horsepower versus Octane

[Splitpin]

Gents,
What sort of horsepower can you get from a ford 351 / chevy 350 using standard grade petrol 95 octane ? Obviously compression ratio has a large part to play.
Looking at the postings there are lots of 400 + bhp engines in use. Are you using super unleaded, fuel additives, and is there a need to convert the heads to avoid the need for lead replacement petrol which is going to disappear soon ?
What sort of number increase do octane boosters provide and are they expensive?
I was thinking of building/buying a 383 stroker 450 BHP which seems very popular, but i'm concerned about future high octane fuel availability.
cheers
Mike

[robert]

Mike

With hardened valve seats, you can run standard unleaded or super without the need for additives, which is what the majority of us are doing.

If you are looking at a stroker with 450hp, then that will need a reasonably high CR, and will have to run super. Drop the output down a bit and you can run standard. You will need to play around with the engine spec a bit, but by doing some work on getting the right cam profile etc, you could have a good engine.

Depends what you are looking for, a racy engine that is quite peaky or a thumper with loads of low down torque.

I might have a play later with the software.

Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[Splitpin]

Thanks Robert,
It seems an inconvenience to find super unleaded because not all stations seem to stock it. I wonder what people do when on a trip, the range of a gas guzzler can't be that high. What do you do when the local garage only does standard fuel ?
Mike

[robert]

You chuck in standard, and in my case, don't use boost, in other cases, don't use wide open throttle and boot it too much.

Most of the time, Super is just a way of getting a little more HP when under load. The majority of cars will run on standard and if set-up properly, will not pink.

Best Regards

Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[dave]

Ditto to Robs reply.
I was advised to use super where possible in a 383 Chevy but it wouldn't be the end of the world if none was available.......Just that if you've paid good money for your engine then why scrimp on the fuel.
I should imagine that super plus will continue to be available for a long time yet as you are supposed to rum the BMW "M" range on it along with other nippy production cars.

[Miket]

Mines a 355ci Chevy, 9.0:1 compression, Comp Cam 454in/454ex, 268/268 advertised duration, 218/218 @ .050", 76cc iron H/D heads, hardened seats for unleaded, Holley 750 vac sec.

Which fuel would you reccommend Dave or Robert, 95 or 98.

Mike

[robert]

9:1 standard unleaded.

The rule of thumb is anything over 10:1 will benefit from super.

Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[graham]

Whilst on this subject then.

My heads seats are not hardened they're very early, so I was thinking of using unleaded with Millers vsp additive, so standard or super unleaded with the additive do you think? Engine is around 350hp with cr of 9.5 : 1 69cc chambers.

GVM

[robert]

For a long time, lead was added to petrol. The reason for this was primarily to provide lubricant to the valve seats. Without the lead, the valve seats and valves would live a short life. As technology progressed, the process for manufacturing valve seats that didn't require lead was perfected.

An added side effect of lead in petrol is that it acts as a retardant to detonation. Without going into too much detail, the lead in the fuel kept a hot running engine from detonating. This meant that you could run a higher compression ratio and not worry about detonation.

Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[Splitpin]

Of the various additives available Millers vsp-plus is one of four recommended by the AA/RAC. The important thing to do is choose one product and stick with. This is because each manfacturer uses different chemicals to achieve the same result. Millers is based on Manganese, others use Sodium,Potassium,Phosphorous. Any mixing can cause reactions and create deposits within the engine.

Mike