304 build

[Farragher]

I am looking for advice and recommendations on 304 build plan. I intend to build a 304 to put in my 1980 terra, and am wanting to gain drive-ability in this vehicle. Currently this vehicle does very well off road, but its performance in daily driving around town, and down the freeway is less than optimal. I am hoping there is a build spec I can use to give me somewhat longer legs on the freeway, better fuel mileage, and maintain it's excellent character for conservative off roading.

That being said, here are the rest of the data. T-19 close ratio, and 3.73s in the axles, 31 " tires. I have the afi throttle body injection on m current 304, and would use it on the new one.

Here is what I am thinking, adn correct me if there are better things to do.

Bore .030 over, and pistons to match
mid range cam
heads - is it possible to put bigger valves in these heads? Are they available?
Port match the heads and intake manifold.
Is there an aluminum intake for two barrel?
Afi throttle body - two barrel.
Headers

anything else I should do?

Any and all feed back, suggestions, advice will be much appreciated.


Thanks in advance.

 

[Michael Mayben]

Virtually all this information is already contained in several engine build threads right here in this sub-forum. Nothing special or secret about an sv engine build!

We do have the rpt aluminum intake manifold in a 4v configuration, that is the only 4v intake manifold ever produced for a 266/304 and also the only aluminum intake ever produced. Simple enough to mount a 2v throttle body or carburetor to a 4v manifold.

Sv engines do not breathe well, that is because of the angle of the intake valve and design of the heads. These engines are mid-rpm, truck and agricultural implement prime movers.

Spend some time reading through every thread in the "engine tech" sub-forum and you will see the issues, the pros, the cons, and the pitfalls of sv (and I-4 engine building. To start with here's one link regarding this same subject that is in progress right now:

http://www.forums.IHPartsAmerica.com/gas-engine-tech/3121-350-buck-truck-project-engine-revival.html

 

[Farragher]

I've now read most of the threads here, as well as on some other sites, and have learned much. I still have a question though. In general, it is recommended to increase the compression ratio, if possible. I know that the stroke can be changed, the heads shaved, or a domed piston can be used to achieve this. If I head in the direction of domed pistons, is there a way to know which piston to use, to achieve a specific comp ration increase? I've reviewed the stock spec, and it appears that the data needed to calculate the volume of the combustion chamber is not available. Likewise, there is no way to know the volume difference between a domed piston and the flat top stock units, so how is a particular comp ratio increase calculated?

 

[Robert Kenney]

Not quite that simple.

First you need to decide where you want the torque to come on then the cam is chosen to give you that rpm band.

Compression ratio needed is determined by your cam choice and what fuel you want to run.

You won't find an off the shelf domed piston for an IH that would fit in most peoples budgets.. Buy silvo-lites that are designed for your engine.

Compression it altered first by machining the block deck surfaces to make the piston even with the deck when at tdc "zero decking". For the mots part 9-1 is adequate and still run on regular pump gas. I find .030-.040 is a good number to machine off the decks to end up with zd. Many say an arbitrary amount is enough but I always mock the engine and measure how far in the hole the piston is then calculate machining.

A 304 will need less cam than a 392 to give you a given rpm band so be conservative. Displacement is your friend when power is in question.

 

[Robert Kenney]

You asked how to determine associated volumes. Here are some photos regarding these operations on a 392e that ended up at 9-1 about and used .040 thock composit head gaskets.

I'm going to say that if you are an experienced engine builder these operations are second nature and very easy. For a newbee I don't reccomend attempting them. Swap in a larger sv or build your 304 stock.

Combustion chamber c'cing

Piston c'cing

Mock for decking

Assembly after machining

 

[Farragher]

Thanks Robert. If I were to do this, it would be an experienced engine builder who actually did it. I am familiar with the procedure of cc'ing heads. I knew this way existed, but was wondering if there was another way, like crunching numbers. Doesn't decking the block change the relationship between the intake manifold and the heads? And, how do you get around that?

