Suck through Vs Blow Through

[240rwkw Gem]

ok all you 16/17tr old listen up...

a few posts ago some guy was asking about jet sizing for his suck through turbo setup. With out offering any help some people outright bagged him for it and simply said "Should have gone blow through", with out backing up their claim.

i feel that if you are going to make a judgement you better have some facts and info to back it up.

so "why" should he have gone blow through?? do you know that it is actually harder and less reliable to do a blow through setup... did you know that you have to have a sealed enclosure around the carby so that ALL the boosted air is used by the carby...????

blow through is only good for 2 things... 1) The all wanky blow off valve noise AND 2) intercooling.

plus with a blow through set up, when you change gears at high revs.. ie the turbo is producing maximum boost... you can bend and even snap the butterfly in the carby.

suck through is probably the easiest way of turbo charging a carbied engine. WHY????
- there is no loss of impeller speed between gear shifts... for there is no restriction for the compressed air... ie very little boost lost between gears

- fuel also help the longevity of the turbine it self... acts like lubrication

- very simple, no need for air tight enclosures to be made up.. just attach the carby to the front of the turbo, pipe the compressed air to the inlet manifold and done.

See if you are going to advise someone on what they should or shouldnt do to their car then state some facts instead of repeating something that you heard from your best mates, sisters boyfriends cousin at a party. It also helps to do some research instead of going on what you hear other people say... there is nothing worse then a 17yr who gets all their "car knowledge" from unreliable forums... for all you know i may be bullshitting about the above info....

but as i say back up your claims with info!

hopefully there will be some more carby - turbo gems running around now!!!!


feel free to hate me!

[Gold TX Sleeper]

100% agree with u on that one, or should i say all the points made in that post. Draw thru will win every time, Blow thru is just asking for problems ranging from head-aches to wallet munching.
Still, each to their own. But back up your claims with reputable reasons B4 you go telling someone to spend their hard earned cash.
Just out of interests sake, i had a blow thru set-up on a Datto 1200. It only took 3 months until i switched to the suck thru system for extremely obvious reasons. Never regretted it once... : )

[murray]

so can you have a blow off valve with either type of turbo

[MatMan]

You can have a blow off valve on a draw through, but of course this will emit air and fuel around the engine bay )

[MatMan]

Personally, I don't have a problem with suck-through setup's. Sure they have their drawbacks, but for the money, you just can't beat them. Hell, Grant Williams Series IV RX7 was running a suck through setup and pulling low 8's. I dont know if hes still running that setup though.

[Ben Wight]

WOW!, this reply is just nasty, so I feel free to hate you.

QUOTE: "so "why" should he have gone blow through?? do you know that it is actually harder and less reliable to do a blow through setup... did you know that you have to have a sealed enclosure around the carby so that ALL the boosted air is used by the carby...???? "

This statement is complete bullshit. How many blowthrough setups have you seen with a complete carb enclosing airbox? The fact is you dont need one. An air bonnet will force all of the air into the carby, where else is it going to go? Throttle shafts? Only really worn throttle shafts will weep air/fuel mixture, but its not much of a leak, more of a nuicance.

Less reliable?? In what way?

Harder?? In What way? Its more simple in my opinion, you dont have to relocate the carby or fabricate a crossover pipe that will bolt to the inlet manifold, you dont have to get a mnaifold to mount the carby on front of the turbo, you dont need a new accelerator cable and bracket system, and you dont need a carbon seal equipped turbo.

QUOTE: "plus with a blow through set up, when you change gears at high revs.. ie the turbo is producing maximum boost... you can bend and even snap the butterfly in the carby."

I've never heard of this happenning! Maybe you better tell all of those automotive manufacturers such as Porsce, Nissan, Isuzu, toyota, Masserati, Ford, etc, that run a blow through efi configuration. They must be all stressing about the butterflies within their throttle bodies snapping and bending.

QUOTE: "suck through is probably the easiest way of turbo charging a carbied engine. "

Agreed, but its not the best if a combination of power, economy and response are the goals of the system.

QUOTE: "- there is no loss of impeller speed between gear shifts... for there is no restriction for the compressed air... ie very little boost lost between gears "

Thats what blow of valves are for! Btw, when the butterflies are shut on a draw through setup, dont you think the compressor wheel with deccelerate due to cavitation?

