Inliners International Forums General Discussion Blown and Injected Draw or Blow?

What do You guys think is the best for a low-boost application,a blow-trough setup or a draw-trough.

Building a truly cheap setup for my 27 ,using a AMC/Jeep 4.0 liter whith "the bad head" cast pistons in a otherwise stock block except for a small Crane cam 216/228 @ .005 and .484/512 lift. will not go that much over 7-8 psi of boost just to give it a chance to survive more than 10 minutes.

Turbo will be either a KKK K29 or a Holset HX 40 so it will probably be able to pump all the air I need and then some,I do have a Holset HX50 if the other ones end up being to small...

Hans

Unless you have a turbo with a carbon seal on the compressor, you want blow throuhg (the carbon seal keeps the gasoline from washing the oil out of the front bearing).

I am not that farmiliar with those specific turbos, so I appologise if they are world famous for draw through compatibilty.

i would also recomend a blow thru setup. you will have better throttle response and the ability to add a intercooler. tom

Nexxussian:Those turbos are intended mostly for truck-engines Garret and Holset is often used by Volvo and Scania in their engines,Volvo often uses Holset-turbos HX35 and HX40 is used in 7-9 liter engines HX50 55 and 60 is used in 10-16 liter 400-660 HP Scania does mostly use Garret GT40-42-45 and 47's 9-16 liters 400-620 HP engines. KKK is used in among others Mercedes Benz trucks,"my truck" at work is a MB Actros 12 liter V6 430 HP and that one uses a K27 the V8 models 12-14 liters has K28-29-31 depneding on power output.

Here in Sweden the guys who want's real power in their 4 cyl engines uses them to get boost-pressures up to 30-45 psi,the more common turbos for regular cars just don't cut it when You want 1000-1200 HP's out of a 2.0-2.3 liter 4-banger.

This is a Holset HX55 not the biggest around but the best pic I found right now:
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Be good: Hans

Hans, I use a draw through on my turbo AMC 258. It is easier to set up as you do not have to seal the carb, use non-collapseable floats and boost referenced fuel pres regulator. I did break pistons 4 times with my first set-up. Detonation will break the ring lands on stock AMC pistons right now. You must avoid it at all cost. I am now using a full dish 232 piston in my 258 with the piston .90 down in the bore. No detonation yet but I drive the car pretty easy. I retired from racing and have the engine in a 27T street rod. Good luck on your project. Mike

.90 down the bore is alot LOL.
Remember,if you are that far down the bore & having no quench area to speak of,you can actually detonate more ,even if you have low compression.

Example (1) an engine .090 piston down the hole, no quench.Running 8 to 1 compression ratio. Running 12 psi boost pressure.

Example (2) an engine running a zero deck, nice quench area running 9 to 1 compression ratio. Running 12 psi boost pressure.

What engine would you think will have a tendancy to detonate more?

The 8 to 1 engine running less compression & no quench area,will more likely detonate more even w/less compression.

Having a good quench area is realy the better way to go.

MBHD

hank, i understand having a good quench is GOOD. but back to a 292. how are you supposed to get a good quench with a stock type piston (even trw forged). the pistons on my engine sit .070 in the hole and have a .300 dish (or small coffee cup). remember no buying 600.00 pistons and the block needs to have enough deck to hold a head bolt. same goes for most of these inline engines. performance parts are nearly nill, esp pistons. most people are just trying to build what they have.

not trying to beatup on you. it is just that you keep bringing it up. maybe it's me being ornry because it's finally normal weather here(hot/humid). i refuse to turn the air on too. the computer keys are even sticky.

Tom,
I keep bringing it up,because they are some people here that still insist it is not good thing to do so,on a 194-250 CI engines.
It is not a manditory thing to do ,,,but it would be a wise thing to do.
When you do deck a 250 block, you are not taking that much material to get a zero deck.

I am saying I had 12-1 compression (on my 250),small cam .540 lift 236 duration @ .050 & my cranking compression was 220 across all cylinders & I ran 91 octane fuel. No detonation @ all, & that having a zero to positive deck allowed me to run such a high compression.

I understand on a 292 engine you do not have much of a choice to get a zero deck using stock or TRW pistons.
You would need to purchase aftermarket pistons or rods to get it close.
I am not telling guys w/a 292 to mill there blocks down .070.

FYI,there are people that can add/weld aluminum to your pistons, even cast pistons.Not sure if this can be an option?

