Boost -vs- Octane requirement
 

Does anyone have a table that indicates the octane required to prevent detonation at a given boost ?

Thanks

If your car is stock, it has spark retard.....which means you can run any octane you want....you will just get less power. I talked with Reeves Callaway regarding this topic for my 1981 twin turbo 928. He recommended always running as high an octane as you can. If you are running 1 bar (14.7 psig), make sure you use at least 93 octane. As boost pressure comes up, the timing and amount of octane become very important in elimination of detonation. Also, not just having the octane, but having enough fuel is critical in keeping things cool. I wouls say you would be safe at 14 psig of boost with 93 octane pump fuel. I run this in my Audi, and you can feel a big difference in powe between 93 and 87 octane fuel.

Twin Turbo 928!?! So you are one of the really few around, even if it is one of the older examples. Care to give us some info on it? :)

As far as octane, go back to our discussion on adding toulene. I think the thread was called Homemade Rocket Fuel, or somesuch. Anyway toulene is octane 114, so mix by volume to improve pump gas. try and buy in bulk to get the price down.

You are never going to find a free chart on octane/boost level that will be worth anything to your specific application.

Yes I have also heard that 93 octane and 1 bar of boost is safe if you run 1 plug colder. It would be interesting to see how much retard is being applied under those conditions. I would expect still some is happening. I wonder where a guy can get Toulene ? Any advice IceShark ?

I buy toulene in five gallon cans from Sherwin-Williams for 25.XX, I run 93 octane in my turbo and add one gallon of toulene per tank full, I was adding two per tank full but have cut down to one.

TurboGuy, as Booster noted you can get it from paint stores. Hardware stores also carry it. Probably the best deal is to get it from a chemical supplier in 55 gallon drums if you have a couple other guys to go in on it to get the price under $5 a gallon.

If you buy a whole 55 gallon drum yourself you better think hard about storage - I would hate to have that go off in my garage. :eek:

Then play with how much to raise the octane ... from most reports with modest boost, shooting for ~ 94 octane seems to be about right. No sense mixing the octane too high and wasting it.

This the stuff you guy's are talking about? http://www.mallchem.com/msds/t3913.htm
If so, it has proven to add the risk of cancer (skin) so be a bit more carefull please...
Take care

Yeah, that is the stuff, Hans.

But those hazmat dopes have a warning out on Mother's Milk. ;) While you don't want to wash with this stuff, it isn't that bad. But don't spill it on the paint without cleaning.

Well I have some interesting news on the subject. I have a copy of turbo calc from Ray Hall turbo and I have input all the related parameters for the 951 i.e. Bore, stroke etc..etc and here is what it gives me for answers. The data is based on a ZERO detonation criteria.

PSI Octane

10 94.96
12.5 97.64
15 100.32
17.5 103
20 105.68
22.5 108.36
25 111

If this is accurate it may explain the head gasket failures in many 951 owners. Very interesting.

I'm gonna do some 60-100mph times with 93octane...then will add a gallon of toluene to the mix and see if times change at all....
Running 1bar boost...about 14.5psi...
I'll get some RWH numbers with the Gtech too...

Here are the mods to my 81 928:

Twin IHI RHB6 Turbochargers
Custom manifolds and exhaust
Remote Callaway Wastegates
High Flow Injectors, 10 of them
Modified Air Flow Meter
Air Research Intercooler
Microfueler Black Box for injectors 9 and 10
A *hitload of pipes, couplings and connectors.
Scavenger pump system for oil recovery

HP is somewhere between 375 and 400.....it depends on the air temperature outside. The torque is best described as A LOT! The car will do 0-60 in about 5 seconds, 1/4 mile at over 105 MPH, and top out at right around 165-170 (runs out of 5th gear). Yes it is a maintenance pig, requiring constant tinkering and tuning to keep things in order. The inners of the engine are totally stock (yea I know, you don't have to say it), and it seems to be holding up well. Clutch is also stock per me (..Callaway had installed a POS sintered metal clutch that eventually led to the destruction of the syncros....it wasn't adjusted properly, and ate the plates up badly). Only 4 of these cars were ever produced. There are two remaining.

I'll take some pictures sometime and post them up here.

I have bought it in 55 gallon drums before but the price is not that much different than the price I pay at the paint store and it's a hellava lot easer to transport in 5 gallon cans. I have been useing this stuff for years in my cars.

Chris at Technodyne offered me some interesting information the other day. He said that he ran a dyno on pump gas then he ran the same setup with 110 race fuel. The race fuel setup had 35 more horsepower! That is how much the knock sensor can effect
overall performance.

Turboguy, how much boost and what other mods did that car have? Was it a 951?

I got it for under $4 a gallon in 55 gallon .... though I did bring my own drum. You are right about being a bitch to move around v 5 gallon cans.

Those octane numbers seem way high, TurboGuy. All of us should have blown up by now if they were good. Many of us are running above 1 bar, though not much more than 20psi as far as I have seen.

Halloween kids were funny but all had parents with them. That is another sign how life changed, Tabor.