Is 10psi a little too much for a stock forged crank225?

I thought 8 would be the max.

At 10psi what would likely cause engine failure... The pushrods?

Stock 904tf i have been told can handle 300+ hp so i think that would cope. Also the stock rear end, what's the max for that?

Thanks in advance, I'm still gathering info from searching etc.

Cheers

If it's a steel crank it should be able to handle a lot more than a cast unit, I would think. Hopefully Dr. Dodge will get in on this. He will know the true strength.

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trying to keep it low key here in my Valiant200

The turbo install I did back in 1979 ran 10-11 lbs on a stock 170 short block, at first. The only failures I had were head gaskets, and pistons, caused by detonation. Stay out of detonation and don't let it run lean, and you will be fine at 10 lbs boost. The 904 trans in good serviceable condition should be fine. A 7 1/4 rear would be the weak link, even though mine held up fine (3.91 sure grip).

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Thanks very much for the help! Car is to be registered by Christmas (if all goes well, but you know it probably won't haha).

About to get hold of two smaller turbos, plan is to run them with an inter-cooler max of 10lbs boost through a blow through carb (don't want/limited to running with a carb setup).

to avoid detonation....

Running highest octane fuel?
tweaking the ignition system?
and making sure the stoichiometric ratio is correct through the RPM band?

Anything else I am missing?
Also if anyone has any info on blow through carbs or a book they found useful I'd be interested to know I'm still gathering as much info as possible!

I plan to pull the head of the engine, and have a look around before I put the turbo on etc.

Next step will be to do some work on the rear end.

Cheers for the help, I still have a lot to learn when it comes to boost.

http://www.hangar18fabrication.com/blowthru.html for Blowthru carb modification. Consider a Snow Performance kit for detonation prevention.

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1970 Dodge Dart Custom w/ 1bbl slant six

Okay; I think I may have found the problem; I was logged into the user help section and unknowingly posted those two notes under that login. I had to go and logout of user help and login under my own board name to post this message.

The admin. may have deleted those two posts under the policy that forbids any posts unrelated to member help issues.

At least, I HOPE that is what happened.

If I have successfully logged in to my own I.D. this time, it won't have the "member help" disclaimer at the bottom of this message.

Sorry for the confusion...

Bill

i dont know if im right or wrong id love to know but either way ive heard the steel is stronger

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trying to keep it low key here in my Valiant200

All I can tell you is what I have learned reading other experienced people's information because our turbo slant six isn't ready for the strip yet, but is getting close. Here is what I have read, and the sources have been people who seem to actually know (from experience) what they are talking about. Keep the mixture around 11.5:1 and that will avoid detonation on pump gas (the 93 octane kind) up to about 10 pounds of boost with no help from a sprayer or intercooler. Get a GOOD 02 sensor and watch that mixture like a hawk. Limit maximum spark advance to 18 crankshaft degrees, if any boost at all is present. Flame fronts travel much faster under boost, so not as much spark advance is needed. The 34 degrees we are used to running in our normally aspirated engines will cause engine damage under boost. We bought a "lean burn" system distributor which comes from the factory with NO vacuum advance unit and NO centrifugal advance mechanism, locked it down at 18 degrees (crank degrees) to preclude any "accidents." It does NOT "kick back" on the starter; starts and runs beautifully, but it will be a 90% strip car and see very little street activity; I don't know how that locked-in spark advance with no curve would affect driveability on the street. We have a Spearco air-to-air intercooler, but we plan to run as much as 30 pounds of boost in this engine, eventually and will need the charge cooling. At 10 pounds of boost, I am not sure that an intercooler would even be necessary. But, if I ran one, it would be a chemical intercooler (alcohol/water injector) like the one Snowperformance sells (BoostCooler.) I think from what I have read, that they do a more effective job than an air-to-air unit of the appropriate size. Of course, the waste gate of choice has to be matched to the engine's requirements or "boost creep" will eventually make itself known and the amount of pressure in the intake system will exceed what you have decreed. A "boost controller" will help keep the waste gate completely closed until the desired boost figure is reached, a bonus in launching. The way it was explained to me was, that when the turbo is spooling under stall at the starting line, when the boost gets near to the desired figure (say, 10 pounds) the waste gate will start to open a little, wasting a portion of the exhaust, defeating your attempt to launch the car under maximum boost. A "Boost Controller" won't let that happen; it will hold back the boost signal from the waste gate until the set figure is reached and THEN let the actuating signal open the waste gate. I hope I got that right... So, if your mixture is correct, spark advance is limited to 18 degrees, your chemical intercooler is working (most people set the Hobbs switch to start the spraying at around 5 pounds, I think), the octane is 93 or above, ring end gaps are wide enough for the added temperature of boost combustion, and there is sufficient fuel pressure to maintain 6 pounds of pressure at the needle and seat regardless of boost, you just might get away with running pump gas at 10 pounds of boost, indefinitely. I hope so!!! As I said, I am a newbie at this, so if any of you turbo-experienced slanters find fault with what I have said here, PLEASE straighten me out. I will appreciate it and so will the O.P. Bill, in Conway AR See our build at: http://www.flickr.com/photos/billdedman/

I'm running 15 psi with a stock forged crank and 200,000 mile stock pistons. Shaker223, Turboram, and others are pushing close to 30 PSI without problems. I agree, that some people have had problems with head gaskets, but I believe that is caused by detination + boost and if you keep the timing mild, it won't be a problem.Also count on having the 904 rebuilt with V-8 cluth packs and a mild shift kit. And forget about dual turbos,twice the cost,twice the fabrication,twice the tuning headackes.

