Just wondering what are the pro/cons of the two, does one make more power than the other? Is one more efficiant and will one move more air? Thanks.
-Jesse

Hi Jesse,

I am not an expert in Turbo installations, but I am interested, and I have read as much as I can find about this subject.

In general, blow through installations are considered more "modern or correct", due to a few things:
1. Suck through designs require a turbo that can stand the suction on the oil seals, otherwise you will suck oil out under vacuum.

2. Suck through designs can end up with gasoline pooling in the turbine housing, or other area in the intake. This causes problems with throttle response, and potentially, backfires. This also means that you really cannot use an intercooler with a suck through design.

3. Blow through systems require less modification to the throttle linkages, manifolds, and pollution controls. The carb, however, might need some significant mods, especially the jetting, power valves, etc. Some people have gotten around this by constructing a box around the carb, and then pressurizing the box. This way, the whole carb (inside and out) is pressurized.

4. Arguably, blow through systems probably make more power, due to fewer restrictions from the carb to the head.


One thought, though. Why do you want to stick with a carb? Step up to fuel injection, and get rid of a number of these problems. See this link:
http://www.bgsoflex.com/megasquirt.html

I am going to do a megasquirt on my barracuda after I get the front suspension sorted out. Maybe next spring/summer.

I just don't care for more electrical $#!+ than I absolutly need or under the hood or I would.
-Jesse

The trouble with EFI is even with used parts and the MegaSquirt it still costs about $500-$700 to make it all work. I picked up a used Holley spreadbore for $15. It will do everything that the EFI will do and it will work quite nicely in a draw-thru setup.

I'm sorry but I'm going to respectfully disagree. While the ultimate goal of either carb or efi is to deliver fuel even a basic throttle body injection setup will likely funciton and behave better then a tuned carb, especially under cold weather driveability. Especially under a forced induciton situation, it may save you from going too lean.

There is no carby, especially a $15 one.... that will ever give you the same degree of tuning flexibility and ultimate results compared to an affordable EFI system. It really doesn't have to cost you bucket-loads of cash to achieve a good working result with EFI. Used parts and wreckers are often your best friends with many of the parts required often able to be picked up for not alot of money. ..... give it a go.

Ray,.

Jesse,

I found this book to be really helpful to me. I got my copy at Amazon, and didn't pay too much. Corky Bell had a good mix of theory and practical application. It might be helpful to you, too.

Good Luck,
Greg

All true, but a tbi is not that much better then a carb, for a mpi setup, here is the parts break down, all prices approximate:

Stock Mustang 65mm throttle body.....................$35 (ebay price, inc. tps and iac)
Stock Mustang 22lbs injectors (8 )........................$35 (ebay price, unknown condition)
Adjustable fuel regulator (30 - 70psi)...................$100 (ebay price, new)
MSD injector bungs (manifold) (8 )........................$60
MSD injector bungs (indvidual lines) (8 )................$60
MSD hold down straps (8 )....................................$60
6an fuel fittings (fuel rail) (8 )................................$40
Various flexiable fuel lines....................................$50
Various hard lines................................................$50
Ford f250 fuel pump..............................................$80
Street rod fuel cell (2 outlets/2 inlets, sender).........$180
MegaSquirt kit & simulator.....................................$250
Offenhauser intake................................................$250
O2 sensor.............................................................$40
water temp sensor.................................................$15
Air temp sensor.....................................................$15
Junk yard wire harness..........................................$15
100 amp alternator................................................$100
total....................................................................$1435

This just sets up the Fuel side of the equation. If you want to do the iginition it costs even more. To dublicate this with a carb setup the costs would be:

Carter AFB 500cfm..................................$75 (ebay price)
Fuel cell (2 outlets/2 inlets, sender)...........$180
Offenhauser intake...................................$250
Total.......................................................$505

Is the power increase really worth the $900 more?

Hell I'd just buy a hilborn mech. setup for a LA engine and put thar in it. I'm trying to do this REAL low budget with parts that are given to me, so far I got a Garret S something(I think)turbo(rebuilt fo free), a 500 cfm Holley 2 BBL., and acces to a machine shop.
-Jesse

Multiport injection will be quite nice with a slant because the distribution will be lots more even. This is even more critical with forced induction because you may toast the outer cylinders too soon. No single 4 barrel carb is going to run the outer cylinders dead even with the inner. Even two carbs on the offy manifold will not provide as precise distribution as MPFI... the only way to get close would be a 1 barrel per port sidedraft type setup.

Yes, multiport will deff cost more, no doubt about that, but you'll get more out of your forced induction and it will be safer. If you want to do fuel injection now, and in the long run you have forced induction in mind, then perhaps you may want to think of MPFI from the get-go. Also, an idea to chew on... you can install a tbi system based on a megasquirt (roughly $500), then in the future upgrade it to batch fired MPFI by adding a fuel rail, injectors, and higher psi pump. Or you can start off with a higher psi pump on the throttle body so you won't have to redo too much fuel line plumbing because the throttle bodies have built in regulators so they don't care if you feed them 18psi or 50psi the injectors will see 13psi.

I'm still using my stock '69 alternator with my EFI/Turbo. I think it is 60 amps but I'm not really sure. I'm also using a $25 ECM (although I do like the MS ECM.). In my EFI article( http://slantsix.org/articles/dibiase_ef ... ersion.htm ) I put the total cost of EFI at more like $500 if you modify your own manifold. Im sure you can do it for less than that if you get creative (e.g. a donor car). Anyway, my guess is that when you actually try to turbo charge a carbureted engine you would find the difference to be well worth it. I guess we should ask someone who has tried both.
I'm sure there are good reasons why the turbo didn't really catch on with carmakers until EFI became standard.
Bob D

For the skinny on blow though versus suck through, check out Hugh MacInnes' book, "Turbochargers". A little dated, but a lot of useful info that still applies. Basically suck through uses less plumbing and is a bit easier to set up, but blow through is better for fuel distribution and power capability, also more forgiving for the carb tuning. If it were me, I'd go for the suck through, mainly due to the simplicity behind the install. BTW, anybody catch HotRod mag a few issues back? Interesting factory slant turbo manifold found by Steve Magnante........almost made production from what I understand.....and yes it was a suck through design.

_________________
"That thing gotta HEMI in it??"

ohhhhh.... TELL me this manifold will see aftermarket production. Or at least that the Doc will have a crack at it. (no pun intended)

_________________
I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Wish I could remember which month it was shown..... .....but I do remember it was like a page 3 small blurb with photo....
Doc, you know Steve right? Maybe he could get his hands on it for "development" purposes and you guys could do a magazine test/article on it?

_________________
"That thing gotta HEMI in it??"

It was a Mopar Muscle issue September 2003 and you're correct that it was a small blurp under "cool finds", Was slated for F-body production and was a stock aluminum H-beam manifold cut up and modified to accept a small Air Research turbo and a two barrel.