Forced head swap.
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
Forced head swap.
My original design for my roller 405 was to use these machined '89 350 heads.
They are bolted in and everything was going fine until I had my LT1 manifold machined. Now, the bolt pattern matches just fine, but the angles are all off, and I don't like the cross over ports where the only thing between water and outside air is a gasket with no head surface over it.
I have decided on LT1 iron heads. I have been reading that they flow better than the aluminum ones, and I won't have to worry about my compression ratio. I am looking at a set of complete heads from a Buick to mod to fit my Gen1 block, and bolt on.
I know the valve covers will fit, but I was wondering if the LT1 springs would be okay with my LT4 Hot Cam. I was also wondering about the accessory bolt pattern on the head. Is it the same as the pre-LT1 accessory pattern?
Any tips or ideas?
It's a roller 405, LT4 Hot Cam, stock rods, valve relief pistons, and an LT1 EFI manifold.
Thanks.
They are bolted in and everything was going fine until I had my LT1 manifold machined. Now, the bolt pattern matches just fine, but the angles are all off, and I don't like the cross over ports where the only thing between water and outside air is a gasket with no head surface over it.
I have decided on LT1 iron heads. I have been reading that they flow better than the aluminum ones, and I won't have to worry about my compression ratio. I am looking at a set of complete heads from a Buick to mod to fit my Gen1 block, and bolt on.
I know the valve covers will fit, but I was wondering if the LT1 springs would be okay with my LT4 Hot Cam. I was also wondering about the accessory bolt pattern on the head. Is it the same as the pre-LT1 accessory pattern?
Any tips or ideas?
It's a roller 405, LT4 Hot Cam, stock rods, valve relief pistons, and an LT1 EFI manifold.
Thanks.
Pro
Joined: Jan 2005
Posts: 535
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From: Southaven MS
If you are talking about the stock springs on the LT1 then I serously doubt they are up the to task of an LT4 cam. To even go from 1.5 rockers to 1.6 the Buick/Impala heads need a spring swap... Reason I know: My father has a 95 Impala SS with the LT1 engine.
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
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From: Columbia Missouri
What springs would you suggest? I have very limited experience and knowledge when it comes to choosing valve springs.
Also, do you know if the head's accessory bolt pattern is the same? I would really like to keep the serp system I have.
Abby Normal
Joined: Dec 2001
Posts: 53,293
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From: Press "2" for English
color me confused. i was under the impression that LT1 heads would not work on a 1st gen SBC. is that wrong??? seriously, 'cause there's a guy here on craigslist selling aluminum LT1 heads for a decent price.
i gotta know.
i gotta know.
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
They are reverse flow, but that's all dictated by the pump anyway. There are also less fluid cross overs and I think there are two ports that have to be welded closed before they can be mounted...but lots of guys have been modding LT1 heads to fit Gen1 blocks. Batman's doing it too, as he's got a 400, LT1 heads, and LT1 manifold just like me.
Pro
Joined: Jan 2005
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From: Southaven MS
LT4 Valve Spring Specifications
Part Number 12551483
Material Chrome Silicon SuperClean
Outside Diameter 1.337”
Inside Diameter 0.906”
Installed Height 1.780”
Seat Load 101 lbs.
Average Spring Rate 331 lbs./inch
Solid Height 1.215”
As for accessory bolt pattern... again not much help.... never really paid attention to that.. sorry
You can go to www.gmpartsdirect.com and type the part number and it will also give you a nice description.
Here is an interesting site I just found giving LT4 and LT1 info (don't know if this helps... but maybe it will)
http://www.grandsportregistry.com/lt1vslt4.htm
Last edited by 1972warship; Apr 2, 2007 at 09:30 PM.
Team Owner
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From: Springfield MO
St. Jude Donor '07
They are reverse flow, but that's all dictated by the pump anyway. There are also less fluid cross overs and I think there are two ports that have to be welded closed before they can be mounted...but lots of guys have been modding LT1 heads to fit Gen1 blocks. Batman's doing it too, as he's got a 400, LT1 heads, and LT1 manifold just like me.
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From: South of giving a damn
St. Jude Donor '11, '17
They are reverse flow, but that's all dictated by the pump anyway. There are also less fluid cross overs and I think there are two ports that have to be welded closed before they can be mounted...but lots of guys have been modding LT1 heads to fit Gen1 blocks. Batman's doing it too, as he's got a 400, LT1 heads, and LT1 manifold just like me.
