[gtome]

Originally Posted by BruceWilkie

"plus they pump air only.." Not true at all! You can get a carbon face seal for the compressor side of quite a few turbos and run in draw-thru mode. You can intercool it the same as with a roots blower as well.

You can intercool a drawthrough? Please educate me.

[Tom Vaught]

Here is a link to a Gale Banks "Draw-thru" INTER-COOLED Engine from many years ago. The air entered a carburetor, went thru a common plenum to the inlets of two turbos. From there the air and fuel went to the inter-cooler which used 2 bricks in a common housing and finally to the intake manifold.

http://www.shadetreemechanic.com/ima...nks_marine.jpg

Yes, It can be done and has been done in the past.

Tom Vaught

[BruceWilkie]

Originally Posted by gtome

You can intercool a drawthrough? Please educate me.

Yes you can intercool a draw thru, just not the way you usually see it done these days! I'll have to scan some pictures and re post. I might include a rough scetch of how I intend to do mine.

[David Holmberg]

A local Chevy dealer (L.R. Cooke) built a SCCA type of Corvette back in the late 70's with a draw thru turbo system. Sounded strange, kind of a whoop- pause- whaaa sound. You could hear the carb suck air, then a second later the exhaust. (of course driving it, it would sound normal).

His son Randy wrecked the car one night.

[gtome]

Thats crazy! I would think it would take forever for the air and fuel to get from the carb through the intercooler and finally to the engine?

[Tom Vaught]

Originally Posted by gtome

Thats crazy! I would think it would take forever for the air and fuel to get from the carb through the intercooler and finally to the engine?

Cold starts can be interesting on any draw-thru turbo. Some have injected a small amount of fuel into the intake using a mechanical fuel pump that had a tee in the output line. The fuel went normally to the car needle and seat but now a small amount went through a solenoid and to a small jet in the plenum above the intake manifold. You crank the engine, the fuel pressure goes up, the solenoid is open and the jet acts like an accelerator pump squirter.

Tom Vaught

[gtome]

I thought I was going to have that problem when I put a drawthrough turbo on my old 65 VW Bug. That damn thing, you can reach in the window and just touch the key and it starts??? I used to keep starting fluid in it because everyone told me it would be hard to start, but never had to use it at all. Dont get me wrong, im running a 450 Holley mechanical secondary carb on it, which is way wrong for the application, but hey.. I had 2 brand new ones on the shelf. There are some problem areas (hesitations), but overall it runs pretty good!

[Tom Vaught]

The hesitation is caused by the long air path that even the double pumper cannot completely cover up. Most of the VW Turbo installations I have seen had the turbo mounted pretty high and gravity helped get the fuel to the engine on cold starts.

Tom Vaught

[taff2]

Just one thing, you can't use an intercooler with a draw through system in competition drag racing,the rules don't allow it. I believe there have been cases where an engine backfire has caused the intercooler(full of fuel/air) to explode.

[gtome]

Originally Posted by Tom Vaught

The hesitation is caused by the long air path that even the double pumper cannot completely cover up. Most of the VW Turbo installations I have seen had the turbo mounted pretty high and gravity helped get the fuel to the engine on cold starts.

Tom Vaught

Ya I redid my whole system to "try" to get it under the decklid. Which with the 4bbl will NEVER happen. Thats what is odd about mine is the fact that it starts so well and will idle all day long.
My next step will be blowthrough EFI with Megasquirt and EDIS. I have never used Megasquirt, but I think I can do this pretty inexpencively with mostly junkyard parts from an Escort or the like.

And if/when I figure that out, the Pontiac is next. Any good links/thoughts on building a TB to fit to a 4bbl intake?

[BruceWilkie]

Originally Posted by taff2

Just one thing, you can't use an intercooler with a draw through system in competition drag racing,the rules don't allow it. I believe there have been cases where an engine backfire has caused the intercooler(full of fuel/air) to explode.

If you use an air/liquid intercooler similar to the ones you can get for roots blowers there should be no issue. I would add a blow off valve to control excess pressure same function as the blow off on a roots blower.

I've attached a corvair draw thru with an air to air intercooler

a 327 sbc(dating back to the 60's) twin turbo draw-thru quadrajets? Intercooled. ( think it would have been better to have the intercooler inputs directly oppose each other.)

I have something similar in mind but will involve a dual quad intake and a much better distribution path on the upper half.

I've included a cut away drawing of a turbo corvair. Take note of the torturous path the AF has. I found pretty good distribution on my Corvair even at 20+ psi. draw-thru super atomizes the a/f mix. Throttle response was better IMO than std corvair 2 carb NA motor despite the much longer path. When I swapped out the side draft for a Holley 2 barrel and higher flow compressor I didnt have any great issues dialing it in. It did like a choke when it was cold but fine within a few minutes. I made my own water injection copied from this pic below of the Dick Griffin scheme.

