Help Me Choose

[Unna]

don't you want to make the compression higher?

[Taz_Rx]

ok i have decided i will go through with charging the 5k

 

ill be putting a 4k head for lower compression, porting it and finding a cam to suit the charged application.

 

ill be doing a blow through setup

 

i don't know if i should start a new thread for this because i have a few questions, but ill give it a shot here

 

1. i remember reading a long time ago when doing a blow through carby set up you have to modify the needle and seat, and you need the fuel to be pumped in the carby the same psi as the charger is pushing. can some one touch on that?

 

2. on a boosted application, can there ever be to low compression? or can you just compensate the loss with extra boost?

 

thanks in advance guys :yes:

 

 

1, Needle and seats don't have to be changed. I just did because it was very simple, quick and free. All small downdraft webers use the same thread N&S. So i used a falcon weber N&S in a Fiat weber. I probably would have filled the bowl twice as quick with that in it.

Fuel pressure needs to be slightly higher than boost pressure (when on boost), otherwise the fuel will get pushed back to the tank.

There a thread in the general mechanical tech article called " how to set up your fuel system". :wink:

 

2, Yes you can go too low. a 4k head on the 5k (with D dish pistons) will get you down around the 8:1 mark which is about perfect.

 

 

 

Unna..... google. :rolls:

[agius]

1, Needle and seats don't have to be changed. I just did because it was very simple, quick and free. All small downdraft webers use the same thread N&S. So i used a falcon weber N&S in a Fiat weber. I probably would have filled the bowl twice as quick with that in it.

Fuel pressure needs to be slightly higher than boost pressure (when on boost), otherwise the fuel will get pushed back to the tank.

There a thread in the general mechanical tech article called " how to set up your fuel system". :wink:

 

2, Yes you can go too low. a 4k head on the 5k (with D dish pistons) will get you down around the 8:1 mark which is about perfect.

 

 

 

Unna..... google. :rolls:

 

just the man i wanna speak to

 

sweet sounds all gravy for now, at least i got the compression ratio basically right

 

fuel system thread is all there for me to use

 

so now down to the how long is a piece of string question

 

the 5k is going to have all stock internals except for the ported head and cam

 

as your 4k was the same whats the highest boost will it handle without the motor exploding to its death?

[Taz_Rx]

I've run over 20psi on both the 4k and (current) 5k I've boosted. The 5k is still going strong in Tar and that old 4k bottom end get accasionally thrashed on a "come play in the dirt day" or fishing trip etc.

 

It all comes down to have an adequate tune that won't hurt you engine, not just how much boost you run. Unfortunately you can't run say a switchable boost controller on a supercharger. Otherwise you could have a couple of settings. Mine give gate pressure (about 6-7psi) and then 18psi at the flick of a switch...... not that I ever switch it off 18psi! :lol:

[agius]

WOWW

 

that is awsome... i really did not see that number coming at all

 

I'm guessing you mean a good tune as in the right spark plugs, timing and the right fuel mixture so she doesnt lean out in boost?

 

yeah thats the thing with a charger I'm happy to leave it on 10-12psi thats enough for me..

 

back down to timing..timing is one of the things that confuse me the most all that advanced and retard and numbers:huh:

 

i think i shall leave the timing bit to the pros :D

 

i will be geting a good performance ignition coil and a dizzy if i can find them also.

[Taz_Rx]

Yeah need to have your fuel tune a bit rich if anything, then you'll know you're safe there. You'll normally end up a bich rich anyway with a blown through carb, atleast in the midrange anyway.

Ignition is a bit different though. Locking the dizzy is the easy way but a bit crude really. You basically just need to retard the timing a bit whenever you've got some boost. Depending on how much you want to spend something like this can be good....

 

http://cgi.ebay.com.au/MSD-6-BTM-Boost-Timinig-Master-Blower-Supercharger-671-/270655203566?pt=AU_Car_Parts_Accessories&hash=item3f044ea8ee

 

....The have the usual 6A CDI features but also have a built in boost retard unit. You can dial in 1-3 degrees of retarding for ever pound of boost you run.