Sleeved Aluminum LS engine Blocks
Flag Motorsports offers in house LS and LT block sleeving, alongside optional machine work processes. Our sleeved blocks allow for bore sizes between 3.780 and 4.185. Each bore is honed specifically to each sleeve to ensure exact press fit, and all blocks undergo vibratory stress relief post-sleeve installation. We use USA made top-hat sleeves to eliminate the chance of sleeve drop. They are installed on our Centroid CNC machine into cleaned, inspected heat-cycled core blocks. These aftermarket sleeves are stronger than factory GM sleeves, more resistant to heat, and rated for 1300 horsepower in a stock block with OEM main caps.
LS7 with sleeves cut out on the Centroid fixture.
Frequently asked questions
Here are some of the frequently asked questions regarding the sleeving process. If you are unsure about any of the options or what you may need to select in our contact form above, you can reach us at our Sales phone number to discuss.
I’m not local, can I ship you my block and/or can you ship me a sleeved block?
Yes, we can help arrange shipping to us and we can ship to you. We work with a freight company that easily ships all over the country, to Hawaii, and even internationally. Please contact us for a shipping quote.
Which Gen 4 5.3 casting numbers are sleevable and why?
If you have a Gen 4 5.3 core that you would like to sleeve, check your block’s casting number. You can find this either on the back of the block near the bellhousing holes, or on the front pad near the timing cover. The two casting numbers that can be sleeved end in 048 or 1900. We can only sleeve these two casting numbers because these are the only ones with siamesed bores. Siamesed bores do not have a coolant passage between the bores, so there is aluminum all the way around for the sleeves to interface with. This is also a more stable and durable design, adding strength to the block. Gen 3 aluminum blocks cannot be resleeved.
Can Flag Motorsports help finish my engine if I buy this block?
Of course, this listing is only for the engine block but we would be happy to build your engine. We also offer a discount on sleeved blocks for clients who are building an engine with us. Please contact us to discuss an engine build.
Do I need to provide an engine block for sleeving?
This is your choice. We have blocks available that we can sell to you, you can also choose to provide a good condition block as long as it is one of the two 5.3 casting numbers mentioned above, or an LS2/LS3/LS7. In the event that you do provide an engine block, the block will be assessed before sleeving for any visible issues, and again once the sleeves are bored out. With LS7 blocks especially, we frequently see cracks behind the sleeves even on a running engine. In the event that the block is compromised, another core will be needed and there is a $300 charge for cutting out the sleeves as this takes a significant amount of time and wear/tear on our equipment. We will communicate the status of any core as we proceed through the process, and are always up front about pricing.
Can you do a single sleeve?
Yes, we can perform single sleeves or even multiple depending on position within the block and potential stress on other sleeves. Please contact us to discuss and bring your block in for inspection. Once a sleeve has been bored out, it is possible that we find damage behind the sleeve. If this happens, you will be alerted immediately so that we can determine the best course of action.
I want to boost my engine. Will a sleeved block hold up to boost?
A sleeved block is a great choice for higher horsepower boosted applications. Whether you intend to run a supercharger, turbos, or nitrous, a sleeved block will hold up better than a stock block. Please tell us if you plan to run your engine NA or boosted, as we do not recommend going over a 4.135 bore size for boosted applications.
Have any other questions for us that we didn’t cover? Contact us to learn more.