87 BFN Exhaust Manifold Porting
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=33280
Printed Date: October-07-2024 at 2:25pm
Topic: 87 BFN Exhaust Manifold Porting
Posted By: mark c
Subject: 87 BFN Exhaust Manifold Porting
Date Posted: April-07-2014 at 1:59pm
I'm finally getting around to pulling the engine with the cracked block in my BFN and i popped the Exhaust manifolds off an saw this. The black marks are where the exhaust manifold is exposed to the exhaust gases, the silver area is where the exhaust gasket was. the exhaust gasket more or less matches the exhaust ports on the 454 heads but the exhaust manifold ports look like they need to be opened up significantly to match the exhaust ports. BBC heads are exhaust flow weak to start with, is it worth my time to open up the Exhaust manifolds while there off, or is that just a waste of effort. there seems like theres plenty of meat in the manifold to enlage the mating surface areas and radius it into the runners. The engine will we getting some HP upgrades, +22CC .030 over pistons, Stock peanut heads are getting dumped replaced with a pair of 71 3993820 LS-5 open chambered, cast iron, large oval port heads (still with the smaller valves), the melling 22220 cam used in the 503 magnum engines, and an RPM air gap manifold. |
Replies:
Posted By: phatsat67
Date Posted: April-07-2014 at 2:18pm
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Good thinking Mark, I noticed that when we pulled the manifolds off Mark's footer. I bet its scabbing off 15 hp or so between all the cylinders. A smooth transition would make a difference I think. ------------- |
Posted By: mark c
Date Posted: April-07-2014 at 2:29pm
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Zach, I need to get you to get me the dark blue, light blue Lightning Bolts for the BFN. It's getting warm enough to wrap up the exterior work as well. Maybe by the time the ice comes back this project will be floatable. (it will never be done). I'll give you a call. |
Posted By: oldcuda
Date Posted: April-07-2014 at 2:45pm
| 820's have 113 chambers and will really benefit from 2.19 intakes and some minor massageing.Are you going to have block 0 decked? Be carfull with quench.Compression is going to north of 10:1 what kind of pistons? |
Posted By: mark c
Date Posted: April-07-2014 at 3:15pm
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Sealed power H693CP Hypereutectic Cast Pistons, full floating pins, aon a Heavy H Beam 6.135 rod. Not cutting the deck, it will be what ever it is once the pistons go in (unless something is horribly wrong with the block). Should be just under 10:1 at about 9.8(my goal) if the block has never been cut. I'll adjust with the head gasket thickness to keep it under 10. But I won't know exactly what it is, till I get the pistons in the bores and see how far in the hole they are (or aren't). Heads are a VAST improvement over the small peanut port heads coming off the engine, and I'm not really looking for a +500HP engine so I'm cheaping out and keeping the stock valves. If its really lame I can always pull them over the winter and have them massaged. I'm trying to keep the engine replacement reasonable in cost for now. |
Posted By: phatsat67
Date Posted: April-07-2014 at 3:32pm
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Mark, Decal operations are down currently (don't know if I told you that). I will keep you posted. I bet she's gonna run good. ------------- |
Posted By: backfoot100
Date Posted: April-07-2014 at 4:06pm
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+1 on what Zach says. The exhaust gases hitting that wall could rob some serious HP. I wouldn't do it based on the exhaust markings unless the exhaust ports on the new heads are the same size. You wanna port match to them. IDK about the hypereutectic pistons either. Unless I've missed something along the way in some of the builds that have happened here, pretty much everybody runs with forged in marine applications including the factory. I have no idea how well hypereutectic will do in a marine engine. Maybe somebody with more knowledge than myself would know better. Just a CYA precautionary warning. ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: oldcuda
Date Posted: April-07-2014 at 4:19pm
| Not quite as simple as adjusting gasket thickness to get desired compression .Top of piston at TDC to flat pad on combustion chamber "quench"should be 0.040-0.045 smaller the problem is obviously bigger you are inviting detonation.Cast piston will not live long in this build one little timing issue and back to drawing board.BBC'S are sensitive to there issues not trying to talk you into more power just like to see you do it one time. |
Posted By: mark c
Date Posted: April-07-2014 at 4:28pm
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The exhaust gaskets do pretty much match the ports on the head. They are maybe 1/32" larger than the actual port, but that portion on the top of the exhaust manifold flange is easily 1/4" high. The 330HP BBC's have cast pistons, and cast cranks, the 502 magnum versions (never used in CC's) have forged guts. |
