POTENTIAL OVERHEAT ON BORED '68 L71

[Jeff Burkey]

Looking at re-configuring back to 11:1 TRW piston set-up with this tri-power engine that has been bored .040 over by Traco Engineering. In order to do so, TRW only offers this piston in .030, or .060 over which would require an additional .020 overbore to accomodate. Am I running into a running hot situation, not because of the overbore, but more to the front nose design / air flow on shark cars...?? I also plan to have lead as part of the fuel mix either via race fuel or tetraethyhl lead additive and do not plan to convert valves/head configs. for unleaded. Use will primarily be "round town", but a mini-road trip / overnighter is not out of the question...??? Tks, Jeff B.

[Patrick H.]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

Jeff,

If the bore is smooth and does not NEED to be bored out again due to condition, I would seriously look into either custom pistons, which are not as expensive as you might think, or another manufacturer. The .040 is a relatively common size, and others may make a comparable piston in that size.

Good luck,

Patrick

[Clem Z.]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

you will need at least 95/96 octane fuel for 11:1 comp. you will have to mix race gas and pump unleaded hi test to do this. do not let any one tell you that you can run a 11:1 bb on pump unleaded. some parts of the country they are selling 100 octane unleaded at the pumps at about $4/5 gallon. even LS-1 need a knock sensor to retired the timing with 10:1 comp and this is a aluminum headed engine which can take .5 more comp than a iron head engine. 4 bolt 427 hi perf BB chevy blocks can be bored oversize to .125 without a problem.

[Larry Rosamond]

Clem, question re required octane...

Do you think that the lead additives available will get Jeff the octane boost to run an 11:1 BB rather than using race gas mixture? Just curious.Regards, Larry

[Clem Z.]

Re: Clem, question re required octane...

the octane boosters will eat the plating off of the insides of the carb float bowls. the TEL that is sold now can not be that strong because back before race gas we mixed TEL that we got from the GULF research labs here in pittsburgh was extremely dangerous, we mixed it at the labs using protective clothing. we put 4/5 cc per gallon

[Joe L.]

Re: Clem, question re required octane...

Larry-----

Not a chance. The lead additives really add very little lead to the gas when used at recommended concentrations. They add just enough lead to provide some valve seat protection. As far as octane boost goes, they usually don't boost the octane by a significant amount, at all, unless you were to use impractically large amounts of the additive.

[Jeff Burkey]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

Patrick: Traco bored this .040 over only 6,000 miles ago, but that was in 1977! Given the reputation for Traco Engineering and the low mileage, I would think the cylinder walls are just fine. Any recommendations for "other" piston mfg. I have not heard good things about Keith Black, but that's the way rumors go.... Tks, Jeff B.

[Jeff Burkey]

Re: Clem, question re required octane...

Joe: My inclusion of lead additives to the fuel was more for keeping the block cool vs. a performance gain in octane boost...!!! Tks, Jeff B.

[Ed Jennings]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

Given your intended use of the car, "round town and the occassional road trip", have you considered keeping the cr at some reaasonable (like 10:1 or less) number and simply telling people "it's 11:1"? I'm serious. Why would you want to create all the potential problems to go to the grocery store?
My 327 fuelie has 10+:1 (don't know the exact #), and I can assure you that when the time comes for new pistons they will be flat tops. The problems aren't bad enough to warrent an engine rebuild, but if the occassion ever arises the domed pistons and the Comp Cams cam are history.

[Joe L.]

Re: Clem, question re required octane...

Jeff-----

In my opinion, the amount of improved cooling performance, which is an indirect function of the octane boost, that you could achieve by introducing the available lead additives in any practical quantity would be de minimis.

[Joe L.]

Re: Clem, question re required octane...

clem------

Yes, the lead scavengers which are a necessary part of tetraethyl lead additive compounds are EXTREMELY corrosive to fuel system parts, especially carburetors. That's why carburetors used to "wear out" so regularly in the old days. The best thing that ever happened to carburetors was unleaded fuel. It makes them practically "immortal".

Also, you are absolutely correct on the toxicity of tetraethyl lead. It is an EXTREMELY toxic substance in its concentrated form. Very few labs could even obtain it that way since it is so deadly. It is RAPIDLY absorbed through the skin and even a drop on unprotected skin can cause death. There is NO WAY ON EARTH that the government would allow tetraethyl lead to be sold compounded in any highly concentrated way. As a matter of fact and as I recall, most of the additives, IN THEIR CONCENTRATED FORM, contain tetraethyl lead at about 1 gram/gallon as lead. This is about the same as regular leaded gasoline used to contain in the 60s. So, if you add 1 gallon of this stuff to 20 gallons of gas, you end up with a lead concentration of 0.05 g/gallon in the treated gasoline. This much lead will produce negligible octane boost. It will provide enough lead to offer protection from exhaust seat recission.

[Patrick H.]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

Jeff,

As the others have noted, what do you have now? Going to a true 11:1 is a real PITA in real modern life.

For custom pistons you can look at Arias, JE, Manley or others.

Patrick

[Mike Baker]

Re: POTENTIAL OVERHEAT ON BORED '68 L71

I recently spent some time trying to hunt down some .40 over TRW pistons as well, with no luck. They actually used to exist as an off the shelf product but seem to no longer be available.

I ended up having some made by JE. They are absolutely beautiful. I was tempted to have them make a 9th just so I could have one around but, I decided that was absurd.

I don't have the motor back together yet, but am looking forward to it.

By the way it is also a 68 L71. The final compresion ratio will be about 9.75.

[Jeff Burkey]

tri-power set-up, or no...??

Mike: Are you retaining the tri-power config. or have you changed to something less rad/more calm..?? Also, if you are working off 3 2's, with the lower cr, do you experience enough manifold vacuum to operate the center carb...?? I guess that is whole crux of my inquiry, which is proper cr for enjoying the trips...??? tks, Jeff B.

[John H.]

Re: tri-power set-up, or no...??

Jeff -

Not clear on your question about "enough manifold vacuum to operate the center carb" - could you clarify?