Turbo Question

[Gelcoater]

im wondering about the advantage or disadvantages of a draw through vs blow through system as far as a carbed engine? i notice most cars run a blow through, most boats[think old school Schiada]run a draw through,and i see many blowthrough paxton style s/c engines,so i dont think the carb being pressureized is the issue. i realize a efi makes it more responsive, and notice efi/turbo as a blow through in the marine side too. so let hear it.

[DaveH]

draw through all the way.

first it is a simpler mechanical setup. no "airbox" or sealed carb to mess with. evertry troubleshooting carb issues when you have no access to the carb?

second, and this is the big advantage, draw-thru runs the fuel right through the turbo. This has a "shredding" effect and helps to atomise the fuel better and also has a better intercooling effect. This can be so dramatic, old setups had trouble with icing the carb. The gentry system had a jacket on the carb basethat circulated hot oil to keep icing down and cool the oil.

[ap67et10]

the old systems have proven to be quite reliable, and make good power for what they are, but they are extremely limited. if you are looking for more than 800-900hp (you can get more with nitrous) its just a bad idea to try and force more efficiency from a system that's inefficient. The new blow through carb technology is far advanced, and quite reliable for what its doing. (2000+hp for a single carb is just nuts...but they are doing it now).. (even though i won't run it...then again, i won't run any carb) if you are looking into the 1200+ hp range its hands down a blow through. no draw through could ever compete with the power output that blow through can. however there are many disadvantages, one being a jacketed header for under hatch will be quite expensive, as the big turbos are typically t6 flange. so you normally are running hot headers, much more heat, but remember heat is why turbos work so well. turbo design is also much better to handle the heat. (the more exhaust you flow the hotter it gets, but the more exhaust you flow the more power you are making).

needless to say there are multiple ways of doing it, but its really about what you are looking for. I thought about doing turbos for my cruiser, but i would never put on a blow through style, because my setup was based around cost, power and keeping it under a hatch. the only way to do what i wanted was with the old style manifolds and small turbos. but i just don't really like those setups as much....especially compared to my procharged deal. its all about efficiency, and compared to the new stuff. the old draw through just don't compete on the same level. that is also the reason they are so hard to compare, because one setup may be perfect for one person, but not work at all to another person. its all about what your goals are for your setup.

Andrew

[Gelcoater]

great info guys:thumbsup sounds like one would have to make some goals before moving forward. i can see pro's an cons to both setups.

question; wouldn't the "shredding" effect also apply to a procharged type deal? I have never seen one set up as a draw through.

seem like this topic may be one like Ford vs Chevy deals,if we can keep it civil,i would like to hear more.:cool:

[DaveH]

question; wouldn't the "shredding" effect also apply to a procharged type deal? I have never seen one set up as a draw through.


sure. but you will also loose some of the atomization quality the longer the intake tract is. multiple elbows in the intake make for spots for the fuel to "fall out" and "pool" in the intake system.

this is where multi-port reigns SUPREME. it all about EQUAL quantities of ATOMIZED fuel reaching each cylinder. with the lower cost of some of the modern EFI systems out there, there really is NO REASON not to go EFI.

if you sit down and do the math for a carb VS efi system, factor in all the parts and fabrication, you will find that it really does not cost that much more to go EFI. Then the payoff is a motor that will use less fuel, last longer, and run better. in the long run, it might even SAVE you money.

[Dave Wettlaufer]

I agree, DaveH. I'm gonna go MegaSquirt EFI w/turbo on a small block mopar 318. :thumbsup

[ap67et10]

I agree, DaveH. I'm gonna go MegaSquirt EFI w/turbo on a small block mopar 318. :thumbsup

that sounds like a sweet little build right there! when can we see this build happening?? you will post pics yes?

Andrew

[Gelcoater]

that sounds like a sweet little build right there! when can we see this build happening?? you will post pics yes?

AndrewYeah Dave! When? WE have talked about this build for some time,you have to start this:thumbsup

For those that dont know Dave,he plans to do this turbo 318 to replace the very hot 340 in his 69 Dart Swinger,a 4 spd car that he has owned for about 20 years now. This car with the 340 is a brute,one can only wonder what it will be like with almost double the hp :skullBack in the day,i was a regular in the passanger seat of this car and watched it outrun all comers,from Irocs,to Saleen Mustangs,Vettes,396 Chevelles,etc anything that would line up with him got spanked. One exception would be that black guy in a Porsche 930,but it was a Dave in front race,until he ran out of gears,he put a lenght or 3 on the guy through every gear untill he hit valve float in fourth,somewhere around 118-120 or so. Damn those 3.91 gears! As we ran away from the guy going through the gears i could see the guy looking at his gauges and back at us mouthing the words "what the fuck's wrong with my car?" because as far as he knew,Forrest green old cars were not supposed th be able to out run his high dollar european super car:D

[Racey]

Draw through is awesome on a boat, blow through gives you better throttle response, much more important on a car.

If you notice EFI turbo setups are blowthrough to the butterflies, they don't control the air coming into the turbo, they control it after the turbo, going into the intercooler. this is another reason why the EFI motors 'feel' so much snappier and throttle responsive. You have way better air control to the motor if you are throttle valving the boost air rather than valving the atmosphere.

Like DaveH said, blow-thrus are a fucking bitch to work on, you have to disassemble all this shit just to get to the carbs, there is no need for a blow through on a boat, you aren't constantly accellerating, decellerating, shifting, going around corners, back on the gas etc. Race cars are one thing, boats are another. All the benefits don't outweigh the extra trouble that blow-thrus are to work on in a boat.

[Dave Wettlaufer]

Good info Racey.

I was going blow-through mainly to keep the turbo and intercooler fuel-free. This was my thought pattern with a carb for induction.
I'm gonna keep that thought but go efi.

I have been gathering parts for a while now, but it's still a ways off.
And Larry, it's a good thing we were young because I don't think going 100+ mph almost every time I drove the car was a great idea......but it sure was fun!:D
4th gear at 94mph with the tires breaking loose and the car shuddering like someone hit it with a big hammer! Gotta love a 340 with a Clay Smith solid cam!

[Racey]

Also there are different seals required for dry vs wet turbos as the gas will eat the seal and cause leakage and turbo failure.

[Gelcoater]

Good info Racey.

I was going blow-through mainly to keep the turbo and intercooler fuel-free. This was my thought pattern with a carb for induction.
I'm gonna keep that thought but go efi.

I have been gathering parts for a while now, but it's still a ways off.
And Larry, it's a good thing we were young because I don't think going 100+ mph almost every time I drove the car was a great idea......but it sure was fun!:D
4th gear at 94mph with the tires breaking loose and the car shuddering like someone hit it with a big hammer! Gotta love a 340 with a Clay Smith solid cam!Dude,that Clay Smith cam transformed that car from lots of fun fast,to scare the shit out of you fast:thumbsupand i liked it.:D