Posted By: oldcuda
Date Posted: April-07-2014 at 4:39pm
| The 330 has low compression less than 8:1 so cast is fine.I have a 85 330 hp with closed chamber 063 heads compression is almost 9:1 about as far as I would push cast piston.Don't understand what mag 502 has to do with what you plan on building |
Posted By: mark c
Date Posted: April-07-2014 at 5:27pm
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That was a reference to a statement 4 posts above about all marine engines having forged pistons, not anything related to your post. Seems like 400HP is the transition from cast to forged parts in marine engines. I'll have to look into forged pistons, as i don't have them in hand yet. But back tothe question at hand, should i spend the time porting them or just bolt them back on and go with it. The picture is deceiving everything that looks lighter black (more greyish) on the top of the port (bottom of the picture) is on the the flange of the exhaust, none of it is inside the port. Thats how bad the mismatch is. |
Posted By: oldcuda
Date Posted: April-07-2014 at 5:52pm
| Can't hurt but stock manifold/performance two words don't belong in same sentence |
Posted By: oldcuda
Date Posted: April-07-2014 at 7:11pm
| Just a suggestion if you are going to buy pistons and rods go with a piston for 6.385 rod length and get 6.405 rods which gets "0" deck without touching block.Making gasket selection easy 0.041.Don't mind me just stting around nothing to do |
Posted By: mark c
Date Posted: April-07-2014 at 7:52pm
Agree, but these are relatively new (2002 casting date) PCM manifolds, and are in very good shape other than choking off about 20% of my exhaust flow. I'm just trying to get anything out of the motor thats relatively free. I'll put in the time to clean them up some, but stock manifolds for the BBC are like 500 new so i can't imagine what "performance" ones cost. If I hadn't noticed how much of the ports are mismatched I wouldn't have thought anything about just bolting them back on. I'm just wondering if anyone else has done it before I spend 2 days with a grinder trying to open up the ports to match the gaskets. I've already got the rods, so I'm stuck with whatever piston height I get when they go in the block. I've got the block as well but I don't know if its ever been cut, or if it has a stock deck height. I need to get the engine in the boat out and apart so I can see how the rest of the parts are going to fall into place. |
oldcuda wrote:Posted By: oldcuda
Date Posted: April-07-2014 at 8:50pm
 Put a set of these on flow better and they'll hear you coming.
|
Posted By: Waterdog
Date Posted: April-07-2014 at 9:22pm
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It sure looks like the bottom of the exhaust manifold is restricted. It can be BLENDED some with a carbide burr and a cartridge roll but not much more than a bevel 1/2 inch into the manifold. The manifold will get thin fast if you go too far into the manifold. If it was me, I'd invest a couple of hours on it ------------- - waterdog - http://www.correctcraftfan.com/diaries/details.asp?ID=3896&sort=&pagenum=2&yrstart=1978&yrend=1978" rel="nofollow - 78 Ski Tique |
Posted By: TRBenj
Date Posted: April-08-2014 at 9:10am
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Those logs are super cool but unless the ports are significantly larger than the PCM's, I'm not convinced they'd offer a performance advantage. Log manifolds have to make relatively short radius bends coming out of every cylinder, and there's just no way to get the runners anywhere near equal length. Alan dissected some SBF PCM's and they actually looked really good inside. Sort of a shorty header design- I would assume the big blocks are similar. I'd spend a few hours on them too, if you're so inclined. Aftermarket manifolds or headers are widely available for bbc's and are actually fairly reasonably priced (at least compared to the limited Ford options). The cheapest options are about $1k though, so still not cheap. |
Posted By: Waterdog
Date Posted: April-08-2014 at 9:47am
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[QUOTE=TRBenj] Alan dissected some SBF PCM's and they actually looked really good inside. QUOTE] Long ago I sliced & diced my cracked PCM's. Alan wanted to see them and was kind enough to post pictures. I really don't remember but I think he paid the postage. Not everybody would send a 40lb. package of broken parts across the country just to see whats inside. I bet he still has it. I still have the other one. That disected manifold picture would go good in this post, but I can't find it (Tim) help a brother out. ------------- - waterdog - http://www.correctcraftfan.com/diaries/details.asp?ID=3896&sort=&pagenum=2&yrstart=1978&yrend=1978" rel="nofollow - 78 Ski Tique |
Posted By: TRBenj
Date Posted: April-08-2014 at 9:55am
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I stand corrected, sorry Andy! I loved seeing that cross section, very insightful. Pictures are in this thread here: http://www.correctcraftfan.com/forum/forum_posts.asp?TID=12311&PN=2&title=new-commander-engine-orig-exhaust" rel="nofollow - http://www.correctcraftfan.com/forum/forum_posts.asp?TID=12311&PN=2&title=new-commander-engine-orig-exhaust |
