By Doug Kaufman
Editor, ENGINE BUILDER
Typically the questions with a stroker are, ‘How big can you make it?’; ‘How big do you want it?’; and ‘How are you going to swing all that mass in there?’” explains John Nijssen, aka Stroker John.
Nijssen, the Apple Valley, CA-based engine builder, operates strokerengine.com and builds domestic V8 engines for the U.S. and international (primarily Australian) enthusiast markets.
He says he doesn’t try to push his desire onto the customer. “I don’t sell you what I like, but rather you and I figure out what you really need for power and price,” Nijssen says.
“Customers (I prefer to call them clients” enjoy discussing their engine build. I ask them what they want the new motor to do for them. From there I can make recommendations and ask for their approval,” he says.
Nijssen considers himself a custom engine builder, rather than a builder of crate motors. "I try to build the best possible combinations within the limits of the client’s budget."
“The main purpose of a stroker engine is to make more power. My company motto is ‘Bigger engines make more power.’ What does that really mean? When I talk about power, I’m typically talking about torque.
“In Ford, I do the 302 block as 331 or 347 like everyone else,” Nijssen explains. “With a Windsor, the 408 and 418 work very well. If you want more torque this block will go 427 and 434. If we step up and use a Dart block, 467 is about the limit. I made 711 hp at 6400 rpm with a Yates Wedge cut head on a 463 Clevor. The 460 block works well as a 545, and with the Kaase P51 heads makes an effortless 600 horsepower.”
Nijssen says, “I do not ‘sell engines’ I build engines. Mostly, they’re street/strip combinations, both lower cost ‘budget’ motors and maximum monster power makers.” His shop is a small operation specializing powerful street V8 engines to meet specific needs, either massive low speed torque or upper rpm horsepower.
“If you increase the cubic inch displacement of the engine it should make more power. Obviously a 460 engine will have a lot more pulling power at 2,500 rpm than a 302 will common sense tells you that and it happens in the real world.”
Nijssen says you can typically estimate the torque that an engine will put out based on a very simple formula: stock heads will typically make 1 foot pound of torque per cubic inch, so a 302 is usually capable of putting out about 300 lb.ft.
If you get a set of performance heads and raise the compression ratio, you’ll typically make about 1.25 to 1.3 lb.ft. of torque per cubic inch. So a 302 at the smaller number equals about 377 foot pounds of torque over the stock heads (Editor’s note: see Larry Carley’s article on cylinder heads in this issue for more information.)
Another way of increasing torque is to raise the compression ratio, explains Nijssen. “There are limits on what you can do with the compression ratio, however, before you run into detonation. Detonation is connected to fuel and is keyed to the octane rating.” We know from experience that the maximum compression ratio we can run based on the fuel the customer plans to run is a set number that number is a variance based on the engine build.”
Nijssen says each full compression ratio increase is worth power. “That is to say, going from 9:1 to 10:1 or from 10:1 to 11:1 is worth four percent more power each time, pretty much across the rpm range. For example, if we have an engine making 500 hp at 10:1, and we raise the compression ratio to 11, we would gain four percent more power or 20 hp.
"That’s not a tremendous gain, so if we raise it to 11:1 and it starts detonating, not only would you not make the extra 20, you would lose some of the 500 you had because detonation is not burning the fuel causing expansion and power, but exploding it causing shock and damage. So, we tend to build motors conservatively, keeping them in the safe zone, perhaps 10.7:1, leaving that .3 as a safety margin and the power loss is like 1.2%, not enough to worry about.”
The choice, explains Nijssen, becomes, how much cubic inch increase do you want and how much can you fit in the block? When you increase cubic inch capacity of the engine you’ll make more torque. It doesn’t matter if you’re doing that by increasing the bore or the stroke.
There is a direct relationship between torque and CID (cubic inch displacement) as long as the CID comes up the same; the torque output increase will be the same. If you’re making 1 foot pound of torque per cubic inch and you multiply it by 350 it doesn’t matter if it has a 4-inch bore and a 3.5-inch crank or a 3-inch crank and a 4.3-inch bore.
However the power curve between the two combinations look different. The shorter stoker larger bore motor will produce less torque at lower RPM and peak at a higher RPM than the long stroke combination. This is why in part diesel motor utilizes very long stroker, more torque or pulling power at low speed. Nijssen acknowledges that if the discussion has been centered on the same cid engine, “You might say ‘I want the bigger bore combination,’” he says. “Great…so you go out and buy an aftermarket block.
