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What kind of CR for boosted engine?
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Author:  65CrewCabPW [ Sun Dec 19, 2010 11:24 am ]
Post subject:  What kind of CR for boosted engine?
I need to be able to run regular gas, and I'm looking at 5-8 psi of boost ( certainly no more), and was wondering what kind of compression ratio I can get away with? I'm thinking that leaving it stock is probably required, but anyone who's played with a turbo might have a better answer.

So, why would I run a turbo? Just to get more horsepower at 2000 - 3500 range so that the heavy rig can run down the highway, even up grades, at highway speeds. The W150 weighs about 4200 or so, and has 3.55 gears and will run a tire from 31 to 34 inches tall.

It's food for thought for possible future mods...
Author:  Sam Powell [ Mon Dec 20, 2010 1:55 pm ]
Post subject: 
What is the induction system? Carb of EFI? And, how will the engine be managed? Will you have electronic timing control, or purely mechanical?
Sam
Author:  65CrewCabPW [ Mon Dec 20, 2010 5:22 pm ]
Post subject: 
Quote:
What is the induction system? Carb of EFI? And, how will the engine be managed? Will you have electronic timing control, or purely mechanical?
Sam
Induction would be TBI. Control of fuel and spark would be by megasquirt..

Mark
Author:  Sam Powell [ Mon Dec 20, 2010 7:35 pm ]
Post subject: 
IN that case, you can take timing out to control detonation. My compression is 8:1 and I do not have pre-ignition with high test gas and 8 lbs of boost. I think I will be able to go higher boost and stay out of preignition with careful management of timing. But so far, I have not been able to get the timing control part of MEgasquirt to work. Others have, so I think I will get there. So, I am stuck with the standard, Mopar timing curve built into the distributor for now.

I hope you go forth with this. How far along are you?

Sam
Author:  emsvitil [ Mon Dec 20, 2010 7:58 pm ]
Post subject: 
Is it better to lower CR and raise boost

or

Raise CR and lower boost?
Author:  Sam Powell [ Tue Dec 21, 2010 5:20 pm ]
Post subject: 
I think in daily driver high CR and lower boost will yield better mileage. But for race purposes, I feel certain higher boost and lower CR yields more power.

That is just a hunch with no real proof. And there are so many combinations and permutations with timing added in, and water injection and intercoolers added to the mix to hold down temps to control detonation. And modern combustion chamber designs also help control detonation, which of course the slant does not have.

Sam
Author:  Joshie225 [ Tue Dec 21, 2010 7:03 pm ]
Post subject: 
With the proper size turbo, low restriction exhaust system, a good intercooler, good control over the fuel and spark you could run it at 8:1 and probably 5psi boost on 87 octane, but you'd have little margin for error. Will Megasquirt do auxiliary injection so you could spray in a little H2O? That would allow quite a bit more boost.
Author:  65CrewCabPW [ Tue Dec 21, 2010 10:41 pm ]
Post subject: 
I'm most concerned with fuel economy and using cheap gas, than in max horsepower.

I am undecided on the turbo aspect, but the TBI and all are definitely a go, though it's going to take me a couple months or more to get started on it, due to needing to save up money for them.

What the issue is, however, is that what I need is about 15 percent more torque at around 2000 rpm than the engine has now, so it'll actually pull the truck around like it means it, rather than having to drive up highway grades, whining along at 45 mph in 3rd gear.

The intention is to pull the timing cover and probably advance the cam timing about 4-6 degrees, go from a 1BBL Holley ( in terrible shape) to a Super Six intake and GM TBI, along with timing improvements and dumping the fixed fan blade (going to electric fan), free flowing exhaust (no, not headers and not duals.. just not practical on this truck), and then, shave the head down to get the compression ratio up to real close to 9:1.

