Using 18* or 15* SBC heads on a LT1 engine

[B'klyn9C1]

Grumpy,

Besides using 18 degree specific pistons in the short block and 18 degree specific intake mainfold and converting over to reverse cooling, what else is required in using these heads in a LTx engine???

Do regular SBC/LTx headers still match up??

Can you still use regular HR lifter and roller rocker arms(in other words a conventional SBC valvetrain)??

Do you think flow number that these heads produce N/A makes the conversion worth it for high performance street???

I am thinking of going this route for my 383 LTx stroker build instead of the usual 23 degree head Advanced Induction or Lloyd Elliot route that everyone seems to go.

One reason in prompting me in going this way is from an article in the February, 2009 online issue of Hot Rod magazine, Lingenfelter Performance Engineering built a 420ci small-block engine with a Bow-Tie block, a Callies 3.875-inch stroker crank, Oliver rods, and a Comp Cams roller. With 11.0:1 compression, 18-degree Chevy heads, and a Bow-Tie single-plane intake manifold fitted with EFI, this big-inch Mouse produced a stout 623 horsepower at just 6300 rpm.

 

[supergass]

That is a great head but it is a race cylinder head. It would require shaft rockers and offset roller lifters to deal with the new valve placements in the heads. THe ports are big usually 245cc and can go close to the 300 cc volume runners so buying used heads can be a horrible experience. Notice the 420 cubic inches in the test engine. A 383 would have to have mucho compression (no less than 12.5:1 and a 6000-6500 stall speed converter so a reasonable shift point would be 7600rpm. Its just not a street engine set up at all. You may not be looking for a street engine, it just seems like that is where you want to go with this engine. If you did run these on a race engine they are really awesome!

 

[B'klyn9C1]

That is a great head but it is a race cylinder head. It would require shaft rockers and offset roller lifters to deal with the new valve placements in the heads. THe ports are big usually 245cc and can go close to the 300 cc volume runners so buying used heads can be a horrible experience. Notice the 420 cubic inches in the test engine. A 383 would have to have mucho compression (no less than 12.5:1 and a 6000-6500 stall speed converter so a reasonable shift point would be 7600rpm. Its just not a street engine set up at all. You may not be looking for a street engine, it just seems like that is where you want to go with this engine. If you did run these on a race engine they are really awesome!

12.5 CR should not be a problem for a Gen III/IV pcm from EFI Connection abd where do get a 6000 stall most guys talk about 3500 to 4000 for dedicated drag race.

BTW this is going a street car that is sometimes road raced.

 

[grumpyvette]

Ive had this discussion dozens of times and without fail its before the persons taken the time to price out the required components and machine work, in detail.
most 15-18 degree heads use expensive offset roller lifters and rockers and pistons, special push-rods and a few other tweaks, like clearence grooves in the block, or other mods that may include shaft rocker arm assemblies, etc.
when you price out all the required machine work cost goes up rapidly
look , if the objects to have 550-600 or more rear wheel horse power, AND retain a reasonable level of street drive-ability.... at that power level with a sbc gen- I or GEN-II your going to either build a stroker using an aftermarket block, heads and cam etc., with killer heads, and a roller cam in most cases or your going to add a power adder like a turbo ,nitrous or a supercharger.the costs add up fast,
build something like these engines linked below on a 383-396 stroker short block and your going to get close to reaching the goal

http://airflowresearch.com/articles/article094/A-P1.htm

viewtopic.php?f=69&t=1040

http://airflowresearch.com/articles/art ... /A9-P1.htm

viewtopic.php?f=52&t=1834

you might want top look into a used nascar style engine, that can at times be purchased for in the $10K-$12K range which for what your getting a bargain.

you can also buy a killer big block for about the same cash outlay, and when it comes to the basics its a whole lot easier to build and maintain a 496-540 big block and drive it on the street without busting parts, or driving your self crazy trying to dive a sbc based engine that needs to pull 4500rpm or more before it really makes power, or use a super charger to get to that power level


http://www.ultrastreet.net/engines/540_realstreet.asp

http://ohiocrank.com/enginespage1.html

http://www.dougherbert.com/108053worldp ... 14_615_749

viewtopic.php?f=69&t=916&p=1535#p1535

viewtopic.php?f=69&t=1420

viewtopic.php?f=69&t=1433

 

[supergass]

The compression ratio is easily achieved. As far as the stall speed on the converter 5000 to 5500 stall has been the norm for dedicated drag race engine for 20 years. As cylinder head technology has improved and camshafts have grown stall speeds are not uncommon to reach 5800 to 6400 stall for bracket racers frequently. Comp Eliminator runs alot of small block combos that use 8000 rpm and above stall speeds, of course this being the (extreme) of the examples of dedicated drag race engines. If you build a 15 or 18 degree engine for the street it will not run well at all with a 3500 -4500 converter. Even if it was in a 2300lbs car. They are big port cylinder heads. I hope whatever you decide to do it works out well for you!

BTW The header flange on the 15or 18 degree stuff looks similar but is bigger and the bolt hole are spread out significantly for larger header diameters.
If you want a set of heads that rival the early 18deg stuff in a 23deg package the AFR 235 eliminator cnc head has flow numbers in the 340cfm range, shaft rockers are still required but no offset roller lifters. They are exceptional heads with a 60/40 split for placement of a bigger intake valve(2.12intake). Still a big head for a 383 but no as much as a mismatch as a larger 18 deg head would be. If you want names to some real gifted hand porters then I would be glad to forward some names there too.