Looking closer at this engine option

[Coleman Bee]

So I'm approaching my timeline to buy engine and transmission. I have NOT ordered the car yet.

I think Im pretty set on Graziano based on conversations with Fran. (I dont want to go above 1000HP at any point during the life of the car).

My personal preference is to get a 427 in some configuration that allows me to build the car, drive it around, and get the car on the road for a couple seasons. Go to some tracks, see where I can work out any kinks, take the wife out on some dates in the city, etc.

When Im ready, a few years into driving it, I want to bump up the HP to about 800. By then I will have been researching alot more about what it takes to track the car competitively, and gotten familiar with this car's capabilities, quirks, and limitations.

My question for the group (and eventually Fran) is: is THIS engine a good choice for 10-15 years of ownership, and is THIS engine configuration a good platform to start with if my plan is to eventually supercharge it? I can spend 6 months completing the engine on a stand in the garage; I actually want to, so that I know my engine.

-Will it fit?
-Is there any issue with the standard oil pans for these SBC's not fitting/developing performance problems in the SL-C?
-Will I have to modify the rear window to accommodate a supercharger at that later date?
-Anything Im missing that would be an obvious regret later?

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[Randy V]

11:1 compression is too high to consider superchargers or turbochargers…. 9.5:1 would be the absolute max I would recommend. Also, adding any boost will increase the load on the cooling systems. Frankly, that engine Normally Aspirated will likely scare the bananas out of you in a lightweight car on the street…

 

[Coleman Bee]

11:1 compression is too high to consider superchargers or turbochargers…. 9.5:1 would be the absolute max I would recommend. Also, adding any boost will increase the load on the cooling systems. Frankly, that engine Normally Aspirated will likely scare the bananas out of you in a lightweight car on the street…

Thats probably true lol--but in the event that I did -re-dress this engine for a supercharger configuration...isnt dropping the compression ratio just one of many steps on the list to change when I perform the upgrade?

It seems like it can be addressed along with the host of other things that would be necessary to "do it right", just like the cooling systems, fuel delivery, etc., whenever I do take that step...

Am I missing something about the compression ratio? Is it hard to reduce?

 

[Jeff W]

Yeah. There's no good way to reduce compression other than increasing volume remaining at top of stroke or shortening the stroke. Head chamber, reduced compression pistons, shorten the stroke, etc. You can get really minor changes with a thicker head gasket, but that's not really a worthwhile pursuit IMO. I also have a higher compression engine (10.7) and could get away with a few PSI of boost, but it's really minimal gain for the effort needed to make the engine FI. Without taking the entire engine apart, the easiest way to lower compression would be a head swap. FI with lots of boost is really trendy right now and I can see the attraction of sort of being able to control your HP output.

I also at some point would like to fully rebuild the engine for FI, short stroke for some revs, and a cross plane crank...but I'm going to check out how the car drives and handles on the 500+hp it's already slated to have. I suggest you try the same on the 625 you're looking at for a while.

I know other members have gone with lower profile oil pans as they mounted their engines lower to bring the center of gravity down, but I'm not sure on that particular engine.

 

[Coleman Bee]

Yeah. There's no good way to reduce compression other than increasing volume remaining at top of stroke. Head chamber, reduced compression pistons, shorten the stroke, etc. You can get really minor changes with a thicker head gasket, but that's not really a worthwhile pursuit IMO. I also have a higher compression engine (10.7) and could get away with a few PSI of boost, but it's really minimal gain for the effort needed to make the engine FI. Without taking the entire engine apart, the easiest way to lower compression would be a head swap. FI with lots of boost is really trendy right now and I can see the attraction of sort of being able to control your HP output.

I also at some point would like to fully rebuild the engine for FI, short stroke for some revs, and a cross plane crank...but I'm going to check out how the car drives and handles on the 500+hp it's already slated to have. I suggest you try the same on the 625 you're looking at for a while.

Hey Jeff thanks for the feedback; yeah so I imagined the same thing: reduce ratio by changing the head/adding one of those extension plate things, or changing the stroke. I know that means perhaps a rougher running engine, and I dont want that either...but I keep thinking with the right build guide, say 10 years from now so that I have time to make it worth my while, I rebuild the engine as far as is necessary to have a properly tuned supercharged 427. If that means its no longer a "427" anymore because of the compression ratio change, I get it. But if it yields a properly running 800HP engine at the end of the day, that was my goal so I'd be good with it.