Posted By: 81nautique
Date Posted: April-08-2014 at 10:13am
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Andy for some reason I can't find that post and I don't have the photos anymore BUT I do still have the manifolds so when I get a minute I'll snap some new photos. I've started to toss those in the scrap pile several times but every time I look at the amount of work that you put into cutting them in half I just can't do it. I figured someday these will come up in a discussion again.... edit, THANKS TIM ------------- You can’t change the wind but you can adjust your sails |
Posted By: TRBenj
Date Posted: April-08-2014 at 10:33am
Alan, I found em:
|
Posted By: backfoot100
Date Posted: April-08-2014 at 11:43am
I respectfully agree and disagree Tim. I've often debated this subject between the angel on my right shoulder and the devil on my left. Your theory definitely makes sense. The logs do indeed make a short radious bend into the log itself but the PCM's do the same into the runners. That point is moot but the PCM's do indeed have the runners which would have some advantage. How much is debatable. I know I've read more than once that every 90 degree bend in an exhaust is the equivalent of adding 10' of exhaust pipe which obviously restricts flow. The path of least resistance wins. With that in mind the riser of the PCM makes a crazy sharp bend well past 90 degrees (just guessing someplace near 110-120 degrees???) and runs parallel to the angle of the backside of the manifold then. The logs elbows (at least in this case) do have a bump to get around but still doesn't have the super short bend of the PCM's. Again, is that any advantage or not? Certainly debatable and if so, how much? My thinking is that the path of least resistance is the path with the least amount of bends. Eliminating the "bump" risers of the logs and replacing them with a 30 or 45 degree elbow would be even more advantageous using that theory. Then again, the relatively large exhaust on our wet marine engines is huge compared to the automotive world and does that theory even apply then? Just interesting debate fodder. ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: oldcuda
Date Posted: April-08-2014 at 12:04pm
| I run them with 45 degree elbows a lot less restriction I believe |
Posted By: phatsat67
Date Posted: April-08-2014 at 12:04pm
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I personally wouldn't be scared of the hypereutectic pistons at that compression level with the lower water temperatures in a FWC engine. My 67 is in the neighborhood of 10.5:1. It has 0 deck height and slightly machined heads with flat top Keith Black Hypereutectic pistons. On pump gas in the summer it detonates like a mother (I think the dizzy over advances past 4000 RPMS). It gets beat on like a rented mule. When I pulled it apart the pistons look like the day I installed them with no detonation damage. Just tune it so it doesn't detonate and it should be good to go. Anything has to be better than stock cast pieces. ------------- |
Posted By: 81nautique
Date Posted: April-08-2014 at 12:51pm
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Long ago I did a flow test on a few styles of manifolds. This was scientific to a very small degree using a shop vac, a water line and pitot, a home made scale and several coors lights. We tested 2 sets of edelbrock logs, one set port matched to my heads, one set stock, a set of stock Holman Moodys and a set of stock PCMs. Simply measuring air flow the ported Edelbrocks flowed best, then the stock Edelbrocks, then the HM and last was the PCM's. In the case of our wet exhaust marine engines I don't think that the short runner length of a pyramid style manifold (even though in theory should be better than a log)is getting us any scavenging effects at all. With that said in our applications an engine is doing more pushing to get rid of exhaust gasses than the exhaust system is doing pulling, so I would think the path of least resistance (logs)would be the better choice. We just don't run cams with enough overlap to generate scavenging that you would get in a tuned dry exhaust so the shorter runner may in fact be better choice.    ------------- You can’t change the wind but you can adjust your sails |
Posted By: oldcuda
Date Posted: April-08-2014 at 1:18pm
| Now we are getting scientific. Coors light being the standard. |
Posted By: phatsat67
Date Posted: April-08-2014 at 1:28pm
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Alan, I have always thought the same. When I think power production and numbers I try to completely block out headers and camshaft selection when I talk boats. Everyone was mind boggled that the 550 was still rated at 550 with the headers or the manifolds. They don't understand that forced induction engines give a rats ass about scavenging. FI engines generally don't care for cams with lots of overlap. As long as it still has the unrestricted flow it needs to produce that power number it still will. Like you said, most of the camshafts available for reveres rotation engines don't really get into the realm of taking advantage of a scavenging style exhaust system. ------------- |
