What blowthrough carb? Where to have it set up?

[harley-jm]

Im fitting a D1SC procharger to a sbc in a MkIV supra. Street/strip car with 1/2 inch cam and AFR heads.
Any recommendations on blow through carbs? I understand with the procharger I can go for a slightly smaller size than for a NA car eg. 650 to 700.
Any opinions welcome.

Also any recommendations on where to get it set up. Most rolling roads I have found (I am in south Bucks) seem to assume fuel injection/ECU and arent interested in old school carbs.
thanks
P

[Adam]

You dont get a carb set up on a rolling road for blow thru. It has to be modified from scratch. I used Kevin at CSU. Excellent service. C&S and also the carb shop do blow thru carbs or can modify your own DP. Thers is a thread you can follow to DIY but if you don't know Holley carbs don't try it. DO NOT buy ebay blow thru carbs. They are nothing more than a regular DP with a fancy sticker. If you want more info pm me.

[gotzy]

Here's the Hanger 18 article Adam was on about, have a long read through it and see if you'd be happy taking it on http://www.hangar18fabrication.com/blowthru.html.

CSU have a very good rep but cost $$$, buy a beat up double pumper and a Proform main body and then mod it for a 1/3 of the price.

Personally I'd go for the sames size carb used for a n/a motor based on its rpm and size. Haven't done it but have researched it heavily, have a look on turbomustangs at some of the quick street stuff and it's a common approach.

[WB54]

I wouldn't bother with that article. All it covers is drilling the angled powervalve restrictors. You could simply buy a billet metering block if this were the only mod needed or blank them and jet up. A blow thru carb is set up to protect and isolate the circuits from the effect off boost above the booster / blades

With reference to carb CFM, can't see any reason to go smaller than a N/A setup. A correctly sized carb in N/A form delivers an optimum AFR and fuel volume for an engines size and volumetric efficiency. The very nature of forced induction, is that it's externally forced under boost rather than reliant on a signal being anplified by the boosters venturi effect, so anything smaller would simply be a restriction in my view.

[harley-jm]

thanks for the feedback -so I will go for a prof conversion and initial set up for my application so it looks like I better get saving! Guess you get what you pay for......

[Adam]

How much boost do you intend on making. If it's around a max of 8 then you could use a sealed box like the Paxton set up. After that although sopme have got it to work there is too much buffering and reversion in the box for the carb to get a clear signal. I may know of a spare blo thru carb. pm me for details and I'll make a few calls.

An 850cfm DP on a blo thu with a top hat can make 1400hp. after that you will probably need dual needle set up and a move to either a 950 or a dominator 4500 style carb.

[evilzee28]

Im fitting a D1SC procharger to a sbc in a MkIV supra. Street/strip car with 1/2 inch cam and AFR heads.
Any recommendations on blow through carbs? I understand with the procharger I can go for a slightly smaller size than for a NA car eg. 650 to 700.
Any opinions welcome.

Also any recommendations on where to get it set up. Most rolling roads I have found (I am in south Bucks) seem to assume fuel injection/ECU and arent interested in old school carbs.
thanks
P


I have a blow through carb "hat" for sale if it's of use to you.

[IainB]

An 850cfm DP on a blo thu with a top hat can make 1400hp. after that you will probably need dual needle set up and a move to either a 950 or a dominator 4500 style carb.

Adam,
I thought an 850 was good to 2000? The 750 is good to 1200 or so (its been a while since I did lots of reading)

Harley-Jim,
Have a read on Turbomustangs / TheTurboForums and YellowBullet there is LOADS of info over there, not to say that there isnt here, but the first forum is dedicated to what you are after :D

[Adam]

Ian
I would say that 1000hp - 1400 hp is comfortable for an 850DP. Certainly a single needle assembly carb. Anything over that I would personally not want something like a carb to be on it's ragged edge in case it went lean for any reason. My thoughts are if you can use parts that are not working 100% then they are more likely to perform as wanted at lower levels. A performance buffer so to speak. It's amazing what these guys are wringing out of these parts nowdays.

[gotzy]

So has anyone done the hanger 18 mods to actually say it's not worth it and it is better to pay for a pro carb or is it just hear say?

As I said earlier, I haven't done it but have read about more people doing it successfully rather than saying don't, just after a balanced informed view, not causing ****.

[harley-jm]

Adam
I know a carb needs modifying for blow through use to operate above atmospheric pressure but what I was also asking about was the set up in terms of fuelling throughout the rev range, under load, in transition etc. I imagine that if I give someone like CSU details of my car (weight, gearbox type, rear end ratio, cam, compression etc) they could try to set up the fuelling right from the start but I assumed I would still need to check it in actual use. Also I am starting with low boost and will crank it up later so assumed I may need to have the carb set up again with each significant change in boost? What do you reckon? Anyway I will do some research on the sights people have referred to above before asking any more questions!
Cheers
Paul

[Adam]

Gotsy, I think for moderate boost levels the home mods work and those that know more can experiment and make them better. The must have though is a wide band data logger. Your lost without one.

paul, Kevin @ CSU is about the most professional guy I have ever bought anything off in the States. Steve Morris is the same. His carbs work right out the box on 90% of applications. My carb & base was damaged in transit. Kevin sent me over a new bowl and billet base plate FOC!!