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V8?? We don't need no stink'n V8!!

Thanks for the rundown! I have a couple of questions, if I may
ask:

It is an ongoing source of fascination for me to try to predict how much power a slant 6 will make with X amount of boost (different configurations and boost numbers.)

I use an online calculator which seems to give reasonably close estimates, but not dead-nuts accurate information regarding this.

For instance, when Tom Wolfe (Shaker223) put 18 pounds of boost to a bone stock 225 (except for adding a 4bbl carb) it went 12.95 at 104 mph in a 3,350-pound car. That computer program says it takes 300 hp to achieve that.

I am wondering if your car is anything like Tom's, and what kind of results you've had with it RE: drag racing times, or chassis dyno figures.

If you could shed some light on that I'd appreciate it.

Also, I was wondering whether you use an alcohol/water injector. I didn't see any other kind of intercooler in the pic you posted.

Any information will be greatly appreciated!

Bill in Conway, Arkansas

Bill that was an awesome turbo 101.

I'd like to add a few things though.

Special blowthrough carbs are the way to go. I don't suggest trying to make your own with an old Holley 4150. I've been driving on the street with a Quickfuel 650 for a month now, pulling full boost, with no flat spots and I haven't even changed the jetting out of the box. My AFR is staying consistsntly in the 10.5-12.5 range

You will want to change your plugs. One heat range down.

You will need a fuel pump that is capable of producing 12 psi if you are going to run 10 lbs of boost. You will also need a good boost referenced fuel pressure regulator to keep it at 6 psi on idle and cruise and maintaining 1-2 psi higher than your boost psi. Otherwise you'll have a flooded motor

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Tyler, 19
72 Dart Swinger /6T

Tyler,

That's good advice! Thanks!!!

Our fuel system consists of a Walbro gsl 392 inline pump that makes 60 psi, and an Aeromotive regulator set to give the carb 6 psi over boost, whatever that happens to be. We got the Walbro pump because it has such high line pressure that even if, down the road, we decide to run 30 pounds of boost, untimately, it can stay on top of it.


Speaking of which, I am wondering what happens to your fuel supply if you achieve 12 pounds of boost. I had the idea that your system was running 12 pounds; I am not sure where I got that idea, but if it's true... the following may apply.

In their online literature, Holley's webpage says the Blue pump make a pre-set 14 pounds of boost.

To overcome the 12 pounds of boost your carburetor float bowl would be "seeing", your fuel pressure requirements would be 12 + whatever inertia the fuel column in the fuel line from the tank up to the regulator would be, and friction in the fittings (negligible, probably,) totaling maybe 13 pounds, leaving only 1 pound to feed the carb's float bowls (where you ideallly, would need 5-6 pounds.) I'm not sure that only 2 pounds over the boost figure would be enough to keep the bowls supplied, properly.

I'd think that unless you have a way to get more fuel pressure out of that Blue pump, you'd be in jeopardy of running your carb out of fuel under extended full-throttle operation.

What do you think?

Bill

Thank you for correcting me bill,

the Holley pump puts out a factory set 14 psi. This is plenty for me because I am limited to 10 psi of boost on pump gas. So in fact, there is 6 psi of fuel pressure before boost, and 14 psi of fuel pressure at peak boost, plenty to feed the bowls under 10 psi of boost.

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Tyler, 19
72 Dart Swinger /6T

Hi Tyler,

The way I sees it is:

The pump is back in the trunk (or, thereabouts) putting out 14 PSI.

You have 10 pounds of boost which is trying hard to push that fuel back into the line.

That leavers 4 PSI (14 - 10 = 4.)

Now, I don't know about your system, but our system has several brass fittings that allow the fuel to traverse the trip between two filters and a regulator, on the way to the needles and seats.

All those have some (minimal) resistance.

You have four (not six) pounds of pressure (14 - 10 = 4) to overcome the resistance in the line to fill those float bowls.

In my opinion, 4 psi (at the pump MIGHT be 3 at the carb, due to the drop caused by the resistance in the fittings...

That may or may not be enough to stave off fuel starvation under full throttle (10 pounds of boost) conditions.

You don't want that float level to drop precipitously during boost. That can cause a lean out tht will invite detonation and that's not healthy for pistons, rings, etc...

This is just my opinion, but I think you're walking a very thin line with this setup. But, as I said, that's just my opinion...

Given what's at stake, I'd look into it a little further (a fuel pressure gauge at the carb that can be read at full throttle.)

Might save you some grief, down the road...

Good luck!


Bill

I agree with what your saying bill. As of right now, I have my boost controller set for about 8 psi so I should be safe.

I'm going to put an extension line on my fuel pressure gauge from the regulator to somewhere I can see it while driving. That way i can see how safe I actually am.

Don't like it but Im gonna need more fuel pressure to stay safe

Can I just put in an inline helper pump to get the 20 psi or so that I need?

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Tyler, 19
72 Dart Swinger /6T