Posted By: JoeinNY
Date Posted: April-08-2014 at 4:00pm
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Scavenging is one thing but conflicting flow fronts is another thing all together, the crappiest of logs dump right into a common tube the flow from each cylinder – which then then pushes out in both directions, not just in the way it should be going, where it will be met with another puff of exhaust from further down the line, impeding its flow and requiring energy to turn it around and send it back in the right direction. Its like bringing waterflow into a pipe with a t instead of Y, no es Bueno. So even the short runners if they set all the gases going in the same direction can be very beneficial even if not to the point of reaching actual scavenging like you would get in nicely matched set of long tubes. The logs above feature swept runners, and possibly an expanding unidirectional design of the actual log, which wouldn’t be all that bad. An old interceptor log though.. that’s a hard son of a gun to push air through. The chyrslers or omcs that go on either side wouldnt be much better eitherI personally doubt that any of the logs offer any performance benefit over a port matched pcm pyramid with the 3.5 inch risers , and most of them I suspect are worse at everything except looking cool and sounding sweet. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: Waterdog
Date Posted: April-08-2014 at 4:31pm
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Thanks for digging up the pictures Tim (i did look) I wonder if when the water gets introduced at the riser if it pulls the exhaust out of the manifold or blocks the exhaust off. (gas vs. liquid) ------------- - waterdog - http://www.correctcraftfan.com/diaries/details.asp?ID=3896&sort=&pagenum=2&yrstart=1978&yrend=1978" rel="nofollow - 78 Ski Tique |
Posted By: oldcuda
Date Posted: April-08-2014 at 5:09pm
| Just checked and ports on the aluminum logs are much bigger than manifold.see if i send pic with phone.Ports where actually little bigger than gasket . |
Posted By: 81nautique
Date Posted: April-08-2014 at 7:12pm
There goes Joe making perfect sense again. ------------- You can’t change the wind but you can adjust your sails |
Posted By: cadunkle
Date Posted: April-08-2014 at 8:54pm
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Wow that's a heck of a mismatch. Hitting that wall out the port is surely creating turbulence as the exhaust exits the exhaust port and enters the manifold. Since you've got them off I would match the ports. Just wait to be sure the gasket your using is a match or very close to the heads you're gonna use. I wouldn't go crazy working that short turn entering the manifold but I would smooth out any rough areas or casting flash you can reach. I wouldn't have thought there was so much of a mismatch, now that I know I'll be checking and gasket matching my 454 manifolds whenever I have a reason to have them off. Doesn't take much time, can't hurt, and probably will help a bit. No reason not to do it if you've got it apart. All the little attention to detail items add up to a better running harder pulling engine. |
Posted By: SNobsessed
Date Posted: April-08-2014 at 11:55pm
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Conjecture: would the water cooling of the hot exhaust be reducing back pressure? If yes, would that effect be the same in all manifold styles? ------------- “Beer is proof that God loves us and wants us to be happy.” Ben Franklin |
Posted By: backfoot100
Date Posted: April-09-2014 at 11:46am
Absolutely agree on your theory Joe but aren't the old interceptors, chryslers and OMC logs those square suckers that look like a block of wood sitting on each side of the engine? Or at least they if they're round they have absolutely no taper to them going toward the riser. If so, then yes, those would be horrible. The gases would be like hitting a wall and pure pressure is the only thing forcing it out the risers. The short radius bend coming out the exhaust ports on newer logs are turned toward the riser end and the log is tapered toward the riser end to at least get the gases moving in that direction. Then in the case of a 1:1 tranny, the logs are even tilted back and down for more scavenging effect. Nothing has to work against gravity. Gases on a PCM pyramid manifold have to go straight up several inches against gravity before the gases hit that wall of a riser. Short radius bends, a riser that practically has to stop and completely redirect the gas flow and gravity are all working against those PCM's. Not to mention that there has been some form of flow testing done that, even though crude (no disrespect Alan), has proven that logs do flow better than than those heavy, ugly ass PCM pyramids. I'm still of the opinion that a newer aluminum or stainless log with a 30 or 45 degree elbow has to be more efficient. ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: halfnelly