QUOTE: "fuel also help the longevity of the turbine it self... acts like lubrication "

Well this is bullshit, first of all, the turbine is on the exhaust side, it doesn't really care about the induction setup. As you are referring to the compressor, the only part of the turbo as a whole that receives any lubrication is the bearings and shaft, these are sealed, so it wouldn't matter if the compressor wheel sees fuel, dry air, or sawdust!

QUOTE: "- very simple, no need for air tight enclosures to be made up.. just attach the carby to the front of the turbo, pipe the compressed air to the inlet manifold and done."

As stated above, you dont need a complete airtight enclosure, only an air bonnet (an air tight box that replaces the air cleaner). And dont forget, a draw through setup requires carbon seals on the compressor, most turbos in the world aren't equipped with these unless they are 1960 or 1970 dinosaurs. Its costs quite a bit to have them installed on dynamic sealed (efi) units.

The fact of it all is, when running on pump fuel, a blow through configuration will deliver the goods, as water/meth injection can run out, plus it erodes the compressor wheel. Intercoolers always work, there is no reliance on water pumps and topping up the tank.

And my cousins boyfirend's uncle also told me about how in general, draw through systems suffer from throttle response issues, and cold start issues prmiraly due to the increased inlet tract length where the air/fuel mix can come out of supension and collect in the inlet manifold, deliverying a slug of raw fuel when given WOT sometimes. Plus, carb icing issues in cold climates, possible causing the butterflies to freeze open on a draw through setup.

I assume you have a draw through setup?

Ben Wight

[Pete]

well i just learnt a whole fukn heap.

[Nick_H]

dont want to seem a smartass...but it wouldnt work....the way a blowoff valve works is if the boost pressure is before the butterfly and u shut the butterfly it backs up the pressure which HELPS opens the piston on your blowoff valve the other side becomes vacume which also helps opening the blowoff valve the compressed air comes out of the blowoff valve making a pissssssssss noise ....a draw through setup ,the boost is after the butterfly so when its shut the engine uses all the boost pressure and becomes vacume which prob wouldnt be enough to open a blowoff valve and there is nothing to vent left so the blowoff valve wouldnt make a noise!!!
correct me if im wrong!!!!!!!!!!

[Benjamin]

That goes for me too, previously leaning towards the theory that suck through is better. I am now enlightened somewhat

On the subject of blowoff valves, IMHO they are toss and sound ridiculous. Fair enough they work, but do they have to be so loud?

That said, I am supercharger man. If only I could find a way to vary the boost pressure of a supercharger according to speed, something like a continuously variable pulley system.
Hmmm....

[MatMan]

You are absolutely right. Just now I wanted to see the reply for my post, but I read my post again first and realised that, no, no it wouldn't work at all.

I don't mind being corrected if I'm wrong )

[GasGem]

Ben you could not have said it any better,

Blow through is far better, Petrol & LPG, I have had both suck through and blow through and I get much better results with blow through, in performance, economy, tuning, and reliability,

And if Suck through is so dam good! then why hasn't all the Auto companies gone for it?

Blow through rocks,

Cheers
Eggy,
210RWHPLPG Turbo daily driver,( Blow through of course)

[Gold TX Sleeper]

Each set-up has it's many and varied draw-backs and pluses to consider B4 setting up. In the end, any good mechanic worth his salt will tell you that a modified engine configuration is only as reliable and promising as the final tuning of the complete pakage. Ultimately either set-up will be doomed if the hours spent fine tuning aren't put into it.
I have my personal preference on which i have based on hands on experience, but it would be arrogant and ignorant to tell someone to complete a certain set-up just coz i did. I have witnessed two 8sec cars (both 13B rotaries) one with suck thru and the other blow thru. And did you think the two owners were bitching about which was better - Hell No! They were swapping notes with each other to learn more about intricicies, do's and dont's, pro's and con's between each set-up.
Some of you will argue your points till you are blue in the face like little girls, just remember every one is gonna have an opinion and preference - some may be wrong and some may be right. Just because yours is different, doesn't mean that the other person has to agree with it.
Either way, stop bitching with each other (have a beer and chill out) and start teaching and enlightening some of these people including me, with stuff they dont know so they can get on with modifying their Gemmies.
Cheers...

[Mark]

I have done numerous blow thru and draw thru setups, and both of you are right and also wrong in my experience.

I have achieved much greater performance from drawthru setups mainly because of the icing effect on the induction pipe b4 the turbo cooling the air charge allowing much higher boost levels without need for water meth injection.

