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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / May 200813-1/2 to 1 compression ...on the street?
Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It apparently has been at some statewide cruises, rod runs, etc, so I know it's been driven. My question is, what kind of fuel must the owner be running for the engine to survive. Heard claim that by retarding the timing somewhat, pump gas with octane booster works(?) Race fuel? Any ideas (...from guys familiar with similar cars or situations). Thanks > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks Need more info, what kind of engine? Cast iron or aluminum heads? Any more details on the engine build will help us give you better answers. I may not be able to directly answer your question, but I know enough to know that you need to give more info :) nate  Signaturereplace "roosters" with "cox" to reply. http://members.cox.net/njnagel > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks #2 diesel? > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks Why not ask the owner ? With a compression ratio that high I think you wiil need race gas. > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks What engine and what type of heads? What cam & lifters? If it has aluminum heads and the proper cam it probably would run just fine on 93 octane with water injection and playing with the timing some. SignatureSteve W. >Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It >apparently has been at some statewide cruises, rod runs, etc, so I know it's >been driven. My question is, what kind of fuel must the owner be running for >the engine to survive. Heard claim that by retarding the timing somewhat, >pump gas with octane booster works(?) Race fuel? Any ideas (...from guys >familiar with similar cars or situations). Thanks How old is it? If it's old enough to run without a catalytic converter, 100LL aircraft fuel should be okay on the street. May not be high enough octane. The "octane booster" in a bottle stuff is usually just MTBE. You can also still get tetraethyl lead. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks Cast iron or aluminum heads? Camshaft spec.'s Carb or EFI What might also help is what is the cranking compression of the engine (Do a Compression Test) > > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > > apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 8 lines] > What might also help is what is the cranking compression of the engine > (Do a Compression Test) I know a bit about cars, but not why the ?? about Al heads is important- is it the fact it's Al and not cast iron, or just that Al heads are likely to be better engineered? Dave On Apr 30, 12:41 pm, spamTHIS...@yahoo.com wrote: > > > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > > > apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 14 lines] > > Dave Aluminum heads shed heat to the cooling system better than do cast iron. You'd think that this would be a disadvantage, but in a high- compression engine, it helps to prevent detonation. I have heard as a rule of thumb that aluminum heads, all other factors being equal, allow you to safely run a half point more compression on the same octane fuel than do cast iron. nate no less than 93 octane should be used and u can do a pass and check the plugs for color if they are tan all is good > On Apr 30, 12:41 pm, spamTHIS...@yahoo.com wrote: > > [quoted text clipped - 25 lines] > > nate > > > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > > > apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 14 lines] > > Dave As Nate said "Aluminum heads shed heat" "all other factors being equal, allow you to safely run a half point more compression on the same octane fuel than do cast iron." But since most Aluminum heads are after market or late model factor design and most are some what better engineered / more efficient combustion chamber design, they can run more compression. > As Nate said "Aluminum heads shed heat" > "all other factors being equal, allow you to safely run a half point [quoted text clipped - 3 lines] > design and most are some what better engineered / more efficient > combustion chamber design, they can run more compression. There are a lot of REALLY shittly-engineered aluminum heads available, too. They're not in any way guaranteed to be better than well-prepped stock iron heads in terms of chamber design, but they will still have a thermal conductivity advantage. >>> Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It >>> apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 11 lines] > important- is it the fact it's Al and not cast iron, or just that Al > heads are likely to be better engineered? Look up the thermal conductivity of iron vs aluminum. Aluminum carries the heat away from the inner surfaces of the combustion chamber and to the coolant MUCH faster than iron, to there are fewer hot-spots to initiate detonation. Alcohol > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. > It apparently has been at some statewide cruises, rod runs, etc, so I [quoted text clipped - 3 lines] > Race fuel? Any ideas (...from guys familiar with similar cars or > situations). Thanks Alcohol My thought, too. If the CR is actually that high I can't see it ever running on pump gas regardless of the heads, cam, etc. > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. > Alcohol > > My thought, too. If the CR is actually that high I can't see it ever running > on pump gas regardless of the heads, cam, etc. Why not? NASCAR runs 12.5:1 on 98 octane using iron heads. They ran 13:1 on the old 105 octane leaded fuel. I have run 13:1 on pump gas with aluminum heads on a 427 with a set of Rhodes lifters to drop the cam down some. No problems at all. SignatureSteve W. > > Alcohol > [quoted text clipped - 8 lines] > -- > Steve W. I would think the Rhodes lifters would actually hurt, not help - they'll improve idle quality but at the cost of increased low RPM cylinder pressures. or am I thinkin' wrong? I will say that at anything over 10.x:1 you probably need