 

[Jeff W]

People here talked me out of a high HP motor for the SLC. I can see why after looking around, these aren't supposed to be quarter-milers at all, and if you drop $15k+ on a good transaxle it's a lot of money if the power makes something go bang in the back of the car. I'd definitely love to hit ~600 at the crank with some nice revs to hear it sing, though. That or get Mazzei to build me one of those crazy rotary motors. lol. Someday. Good luck with whatever you choose, It'll be fun regardless.

 

[Neil]

Hey Jeff thanks for the feedback; yeah so I imagined the same thing: reduce ratio by changing the head/adding one of those extension plate things, or changing the stroke. I know that means perhaps a rougher running engine, and I dont want that either...but I keep thinking with the right build guide, say 10 years from now so that I have time to make it worth my while, I rebuild the engine as far as is necessary to have a properly tuned supercharged 427. If that means its no longer a "427" anymore because of the compression ratio change, I get it. But if it yields a properly running 800HP engine at the end of the day, that was my goal so I'd be good with it.

Most people obsess over horsepower but you can accomplish the same thing (improve power to weight ratio) by reducing weight. This also reduces stress in the whole drive train. Changing from an iron block engine to an aluminum block & heads will save LOTS of weight.
BTW, changing the compression ratio does not change displacement.

 

[Coleman Bee]

Most people obsess over horsepower but you can accomplish the same thing (improve power to weight ratio) by reducing weight. This also reduces stress in the whole drive train. Changing from an iron block engine to an aluminum block & heads will save LOTS of weight.
BTW, changing the compression ratio does not change displacement.

I understand I think I just worded it badly. If I wanted a supercharger and the engine shop I went to for it said I need to change things in my engine to have it run smoothly and at its maximum potential, they could ask to change the stroke. Change stroke changes the displacement, which changes the compression ratio. Several other things should change as a result of that too, so Im assuming a lot of stuff has to be swapped out to make it work it's best.

One might just give up on this idea entirely and say "save for another several months and buy your engine finished, with the SC on it and your target horsepower already at its goal when it arrives at your house."

I kinda want the task of tearing down the engine at some point in the future. Maybe my son will want to help idk

 

[Roger Reid]

If you haven't ordered the car yet you're adding time to the completion date. My experience is it takes 3 to 4 months to have an engine built to your specifications. The kit can take much longer to deliver depending on parts availability and other factory workloads. Yes, you should know what motor you want to put into it but again my opinion is don't order the motor until the kit is delivered. There is a lot of work to do before the motor plays a part in the build. Who knows, GM might make available the ZR1 flat plane crank corvette motor as a crate engine.

 

[Alex]

I kinda want the task of tearing down the engine at some point in the future. Maybe my son will want to help idk

No you don't - after a few years of building, a few years of driving, a few years of fixing things that don't readily exist and then life getting in the way you'll just be happy to have the car stay together.

Build the engine you want from the getgo and be done with it.

 

[Frank Clark]

If you are looking for a boosted application (eventually), you probably don't want a 427. The large bore does not leave much cylinder wall causing various issues. Over the last few months I've put a LSX376-B15 (GM Crate Engine) in mine. Probably the same block as the Blueprint Engine above, but "only" 376cid. It already has lower compression. Makes about 430-450 HP with it's lower compression and reasonable cam. It's meant for boost (B15 = 15psi Boost). It's a bit cheaper, but does not include intake/TB/Coils/ECU/Injectors so will cost more in any finished form.

MOST guys shy away from iron blocks and if you are not getting anywhere near 1000hp most factory Aluminum blocks are fine. Will cost a bit more and save you about 100lbs.

 

[Rich Kruger]

Oh the confusion of compression ratio and super/turbocharging. The ultimate goal is how much fuel and air is in the cylinder at time of detonation. A top fuel dragster runs approx 6.5 to 1 compression ratio with ALOT of boost. Hence a relatively large combustion chamber with a heck of a lot of KABOOMABLE STUFF IN IT MAKING 10,000 HP. Run a smaller high revving engine with a reasonable (drivable) compression ratio on a variable diet (high test, E85) with a fuel system designed accordingly and a few quality, adjustable boost, well managed turbos and LIVE LIFE LARGE with a BIG SMILE.

 

[Ken Roberts]

For just a little bit more money you could find a low mileage take out LS9 engine. It uses titanium connecting rods and titanium intake valves. The piston oil squirters help with detonation. In stock trim it puts out 630hp at the crank and with a simple pulley change it jumps to 680hp. Only problem is the rear bulkhead will need to be modified.

 

[DaveC]

I wouldn't even consider an iron block in an SL-C or similar car that already has a rear weight bias. That engine is best for a car that only knows how to drive straight.

 

[Neil]

My black Mirage weighs 1950 lbs dry and has an aluminum block Donovan 383 running somewhere around 600 bhp. This is plenty, no need for boost.