Old 4v head, modifying for tumble and velocity vs flow

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BLSTIC
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Old 4v head, modifying for tumble and velocity vs flow

Post by BLSTIC »

So I'm looking at my current car powered by a 4G94 with its head design from the early 90s (I believe the first SOHC 4 valve 4G9 head was in 91 and it wasn't updated before the GDI version appeared). From pictures (I haven't measured it or seen it first hand) it looks like a traditional dump port with very large ports. It's also fairly low compression compared to modern 4v engines at 9.5:1.

I was wondering what to expect if I were to fill the ports with resin to convert them to a more modern very high tumble design and take up a lot of the excess volume. I'd be losing use of a considerable portion of the valve diameter by design and making the "ski ramp" that points flow at the long-side of the valve. I'm also not seeing much of a reason to have a traditional bowl so the port can be smaller again. Feel free to correct my on any design flaw that doesn't go with what I'm trying to achieve.

My copy of engine analyzer plus has no function for tumble that I can find so I can't simulate that, but it does tell me that with an arbitrarily narrower and lower flowing port the torque curve starts and ends about 500rpm earlier. I lose 10 or so of my 120hp but the only losses take place above 5000rpm and the only gains are below ~2200. This is leaving cam specs exactly the same, which I'm all for. For what it's worth the cam has about 12 degrees of seat to seat overlap. I'm assuming that the detonation resistance and increased burn speed from high tumble will provide some gains.

What results could I expect from this?
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by mag2555 »

Your on the right track by wanting the runner volume smaller to gain velocity.
If you measure the minimum area of the Intake bowls in that head you will see that is where the pinch pont / choke is in these heads.
Once you have that number in square inches you can do the same with the main part of the port runner to see how much to shrink it down.
Be sure to leave a 1% area expansion rate back up stream from the center back side of the Intake valve.

Don't forget that tweaking the valve job can pick you up atleast low lift and some mid lift flow and and any flow increase even at low lift will add to total port velocity number.

By the way I hope you have access to, or your own flow bench to make and prove out these mod's?
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by ptuomov »

Any photos of cut heads to see the current port shape? I think doing this in practice would require a tumble wheel on a flow bench. One wants to be on the efficient frontier trading off port efficiency in terms of flow per area and tumble generated.
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by hoffman900 »

Isn’t that one of those sewer port Mitsubishi heads? I think shrinking those is always going to help.

I think you need a flow bench with a tumble meter. As Logan has shared it’s about flow / tumble motion. You still need the required flow for a given power level.

Secondly, more tumble and better combustion allows you to run more compression (or boost) for a given octane. That’s where the real work is.

Piston top shape is important too.
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by David Vizard »

So I'm looking at my current car powered by a 4G94 with its head design from the early 90s

I may be able to help if I knew what make a 4G94 head was off.
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by Kevin Johnson »

David Vizard wrote: Sun Nov 17, 2019 9:16 pm So I'm looking at my current car powered by a 4G94 with its head design from the early 90s

I may be able to help if I knew what make a 4G94 head was off.
DV
https://en.wikipedia.org/wiki/Mitsubishi_4G9_engine
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by David Vizard »

Kevin Johnson wrote: Sun Nov 17, 2019 9:44 pm
David Vizard wrote: Sun Nov 17, 2019 9:16 pm So I'm looking at my current car powered by a 4G94 with its head design from the early 90s

I may be able to help if I knew what make a 4G94 head was off.
DV
https://en.wikipedia.org/wiki/Mitsubishi_4G9_engine
Kevin,

Thanks,

My memory is still a little blotchy here. The head I modified using the PolyQuad valve and port layout was for a 2 litre engine. As I remember it was a twin cam setup and there were 2 versions - a big and small port. The small port head was the way to go.

Just for the record chasing tumble on these or for that matter on almost any head with a CR over about 10.5 is difficult as the higher the CR goes the more it quenches the tumble. To get comprehensive details and drawings Google 'PolyQuad patent'.

Using this spec of head on a turbo 86 Lancer just wiped the deck of even the highest dollar factory supported entries in the 2004 import finals in Palmdale.

DV
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Re: Old 4v head, modifying for tumble and velocity vs flow

Post by Kevin Johnson »

David Vizard wrote: Mon Nov 18, 2019 1:03 pm
Kevin Johnson wrote: Sun Nov 17, 2019 9:44 pm
David Vizard wrote: Sun Nov 17, 2019 9:16 pm So I'm looking at my current car powered by a 4G94 with its head design from the early 90s

I may be able to help if I knew what make a 4G94 head was off.
DV
https://en.wikipedia.org/wiki/Mitsubishi_4G9_engine
Kevin,

Thanks,

My memory is still a little blotchy here. The head I modified using the PolyQuad valve and port layout was for a 2 litre engine. As I remember it was a twin cam setup and there were 2 versions - a big and small port. The small port head was the way to go.

Just for the record chasing tumble on these or for that matter on almost any head with a CR over about 10.5 is difficult as the higher the CR goes the more it quenches the tumble. To get comprehensive details and drawings Google 'PolyQuad patent'.

Using this spec of head on a turbo 86 Lancer just wiped the deck of even the highest dollar factory supported entries in the 2004 import finals in Palmdale.

DV
I am guessing this is the patent you mean: https://patents.google.com/patent/US6615795B2/en

Unfortunately, "PolyQuad" is also a registered name of an antimicrobial agent.
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