to have someone GOOD (not me!) tune the engine to avoid an inadvertent detonation incident. nate (currently running 10.25:1 with iron heads - stock 63-64 spec Studebaker R1 engine...) >>> Alcohol >>> My thought, too. If the CR is actually that high I can't see it ever running [quoted text clipped - 19 lines] > (currently running 10.25:1 with iron heads - stock 63-64 spec > Studebaker R1 engine...) No real pressure increase. You just need to play with the bleed rate some. Mine was set up to "hide" the real power of that engine. The only problem I ever had with it was that I kept putting my foot through the firewall.... Tuning of a true HP engine is an art. Not something you get from books or online. SignatureSteve W. Near Cooperstown, New York >>>> Alcohol >>>> My thought, too. If the CR is actually that high I can't see it ever [quoted text clipped - 26 lines] > Tuning of a true HP engine is an art. Not something you get from books > or online. OK, so you tuned down the rumpity idle some... but how do you tune out that "sharp" exhaust sound that you only get with high compression or a blower? nate (appreciates stealth performance) Signaturereplace "roosters" with "cox" to reply. http://members.cox.net/njnagel > OK, so you tuned down the rumpity idle some... but how do you tune out > that "sharp" exhaust sound that you only get with high compression or a [quoted text clipped - 3 lines] > > (appreciates stealth performance) Tuned the collectors, Installed an H pipe and used 4 mufflers. The first two were custom made and designed kind of like a straight through with concentric baffles(like a silencer). Behind the baffles were channels that allowed the exhaust to cancel out those hard notes. These fed into a normal pair of flowmasters. Until you really climbed on the loud pedal it sounded just a bit warmer than stock. Surprised more than a few folks. SignatureSteve W. Near Cooperstown, New York >> Alcohol >> [quoted text clipped - 5 lines] > aluminum heads on a 427 with a set of Rhodes lifters to drop the cam > down some. No problems at all. Actually, NASCAR runs aluminum heads. >> Alcohol >> >> My thought, too. If the CR is actually that high I can't see it ever >> running on pump gas regardless of the heads, cam, etc. > > Why not? NASCAR runs 12.5:1 on 98 octane using iron heads. Your local stations have 98 octane "pump gas"? Iron heads? Not likely > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know > it's been driven. My question is, what kind of fuel must the owner be > running for the engine to survive. Heard claim that by retarding the > timing somewhat, pump gas with octane booster works(?) Race fuel? Any > ideas (...from guys familiar with similar cars or situations). Thanks Having driven a high powered high compression car on the street for a few years, I will say that it is not always as much fun as one thinks it might be. Others have already posted that it depends upon the engine, timing, etc. In my case, the car's cooling system was marginal for that type of engine, and that added to the distress. I had to run 98 octane at all times, and was running less compression than this car. It just wasnt a pleasure at all. But the suggestion to ask the present owner what is involved is a good one. > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks But why retard timing on a performance car. That handicaps it seriously, and can lead to overheating and other problems. Yet it takes a LOT of octane to run that kind of CR. I would think alcohol would be the fuel of choice. If it has a carb, conversion for alky is easy. Not so easy with FI. > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > apparently has been at some statewide cruises, rod runs, etc, so I know it's > been driven. My question is, what kind of fuel must the owner be running for > the engine to survive. Heard claim that by retarding the timing somewhat, > pump gas with octane booster works(?) Race fuel? Any ideas (...from guys > familiar with similar cars or situations). Thanks It depends on a lot of things. How radical is the cam? If its a HUGE cam with a ton of overlap, then the actual compression pressure might be manageable enough to live on pump premium with a mild octane booster. Same if it has aluminum heads with polished chambers- that will reduce octane requirement, but as deposits build up as the engine is run the octane requirements can creep back up. But at 13.5:1 (assuming that it was computed correctly, most people tend to over-estimate the true compression when they build an engine) then it would be pretty hard to make it live on pump gas. Retarding the timing is a band-aid, and not a good idea. It makes the exhaust valves run cherry-red hot all the time and can cause valve seat recession and burned valves. > > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It > > apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 6 lines] > with a ton of overlap, then the actual compression pressure might be > manageable enough to live on pump premium with a mild octane booster. explain to me how overlap and not IVC will effect low rpm cylinder pressure? > Same if it has aluminum heads with polished chambers- that will reduce > octane requirement, but as deposits build up as the engine is run the [quoted text clipped - 7 lines] > exhaust valves run cherry-red hot all the time and can cause valve seat > recession and burned valves. >>> Looking at a nice Pro Street car with 13.5 to 1 compression pistons. It >>> apparently has been at some statewide cruises, rod runs, etc, so I know it's [quoted text clipped - 9 lines] > explain to me how overlap and not IVC will effect low rpm cylinder > pressure? You obviously understand the issue. IVC timing is the key event that controls low RPM cylinder pressure. But late IVC which lowers cylinder pressure usually goes hand-in-hand with a bunch of overlap, so the slang creeps in. Lots of overlap means that the IV has to stay open even longer after the EV closes for optimum cylinder filling at high RPM, so it leads to lower pressure at low RPM. |
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