The GM/Merc Rectangle port head. Discuss.
01-19-2015 | 04:54 PM
#51
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From: chicago
True. Plus some numbers are with and without a pipe on the exhaust, some on a 4.31 bore, some 4.500 bore, etc.
What does seem to be consistent though, is the flow numbers for the 188, 088, 990 heads is well below the flow of most aftermarket heads, especially those that have raised exhaust ports.
What does seem to be consistent though, is the flow numbers for the 188, 088, 990 heads is well below the flow of most aftermarket heads, especially those that have raised exhaust ports.
01-19-2015 | 05:46 PM
#52
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From: westville, NJ
another thing with old iron heads. they ain't very thick between water and valve guides. iron GM heads really don't like not having antifreeze in them. they rot through at the exhaust guides. even with fresh water only. AND you can carry an extra point of CR with aluminum heads.
Last edited by dereknkathy; 01-19-2015 at 05:49 PM.
09-01-2015 | 05:28 AM
#55
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From: westville, NJ
09-01-2015 | 05:42 AM
#56
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From: Lees Summit ~ LOTO 10MM
09-02-2015 | 02:17 PM
#59
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From: Portland, OR
Here is the gist of a conversation that I have with guys on an almost daily basis.
We start talking about power output, budget, head choices, etc. When you are freshening up an engine completely and are replacing all of the head hardware, you are looking at about $1000 in parts. This includes Manley valves, ISKY (or similar) springs, Comp (or similar) retainers, locks, etc. You have about $600 in Manley Severe duty intake and Inconel exhaust valves and about $400 in the rest of the parts. These are just rough numbers. Now, whether you are freshening up the stock cast iron heads, aftermarket cast iron heads, or aftermarket aluminum heads, the price of the hardware is the same. It really doesn't matter as far as the price is concerned. The issue is that none of that hardware is interchangeable between the stock cast iron heads and aftermarket aluminum heads. The alum heads use longer valves (usually) with larger heads and smaller stems. They will not work in a stock cast iron head. Typically, the springs will install a little taller, so they won't work in a stock head. You get the picture. You are going to spend that $1000 one way or the other, but then you are stuck with it.
Now, the only difference you have is the price of the bare aftermarket heads. Let's say that you are looking at aluminum heads that sell for $1400 bare. You don't want to spend the money but you want more power. First, your heads need some work though. The guides are worn out so they need liners. Of course, they need a valve job and they need to be surfaced. None of that will help power though. You decide to do some port work to them. You will never do enough porting to them to make them flow as good as a decent aftermarket aluminum head though. It's one thing if you can do the port work yourself without actually making them worse. If you have to pay someone to do it, you could spend $500-$1000 for really nice port work. You have now eaten away at just about all of that $1400 cost of the new heads. Even if you don't port them, you can easily dump $500 or more into the stock heads just to make them fresh and usable. Now, the new heads are only $900 more. The more you spend on the stockers, the smaller that price gap gets. I realize that it's a bunch of money, but you will never get into a set that cheap again. If you want to change them in the future, not only will you have to buy the heads, but you will have to buy all of that hardware again. You are already going to dump a bunch of money into some dinosaurs, why not spend a little more, get all of the benefits that aftermarket heads offer and only buy it once.
Eddie
We start talking about power output, budget, head choices, etc. When you are freshening up an engine completely and are replacing all of the head hardware, you are looking at about $1000 in parts. This includes Manley valves, ISKY (or similar) springs, Comp (or similar) retainers, locks, etc. You have about $600 in Manley Severe duty intake and Inconel exhaust valves and about $400 in the rest of the parts. These are just rough numbers. Now, whether you are freshening up the stock cast iron heads, aftermarket cast iron heads, or aftermarket aluminum heads, the price of the hardware is the same. It really doesn't matter as far as the price is concerned. The issue is that none of that hardware is interchangeable between the stock cast iron heads and aftermarket aluminum heads. The alum heads use longer valves (usually) with larger heads and smaller stems. They will not work in a stock cast iron head. Typically, the springs will install a little taller, so they won't work in a stock head. You get the picture. You are going to spend that $1000 one way or the other, but then you are stuck with it.
Now, the only difference you have is the price of the bare aftermarket heads. Let's say that you are looking at aluminum heads that sell for $1400 bare. You don't want to spend the money but you want more power. First, your heads need some work though. The guides are worn out so they need liners. Of course, they need a valve job and they need to be surfaced. None of that will help power though. You decide to do some port work to them. You will never do enough porting to them to make them flow as good as a decent aftermarket aluminum head though. It's one thing if you can do the port work yourself without actually making them worse. If you have to pay someone to do it, you could spend $500-$1000 for really nice port work. You have now eaten away at just about all of that $1400 cost of the new heads. Even if you don't port them, you can easily dump $500 or more into the stock heads just to make them fresh and usable. Now, the new heads are only $900 more. The more you spend on the stockers, the smaller that price gap gets. I realize that it's a bunch of money, but you will never get into a set that cheap again. If you want to change them in the future, not only will you have to buy the heads, but you will have to buy all of that hardware again. You are already going to dump a bunch of money into some dinosaurs, why not spend a little more, get all of the benefits that aftermarket heads offer and only buy it once.
Eddie
Last edited by Diamond Dave; 09-02-2015 at 02:40 PM.
09-02-2015 | 02:40 PM
#60
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There have been quite a few OSO'ers who have done just that - bought a set of fully assembled aftermarket heads and installed them out of the box, and done just fine. But there are also some who have been burned doing that. One major issue is that marine engines, particularly those that are forced induction, require larger than usual valve stem clearances. Many head manufacturers actually have a warning on their sites and instructions advising to check guide clearances for marine engines and those running power adders like forced induction or N2O. So at the end of the day, you have decide how much of a gambler you are.