The point of all this, is that if I can't make enough power improvement with everything but the head, then perhaps going to around 5 psi of boost will do the trick, but I need to not go to far with shaving the head down (dont' want to buy another, after refreshing this one).
Author:  Joshie225 [ Wed Dec 22, 2010 12:37 am ]
Post subject: 
I wanted to go faster without touching the bottom end. I put bigger valves in my head, ported it, used an Offy intake and Holley 390 carb (I seem to have better luck with these than most), 2 1/4" exhaust off a stock manifold, Walker Dynomax Super Turbo muffler and took .080" off the head. The compression ratio is now a true 8.5:1 and the car went from 19.4 second ETs to about 17 flat. Still with the '67 cam and worn cylinders.
Author:  turboram [ Wed Dec 22, 2010 4:08 am ]
Post subject: 
my first turbo setup on the truck was a gm 3.8 maf fuel injection. I was able to run 10 psi of boost with low octane fuel.But I had a large intercooler and the knock sensor hooked up. I used a t3 garret chrysler turbo (the slightly bigger auto one)never had it to the track but it had great of idle boost and good drivability.that was a 7.9 cr motor all stock. the truck ran a high 14sec quarter at 12psi before I went crazy and the bug bit then bigger turbo,megasquirt,bigger intercooler,water/meth,drag radials,and sawzall took over :twisted:

If I were to do it again and build a turbo/6 work truck it would be a 9.0 cr, t3 external waste gate turbo setup with a large intercooler and run 8 psi max boost, ether with water injection or run mid-premium fuel
Author:  Sam Powell [ Wed Dec 22, 2010 5:43 am ]
Post subject: 
You are absolutely right, the turbo will get you over the hills seamlessly. But, be aware that once you dip into boost to go over the hills your gas mileage will likely take a big hit. Rich mixtures are one way detonation is controlled in boost with a turbo. And in your tuning process you WILL enrichen the fuel map in that range to help control it. You just will. So, if you are shooting for mileage, try to design a set up that will not go into detonation easily. This would suggest low CR. If you are truing the head, then take off a minimum amount. And, maybe use a thicker head gasket when reassembling things.

If you have the time, and don;t mind puttering, it would be good to calculate the CR before you reassemble. What kind of pistons are you intending to use? Not to confuse you here, but a fresh rebuild, high CR engine might meet your needs in a simpler, more straightforward way. Get an RV grind cam and advance it a degree or so.

Sam
Author:  66aCUDA [ Wed Dec 22, 2010 6:31 am ]
Post subject: 
I dont think you will need to do anything more than mill the head and open up the exhaust. This will net you at least 15% over stock. Couple that with your super six and a Dizzy recurve and you will be 20% more.
Frank
Author:  65CrewCabPW [ Wed Dec 22, 2010 9:41 pm ]
Post subject: 
Quote:


If you have the time, and don;t mind puttering, it would be good to calculate the CR before you reassemble. What kind of pistons are you intending to use? Not to confuse you here, but a fresh rebuild, high CR engine might meet your needs in a simpler, more straightforward way. Get an RV grind cam and advance it a degree or so.

Sam
I'm not tearing the engine down. If I need to do that, I already have another motor that I'd start on first, while continuing to use this one, and build it purpose-built for whatever I wanted the outcome to be.

So, it means I'm kinda stuck with intake, exhaust, cam timing, and headwork, and of course, the load changing stuff, and maybe even gearing. The little slanter will pull just fine with 3.55 gears, I know that from experience with previous engines. I did an 8-10 degree advance with a bigger Isky cam, and it made a whole new motor out of it.

Amazingly enough, with just a offy intake, a 625 AFB, Isky cam (run advanced), you could stomp it at 1800, and after a momentary bog I could not get rid of, it would get right with it and pull like gangbusters to 4500 +, howling all the way. Slants have a very unique sound while pulling hard in the torque range of 1800 to 3200. Not real loud ( the exhaust was!), but definitely a fascinating sound utterly unlike a V-6 or V-8.
Author:  65CrewCabPW [ Wed Dec 22, 2010 9:46 pm ]
Post subject: 
Quote:
I dont think you will need to do anything more than mill the head and open up the exhaust. This will net you at least 15% over stock. Couple that with your super six and a Dizzy recurve and you will be 20% more.
Frank
This engine has a severe torque lack below about 2000 for some reason. I am going to bump the cam timing a little, I'm sure (or I may find the chain is stretched a lot). It likes to wind just like my old Isky bumpstick motor did, thought not nearly as high. With 3.55's, it would pull to 65 to 70 in 3rd, which translates to about 5000 or so. Stock, it all but died about 3600 or so. This thing just will NOT, no matter how I time it or otherwise, develop any oomph until 2000 or so.
Author:  66aCUDA [ Fri Dec 24, 2010 5:46 am ]
Post subject: 
Thats interesting. I would pull the Dizzy and refurb it. It sounds like the weights are not moving freely. Sounds like they are stuck advanced. Take it apart clean it really good and see where you stand.
Frank
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