I have a question regarding mixing 93 octane with 105 octane gas.  I'm running 11.0:1 CR.  It seems to run fine with 93 but I remember hearing\reading about mixing the two fuels.  Would I benefit from an 80/20 mix (80% 93 and 20% 105).  Would hat be enough to raise the octane a few points or would I need to add more 105 to the mix?

Jeff

That's too expensive.  Go buy some lucas octance boost the good kind, and try it with the 93 octance.  This stuff properly mixed can easily add 3 octance to the 93 octance, and see how see runs. 

You won't benift from using the higher octane rated fuel. Just because there is a higher octane number, dosn't necessarily mean that you will make more power just by switching to the higher octane fuel. On the other hand if you are experiencing detonation under high load, a mix of the fuel could be benificial.  

My theory behind this is to try and squeeze out a bit more timing.  I currently run 18 initial, 36 total.  Would a higher rating allow me to run 37-38?  Would this equate to more power?

Jeff

It may, but it just depends on the engine, some would benifit from the advance, some wouldn't. Have you tried advancing the timing with the 93? do you get a knock then?  

Not necessiarrily productive. Too much advance makes the engine surge even without detonation being present. Keep in mind that running on the edge of detonation can be mighty expensive since cylinder conditions vary from cylinder to cylinder because an engine doesn't cool every cylinder the same, mixtures vary from cylinder to cylinder especially with a carburetor or continous flow injection. Atmospheric conditions change from moment to moment, place to place, this causes changes in mixture ratio and absolute cylinder pressures and air/mixture density. A little too much oil left behind by the rings will decrease the fuel's octane rating. If you're running hard and on this edge, and variation leading to increased temp, decreased mixture ratio, increased mixture density, or a miniscule amount of oil from a ring or guide will lead very suddenly to a new engine.

Not to mention that excessive timing lead causes too much pressure too soon and the engine looses power both in trying to turn backwards and trying to compress excessive cylinder pressure. This leads to failed head gaskets at the minimum to blown pistons, crushed rings, failed rod bearings from the oil wedge being squeezed out, fried valves and seats.

There is more power to be had from fast burn type heads which require less spark lead and tolerate more compression than can ever be had with timing lead beyond 38-40 degrees.

Bogie

I never really noticed any detonation beyond 36, it just ran sluggish.  As an FYI, my current setup is as follows:

- 383 SBC

- Edelbrock Performer RPM package with Edelbrock HR cam

- Edelbrock 100HP nitrous

- 11.0:1 CR

- Hooker Super Comp Headers

- MSD ignition

- B&M 2500 stall converter

Not sure if this makes much of a difference but thought I would mention it.

Jeff

Sluggish running as the advance goes up is a sign that the timing is as far advanced as the engine likes.

Detonation isn't always audable, but it's always distructive.

With a 100 shot of nitrous, the timing should actually be retarded when on laughing gas. The system you installed should have that provision.

Compression above about 9 to 1 is there to recover the lost bottom end torque of a long duration, long overlap, late closing cam. One needs to be careful of too much compression with too little cam, but that's not a problem with your set up.

Does your Performer package include Mr. Edlebrock's heads? Or something similar? If not, you could be walking away from 40-60 horsepower if you're using an open chamber head. The 383 has a lot of bore for the flame front to get across, a fast burn combustion chamber combined with a "D" dish or flat top piston does a lot for speeding up the burn without a lot of spark lead. That or dual plugs! and you can guess which is easier to do on a Bow Tie small block.

I would think that if you need more power, more laughing gas is the way to go.

Rear gear (or overall gear) ratio and tire size, and vehicle weight are also important tuner data. Type of transmission is helpful, sounds like an automatic of some sort.

I expect this thing runs pretty hard!

Bogie

I rarely use the nitrous and when I do I retard the timing 4 degrees.  I'm looking into MSD's digital multi-retard so I don't have to make this change when I want to run nitrous.  It also would give me the best of both worlds where I will have full timing on motor only yet proper timing when on the bottle.  I have the Performer RPM heads w/ 64cc chambers and 2.02/1.60 valves.  I also have the RPM Air-Gap intake and their 750 carb.  I have an Auburn LSD with 4.10 gears behind a 700r4 with a B&M shift kit.  Govenor set to shift from 1st to 2nd around 6200 RPM.

It does pull hard for a full size 4x4 pickup.  I don't really need a bunch more power.  I just want to tweak what I have.

Jeff

Ya know, I'm arriving at the point where I think that when a project is running so good that I start to tweak it, it's time for a new project.

Enjoy, sounds great!

Bogie

this may help with your math.... octane is linear. example.... 1 gal 110 octane + 1 gal 94 octane is simple as 9th grade math 110+94 =204

204 divided by 2 = 2 gal 102 octane engine oil works the same way.

 1 qt 30 weight +1 qt 40 weight equals 2 qt 35 weight. get it?

good luck keep the sport alive

i mix it. but some fues wont mix put bolth in a clear bottle and wait a few days if they dont jell your good to burn,i have $100 worth of turqo fuel that wont mix.