I am interested in building a forced induction 383 LT1 using the iron heads.

"Why" is a whole 'nother subject, so I wont bother to address that now.


Anyway, I know that with any particular head, there are limits to what you can do with it. I also know that the flow considerations for turbocharging and supercharging are different, and require a different approach to how the head builder will improve the head.

So, assuming that you want to completely optimize the LT1 iron head, and I mean REALLY do it right, there has to be certain limits in what you can do before you reach the design limitations of the heads.

Now, I really don't know what those limits are, but I am assuming that you guys most likely have a pretty good idea.


Taking those limits into account, would you say that a fully optimized iron LT1 head is better suited to the flow characteristics of supercharging or turbocharging?


(Hopefully you can see why I asked this question in this forum instead of Forced Induction. But if the mods disagree, I won't complain about it being moved.)

 

what you're wanting to do is use the iron heads because you think they will seal better, right? I haven't heard of too many alum head LT1s blowing the head gasket out recently. A better idea would be using AFR heads with their extra thick deck and Cometic gaskets. You'd get very good sealing and a much better head while saving 50# off the front of the car.

 

as far as changes in how the head is set up differing on a forced induction engine ya got me there. only thing i can think of is whenever i've built a blown engine i usually pick a much larger cyl head than i would for a n/a application. since by forcing air the velocity created in the intake port will be much greater than normal even with a huge intake port.

jdavis

 

AdioSS -

Better sealing is a fringe benefit.
I am more interested in the thermal conductivity of iron, as opposed to aluminum. By using iron, in conjunction with thermal coatings on the entire combustion chamber, I am hoping to retain more of the heat energy of the combustion process, as well as minimize temperature fluctuations.

 

Is this for some kind of dyno racing like the Engine Masters? If not, then go with aluminum. The weight difference will make the car perform better than the very, very small difference you are looking at. The much better AFRs will make more power than the best ported LT1 or L99 heads ever. Remember, these are factory castings that were designed for the big heavy Caprice/Roadmaster/Fleetwood.

If you are that worried about the thermal dynamic efficiency, just coat the chambers and ports

Also, you can get the AFRs with larger combustion chambers what will let you run a better piston that wouldn't have as much of a dish.

 

that pretty much sums it up.

 

No, it's...

Have you ever done something just because the concept struck you as interesting?



BTW, I like a dished piston.

I like to have the smallest possible chamber in the head, with the needed CC's in the piston.

Ever see the head from a volkswagen VR6?





Here's one where you can see the pistons. It's not the best picture, but it does let you see how the squish area completely circles the piston, creating a highly turbulent area right in the center of the piston, and directing the force of burn to the center as well. It also lets you use a shorter piston/longer rod, without the top land problem.

 

Yeah, the concept of making big cars go fast is interesting to me


the VR6 doesn't have a supercharger or turbo, does it? the forced induction will make plenty of turbulence

Personally, in a forced induction application I would want more piston strength

 

How do you figure that having all the squish in the piston allows a longer rod? The fact is that it DECREASES the available space for the connecting rod, since the piston now needs a huge dish. The design goes against basic hotrodding ideas that have been hammered out over the past half century or so. Sounds like a terrible idea to me.

 

AdioSS -

Actually, it was originally designed as a diesel, and a lot of people do turbocharge them.


Nos -

Normally, one of the limitations on making a rod longer is the way it pushes the ring pack together at the top, leading to a weak top land.
The dish in those pistons aren't much deeper than dishes on many other pistons, it just looks deeper because of the design.
What that piston does have, due to it's 360 degree squish area, is a lot more meat above the top ring.
As to it being a bad idea, the engine produces 1 hp per cubic inch in fairly mild form from the factory, and 5-6 pound sof boost get's it up in the 250-275hp range, which is 1.45 - 1.59 hp/ci.
Those stock pistons will go to over 400hp (On 173 cubic inches!) before ring lands start to go and the stock engine, with 10:1 compression will handle 9.5 lbs of boost. 10 lbs if you stud it so the head gasket doesn't blow out.
A lot of VR6 people are using a thicker head gasket to lower compression and running mid-high teens of boost.

Point being, it can't be THAT much of a bad idea.

 

Anybody can put a non-stock turbo on any engine and make plenty more power. For example: you can take an LS6 which makes 1.17hp per cube with "old school" OHV 2 valves per cylinder and a flattop hypereutectic piston, then put a turbo setup on it and make over 2hp per cid without doing anything to the longblock.

 

That squish area, (surface) is the surface that detemines the quench hgt./clearance. That surface does not change locations, relative to the deck of the block. It is the piston surfaces around it, that can change, or be altered. IOW, they can be lower, as in a dish area, or they can be a domed surface, commonly used to raise CRs to extreme. In extreme cases, the valve clearance, in the piston, can 'dig' into the edge of the piston, in the area above the ring. In regards to the amount of squish around the circumference of the average piston, that is determined by the design of the combuston chamber, in the head. As for rod length limitations, they can be either the ring stackup package, or the thickness of the piston, in critical areas. For FI applications, it should end up being the piston thickness.

A lot of VR6 people are using a thicker head gasket to lower compression and running mid-high teens of boost. Point being, it can't be THAT much of a bad idea.

No, but I consider that, the 'monkey see, monkey do' syndrone. Just cuz some people jump off a bridge, doesn't mean it is the better approach. In regards to the engine, it is the quicker, less expensive approach.


Hey, the 'hat trick'.

 

Guys, we're getting kind of sidetracked here...

Lets just say that I'd like to use iron heads because I'm a freakin' nutjob who howls at the full moon and cannot be expect to make rational decisions in the first place.


The original question still stands:

Essentially, based on what you know about the advantages and limitations of the iron LT1 head, would it ultimately "prefer" turbocharging or supercharging.

I know it will TAKE both just fine. But that's not the question.


And, if I'm doing a really bad job of framing my question, and you don't understand what I'm trying to figure out, please tell me so I can try again.

 

I'm familar with the VR6 used to have a GTI with one, great motor design and sounds mean at full tilt.


The whole thicker head gasket trick is something I never liked be it on a VR6 or a SBC.

Here are some of the better points of the discussion so far in terms of the head....


"only thing i can think of is whenever i've built a blown engine i usually pick a much larger cyl head than i would for a n/a application. since by forcing air the velocity created in the intake port will be much greater than normal even with a huge intake port.

jdavis"

"Is this for some kind of dyno racing like the Engine Masters? If not, then go with aluminum. The weight difference will make the car perform better than the very, very small difference you are looking at."

"If you are that worried about the thermal dynamic efficiency, just coat the chambers and ports "

"Also, you can get the AFRs with larger combustion chambers what will let you run a better piston that wouldn't have as much of a dish."

And something that should end up in my sig.....

"No, but I consider that, the 'monkey see, monkey do' syndrone. Just cuz some people jump off a bridge, doesn't mean it is the better approach. " Thanks for that one Arnie!

God reading thru this and quoting makes a post so much easier!

Bret

 

Heh, 3 out of 5 of those quotes were from me I think...