"draw through" VS "blow through" Turbos?

R. Mutt · Postby **R. Mutt** » November 12th, 2004, 4:46 pm

I was reading up on a car and they mentioned it used a draw through design turbo as opposed to the commonplace blow through design. The page explained thar the blow through concept does not involve any fuel going through the turbocharger, whereas the draw through method does.

I would like to know:

1.If their are any other differences between the two turbo designs.

2.What are the disadvantages/advantages to this design as opposed to strictly air being sucked in.

Postby **W2J** » November 12th, 2004, 5:34 pm

Well for One If you happen to backfire using the draw down system and your intercooler is full of gas guess what you better run because you ent going to out the MOFO.

R. Mutt · Postby **R. Mutt** » November 12th, 2004, 6:34 pm

I have not seen any pictures of intercoolers used with draw through turbo setups. The car I was looking at was the 1980-81 Pontiac Trans AM turbo. It had a turbocharged 4.9L V8 and would make anywhere between 7.5 and 9 psi. The car only put out 210 hp @ 4000 rpm and 345 lb*ft of torque @ 2000 rpm. Based on what you are saying W2J, I suppose that is why Pontiac didn't use an intercooler on the T/A.

But then this raises questions as to why did they go with such a sh!ty turbo setup? Why not use a regular turbo design?

For the next model T/A they used the 3.8L turbo V6 from the Grand National (was an anniversary car: only 1550 were made) before making the regular models with big ol 5.7L N/A V8s.

What are your thoughts guys?

InDeForest · Postby **InDeForest** » November 12th, 2004, 9:25 pm

I think hardly any factory turbos then were getting intercoolers, the bmw 2002turbo didnt (didnt even have a wastegate), and im sure the first of the grand nationals didnt have an IC either.
I personally cant think of any reason to have the draw thru, the blow thru seems better safetywise and .. mounting-wise

X2 · Postby X2 » November 18th, 2004, 7:53 pm

Forest, the first gen GN's didn't have intercoolers.

That 80-81 pontiac was basically Gm's foray into turbocharging before the GN I believe. Remember that turbocharging was still new overall and to the US manufacturers, turbo was a black art... they still had the ole displacement addage, which is why they went back to n/a after.

I don't see how the method running fuel in the piping would work (well). Once the fuel starts touching those smooth pipes, it will stick to it and prolly pool in the manifold, etc... not to mention it would prolly be sucked into the vacuum ports. Fuel metering would be random at best....doesn't sound useable at all nah.

X2Board · Postby **X2Board** » November 20th, 2004, 3:13 pm

X2 wrote:

I don't see how the method running fuel in the piping would work (well). Once the fuel starts touching those smooth pipes, it will stick to it and prolly pool in the manifold, etc... not to mention it would prolly be sucked into the vacuum ports. Fuel metering would be random at best....doesn't sound useable at all nah.

you're right on the money there X2
the draw thru systems suffer cuz there is not enough continuous turbulence being set up in the manifold to keep the fuel suspended in the air and as a result , u end up with fuel poolin in the piping & inefficient metering

Also , draw thru systems are mainly used on carb'd engines which suffer from fuel metering issues at the onset of boost, ...boost compensating fpr's and additional injectors are just band aids to the problem. the life of the turbocharger is reduced if the seals are not designed to see fuel and u cannot use a bov with a draw thru system etc

some ppl use sharp bends & log designs in the intake manifolds to create turbulence but even these are a give and take situation bcuz driveability & low end performance suffers until boost comes on...

EFI is the only way to turbo efficiently and if u turboing a carb'd engine: blow thru with additional injectors and rising rate fpr is the best solution... and u still need to find a way to retard ignition in proportion to boost..but that's another thread by itself.

R. Mutt · Postby **R. Mutt** » November 22nd, 2004, 8:08 am

I was curious because my pops use to have a turbo trans-am in the 1980's, when recently exploring the performance figures I was stunned to see a 4.9 turbo V8 only doing 0-60 mph in a sluggish 8.7s and the 1/4 in 16 flat. The car is decently heavy at 3313 lbs, and with the size of the motor and it being boosted I thought potiact should have made more power (200 hp @ 4000 rpm). Thanks for the info, he should have got a Grand National.

X2 · Postby X2 » November 22nd, 2004, 11:40 am

The old V8's had highly inefficient head designs, which lent itself to low power production numbers and typical trans ams of the time would make 160-200 hp out of huge displacement numbers and turbo was still 'new' technology, but that low... dunno why at all... it's almost pathetic.

My pops turbo'd his corvette back then at home, I gotta ask him how that went... I know he was making mid to high 400's as far as hp.

R. Mutt · Postby **R. Mutt** » November 22nd, 2004, 1:09 pm

which year corvette?

X2 · Postby X2 » November 22nd, 2004, 1:57 pm

1976 Stingray... lawd it was sexy.

You prolly won't believe where he got the turbo from !!! 3 guesses.... :wink:

InDeForest · Postby **InDeForest** » November 22nd, 2004, 2:23 pm

Man, those V8's were running SLACK in those years, mid 70's onward, the 1970 stingrays had up to L88 option with 560hp, definitely the sexist car ever in my eyes

R. Mutt · Postby **R. Mutt** » November 22nd, 2004, 11:20 pm

An 18 wheeler?

A cereal box with 3 proofs of purchase?

a big fat cyat?

I give up.

cheese pie · Postby **cheese pie** » November 24th, 2004, 4:06 pm

i think after the fuel prices went up in the 70's the car manufactures played around with the design to try and get some sort of economy

just my guess

A cereal box with 3 proofs of purchase?

X2 · Postby X2 » November 25th, 2004, 7:20 pm

CT9A wrote:An 18 wheeler?

A cereal box with 3 proofs of purchase?

a big fat cyat?

I give up.

If you mean the turbo kit company... it was ACCEL !!! You know them... they make plug wires and crap now.

X2Board · Postby **X2Board** » November 26th, 2004, 10:21 am

X2 wrote:If you mean the turbo kit company... it was ACCEL !!! You know them... they make plug wires and crap now.

yuh know i was wondering about this ..... I used an ACCEL street strip clutch disc on an L28 engine a coupla years ago .. never knew they made clutches either.....

X2 · Postby X2 » November 26th, 2004, 12:02 pm

It seems Accel was one of a few pioneers in their time for early turbo systems. The kit used on the corvette didn't even have an available intercooler.