I have comfortably run 25psi boost with a 1.8l t03 with no other form of cooling (ie meth ) on super fuel with a draw thru setup.

Same type of turbo i could only manage 10spi blow thru, though admittedly it wasnt intercooled, but any higher boost it pinged its head off. It was similar motor specs, including dizzy and compressions.

On the other side of the coin i have always found draw thru setups use shitloads of fuel where as blow thrus are normally comparitively fuel efficient.

Tune ability is similar as is throttle response....boost still has to come from the same spot people, doesnt matter where the fuel is cos its always moving at pressure, be it suction or boosted.

Draw thru takes more work in manifold fabrication and carby mounting but blow thru takes more pipe work if intercooled, plus you need to make some sort of enclosure to seal to the top of the carby, and no silastic does not seal as i saw some idiot do.

Draw thru requires more effort in brake booster hose and boost gauge, cos you dont want fuel inside those babies, but blow thru requires more effort and expense in fuel pumps cos you have to have alot higher fuel pressures.

You run the risk of damaging the carby under high boost (ie collapsing the float etc) in a blow thru setup, but you have to spend $300 up front to put a carbon seal in your turbo to run draw thru. ( or you blow up turbos every 6 months or so )

summary, more power from a draw thru setup, thats why all the quick carby fed cars run them. Alot better fuel economy and probably engine component life from a blow thru setup.

moral of the story, do what you feel like and what you can afford.

And if one more person spouts of about efi being blow thru im going to slap them. Totally different concept kiddies. They have electronic idle air bypasses to keep em runnning instead of tiny air bleeds, no crushable items like inside a carby. They have idle speed control motors, fuel injected directly onto the back of the valve etc etc. Blow thru carby fed is not even remotely similar to efi setups.

Also keep in mind all the manufacturers that were menitoned by ben wight, always run draw thru carby setups from factory, ie/ esp falcon turbo was draw thru, sigma turbo was draw thru, even the laser turbo was draw thru. I cant think of a single factory blow thru carby fed turbo setup......although im sure someone will prove me wrong..

[Ben Wight]

Too right you bunch of little girls!

Shame shame!

Both setups have to be tuned similarly with repect to ignition curves and fuel distribution and mixture issues. I agree with you sleeper dude, I shouldn't have tried to influence people toward one way if they were condident in doing it the other.

Ben Wight

[Ben Wight]

Hey Mark, I am amazed that you got that much boost (25psi) draw through with the same turbo and only 10psi blow through. Did you dump heaps of fuel in the draw through setup (ie overly rich mixture)??

What were the turbo specs?

I could only get about 15psi out of a draw through 45mm DCOE before detonation, and I got the same when I converted to blow through, no intercooler. Both without water/meth.

QUOTE: "And if one more person spouts of about efi being blow thru im going to slap them. Totally different concept kiddies. They have electronic idle air bypasses to keep em runnning instead of tiny air bleeds, no crushable items like inside a carby. They have idle speed control motors, fuel injected directly onto the back of the valve etc etc. Blow thru carby fed is not even remotely similar to efi setups."

I wasn't referring to how they deliver their fuel, I was referring to how an efi "blow through" config blows air through a throttle body (butterflies) just as a blow through carb does. The point was made that it is possible to damage the butterflies when closing the throttle at high boost when blowing through the carb, but this would be the same as blowing through the throttle body on an efi setup.

AFAIK, the auxiallry air valve opens purely at idle to give extra airflow and bypass the throttle body, and would be of no benefit in an efi config with respect to prolonging the loife of the butterfly valve.

QUOTE: "Also keep in mind all the manufacturers that were menitoned by ben wight, always run draw thru carby setups from factory, ie/ esp falcon turbo was draw thru, sigma turbo was draw thru, even the laser turbo was draw thru. I cant think of a single factory blow thru carby fed turbo setup......although im sure someone will prove me wrong.."

I'll correct you when you are wrong

Ford and GM (dodge and chev) in the US have all had carby blow through configurations as well as dray through, I am confident that there were more blows than sucks, we had an early laser TX3 turbo (front wheel drive) here is aus that was a blow through setup.

Perhaps the most famous of all, the masserati and Lotus esprit blow through turbos, both cars using different setups, the lotus used a pair of Dellortos carbs, and a beautiful airbonnet containing a water/air intercooler.

The masserati has twin turbos (bi-turbo).

They later went to efi.

Cheers!
Ben Wight