to 1 ratio. The easiest way, is to use flattops with a 1.610 comp height, and combine that with 54 cc heads (66-67 289) That will yeild a 10.5 or better ratio. Even with the 70-71 pistons the only way to 10 to 1 is to use the 289 heads. If you're shooting for 12 or better, the only route is the old 12.5 to 1 pop up pistons, I think these are still made. I don't see the reasoning in using Propane, unless you haul it and get it free. It cost's nearly the same as gasoline, but it yeilds less BTU's so you lose MPG.I have 1973 302 motor, as I'm reading the compression cannot be easily increased.
I.e. up to 9:1 maybe 9.5:1 with new 289 heads, and further using new pistons. If new pistons are needed, can the compression be increased from the other end, i.e. longer connecting rods, while keeping stock heads? the reason I ask is that I really would not like to spend $400+ for old cast iron heads and who knows what other valvetrain parts would be needed to fit them to the aftermarket cam, and what condition the heads will arrive (I would most likely get them from ebay). On the other hand, new connecting rods are cheaper than 289 heads+possible complications. If save some money I will get new alluminium heads with larger ports anyway if needing still more hp.
Can the compression be increased using connecting rods+pistons on this motor? PS I want propane because will move to Europe soon and gas is there about twice as expensive as propane. I once run carbureted car on propane with about 9:1 compression, worked OK. Many cars there are converted to selectable LPG/gas with even lower compressions.
I.e. up to 9:1 maybe 9.5:1 with new 289 heads, and further using new pistons. If new pistons are needed, can the compression be increased from the other end, i.e. longer connecting rods, while keeping stock heads? the reason I ask is that I really would not like to spend $400+ for old cast iron heads and who knows what other valvetrain parts would be needed to fit them to the aftermarket cam, and what condition the heads will arrive (I would most likely get them from ebay). On the other hand, new connecting rods are cheaper than 289 heads+possible complications. If save some money I will get new alluminium heads with larger ports anyway if needing still more hp.
Can the compression be increased using connecting rods+pistons on this motor? PS I want propane because will move to Europe soon and gas is there about twice as expensive as propane. I once run carbureted car on propane with about 9:1 compression, worked OK. Many cars there are converted to selectable LPG/gas with even lower compressions.
ratio411
Founding Member
With a piston replacement, you can get any compression you want.
There are almost unlimited pistons to choose from, and even if you don't find one that is perfect, you can fine tune them with reshaping.
That way you don't need to change/modify/shave anything at all.
The only thing you should be careful with is the heads.
Make sure the pistons are compatible with whatever heads you intend to use long term.
If you think you may change heads in the near future, wait to get your pistons until you get the heads. Often the dome on a piston requires it be used with a specific combustion chamber size or shape.
That is about all you need worry about.
Rods will not increase compression at all.
Bore and stroke will...
There are almost unlimited pistons to choose from, and even if you don't find one that is perfect, you can fine tune them with reshaping.
That way you don't need to change/modify/shave anything at all.
The only thing you should be careful with is the heads.
Make sure the pistons are compatible with whatever heads you intend to use long term.
If you think you may change heads in the near future, wait to get your pistons until you get the heads. Often the dome on a piston requires it be used with a specific combustion chamber size or shape.
That is about all you need worry about.
Rods will not increase compression at all.
Bore and stroke will...
65ShelbyClone
Founding Member
I think the idea behind longer rods was to pop the piston up higher. It will work in theory, but not in practice. SBFs don't typically have the pistons down the bore any more than ~.020". Rather than change the rods or mill the block, pop-up pistons like was mentioned by ratio411 will be easier and just as effective. Another option is leaving the low compression and super/turbocharging the engine.
Usually engines are built around a special fuel or the fuel is picked based on what the engine needs.
Usually engines are built around a special fuel or the fuel is picked based on what the engine needs.
I think the idea behind longer rods was to pop the piston up higher. It will work in theory, but not in practice. SBFs don't typically have the pistons down the bore any more than ~.020". Rather than change the rods or mill the block, pop-up pistons like was mentioned by ratio411 will be easier and just as effective. Another option is leaving the low compression and super/turbocharging the engine.
Usually engines are built around a special fuel or the fuel is picked based on what the engine needs.
giving it second thought you are right (411, 65shelby, d.hearne); don't need connecting rods. Most likely will try these (or similar):
http://store.summitracing.com/partdetail.asp?part=UEM-KB115&autoview=sku
These are flat top pistons. Is there any easy way to figure out what piston's compression distance is needed (whatever this distance means) at stock 58 ccm chambers and .5" max valve lift (will be less but to be safe), to get CR as high as possible (but not beyond 11:1)?
The ones you linked will get you to 9.76 with 58 cc heads. Once you have everything on hand, assemble one rod/piston on the crank, then verify the deck clearance. If there's room, you can always mill the deck to get to a zero deck. Actually milling should be done anyway to insure the decks are square and level with the crank centerline. Then have the heads milled to 54 cc, that will get it to 10.28 to 1.
ratio411
Founding Member
Since 73 was 8:1 compression, I am wondering if that was one of the years with the tall deck blocks.
Rather than change heads or pistons, Ford played with the head gaskets and cylinder blocks some years.
For a time, the 302 block was raised .020" taller to gain deck clearance and therefore lessen compression.
If 73 was one of those years, you know right away that the piston is .035" or so in the hole, vs the usual .015"+/-.
Sorry I don't have the details handy!
Thought I would throw that out though, so you could be on the lookout.
The idea behind longer connecting rods is to keep the piston near the top of the bore for a longer period of time during the cycle. It is supposed to increase efficiency during combustion because the volume is smaller during the time it takes for all the fuel to combust.
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