Re: drawthrough 512" caddy, may convert to blowthrough

You've got the coolest projects dude!

 

Re: drawthrough 512" caddy, may convert to blowthrough

Its a shame you have to go through the engine again, That is one hell of a setup. If you were to reuse the turbos and go to a blow thru set up it would probably free up a bit more on the top end. The carb should be ok and the turbos would flow more air in place of the vaporised fuel. probably inprove the drivability as well.

 

Re: drawthrough 512" caddy, may convert to blowthrough

wtatman [and turbomike],

thanks for the kind words.

I'm hoping that the flaking cam bearing was a fluke, and that's all I'll find. I'll pull it down this coming week and find out.

Actually, the driveability was pretty darned good. The carb plenum has bypass valves in the bottom which allow air/fuel a short route down directly into the intake off boost. Under boost, they snap shut.

I was going to keep the little turbos and go blowthrough, but I know that even at 650 horse worth of air, they're not happy. The real problem, I believe is the downpipes. 2.5" for 30" or so before it goes to 3". There's only 1/4" clearance at several places. The power bug has bitten, and I don't think I'll be happy unless I go to the larger turbos.

Thanks again.
Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

Please keep us posted as this progresses. Every time I follow something like this I learn quite a lot!

Thanks.

 

Re: drawthrough 512" caddy, may convert to blowthrough

slap a pair of T-70s on there and you will make more than 650 h.p. you can get two masterpowers for a little over five hundred a piece. I love the truck, wicked project

 

Re: drawthrough 512" caddy, may convert to blowthrough

wtatman - thanks

pdonk,

I know, I know, a big pair would kick ass. However, I have several E/E Rajays "in stock". I believe that they'd give me much more, but I really only want about 700 horse worth of air. Afaik, the E Rajay compressor will be pretty happy at 350 horse worth [x2].

It's really a cruiser, although I'll take it to the dragstrip just for shits a time or three. I'm looking for decent mileage, quiet, tire spinning fun truck.

Thanks.
Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

Btw, in case anyone might get a kick out of it, here are pics of the old drawthrough carb plenum. From a 1980s single turbo kit. I hacked a hole on the other side to make it work with twins. I also put a bigger inlet in the front, and the original was only 2".

Note the little bipass ports in the floor. They allow a shortcut for a little air/fuel when not on boost. Snap shut under boost.

Dave

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Re: drawthrough 512" caddy, may convert to blowthrough

I remember seeing those a lot in the magazines in the late seventies. Back then all the aftemarket makers were trying desperately to make power with the smog motors. Been trying to scratch that turbo bug ever since.

 

Re: drawthrough 512" caddy, may convert to blowthrough

I had an itch since I was a kid and saw the turbo Corvairs and Jetfires. We've had three DSMs, but this ole truck is my first dyi. Hopefully, it'll get out of it's own way this season coming.

Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

When I saw this, all I could do was !!

It reminds me of my very first cool hot rod truck, I had taken a 500ci caddy engine out of a 76 eldo, and stuffed it in a 1970 SWB Chevy truck, and painted it the exact color you have there.

Damn, that's scary!

Back to your build!

 

Re: drawthrough 512" caddy, may convert to blowthrough

Thanks. My first caddy swap was a beater '71 C-20 camper special. Damaged a few egos with it.

Broken record mode on now: I think the 2.5" downpipes were hurting me the most, killing the top end. I'll eventually pretty much start over with a better location on larger turbos that'll allow at least 3".

Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

All the turbo books Ive read always stated a drawthru is largely restricted by the carb size. Its easier to force air in then draw it thru. I would think even an 850 would be to small. But if you going BT than its not an issue now.

Just my .02

Oh yeh, very nice setup there.

 

Re: drawthrough 512" caddy, may convert to blowthrough

tbird,

I agree, and I expected it to be an issue. I had an old 950 three barrel that I was going to try if I saw boost drop at high rpm. However, testing [not too safely tuned] when the head gaskets lifted showed that although top end was weak, boost stayed rock steady from off idle to 5500 at 10.5 lbs. This tells me that the 2.5" dowpipes were a restriction, and in effect, backing the boost up in the engine.

thanks.
Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

If you got to were you thought the carb was the weakest link you could do a ron's terminator alcohol injection and run E85....

 

Re: drawthrough 512" caddy, may convert to blowthrough

If it ran out of carb drawthrough, I'd probably put a carb on each turbo, or maybe a dom. [or blowthrough]

E-85 would be nice. None within 1.5 hours of me.

Thanks.
Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

2 should be good for around 850 hp!!

 

Re: drawthrough 512" caddy, may convert to blowthrough

Sorry, I didn't see your reply 'till now.

I figure they'd be good for 800+ too, but I would not need that much. I figure that they'd be really happy at 350 each worth.

Temporary setback on it anyway. Pulled it apart to fix head gaskets, and saw chunks of cam bearings hanging out. The other bearings look fine, as does the rest of the stuff. The oil hole were lined up properly etc. Cam went in nice and spun fine. I still haven't a clue. Took block in for tanking and new cam bearings and they found a crack in the deck. When it rains it pours.

Sticking a re-ringed std bore engine with a little cam in it N/A'd for now just to cruise some. Will re-group with the 'jays.

Dave

 

Re: drawthrough 512" caddy, may convert to blowthrough

Exhaust gass out of the turbine will want to spin in the downpipe. I would imagine that anything that disrupts that will be detrimental to flow.

 

Re: drawthrough 512" caddy, may convert to blowthrough

Just wanted to say if you think the exhast is a restiction then put a pressure gage on the end of there. If it measures anything more than 2-5psi then go to a larger size. And really 5 psi is WAAaaayyy too much. It should really be 1-2 psi.

-bix

 

Re: drawthrough 512" caddy, may convert to blowthrough

Your doing well to keep it even with your boost pressure.