So Jim, your conclusion for best performance is to mix 93 and 110 octane instead of 93 + lead additive? That seems to make sense if you assume the 110 is all "gas" and the 93 is a mixture of gas, crap, and ethanol that contains less energy. You'd have the octane plus more energy. 110 here was about 6.50/gal last time I checked but it wouldn't end up being that much more than using the additives.
Yes, mixing 93 and 110 turned out to be the best for performance. The lead additive is a good substitute for those that do not have a choice because of limited access to the 110. It would be good to use the additive now and then if you have stock heads. The lead will build up a film and protect the valves and seats. It doesn't take much lead to get a good protective film. And it will last quite a while once the film is there.
I haven't kept up on the market of fuel additives lately, but if these additives contain tetra-ethyl lead be very careful handling it. Don't get it on your skin for it will transmit lead into your bloodstream. It's very nasty stuff.
You can run a properly tuned 10-1 motor on 94 octane from Sunoco. Their fuel has a actual rating of 95-96. The lead additive should be used for valve lube to prevent seat recession and as an added buffer to the Sunoco 94.
You do not need to mix if your timing and distributor are tuned and you are at an actual 10-1. Check cranking pressures as well.
Simple questions deserve simple answers.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
Two other things that are important are having a 0-deck block and keeping the cranking compression at about 175 lbs by using a cam with more overlap. It works and gives more power.Also helps to keep motor cool. Able to run on 92 octane.
You can run a properly tuned 10-1 motor on 94 octane from Sunoco. Their fuel has a actual rating of 95-96. The lead additive should be used for valve lube to prevent seat recession and as an added buffer to the Sunoco 94.
You do not need to mix if your timing and distributor are tuned and you are at an actual 10-1. Check cranking pressures as well.
Simple questions deserve simple answers.
If you read through this thread you will understand that things aren't always so simple. It can be simple if you do have access to the high octane fuel. Greg asked for the lead study because he didn't have that luxury living in Springfield, MO. He's running a 428 with higher than 10-1(read) which further complicates his situation.
Two other things that are important are having a 0-deck block and keeping the cranking compression at about 175 lbs by using a cam with more overlap. It works and gives more power.Also helps to keep motor cool. Able to run on 92 octane.
Jim G. 67 conv 400
I'm skeptical on the zero block clearance issue. I have one 400 that is zero decked and one that's 'in the hole'. The 'in the hole' engine actually runs cooler. I can attribute some of it to the manual trans. If I run it without a thermostat, it will not go above 150 degrees.
Jim , cooling better is a side effect of 0-decking the block. The main reason is to improve the squish area of the combustion chamber which helps control detonation in Iron heads. So you can run 92 octane gas and keep timing up were it should be. Do you know what the cranking compression is on your two motors,to get a reading on cranking compression verses temperature?
I posted the pressures on my zero decked block previously(page back). The 'pistons in the hole' engine has these pistons. See note for applicable compression. I'm using 62's(heads) on both engines.
Those Speed pros are the same ones I use, the compression listed is the dynamic compression not cranking. I have #16 heads on my car now (got them from you) and my cranking pressure is 175 LBS. I think maybe the difference is in the cam I use a Crower 60916.This cam has a later opening of the intake valve and that may be bleeding off some pressure. So you can see how two motors with almost the same parts can act different.Has to be the hole package. Do you have to run octane booster in both motors equally?
Glad those heads are working great for you! Yes, I can see the difference between the two. But not very much difference when it comes to what they like to burn. I have the same problems with octane on both. And have to use the racing fuel on both. The lower temps on the one with the speed pro's does not seem to stop the detonation much. I think you are right on with the cam selection. I think it's helping you substantially. Definitely great info!
I can not take credit for this build. I got it from Cliff Ruggles, he builds motors and carbs. Here is some of what he has done.
would zero deck For medium compression engines built to use pump fuel it becomes much more important to maintain the quench distance of .035-.040". The engine will also run cooler zero decked. Without exception, every Pontiac engine I've had in here that had running hot/overheating problems had the pistons .020" to .030" in the holes.
The following is a recent example: We just finished a well prepared 400 engine for a 66 GTO. The owner is a very competant mechanic by trade, he owns several older high performance vehicles. Last year he completely rebuilt his 400 engine with catastrophic results. A set of #62 heads were used with stock replacement cast pistons, Summit 214/224 cam, Torquer I intake and Edelbrock 750 carb. The engine ran so hot he could not drive it. It also detonated under all circumstances, after an entire summer of tuning without improvement, he removed the engine and brought it here. We made a few minor changes.
