quick blower questions!

afraid there is no definitive answer here.

1. What pump gas? As there are many octane ratings 87, 91, 93 and probably more.

Also you need to check which octane rating system you are refering to:
-RON
-MON
-PON

In the UK petrol is rated on the RON system whereas usually in the US it is rated on the PON system. However it worth checking as 95RON is about the same as 91PON.

2. The reason I say this is as far as my understanding goes FI is all about detonation. You need to be able to keep your Air/Fuel ratio within set bounds else you will have problems.

The more psi then the more octane is needed to control the A/F. KB reckon you should be able to safly run 9psi with 91PON fuel but for a more agressive tune (and safer) 93PON would be better still. This will take the standard block to about its limits (400-450bhp crank).

Using 100PON fuel over 500rwhp is possible @ 14psi but you are in real danger of it going bang. However this would more likly be due to the limitations of the engine internals, forged internals on a built block would handle it but with the stock CR 100PON fuel would still be a MUST.

The other alternative is to lower the CR of your engine, this will then allow you to run higher psi's on the lower grade fuels and still control the A/F. Ultimatley a low CR engine will make less power at the same psi but because it can safely run higher psi's they can produce more power.

Hence a built 2v 4.6 can rival a DOHC 4.6 Cobra for power even though the SOHC is less technically advanced.

3. If it turbo route you are going then the same problems exsist to an extent. But you will find that ALL mainstream production turbocharged engines run very low CR's and then usually quite high psi levels. There are a few reasons for this, reliability and also because a turbo affects the resistance in the exhaust where a s/c doesn't.

The down side to a low CR is that off boost the engine will have very little power, this in turn then exagerates the feeling of 'turbo lag'.

A light pressure turbo (6psi??) on a V8 with a fairly high CR will not produce massive PEAK bhp numbers but should provide good power most of the time and not feel as if its bogged down off boost.


For this reason IMO a supercharger is the much better aftermarket addon, as you can get good power and driveability from the engine as it is now.

A turbo setup will require much more work and R&D to work as well but will certainly cost more. If done correctly however I'm sure it would be awsome, but then again so is a good s/c setup.

Remeber PEAK numbers won't mean you have the fastest car, even more so on the street. What you want is usable power across the entire rev range with a broad power band. Take a look and research your options, The Roots s/c is not as bad as many think, as it does provide good power increases but more importantly it produces where you want it - low down in the rev range. The twin screw setup does exactly the same as the Roots but requires less power to run it (increase in net gain) and delivers air at a lower temp to the engine (bigger bang - more power), so the gains you get behind the wheel are likly to be 10-20% with a twin screw over the Roots. Centrifugal s/c's are taken from the aviation industry and are basically a belt driven turbo. They have the capability to produce the highest PEAK numbers of all of the s/c's. But it comes at a price, they produce very little power down low, even in the mid range rpm's they will still struggle to match a Roots blower for output and be way behind the twin screw. Once up in the higher rpms though . BUT it is likley that a centrifugal will only produce slightly more HP than a twin screw over the last 2000rpm, where the twin screw will produce significantly more power the rest of the time.

So the question is, how often are you going to spend at the red line compared to using the rest of rev range. If you have a gun hoe WOT style of driving then the Centrifugal will be for you, however is you just want instant POWER at any time no matter the rpms of gear you are in then a twin screw really is the only answer. As it will produce the most power most of the time .

there are some factors to consider, intercooling, climate, elevation and compression. best bet with a paxton blower w/91 or 93 octane is about 10psi to be reliable and emissions friendly but also depends on the cars tune. you may get more boost and still be ok but most street cars stay at about 10psi