What you also need is a regulator referenced to boost above the carb so this can rise at a 1;1 rate with the boost pressure maintaining hat 6# of fuel pressure you need to feed the engine. Also a return system not a dead head as this will cause havoc with fueling. Return line the same size as feed line and the tank vent no more than 1 size smaller (same if poss). What boost level do you intend to run?

[harley-jm]

Thanks Adam.
I planned to use an aeromotive fuel pump (A1000) and 1:1 boost referenced regulator (I was hoping the pound would recover against the dollar before ordering it from the States but I think I will just bite the bullet and order them). I will use -6 fuel and return line. I have a wide band 02 sensor set up from Innovate (which can record mixture and other inputs throughout a run although it is not perfect as it has a single sensor and is positioned slightly further down the exhaust where the two headers merge into single system but I figure it should be adequate).
I note the tip on fuel tank vent - cheers.
I plan to run about 0.5 bar/8-10psi to start with which I figured should be fine with the existing compression ratio of 9.5:1 especially as I have a 3 core air-air intercooler.
Spent some time looking at YellowBullet which is a great general forum - dont know how I havent come across that before. Turbomustangs is also a good info source and not limited to turbos or mustangs! Thanks for those references.
Learning about new stuff is half the fun!
cheers
Paul

[Adam]

Paul, the regulator to get is the Aeromotive 132-02. Expensive by comparisson to others but cheaper than a new engine! For 10# boost which you will want to increase as soon as your used to it -6 is IMO wholly inadequate. Your using a return system here with the pump at full flow all the time. I would consider -8 a minimum size for both feed and return and would say for a system that grows with you -10 feed and minimum -8 return. There is a controller you can buy for the A1000 which deliver's voltage based on engine requirements and therefore fuel flow to match if you want but not needed. It does keep the pump cooler if it is not in airflow or in tank mounted.

If you have the -6 I'd suggest selling it and consider the larger sizes. Ask on either forum for more expert advice as I am still learning but I'm sure the concensios will be for larger id line.

[harley-jm]

Thanks for the heads up. I dont see any down side with "going large" on the fuel line even if -10 seems HUGE! Since there isnt much difference in cost and no difference in effort to fit it I may as well go large and do it only once.

On a separate note - I'm also into Jap performance cars where everyone runs turbos with boost controllers. I was planning to simply using different pulley sizes to control max boost to start with on the procharger but was planning to fit a proper wastegate and electronic boost controller later. Dont see why more procharger guys arent using one to more precisely control boost eg for different track conditions. I used to love it because I could turn down the boost when my misses drove the car!

[WB54]

I think there is a correlation between pump pressure required to generate the line pressure needed at the regulator, ie -10 line requires more pump pressure to deliver the desired line pressure at the carb, so make sure your pump i up to it. A good investment would be a set of the Braswell Super bowls with dual float needles. Commonly used with alky due to the increased volume needed but now being used with big inch single 4 barrell bracket engines which need more volume delivered than the holley needle valve is capable of.

If anybody needs fittings or braided hose, I can still do Goodridge bits, now cheaper than importing due to FX rate.

[Adam]

Turbo's have a waste gate superchargers have a blow off valve. When you come off the throttle on a turbo the excess pressure is thrown out via the waste gate. A Procharger needs a quicker exit of the pressure built up in the intake thus the need for blow off valves. They vent directly to atmosphere and need to evacuate quickly as the pressure can stall the blower vanes which can throw belts, bend them which is very expensive or cause an air to air intercooler to burst. Procharged vehicles use a BOV for the good reason that they work and work well. You can use a boost controller but it will be referenced to various parameters. I have a prologger which is a boost controller and wide band combined. Using different pulleys is exactly how you do tune for boost but also with the step up ratio's of the internal gears engine rpm has a more profound effect on boost than a rootes blower. If using wastegates was a better option I'm sure all of the blow thru owners would be using them.

I mentioned -10 as a fuel line size based on the fact your running an A1000 pump. This is more than man enough to feed correct pressure and volume to the reg. In fact I would say use -12 from the tank to the pump then -10 from there. Phill the dual needle bowls are only needed once up to and passing around 1,400hp. Before that a CSU or C&S carb is more than capable of supplying enough.

I'm using 2 BOV's. One directly linked to vacumn to vent if the throttle is snapped shut and the other as a launch control + a back up to the first one.

http://inlinethumb09.webshots.com/2376/2425587880083006433S600x600Q85.jpg (http://rides.webshots.com/photo/2425587880083006433topTlV)

[harley-jm]

I definately defer to greater knowledge but I thought a BOV and wastegate did different things. As you say a BOV is to release built up boost pressure quickly when you shut off the throttle to stop the intake air stream being stalled when the supercharger is still spinning fast and a wastegate was to release excess boost over a predetermined maximum when the throttle may still be wide open?
I agree there arent any magic solutions and if it was worth doing people would be doing it!

[Adam]

Thats correct re the BOV but the prologger I have and I assume other data loggers have a facility to also dump boost at a predetrmined level. Wheelspin, missed shift etc protection. Also if the rpm gets too high. They have a mechanical adjustment too so if on the street you can bleed boost from a high hp engine if you wish keeping it tuned for a specific pulley combination later say on a cruise then race the next day. The BOV works off manifold vacumn so it's constantly opening and shutting as the throttle is opened and closed. A wastegate will normally? (dont know too much about them) only dump excessive boost. I have 2 x procharger ones but a similar Tial BOV from ebay is 1/2 the price and worth a look. Whats your set up Paul? If your local or passing your welcome to pop in a have a nose.