About Custom LT5 builds

[tpepmeie]

I thought I would write a few words about the effort and time required to build a custom, large displacement LT5 engine. There are only a few guys building these, and some members have them in process or are thinking about it for the future.

These are unique engines. Virtually all of the components in a high-end build are custom. We all wish it was as easy as the LS-platform, with a menu of off the shelf parts readily available. Here's what a typical build looks like for me, the other guys are probably similar.

1) Crankshaft. Anything more than a 3.750" stroke has to be a new billet piece. Moldex and Bryant are the two main suppliers. Moldex is 26-week leadtime from order placement. Bryant is even longer, and slightly more expensive, but good. The price of these are so high, I don't know any of the builders who keep them in stock, on the shelf.

2) Cylinder Block. 4.000 bore LA Sleeves are available, but there is an approximate 6-8 week leadtime. Custom sleeves (4.125"+ bore) are available and slightly more expensive. The engineering cost for those of us who've designed these is something that must be amortized/and included in the price.

For the bigger sleeves, the block has to be machined in the lower bores to fit the sleeves. That must (should) be done only on a CNC mill. In addition, there are other features such as closed deck, and/or deck supports which require precise machining of the top deck surface of the block as well.

Finally, the block has to be relieved in the lower crankcase to clear a long-stroke crankshaft. That can be done by a hand grinder.

3) Cylinder heads. Basic porting, with stock seats and valves is easier and faster. But still not fast. The few shops who do this properly often have a backlog of other work. I have experienced this taking 6 months best case, >12 months once.

On many of my builds, I use larger stainless or titanium valves which have a leadtime of about 6-10 weeks. There is additional machine work for new seats and guides. If the valve job is done in a shop with a Newen grinder, for example, there is always a wait time to get those done. Worth it, but extra time & $$$.

Also, with high lift cams, the cylinder heads and camshaft covers must be machined for clearance to the cam lobes. Not hard, but tedious nonetheless.

4). Intake porting. This can be done in-house if one has the equipment and skills, or there are a couple guys with decades of experience in porting these parts who do great, reliable, effective work. Again, there can be a 6-month wait in line. I try to make sure the entire induction system is optimized to work together for maximum performance. A welded "siamese" style plenum usually takes very long, and risks distortion.

5.) Camshafts. I have been fortunate to stock new billet tool steel cores on the shelf, which can be finished to my specifications for a given application. Those are now gone. New cores have a 6-month lead time, including proper heat treatment. Finishing the profile is quicker, usually 4-6 weeks. They also have to be heat treated when finished. As I mentioned in another post, the other option is welded cams. I don't know the leadtime on those, because I don't use them.

All of the above is (obviously) after a complete disassembly, cleaning, and inspection of the base components. That, and the re-assembly is all within the builder's control. But, as you can tell, a lot of the other work is usually not. I don't know if Marc or Graham have their own in-house machine shops to prioritize their work on their schedule, but most do not. If only we did, timelines would be easier to control.

I don't commit to a firm completion date for any build for those very reasons. The old saying goes something like, "you can have it cheap, fast, or good", but not all three! Clearly some of the items above can be done in parallel, so it's not purely a sequential timeline, but a lot of it is.

This isn't meant to discourage anybody. The LT5 at 650-700 hp is an experience like few other. There are probably less than a dozen examples out there at close to 700hp. My purpose here is to articulate the best I can how involved these custom builds are, so folks can form reasonable expectations if they are thinking about going this route.

Todd