The #62 heads were mildly ported, combustion chambers polished to a mirror finish and the exhaust crossover filled with aluminum. The cast pistons were the 8 valve relief replacements and were .030" in the holes, they were replaced with TRW forgings and the block was zero decked, a set of .039" head gaskets were used. A larger 221/229 cam was installed with HS high ratio rockers. The Torquer intake was replaced with an RPM. An 800cfm q-jet and HEI distributor were prepared for the new engine. The new engine manages pump fuel without problems despite being slightly over 10 to 1, compared to the previous configuration being closer to 9.5 to 1. It never gives the first indication of wanting to go past 190 degrees even on extended cruises at freeway speeds. The previous set-up would continue to heat up on extended cruises eventually reaching over 220 degrees where it had to be shut down to cool off.
I know that some of you suspect that it is the TOTAL package that changed the results. About 5 years ago I had a nearly identical 400 engine in here with the same history. I DID NOT rebuild the engine, but spent countless hours trying to tune it to get rid of the detonation/overheating. This included a new (expensive) radiator, waterpump/pulleys, several types of fans, etc. When I finally threw in the towel and pulled the engine, you guessed it, the TRW forgings were .032" in the holes. The engine was zero decked, slight cam change and no problems thereafter.......Cliff
Here, we use Crower's 60916 cam (221/229, .455"/.470", 112) with excellent results in the early 400 engines with small chamber heads. You may find the pistons end up well below the deck at TDC. Most of the 400's we've assembled with the forged replacment pistons have been .028" to .032" in the holes. We always deck for zero and haven't had the first problem managing pump fuel at or near 10 to 1 compression ratio.......Cliff
That is the exact set up I have in my 79 TA. With the exception of the .028 cut that zero decked your pistons. I do not have any overheating at all. I do have detonation with 93 octane. I have to bump it up to around 100 to get the best performance/power. The audible detonation disapears at around 94 to 96 octane. There can still be combustion problems that are inaudible. A sure sign would be a slight bog when quickly accelerating. If you find that you have better power with a little higher octane then it's better to be safe and use the octane level at which you get the best performance. You can get piston, rod and bearing damage from inaudible detonations.
Late post, but after Jim's testing and more checking around, I started using 2 oz of lead to a gallon on 93 octane gas. I also put 1 gallon of toluene to 10 gallons of that. Now there is some snappy fuel that you can feel a difference in. And I can load up the trunk with bottles of the products and go anywhere I care to. More importantly, I can gas up and come home. After around 1300 miles of this I pulled the plugs and see nothing to raise suspicion.
Any canucks out there know what the best additive available up here is? Could not find Max-lead and they wanted to ship it UPS only, so it would kill the end cost of the stuff shipped.
Seen some stuff in a few places ...STP etc, but nervous about them.
I've heard all kinds of humours about which brand is good and which are not. On one of the boards it said to make sure it was in a metal container or it wasn't strong enough. The stuff Greg sent me was in plastic bottles and it was good stuff that worked good. I bet a big company like STP would have real lead.
Yes, it was a long time. We were out of power all together for 9 days and I lost my DSL for 3 weeks, so I have in fact been out of touch. I'm not feeling sorry for myself however as I did have a home to come to, unlike the folks in FL, and now LA. We had tons of ice, but no 120+ inches of snow. I'm in GRRRREAT shape as compared to many. The toluene comes from a paint store. I first paid as much as $20.00 for a gallon at the hardware store, but buy it in 5 gallon pails from sherwin-williams for just under $7.00 per gallon. If you'll google around on toluene, you'll see that it is an acceptable practice so to speak. It is 114 octane by itself. It is an old racer's mixture.
Noted Pontiac Tuner Dave Miranada who used to be involved with Superjet Specialities in Queens, New York.
He deduced that the detonation threshold of a Pontiac V8 was right at 185 psi cranking compression.
Dave also came to the following conclusions:
The optimum (maximum) cranking cylinder compression pressure for a performance/street application using 93 octane fuel = 160 -170 psi
Changing the position of the camshaft (and thus intake valve closing event) by 4° changes cranking cylinder pressure by about 5 psi. (Advancing increases pressure, retarding decreases pressure.)