Date Posted: April-09-2014 at 12:17pm
I don't think that 800 degree, high velocity exhaust gasses are affected by gravity too much. Otherwise, no racers would still be using zoomie-style headers. Plus, as Joe mentioned, there's much more to it than just flow. I'm sure a good set of 1 5/8" shorty headers would probably flow around the same as a pair of 1 5/8" longtubes on a flow bench, but the longtubes would make more power on a running motor since the runners are closer to the proper length for each cylinder pulse. The runners are obviously slightly longer in a PCM than a log (almost like a set of block hugger headers), as opposed to a log-style manifold that is similar in design to an automotive cast-iron exhaust manifold. |
Posted By: mark c
Date Posted: August-30-2015 at 3:09pm
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Well I'm nearing the time to put the exhaust manifolds back on, so I busted out the grinder and went at the exhaust manifolds (only one so far). Took about an hour to get this far and I still have a bit of cleanup to do on cylinders 3 and 7 but you can see between the ported one and the virgin one how much material came out. I painted the face of the manifold engine orange using the gasket as a mask to use as a guide , Theres just a bit of orange left on the ported manifold and some of that is down inside the port. The difference in the port size between the two manifolds is pretty large, and it should make some kind of difference in the way the engine performs. .  Now I just have to get at the other one. |
Posted By: DayTony
Date Posted: September-01-2015 at 6:34am
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nice, job, don't forget to check alignment with your gaskets too. Did you bolt the manifolds up the the head and look down inside or just go by the exhaust soot marks as to wether they match up or not? ------------- 1988 Barefoot nautique-454 |
Posted By: mark c
Date Posted: September-01-2015 at 8:45am
| Its gasket matched to the exhaust manifold gasket which is maybe 1/32 of an inch larger than the exhaust ports on the heads, |
Posted By: TRBenj
Date Posted: September-01-2015 at 11:49am
| Wow, looks great. |
Posted By: mark c
Date Posted: September-01-2015 at 4:41pm
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Just looking at the gasket markings on the manifolds when they came off you wouldn't think there would be that big a difference in the port sizes, and until I put the unported one up next to the ported one I didn't realize how much they needed to be opened up to match the heads, but theres the evidence. The ports are probably 20 to 25% larger than they were when I started. Before i cut the second one, I may try a simlar setup to what was discussed above with the shop vac and manometer to see how much, if any difference there is in pressure drop there is between the ported and stock manifolds. |
Posted By: phatsat67
Date Posted: September-01-2015 at 6:10pm
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So much for the 330 hp big block. That much restriction stock engines should make 350! ------------- |
Posted By: 8122pbrainard
Date Posted: September-01-2015 at 9:45pm
Great idea.  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: backfoot100
Date Posted: September-01-2015 at 11:49pm
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I would bet that this is pretty common with most exhaust manifolds on these boats. I would also agree that it has to make a difference in the breathing. The exhaust gasses hitting those sharp edges have to cause some power robbing restriction. Just getting rid of those sharp edges has to be fairly significant. These were mine when I did my rebuild. Before and after.   ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: quinner
Date Posted: September-02-2015 at 11:22am
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A secret source told me you guys need to be straightened out on this subject. It should be to the heads port unless you are doing both. Exhaust only will create a pressure drop and the engine can loose back pressure and not run as well. Got It?? |
Posted By: JoeinNY
Date Posted: September-02-2015 at 11:37am
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Tell your source to work on their reading comprehension… the people here are talking about matching the exhaust to the existing head ports, which is fine. Going past that would in fact be not advised, but that’s not what’s being discussed. I doubt there is a ton of usable hp to be gained either way but done well porting the pcm manifolds to match the heads in my experience does at least make them sound better. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: 81nautique
Date Posted: September-02-2015 at 11:51am
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Really all you're doing is gasket matching for a smooth transition from intake to head to exhaust. This isn't really a measured port job that could have real consequences in either direction, it's more of a clean up of mating surfaces. Quinner, On the motor you have for the MQ the heads were proffesionally ported and flowed, Then I gasket matched both intake and exhaust before and after     |