 

[Robert Kenney]

Sorry I clicked the wrong button when I replied so you May see that I edited your post. I did not.

Compression calculation is this. All volumes need to be in cc's or cubic inches

combustion chamber volume: a
head gasket volume compressed: b
piston volume if a dish use a positive value if a dome use a negative value: c
piston below the deck use a positive value if proud use a negative value: d
sweped volume ( piston area x stroke): e

cr = a+b+c+d+e / e

a warning on z-decking. Use only silvo-lites. They are standard copression height piston and require the least material removal to reach a z-deck condition. Many others like federal mogul are decompressed .025 + so .025 more needs to be removed to reach zd.

Yes decking the block or milling the heads does effect head location but for the most part the locations are not effected enough to cause a problem. I have had to machine a few manifolds but those were engines where al lot of material had been removed from both the block and heads. More than .060 combined. As you can see from the pictures this 392 had .031 removed so no issues occured.

If you are using composite head gaskets like felpro pt's you want to zd. With the oem steel shim type of gaskets you want to leave the piston .015 in the hole so the quench remains at .040.

 

[Farragher]

Alright, if I have this right, silvo-lite lists two pistons, one flat top, and one contoured both say not destroked. I note that you were using a contoured piston, but I don't understand why you would do that if you were intending to increase compression. Seems like the contour would be counter productive to the goal of decreasing combustion chamber volume. Anyway, say we use the flat top unit, then we're going to take off only enough material to zero deck the block. What ever that is, and call it a day, if using felpro gaskets. No shaving the heads. What compression ratio do you think that would give us? Somewhere shy of 9:1?

 

[Robert Kenney]

Ok here is the piston deal.

The ones I used are oem for the 392e the d shaped notch it there to reach the cr IH desired. They are not "contoured" they are designed

you need to determine which piston your 304 requires. The contoured piston is used in nonemission rated engines the number on the id pad will not have an "e" along side the 304.

The flat top piston is for the e 304 . You can not interchange the piston between there respective engines. The heads are specially shapped to accept the dome.

Thanks for suggesting you know more than me about building engines and that I made a poor choice in pistons. You don't have a clue how this engine came to me or how/why it was built the way it was. Focus on your build not others. We won't be able to help you any further if you dont get it now.



Contoured piston

 

[Farragher]

Thanks for your help. I don't know where that last comment came from. I was simply trying to understand. No suggestion that I knew more than you. In fact, I was saying that I didn't. I was reading what you said, and looking at your pictures and seeing a difference. Why is everyone so defensive on these boards. Cripes, I came here to ask questions and learn because I've got to communicate with my engine builder who is not necessarily a IH guy. I figured the knowledge is here, and I was right. But you are wrong about me thinking I knew more than you and it is unfortunate that you jumped to that conclusion. Thanks again for your help. And, by the way, those are mighty funky looking pistons, in my humble opinion.

 

[Robert Kenney]

The pictured piston is an IH "contoured piston" used in 4 poppers and v8's that are non e. The others use flat tops or in the case of the 392 a decompression d shaped notch.

Have you tore the engine down? Before I can tell you what the cr would end up at in any configuration the head needs to be cc'd. Get to that point then we can continue.

 

[Farragher]

Thanks Robert. I'll be parking the Scout this weekend, and beginning the disassembly. As soon as I get to the heads, and get them cc'd, I'll be back. I would like to ask two questions now though. With 150k miles on the engine, would it be a advisable to replace the rods, given where I am headed? Also, if the crank is not damaged/worn, would it be ok with increased compression, and a hotter cam than stock?

 

[Robert Kenney]

The stock rods are ok for mild performance and a rpm limit of around 4800. They are fine at 150k so long ad they are magneflux inspected. One other thing, don't let the shop resize the big end. The rod cap is not doweled/registered to the rod body like other manufacturers. No way to line them up well enough to measure them without a bearing. Install arp bolts but I need to see pictures to determine if the new bolt is applicable to your rod version. IH had several that will not work with them.

The engine from a port flow stand point will be done at that point(4800 rpm).