My friend had it done to his cast motorcycle piston on a single cylinder,maybe an option????????? don't know what the cost would be.

The dish is not hurting you that much,it just has less quench area.

It would help guys to buy aftermarket 292 pistons,they are much lighter than stock,easyier on the rods,but ,like you say $600,,,but,why no buying $600 pistons??? Not available?

MBHD

Hank, I agree that you need Quench to minimize detonation. I had not intended to turbocharge my engine again when I bought 232 pistons off ebay. I assumed they would have a smaller dish that 258 pistons. I was wrong. I received a piston that was highly polished and had a huge full circle dish. Sat .090 in bore so I figured it would have way to low comp. ratio so I turbocharged it. I must be lucky as when I ran stock 258 pistons I had lots of detonation under full boast, I have none now. Sometimes we just get lucky. Mike

How much boost do You have on that engine,wondering if my intended boost-level is to high or maybe it's way to low.

Would like to use as much boost as possible without endanger the motor,why stay at a low level if it can take more.

Hans

with almost any stock engine 6 lbs would be safe. tom

I should have known that they were large turbos, I've never heard of Holset making a small one. IMHO that size turbo will be too big for what you want to do (FWIW I have a T50 that's about that size) I would expect alot of lag, and a major boost creep problem with the lower boost levels (anything 1.5 bar or less).


Sorry for taking so long to get back to you, I've been away and my laptop was being uncooperative.

Back to the original topic: Draw-through is easier, blow-through is better.

Jon.

X2
MBHD

Hans, with my first set-up with stock pistons I used the stock waste-gate actuator from the Buick V6. I believe they were set at 7 pounds. Never a problem on the street but at the drags the boost would continue to climb with waste gate wide open. Probably because of bigger engine and running to 6000 rpm. Saw 12 pounds once before pistons broke. I used a Jacobs ignition retard that retarded ignition the amount I dialed in starting at 3 pounds boost. I also used water injection. Still broke pistons. The present set-up uses the same waste gate actuator but with no ignition retard or water injection. I have never really stood on it for an extended time. Have seen 5 pounds boost with no detonation at all. The lower comp pistons seem to do the trick. Also my 27 roadster weighs half what the 65 Rambler I had engine in does. That may be a big help too. Mike

Jon, What has to happen to a stock carb for blow through to be effective. I don't really have plans to put a blower on my new engine but just for grins I'm wondering if I could. I have a 400 CFM Edelbrock on a Clifford intake, lumps, big valves, 500 lift cam, flat top aluminum pistons.

Find the biggest needle & seat,or make it as large as possible,if your float bowl area is small,like on Webers.
You need a float that will not collaspe under boost pressure.
Float that is made of plastic or fill your brass float w/foam then reseal it.
Throttle shafts can leak.Accel pump,idle adjustment screws etc.
Or enclose the entire carb,then you do not need to worry about leaks.
here is some good info: http://www.vs57.com/carb.htm
If you use a holley 2 bbl or 4 bbl carb they have aftermarket parts that I mentioned.
A boost reference hose to your fuel regulator,top side of diaphram.
Probably need to mess w/your needle & jets.
Good Weber carbs usually do not leak on the throttle shafts,they have roller bearings & seals on the shafts.

MBHD

Typically, there are three issues:
(1) sealing all areas where fuel might be blown out (throttle shafts, pump shaft, idle mixture screws, etc.)
(2) modifying the float to not collapse
(3) a "reference" line to the fuel pump, making the pump variable pressure.

Jon.

An HX-35 is good to about 450hp. An Hx-40 is good to about 550-650, depending on if it's a 6 blade (550) or 7 blade housing. Tim's turbo's (google them) makes a turbine housing for them. There are some diesel places that do too. You probably could use a 12cm2 turbine housing on a 292. These are good turbos. No draw through seals though, so you've pretty much got one choice. Scrap the edelbrock carb and go with a holley. CSU carbs is who to talk to to get one set up properly for blow through. You are either going to have to spend some money for a proper carb, or spend some money for a turbo with seals. I recommend the carb.

Carter offered a factory sealed blow-through carburetor AFB). So you don't have to do any engineering, simply duplicate the factory modifications. So any genuine Carter AFB could be modified. I wouldn't want to try it on any of the clones.

Earlier Holleys had leakage problems. Possibly the newer gaskets have solved this issue.

Jon.