Posted By: phatsat67
Date Posted: September-02-2015 at 11:57am
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Those RHS Heads look bad ass. ------------- |
Posted By: backfoot100
Date Posted: September-02-2015 at 12:49pm
Look at you!!!!!!! Mr. Wizard...LOL True Dat, but my assumption is if you're going through the process of gasket matching the exhaust ports, at bare minimum, the intake to head matching has also been done (but you know what happens when you ASSUME....right). My bad if it's to the contrary. You really just want to smooth the flow and eliminate the sharp turns and/or edges. Anything that hinders flow is a bad thing. I don't know about the back pressure thingy, but smoothing the flow will never hurt anything. Period. If you've gone that far, you might as well do the head porting then. That's where you'll really see some HP/torque gains. Then if you have a four hole carb adapter, you should match that with the carb throats as well. It all works together from start to finish. It's extremely time consuming to do but the net results can be pretty significant. I have no idea how much difference it really made doing all this when I did my rebuild but I couldn't imagine not doing it in hind sight. It runs pretty well. ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: mark c
Date Posted: September-02-2015 at 1:19pm
Yeah you're right its not technically porting, but when you have a manifold mismatch as bad as this, with a 1/4" to 5/16" high flat wall on the short radius of a PCM manifold it can't hurt. The lighter grey area in the picture is all on the face of the manifold , none of it is on the inside of the port, and its a flat machined edge that the exhaust gas hits head on coming out of the cylinder. Porting heads in a relatively low rpm operating engine, is not really going to buy me much anyways, Unless you really want to go crazy with modifications to the rest of the head and spending huge money on some custom cam work this "gasket matching" will at least bring a stock BBC engine back up to its 330 HP factory raating and at the moment with the engine still apart, its not taking any time away from using the boat and its relatively free so why not. My 820 heads flow relatively well for a factory cast iron head but by know means are they the best ones out there, these are typical numbers vs valve lift for these heads stock out of the box and the exhaust flow is fairly weak to begin with. no matter what kind of exhaust they are bolted to.. INT EX .2-145--------132 .3-207--------166 .4-256--------193 .5-295--------201 .6-308--------214 .7-301--------221 The other thing to note is that in my case I'm going from peanut port 236 casting oval port heads that really suck on the exhaust side to the 820 heads. So if it was choking off exhaust flow before, it will really be chocking it now, so any little bit helps. peanut port flows: INT EX .2-125--------87 .3-183--------111 .4-215--------130 .5-233--------144 .6-235--------150 You will have real trouble finding a reasonable (under $500) BBC reverse rotation cam with lifts much over .5" so every so you certainly don't want any extra material in your exhaust cutting down your flow unless you've got deep pockets.. The only thing i did to my heads was to lap the valve seat, put in new under cut stem SS valves, and new umbrella seals. The heads themselves had nothing else done to them. |
Posted By: Gary S
Date Posted: September-02-2015 at 3:50pm
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You say port mismatch but on the exhaust I had always heard the above picture is correct - the exhaust manifold is larger than the port. The exposed ridge of the head also slows exhaust gas reversion. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: C-Bass
Date Posted: September-02-2015 at 3:59pm
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Aren't we looking at the manifold here Gary? If so it's the head port that is larger and the manifold ridge is exposed. ------------- Craig 67 SN 73 SN http://www.correctcraftfan.com/diaries/details.asp?ID=6103" rel="nofollow - 99 Sport 85SN |
Posted By: Gary S
Date Posted: September-02-2015 at 4:12pm
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Your right Craig the closer I look I see it now,optical illusion I guess or old age-- so if it was changed around like I thought it would be ok ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: mark c
Date Posted: September-02-2015 at 4:50pm
| Yes thatis a PCM pyramid exhaust manifold flange for a 454 Chevy not the ehaust port on the head.itself, the blue behind it is the rug in the boat, not the paint on the head. (Plus its a Chevy, it should be orange - I don't care what color the marinizers paint them) The exhaust manifold has a way smaller port than the head has. |
Posted By: 8122pbrainard
Date Posted: September-02-2015 at 9:13pm
The eye's are going from all those years of looking at the tracer colors! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |