I've been thinking about this for a while. (Not like I'm going to run out and do it, or anything. )
The Gen II smallblock, aka LT1, LT4, etc, uses a 4" bore block. There is a 4.3 liter engine based upon the same architecture, that uses a 3" stroke.
Why not an LT1 or... even an LT4 based 302, utilizing that architecture?
Yeah... I know about the LS engines - especially the LS4 -, and I know about the "gotchas" associated with the LT1 Optispark, but it just seems like it might be a cool, unique thing to do. Moving the power band up in the rev range will help to save transaxles, and the high revving nature of a 302 would seem to suit the Fiero's character better. This is all based upon the premise that everything in the engine is built to support the high RPMs that would be expected.
Well, at Hi RPMs balancing the rotating assembly is king. 2oz off and you'll rev it to 8200rpm and something is goung kaboom. That 2oz at 1200rpms will grow exponentially at 8200rpms. I've built a couple of LT1s and they were monsters, but I made sure that every item complemented the other. The higher they would rev, the more money you'll spend in parts and machine shop fees because everyting has to be balanced.
431WHP and 497WTQ And that is with the trans, driveshaft and diff of an Fbody car. In a Fiero this engine would have at least another 50WHP/WTQ
Look at the dyno above, I did the heads, designed the cam according to the rotating assembly geometry. This one went from a 350 LT1 to a 377 strocker. The rod ratio changed, so I had to make the rest of the package to take advantage of the lower rod ratio. Lower rod ratio increases piston speed. The increase in piston speed draws in and air/fuel mixture faster than a higher ratio engine and from half way the exhaust stroke to half way the intake is a lot faster than a higher rod ratio engine. This means acceleration is instant. In a Fiero, this 377 strocker would break axles left and right!
... In a Fiero, this 377 strocker would break axles left and right!
I'm sure of it.
Thanks very much for your response. And yeah... all of that gearbox and axle shattering torque is precisely why I was thinking a lower torque, but high revving engine. (Where did the original 302 redline? 7K? 7200?) Again... I recognize there are much more realistic, less expensive, and more easily accomplished swaps than this. Just a bit of "off the beaten path" thinking. (The sound would have to be amazing.)
[This message has been edited by Raydar (edited 09-11-2020).]
I read an article at one time that there is a way around the opti-spark and to use the 1 coil per plug type set up. not sure which hot rodding magazine i read that in but should not be hard to find if you seriously consider the LT1. Want to say Car Craft because what I do remember was a parts list of things to grab while at a junk yard for the set up and that is something that would be on par for them.
Years ago when considering an Archie kit, was thinking a 302 SBC with modern aluminum heads would be a fun conversion. With a velocity stack sticking through the deck right behind your ears; wonderful sound I bet. Kinda where your going.
Over the years building a later model 302 using the 4.3 L99 crank and rods has been discussed. I even looked at it a couple of times. The reality is you no longer need a 3" stroke to run 7000 rpm and doing anything with a SBC platform will take a lot more work and money that starting with the LS platform. 7000 RPM and 400+ fwhp is literally a camshaft swap with the 4.8 and 5.3 LS engines... no porting, polishing or other custom work needed.
Fore example, here is my LS4 dyno. The goal was a high rpm power band using as many stock GM LS based parts w/o any custom porting or other optimizing work. Only aftermarket parts were the camshaft, pushrods, and springs, the rest of the engine wasn't even opened up and I even kept the DOD lifters! The combo had a 5000 rpm power band with 80% of peak torque available. The overall toque level was a good match with the F40 torque rating (only about 25% higher than the GM rating), but still plenty to shred the 285 rear tires at will, and put 55K miles with the combo w/o breaking anything. Yes, there was a lot of power left on the table, but the goal was to demonstrate how good the stock GM LS parts were and the power potential from a super simple setup.
I've been thinking about this for a while. (Not like I'm going to run out and do it, or anything. )
The Gen II smallblock, aka LT1, LT4, etc, uses a 4" bore block. There is a 4.3 liter engine based upon the same architecture, that uses a 3" stroke.
OK, I'm gonna be "that guy".
Why not just use a smaller engine? For example, the 4.3 or 3800 V6 would fit the bill nicely. Swap in a more lively camshaft, and you're done.
Another alternative would be a small-displacement V8, like the 4.0 version of the Northstar used in the Olds Aurora. The downside to that would be lack of aftermarket support.
Anyway, there's a pervasive myth that destroke = high RPM. Destroking an engine, in and of itself, will not necessarily increase the usable RPM range of an engine. The maximum RPM of an engine is often limited by the valvetrain. If the valves float at 6500 RPM, then no amount of destroking will change that. So if you destroke the engine and leave a stock-ish valvetrain in it, then you have the worst of both worlds: weak low-end torque, and it can't rev high enough to make decent power.
And as Rei mentioned, at high RPM engine balancing becomes critical. Plus you need to worry about things like the harmonic balancer or the flywheel ring gear flying apart. It's a whole new ball-game.
[This message has been edited by Blacktree (edited 09-14-2020).]
[B]Originally posted by Raydar:[/B Moving the power band up in the rev range will help to save transaxles, and the high revving nature of a 302 would seem to suit the Fiero's character better.
Nowadays with throttle by wire (some aftermarket ECUs can control this), you can just open the throttle less in 1st gear. Also you can open the throttle more slowly than the pedal under the driver's foot, reducing the drivetrain jolt.
A turbo engine does this naturally; the lag slows the response; it's like a way of mechanically pressing the gas pedal slowly to the floor.
None of these ideas are good for response / controllability, but they could help a transmission stay alive.
The throttle-by-wire is probably better for this; you can (with a laptop) tune how fast or slow the throttle opens, allowing you to find the response vs. transmission niceness compromise you want. With a turbo, you're kind of stuck without changing the hardware.
A lot of people just assume that big American V8s were always slow turners (Basically).....Back in the early 60s the popular racing was stock cars, so Chevrolet, Ford and Chryco all built production V8s that were based on the setups used there; These engines (Chevy 348/409, Ford 406, etc) were HP rated at 5800 to 6000 rpm!
The Ford and Chevy 302 Trans Am engines were rated at approx' 290 hp stock at 5200- but with headers and a super tune you were probably going to see over 350 hp at 6000 plus RPM.
An interesting bit of info; The new Ford Coyote engine has 4V heads (Obviously) but the 1969 BOSS 302 heads (Basically 351 Cleveland 2 valve heads ) breath BETTER on the intake side! (The exhaust is bad because of the turn required to clear the spring towers in the old Mustangs)
I've been thinking about this for a while. (Not like I'm going to run out and do it, or anything. )
The Gen II smallblock, aka LT1, LT4, etc, uses a 4" bore block. There is a 4.3 liter engine based upon the same architecture, that uses a 3" stroke.
Why not an LT1 or... even an LT4 based 302, utilizing that architecture?
Yeah... I know about the LS engines - especially the LS4 -, and I know about the "gotchas" associated with the LT1 Optispark, but it just seems like it might be a cool, unique thing to do. Moving the power band up in the rev range will help to save transaxles, and the high revving nature of a 302 would seem to suit the Fiero's character better. This is all based upon the premise that everything in the engine is built to support the high RPMs that would be expected.
Anyone?
The L99 (cast!) 3" stroke crank will fit any one-piece rear main seal Chevy block, so using the Gen II block/architecture is not necessary. If you can use the Gen I block, then you can use a 4.125 bore and have a 321" Chevy that's even more oversquare. The greater "overlap" of the main journal with the rod journal as a result of the short throw makes this crank significantly stronger than a cast 350 crank. There are 6.385 BBC rods cut for 2.100 rod journals to decrease surface speed on high RPM BBCs. Using these rods will get you a rod ratio >2:1. That assembly goes together with the same pistons as a 383 or 400 with 6" rods would use.
As was said above, de-stroke does not mean more RPM. To spin a Chevy (or any pushrod engine, really) to 8000+, you'll spend as much money on the valvetrain as you do on the rest of the rotating assembly. Modern aftermarket cylinder heads flow well enough to make absurd power... 500-600 naturally aspirated in a street engine is possible. Think about how fast you'd have to turn a small engine to take advantage of that airflow... you quickly get to a point at which a larger displacement engine makes much better $$$/horsepower sense.
The LS engine family can build a similar engine in by using the 6.0 or 6.2 block & pistons with crank and rods from a 4.8. The 4.8 has an 83mm stroke. GM never built a LS with 3" (76mm) stroke, so an LS crank with that stroke would be a custom piece. I may have seen one on the market at some point.
Just for giggles, as I have been watching this thread.
The LS4 crankshaft is a little different on each end, as I understand. So, does someone make destroked, or 4.8 cranks, that will drop in an LS4 block. (forged crank for 5-600 horsepower engines ) I ask as the point of using an LS4 block is a F40 trans axle fits it directly. Also, what about Darton sleeves in an LS4 block. Any reason why not? Yes, cost would be high. But I would like to know if it can be/has been/ done. A destroked engine would move the power band higher, all things the same. But that would be not such a big deal in a FIero. Maybe a little easier on the F40, unless you jump in that power band range right off. A takeoff with less torque and horsepower would not be a hindrance moving a light Fiero,right?
Or just put a regular LS block in it and make a combination bore and stroke?
If you can find one. But I had always had liked the Buick small block. The engines that the Buick 3.8 was based off of. I have taken water pumps for the 3.8 and installed them on Buick small blocks. That I could tell. The timing cover and a lot of the internals were interchangable between the 300V8 and 225V6. I had a stock 1964 Buick 300(310) V8 in a Chevy LUV truck. It would take RPMs over 8000 without issue. The Brits love the 215 aluminum V8. There are a few different versions. The Buick 215 had issues with head gaskets. The Olds version had 5 head bolts per cylinder as Buick had 4. The Olds design, went on to become the V8 that Land Rover used for almost 3 decades. Their later ones had bad cast. It used the round bell housing style that GM used up to 1963. However there was the aluminum 215 2bbl, 4bbl, round bell housing, BOP bell housing, 4 head bolt, 5 head bolt. 300 came a few different ways 2bbl, 4bbl, up to 1963 round bell housing, 1964 and later BOP bell housing. All cast iron or cast iron block with aluminum heads. Then there was 1965-1967 340. That I know of it only came in the GS(grand sport). These were used in Buick Special, Century, GS. Olds Cutlass, F85. The 300 was also used in GMC trucks. Saw a few in school buses. 2 known issues. Hard on valve guides(but you would reman them anyway). Also the oil pumps were very dependable but did bring up pressure slower then submerged pumps. Free reving with no load, spinning them up cold. could damage bearings. However this is still applied to the 3800 even after getting a gearrotor in the timing cover. Other than that they would take punishment. Just on the 300 I had. I had the Special that the engine was in. Bought from someone for $50 in 1980. The guy said that the engine had been gone through about 80,000 miles before they let it sit since about 1974. It had mud about 1/2 full in the starter. Cleaned every thing up and fired it up. Then the Flinstone floors(see through) were too bad to drive it anymore. Mom had a LUV truck setting in the drive way. This was after 2 of my brothers tried to use it to tow a 1965 Barracuda and fried the engine. So the 300 went in. Drove it well over another 100,000 like that. I was brutal on that engine. It just seems that, that would be a sweet engine for a Fiero.
Heh... Interesting how this has evolved. Lots of good advice and good info here. And yeah. I get it. High revs require expensive valve train bits, among other things. This was merely a "what if" proposition.
Since were talking about expensive, impractical stuff... I'll mention that, a few years ago, I saw a non-GM SBC race block that was designed to fit LS heads. I posted it in another thread here, but I'm pretty sure it's no longer available. If, indeed, they ever sold even one.
Just as an aside, I'd like to do something similar with an LS based engine. For example, mod a 5.3 to turn 9k RPM. They can already handle 7k RPM stock, which should make things a bit easier. Maybe one of these days...
Just as an aside, I'd like to do something similar with an LS based engine. For example, mod a 5.3 to turn 9k RPM. They can already handle 7k RPM stock, which should make things a bit easier. Maybe one of these days...
Now that's something way more practical that what I was thinking. And it's not even based on the state-of-the-stone-age art.
One thing to keep in mind is that with the valvespring requirements to turn that RPM, you'll basically need aftermarket cylinder heads, as the loads stand a real chance of breaking a rocker boss off a production head...
The limits of your RPMs are not that related to the displacement or stroke or rod length, its more related to your heads/valves. Just because you have a 5.7 over a 5.0 does not mean there are any issues with spinning it at 7500rpms.... My stock LS2 is a 6.0 and shifts at 7200 commonly with plenty of valve float over 6500, lol.
Just thought I would weigh in here, because I had a similar idea with my last 3rd gen Trans Am. If you can find an L99, and by L99 I mean the LT1 based 265ci engine, you can pull the crank and rods from it and drop it right into an L98 block. Upside to the L98 block is HEI instead of that dang optispark. Should make quite the screamer, and from the the research I did, the PM rods used in the L99 should hold up no issue to the RPMs you could reasonably turn. Could always have a custom forged crank and rods built for the combo, but break out your wallet!
The limits of your RPMs are not that related to the displacement or stroke or rod length, its more related to your heads/valves. Just because you have a 5.7 over a 5.0 does not mean there are any issues with spinning it at 7500rpms.... My stock LS2 is a 6.0 and shifts at 7200 commonly with plenty of valve float over 6500, lol.
The cam/head combo ( with a valvetrain that can move that quickly)from your LS2 on a 5.3L, or 4.8L (if it where to fit) would produce its power peak at a higher RPM due to the different displacements.
Originally posted by FieroWannaBe: The cam/head combo ( with a valvetrain that can move that quickly)from your LS2 on a 5.3L, or 4.8L (if it where to fit) would produce its power peak at a higher RPM due to the different displacements.
And if the engine could rev to that RPM, it would scream! That's a big IF, though.
I know inquiring minds wanted to know, so I checked with Darton.
The LS4 block can go to 4.000-4.155 bore with the wet sleeve install. Then with the combinations of crankshaft strokes factory and aftermarket, and a good valve train,there is much fun to be had. However, the wet sleeve install runs $2500.00 alone. Still should be less than buying a LS3 block and adapter kit. What is it they always say? Speed costs money.
But, it can be done.
[This message has been edited by gatorfrey (edited 09-17-2020).]
Originally posted by gatorfrey: I know inquiring minds wanted to know, so I checked with Darton.
The LS4 block can go to 4.000-4.155 bore with the wet sleeve install. Then with the combinations of crankshaft strokes factory and aftermarket, and a good valve train,there is much fun to be had. However, the wet sleeve install runs $2500.00 alone. Still should be less than buying a LS3 block and adapter kit. What is it they always say? Speed costs money.
But, it can be done.
It has been done. There is a place in Ohio that makes LS4/F40 conversions for the Rossion. They sleeve all their blocks and do some additional custom machining on the engine and transmission to help them fit the engine bay that is narrower than the Fiero.
I know inquiring minds wanted to know, so I checked with Darton.
The LS4 block can go to 4.000-4.155 bore with the wet sleeve install. Then with the combinations of crankshaft strokes factory and aftermarket, and a good valve train,there is much fun to be had. However, the wet sleeve install runs $2500.00 alone. Still should be less than buying a LS3 block and adapter kit. What is it they always say? Speed costs money.
But, it can be done.
People were sleeving LS1's to make 427's for quite while before the LS7 and Gen IV engines came out.
Originally posted by gatorfrey: However, the wet sleeve install runs $2500.00 alone. Still should be less than buying a LS3 block and adapter kit. What is it they always say? Speed costs money.
Ouch. I paid $288 including core charge pulling my last used LS4 with all accessories and harness. But the Sun beat me to death doing it too.
)
