Hello,
i have a stock 351M on my Bronco,on all literature that i look, they say 136hp and 265lb-ft.But for what octane of gas?.I removed the cat and i run on 97 leaded or 98 unleaded.The engine has low miles on it and go very,very well.Anyone knows if this can improve the engine output?
Thankyou!

 

[updated:LAST EDITED ON 22-Apr-02 AT 10:51 PM (EST)]>Hello,
>i have a stock 351M on my Bronco,on all literature that i
>look, they say 136hp and 265lb-ft.But for what octane of
>gas?.I removed the cat and i run on 97 leaded or 98
>unleaded.The engine has low miles on it and go very,very
>well.Anyone knows if this can improve the engine output?
>Thankyou!

Increasing the octane will only slightly help performance on a stock engine - if you advance the timing. Where it really benefits performance is allowing you to run high compression without detonation. Your engine is likely running 8:1 compression and since it would not detonate even with 87 octane fuel, 98 octane fuel (where do you find that anyway?) would make almost zero difference.

Now, if you bumped your compression to 10:1 by changing pistons, you would need 93+ octane fuel to avoid detonation (knocking) or you would have to retard timing a bit. If you dropped Aussie heads on, you could go a bit higher in compression since the quench chambers help avoid detonation (particularly if you polish the chambers).

What you could do to your engine to cheaply take advantage of the higher octane fuel is to advance the timing a bit. Listen for knocking and retard it a bit if you hear any. Also, since you have opened up your exhaust by removing the cat - you may want to check the jetting on the carb to be sure you are not running too lean. Before you do that, you may want to swap your muffler for a free flowing one - then check the jetting.

 

leaded? do you mean an additive that boosts octane using lead? You can't still get leaded gas can you? No way!

 

The easiest way to boost compression is to install Aussies 2v heads, change the timing, get an aftermarket 4v intake and carb, and put on headers.

 

In Japan 98 octane unleaded is the standard... Here in Australia 98 octane unleaded is available at maybe half of petrol stations, and up until a year ago 95 octane leaded was also available. In the middle east (and I'd say most of the developing world too) high octane leaded fuels are still available.

 

Hello,
thankyou all.I am in Spain,and here we still have leaded gas,but now
is drop out in favor of the "new super 97".The gas supplier says that it no contains lead,it contains a replacement for lead.
I think that the lead is the best,so the "new" gas can´t contain any component to equalize lead.
The others are without lead,95 octane regular, and 98 premium.
Oh yes the engine sometimes on raised roads(plenty here),and with standard c-6, 3.50 gears and 32" tires,make that knocking.I have a small glasspack muffler only from the stock manifolds to exit.
How i can eliminate knockin? only adjusting timing?
the carb has the regulaton bolts sealed.Maybe it be run too poor.

 

>Hello,
>thankyou all.I am in Spain,and here we still have leaded
>gas,but now
>is drop out in favor of the "new super 97".The gas supplier
>says that it no contains lead,it contains a replacement for
>lead.
>I think that the lead is the best,so the "new" gas can´t
>contain any component to equalize lead.
>The others are without lead,95 octane regular, and 98
>premium.
>Oh yes the engine sometimes on raised roads(plenty here),and
>with standard c-6, 3.50 gears and 32" tires,make that
>knocking.I have a small glasspack muffler only from the
>stock manifolds to exit.
>How i can eliminate knockin? only adjusting timing?
>the carb has the regulaton bolts sealed.Maybe it be run too
>poor.


If you are running a motor with stock compression and it still knocks on 97 octane fuel, then either your timing is way too advanced already, your vacuum or mechanical advance is defective - or what you are hearing is lifter noise rather than detonation. With 97 octane fuel, you should be able to run at least 10:1 without detonation. I suggest that your first step is to check your timing and set it back to about 6 degrees to start with and see how that does. If it is already correct, then examine your mechanical advance springs. If it is a vacuum advance problem, make sure it is connected to ported vaccuum (and not full manifold vaccuum). Also be sure that the vaccuum advance adjustment is correct.