[taff2]

I'm assuming that your tracks run the same safety rules as ours Bruce,NHRA/FIA are the source of reference for us. GSR: Intercooler-Addition of fuel to intake air before intercooler prohibited.
I was pulled up on this years ago by a track scrutineerer when I had a draw through turbo system, I then switched to blow through,it was harder to tune and needed more expensive parts to make the fuel system work. However nowadays,there is a load more blowthrough info available.
I liked the old drawthrough system and never had any problems starting it,no choke and a couple of pumps always did it,and throttle response was fine which surprised me.

[firechicken]

Originally Posted by taff2

I liked the old drawthrough system and never had any problems starting it,no choke and a couple of pumps always did it,and throttle response was fine which surprised me.

My system works well too.
Starts easy and good throttle response.
Here's a pic I found of a water/air intercooler I built a few years ago. I tested it briefly in the shop but didn't like the size/look of it so never ran it.

http://forums.maxperformanceinc.com/...1&d=1141871116
Another pic
http://forums.maxperformanceinc.com/...2&d=1141871116

[gtome]

Wouldnt water/meth injection work better on a drawthrough than an intercooler?

[Tom Vaught]

Originally Posted by gtome

Wouldnt water/meth injection work better on a drawthrough than an intercooler?

With the water-meth injection deal you are constantly mixing and adding fresh mix to the reservoir. With a typical water to air inter-cooler deal you fill it properly and check the fluid once in a great while and typically you will never add fluid.

Both will do a good cooling job, just the meth deal is like filling a NOS bottle vs having a belt supercharger, you get to be really good friends with the NOS supplier and the methanol supplier.

Tom Vaught

[BruceWilkie]

Originally Posted by firechicken

My system works well too.
Starts easy and good throttle response.
Here's a pic I found of a water/air intercooler I built a few years ago. I tested it briefly in the shop but didn't like the size/look of it so never ran it.

http://forums.maxperformanceinc.com/...1&d=1141871116
Another pic
http://forums.maxperformanceinc.com/...2&d=1141871116

Hey, look how far those carbs are from the intake gang!! "Starts easy and good throttle response."

Ive got something similar to your intercooler in mind. However, a few changes.

1)Dual quad intake modified much the same as Taff2 has done with his. A low profile offy version could work nearly as well too(depending on your hp needs). Even a P-65 dual plane dual quad in mild tune should be ok as some people have run dual planes successfully in draw-thru and blow-thru applications.

2) Longer intercooler. Definately liquid/air type. More compact, more efficient (potentially), less ducting and easier to make safe than using an air/air intercooler in a draw-thru application.

3) A tee in the piping at the middle then two inlets each side (90deg off the tees) each elbow's outlet centered over the runner pairs(centered over the plenums) horizontally. This forces the mix at the inlets to collide and scatter but still blend for max even distribution over the intercooler. The cooling fins redirect the charge to the lower plenum in a vertical direction.

BTW if blow-thru application you can skip the tees/elbows and just mount a pair of carbs over the intercooler. 450 mech sec holley (street tunnel ram carbs are low low $), 600 dp's or 4224 660 center squirt 1:1 linkage depending on your needs.( Two or three 2 barrels if you wanted might be ok)All three 4 barrel choices give you the advantage of 4 fuel inlets and bowls, double the vent tube area, and likely better cyl to cyl distribution than a single. Fuel/air gets wider intercooler coverage. (Draw-thru can usually use a larger carb(s) because they pretty much still function as if NA, tho some apps use smaller carb(s) to control boost.)

4) Safety! Roots blowers use burst panels to control explosions from backfire turning the blower into a bomb with moving parts besides. Id mount a burst panel on the intake.(Argue with tech if they let the roots boys run and not this set up. Technically your doing the same thing without the moving parts in it. I do understand their concern) I'd also add a blow off valve(s) that is adjusted slightly less psi than the burst panel and plumb the "exhaust" of the blowoff to a safe area to prevent fire hazard, explosions or fuel on tires. Use the blow off to help control backfire pressure or runaway boost from a wastegate failure. Overall it can be made far safer than most roots blown engines that ARE allowed as long as they have the burst panel. Worst case I think you might have to "prove" you are safer than a roots combo or at least equal and get an exception from your sanctioning body.
I do think an air/air type intercooler and draw-thru would certainly be a safety hazard due to the size that an air/air intercooler needs, along with the far greater duct work. It would be very heavy to be strong enough as well. All that volume, a few drops of gas, and an ignition source(like high underhood heat soak) could be a big bomb just sitting parked!

5) back to #3! All those turns look restrictive but if plumbing is same id as compressor outlet ID it wont lose much of anything to restriction. The intercooler will make far more hp than you might lose from the extra turns. Those turns look like a distribution problem. Again, with draw thru the mixture is very, very well homogenized even at low speed no boost.

I included the Corvair motor pics in my previous post for a reason. With all the turns that system has before the mix hits the cylinder, it still gave very good distribution across all 6 cylinders. Where the upper manifold enters the lower manifold on the Corvair was between the center and an end port on each side.(offset slightly off from the center port) The far port cylinders still showed good even plug color. That is the inspiration to my design. If your handy this can be fairly low profile and look good as well. I plan on using some stainless steel (polished) I have for my intercooler cover and my tees and elbows shouldnt be visible.