mods to 350 holley for blow though turbo

[xyturboute]

hello everbody from New Zealand.

i know what i am about to ask has been covered before, BUT so i get in right,
What do i need to do to my 350 holley for turbo. apart from soild floats.
this is what i have been told, boost reference the power valve, so it gets a signal from the intake boost?
8.5 power valve, #66 main jets.

my engine is this.
pre crossflow 2v 250, To4e turbo, 300x600 intercooler, turbonetics wastegate, blowoff valve, large fuel pump,malpassi rising rate fuel regulator, mallory unilite dizzy, msd 6al BTM ignition.
this was all on a going 250 2v engine when i got it. running 9psi.
any help with carb and ignition would be great.

 

[Does10s]

We were using a 350 Holley until we went with the Aluminum head and a 450 4bbl Holley.

I never understood the "boost referenced power valve" idea. In normal confuguation the PV is already referenced to the intake manifold. So it'll also already be ready for boost!
There's an open cavity in the main body that goes down thru the base. Just make sure that hole is clear.

The most important thing with running boost thru a Holley. Enlarge the Power Valve Channel Restrictions (PVCRs) in the metering block. They are two little holes (fuel passages) that are behind the PV.
We've been running them at .093"(2.36mm) in diameter. You just need to drill them out. But be careful not to drill to far. You're drilling into a fuel well so you only need to go thru the outer layer.
It's real easy so don't sweat it! You'll know when you go far enough. The bit will "break thru" into air.....then you'd better STOP!
You'll also may want to start a little smaller than .093". You can always drill bigger. It's more difficult to make a hole smaller!

The other thing is to remove all of the choke equipment. Fill in the choke rod hole with a little piece of metal (or really anything that'll take up the space) and use some JB Weld to keep in in place and sealed.
Another little trick I've learned is to increase the length of the bowl vent tube and point it into the direction of the incoming air from the carb hat. This helps in reducing the jet sizes a little bit. We dropped 3 jet sizes just with this!

The goal of all of this is to get the jets at a normally aspirated level as possible. That way where you're puttin' around town it'll get decent fuel mileage, but still dump in the fuel when under boost.
You'll have to fool around with it to get it dial in of course. For instance.....if your PVCRs are drilled out to .075" and your jets are at say...72s and you're running rich just driving around town, then you can go larger on the PVCRs and reduce your jet size so that it'll run right under vacuum. Obviously normal PV selection practices are in place here.
Hope that helps!
Later,
Will

 

[xyturboute]

thanks for your reply does10, that is pretty much what i thought, will start with the smaller holes in PVCRs.
and see what the air/fuel mixture is like.

one more thing the mallory unilite dizzy ( model 4763001h vac) i have, I have not see anyone else using the same dizzy on this site?
is there a problem with them? that dizzy and msd BTM were not used when the last owner of my turbo setup run it on his car. from what i have read on this site, i need about 10 degreess inital, and about 20
total. i will also be able to take out 1-3 degrees per pound of boost, with the MSD controller, any help with base line setup would be great.

what i brought was a very well setup kit, the last owner just run very rich jetting, and just used a standard points dizzy and welded somesort of stop on, i never saw it running but he did say that tyres did not last long. here in NEW ZEALAND all these engines are going to the dump,as the v8 boys think they are not performace engines. if i new how to put pics on here i would.
grant

 

[Does10s]

I'm not sure why nobody's using the Mallory.
It should work just fine.

There's a couple of ways to limit the amount of timing and still have a streetable car.
Since you already have a BTM, that makes it much easier!

Here's what we're doing.
We have a Duraspark dizzy. So it's just signal for the MSD BTM. I have the dizzy modified so that it only will adv. the timing 10 degrees total. That's mechanical adv. ONLY.
I removed all of the vacuum adv equipment. Although if someone was sporty enough, the vacuum adv. could easily be used for boost timing retard, but I haven't worked on that yet.
So I'm relying on the BTM as my only timing retard device.
The reason I want only 10 degrees adv. is so that I can have more initial timing in there. It really helps with idling.
I'm going to modifiy another dizzy so that it has zero mechanical adv. I'll set the timing at around 33 degrees BTDC initial (which would also be total in this case) and then pull out 10-12 out with the BTM.

