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Thread: Mild port & polish on the intake - what's it gain?

  1. #1
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    Mild port & polish on the intake - what's it gain?

    So I just got my heads back from the machine shop. Blew the headgasket earlier this year, so I finally got the teardown started last month. Had them milled, 3-angle valve job & a mild port/polish on the intake side. The shop that did the work has some experience with the supercharged 3.8s & said they've only seen 6hp at the wheels from a port/polish on a mild street build with a negligible torque increase. That probably translates to about 5hp per head, which isn't very much.

    Seems kinda low to me, but all of my engine-tuning experience is on 8s, not 6s. Thoughts? Anyone here got any dyno examples after having done some light head work?
    Last edited by Rancor Keeper; 10-10-2017 at 10:41 AM.

  2. #2
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    Port work is one of the most important things you can do to as supercoupe. if they are seeing that little of a gain they arnt doing much to the heads. Port and polish is a thing of the past there is no sense in polishing exhaust ports.
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  3. #3
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    Quote Originally Posted by davec73 View Post
    Pif they are seeing that little of a gain they arnt doing much to the heads.
    So what number should they be seeing? I agree with you, but I'm not finding any actual data to dispute their claims, which they've got dyno results to back up (on mild, street driven cars with stock longblocks).

  4. #4
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    I think that porting, as an example, is rarely done as a singular goal, where there are usually other mods done that work to compliment each other. Just porting alone would be perhaps better measured on a flow bench (and then biased against other specific mods), I think, rather than jumping on a dyno. I wouldn't expect big numbers if porting is the only mod.

  5. #5
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    yes Kmt is right cylinder head porting is done as a combination upgrade. If you dont improve the valve train cam and other components while your there you cant take advantage of what the porting does. my cars heads flow 228 int 187 exhaust but i have 184 150 valves and springs that have 180 lb seat pressure. my camshaft is around 570 lift etc. in a built engine all things work together. you want my advice send your culinder heads to somone who works on cylinder heads not a general engine builder.
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  6. #6
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    Just decking the heads and the valve job may give you 10hp...lol...
    Matt Haub
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  7. #7
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    Quote Originally Posted by DrFishbone View Post
    Just decking the heads and the valve job may give you 10hp...lol...
    Give? Or 'recover'..?

    Heck, retracting the power antenna is worth at least a .005 hp gain

  8. #8
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    Quote Originally Posted by DrFishbone View Post
    Just decking the heads and the valve job may give you 10hp...lol...
    Yeah, motor had close to 100k on it, so just cleaning the piston heads is prolly worth something, heh.

  9. #9
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    Quote Originally Posted by KMT View Post
    Give? Or 'recover'..?
    Deck heads - GIVE

    Valve job - RECOVER

    Just posting about it on here is worth about 10hp too!
    Matt Haub
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  10. #10
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    I have had 3 engines in my Sc. First was the stocker i bought it with. When the crank snapped and i replaced it I home ported everything. I have done my fair share of porting and research to do it correctly. I did not have a valve job done. I did not have the heads decked. That engine was only in the car for a short time before an overheating issue rendered it usless. In went a stocker from Dr. Fishbone and the lack of power was very evident. Since he had recently done the head gaskets i didn't want to pull the heads and do them again/swap the one from the previous engine. Everything else was swapped engine to engine. Only difference would be the long blocks. One home ported heads one completely stock. The difference was easily noticed in the seat of the pants. Yes ported heads are usually saved for full on builds but you can easily add them at any point you want. If your builder is only seeing a 6hp increase though i would doubt there isuch if any actual port work done.

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