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
I know you are chasing all this stuff down & being economical and all but your time is worth something. In the long run wouldn't it be better to just get a decent set of aftermarket aluminum heads? The flow has to be better. The LT-1 heads only went on 300hp engines & I'd think you'd have to port the heck out of a set to get much more than that.
I've been talking to a GM guy, and he says the LT1 iron heads were good up to 400 HP without MAJOR modifications. Maybe he's blowing smoke up my you know what...but it's something I have heard a few times before him.
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From: South of giving a damn
St. Jude Donor '11, '17
I thought the iron heads went on the the Impala SS & maybe the Camaros. Both of those engines were down rated to the Vette LT-1 & I thought that was mainly in the heads.
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
You may be right, and that's what I thought, but there seem to be a lot of guys who's been up this river, and seem to think the iron heads have plenty to offer as a stock head.
I will find out. Luckily the motor I have is a torque monster, and won't see a lot of high RPM playing. I just want gobs of torque and a good strong cruising speed.
Team Owner
Joined: Oct 2004
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From: Springfield MO
St. Jude Donor '07
I think the cam was detuned. The iron heads were the intermediate step between the LT1 aluminum heads and the later LT4/Vortec designs. The chamber is a bit bigger than the aluminum heads, and the ports have a better design.
Le Mans Master
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From: Unreconstructed, South Carolina
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
I have a Cloyes timing cover that has the cam button built in. It's adjustable so I can control how far the cam moves forward and back between it and the rear plug.
Burning Brakes
Joined: Sep 2005
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From: whitman massachusetts
Heads
If you can find a copy of John Lingefelters "Modifying Small-Block Chevy Engines(Borders Book Store has a reading room) it has some great info on the use of stock cast iron GM heads, gives huge info on the top six cast iron heads produced, flow characteristics, chamber sizes, etc., also the pros and cons of iron over aluminum. DB, don't take the chance of inhaling smoke up the wrong end,LOL. This guy knows his stuff!
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
I've seen the LT4 cams on feebay for pretty reasonable $ ... but haven't seen a conventional ready-made retainer & cam button for late step-nose cam. It seems the cost of discount LT4 cam AND Cloyes cover setup might be about as much as a conventional roller cam setup ... most any Doug Herbert billet steel early sbc rollers are $190 ... plus Herbert's got plenty of profile choices.
I too have a roller 400 planned using short V6 lifter conversion ... but long rods, aftermarket heads etc ... need more time.
And a planned clone of GMPP's new HT383E (17800393) ... for OE fuel injected 96-99 GM PU ... works w/ factory FI & ECM without reprogramming. Have complete core iron vortec from throttle body to pan ... have found a cheap takeout cam as in HT383E ... just need cheap crank, rods & pistons ... and time.
I too have a roller 400 planned using short V6 lifter conversion ... but long rods, aftermarket heads etc ... need more time.
And a planned clone of GMPP's new HT383E (17800393) ... for OE fuel injected 96-99 GM PU ... works w/ factory FI & ECM without reprogramming. Have complete core iron vortec from throttle body to pan ... have found a cheap takeout cam as in HT383E ... just need cheap crank, rods & pistons ... and time.
Thread Starter
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
And a planned clone of GMPP's new HT383E (17800393) ... for OE fuel injected 96-99 GM PU ... works w/ factory FI & ECM without reprogramming. Have complete core iron vortec from throttle body to pan ... have found a cheap takeout cam as in HT383E ... just need cheap crank, rods & pistons ... and time.
Ooh that sounds like a LOT of fun. Got any LT1 heads laying around?
Pro
Joined: Jan 2005
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From: Southaven MS
From what I understand the iron heads flow about 10-15% better versus aluminum(stock vs stock)... at least that is what I have read... no real world knowledge 
, and yes GM did not want the B body cars to have as much power as the firebirds, camaros, and corvettes so they detuned them by putting in a smaller cam..(losing about 20hp) That is why the springs on a stock iron head lt1 will not handle an lt4 cam. They ar
, and yes GM did not want the B body cars to have as much power as the firebirds, camaros, and corvettes so they detuned them by putting in a smaller cam..(losing about 20hp) That is why the springs on a stock iron head lt1 will not handle an lt4 cam. They ar
Last edited by 1972warship; Apr 3, 2007 at 10:10 PM.
Pro
Joined: Jun 2005
Posts: 725
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From: FL.
I know you are chasing all this stuff down & being economical and all but your time is worth something. In the long run wouldn't it be better to just get a decent set of aftermarket aluminum heads? The flow has to be better. The LT-1 heads only went on 300hp engines & I'd think you'd have to port the heck out of a set to get much more than that.