So for a baseline I'd go with a total timing of around 30 and then pull maybe 3/4 degrees per pound of boost with the BTM. Start your BTM "ramp" around 2500rpm or so. I think I have our's at 3000rpm.
Remember that we race Kelly's car mostly. So our setup is really tuned for just that...racing. It does work on the street, but could be better.
If her car was just for street, I'd probably go with the locked down mech. adv. and more initial timing to help with off idle normally aspirated kinda stuff. Then pull more out with the BTM.

So if you ready between the lines, depending on the fuel you're running, you should shoot for a overall, total timing after boost retard somewhere around 20 to 27 degrees BTDC.
Obviously more timing is better, but it can be destructive!
Have fun!
Will

 

[xyturboute]

thanks for all the advice you give, just so i am on the right track, i should set the initial to 20 btdc, and have a total of 30? and what do you mean by starting the btm ramp at 2500rpm? the controller on my btm lets me take out 1-3 degrees per pound, so if i had that set at 1.5 and set the wastegate spring to 9psi, that would see 13.5 degrees taken out, so 30-13.5=16.5 total after retard?? ( i know i must be wrong with that :nono:

please note that do not have any of turbo setup on a engine yet, will be putting together a engine in the next few weeks. so am just getting a good base line setup. so am abit GREEN when it comes to turbos!!
i had a look inside my 350 holley last night too see how much i am to drill the PVCRs out to. and to my surprize they had only a 1.6mm hole, so a 2.36 mm hole will give twice the CSA. will start small. also my float was plastic ( was orange is that just a newer float than the old brass ones??)
are the ARP studs that classic inlines sell for the 250cid, the same as the ones to fit my ozzy/ nz precrossflow 250cid, have not had any luck with pics, so if anyone is interested in seeing what i am doing go,
to hotsixes.com and look in there forum and under ""xyturboute"" you will see sum pics i posted.

 

[LateApex]

I don't mean to jack your thread, but what I'm doing on mine is to pressurize the entire carb(s) inside a plenum.

I'll be running Webers repurposed from a Maserati Biturbo and that's how they were set up on the original vehicle.

Would something like that work for you, with not just a carb hat but the entire carb pressurized in a box?

 

[xyturboute]

I don't mean to jack your thread, but what I'm doing on mine is to pressurize the entire carb(s) inside a plenum.

I'll be running Webers repurposed from a Maserati Biturbo and that's how they were set up on the original vehicle.

Would something like that work for you, with not just a carb hat but the entire carb pressurized in a box?


thanks for your advice " lateapex" putting boxes around carbs does work, i have seen it done. still does have sealing problems. from what i have read webber carbs are very suitable for blow through turbos.i am going to use a holley as that is what i have and parts are cheap, should have an engine built in about a month, when i figure out how to post pics on can i will do abit of a progressive sort of thing, am very new to this turbo stuff, with most of my tuning done on NA big block fords, have been thinking about turbos on old precross flow engines for about fives years, then about a year ago found out that you guys had them in your mustangs, and that you were turboing them, so this is great a great sauce of information for me. grant

 

[woodbutcher]

Hi Grant.I remember back many moons ago,that Studebaker had the carbs completely enclosed on their supercharged Golden Hawks.Don`t have the foggiest idea where to check a web site that MIGHT have some pics of the setup,but maybe Google might be of some help there,if you wanted to go that route.
Good luck,and have tons of fun.
Leo

 

[LateApex]

Don't overlook youtube as a source of tech info. It sounds weird, but sometimes you find just the right shot that shows what you need to know.

That's how I figured out how to plumb the vacuum lines for my Webers: there was a 2-second shot in a video of a 1985 Maserati Biturbo with the carb hat off.

Good luck!

 

[xyturboute]

thanks everbody for your help, have really just got to put together a engine and have a play. was just getting a lot of mixed mesages about what to do with the power valve side of the carb, am hoping that now that i have some time to get started with this project, things should not take to long. as for youtube, have not seen any precross flow turbo engines on there??? does anyone know if the arp studs that classic inlines sell will fit my ozzy 250cid?? is there any differace between your yank 250 and the ozzy 250?? grant