“Now we can take a 351 W from a 4.030˝ optimal bore size to 4.155˝ (a .030˝ over) or some blocks you could push it out to 4.200˝. So instead of a small bore with a plus 1/2˝ stroked 408 ‘stump puller’ you can build a 1/8˝ stroked 402 ‘screamer.’”
But once you have a nice big bore block what happens if you put the big crank in there as well? “Well then you can go from a 434, which is the biggest crank you could put in there to a 471 cid motor,” he says.
“For the street, because most of the time you’re driving around in the 2,000-4,000 rpm range, having the big stroke crank will pay off more often. On an oval track, having a shorter stroke will have the advantage because you’re not only dealing so much with torque production and acceleration you’re dealing with miles per hour and the issues involved with that.”
For drag racing Nijssen says there’s a balance between the longest possible stroke and something a little less.
“Choosing the stroke has a lot to do with the maximum rpm requirement of the engine. For example, in the Ford family on a Windsor block, I might encourage the use of a 4.000˝ stroke crankshaft to turn to 7,000 rpm, whereas on the street, I might want to suggest a 4.100˝ stroke crank to turn to, say, 6,500 or I might even suggest a 4.250˝ stroke if we’re only going to 6,000 rpm because of the frictional loss concerns.
“However, while a longer stroke crankshaft tends to make more torque early on in the rpm range, and about the same amount of torque at peak horsepower,” Nijssen continues. “But what happens is, the longer stroke crank pulls the piston down the cylinder a longer distance. You’re dragging the rings further, so friction becomes an increasing problem as rpm increases because it’s putting the brakes on and it’s absorbing more energy. As the rpm goes up it’s robbing more and more power they call it friction horsepower like anti-horsepower.”
Nijssen says that since the piston has to travel a greater distance in the same half a revolution, then accelerate from a dead stop, then stop it and start it again it requires more energy usage, so it loses power again.
“A longer stroke crank won’t make the same amount of torque at the higher rpm so it won’t multiply out into horsepower, he says. “The bigger bore, shorter stroke motor will typically make more horsepower and if max rpm is a concern it will have an advantage. But for sheer acceleration off the line and 60 foot times it’s hard to beat the long stroke small bore because it will just push you back in the seat harder as it accelerates from 2,000 rpm up. But once you pull it out of gear at 6,000 and put it in 2nd gear it drops down to 5,000 rpm and it’s now operating at a higher rpm range and will do so through all the gears until you lift your foot. So a bigger bore short stroke motor will have an advantage.”
Nijssen says another point to consider on the particularly long stroke motors is the feet per second travel of the piston.
“There are limits to how fast a piston should be accelerated and decelerated,” he cautions. “There are structural limitations of all the internal components.”
You can typically buy a 2618 forged piston that can handle a lot of abuse. Pistons seldom fail; they’re usually destroyed by something else going wrong. So if you were to rev the engine particularly high you would want to use a better quality crankshaft, typically American made, than say a cheaper crankshaft.”
When it comes to comparing a Ford stroker to a Chevrolet stroker for the street, there are other issues involved. For example, the angle of the valves plays an important role. The small block Chevy has a valve angle of 23 degrees; the small block Ford has a valve angle of 21 degrees. When you have less valve angle the turn from the port into the valve pocket isn’t as severe. Nijssen says this is an important point.
“Aftermarket modified racing heads often have valve angles of 14 degrees and 11 degrees when you look at the cylinder head itself the intake port is standing up more toward the vertical making the heads very tall, and the exhaust side becomes very long, in comparison. So, the Ford heads have a slight advantage over the Chevy heads due to the valve angle, he says.
“In the case of a Cleveland cylinder head, because the valve is canted on a second angle, there are other benefits as well. The incoming air stream doesn’t just flow straight in, arriving 90 degrees over the top of the piston you’re tipping it a little more toward the center of the cylinder, which helps the air swirl around in the cylinder as it comes in. Like water going down the drain, it swirls around going into the cylinder, which is good for keeping the air and the fuel thoroughly mixed up. Homogenization is maintained so you don’t get rich and lean pockets throughout the air-fuel charge,” he says.
Typically, says Nijssen, you can put a pretty big crank in a small block and rev it to 7,000 rpm. “But when we get into the big blocks and we start putting in 4.500˝ or 4.750˝ strokes, that rpm limit starts coming down to 6,500 to 6,000 rpm. If you’re using an iron crankshaft, 6,000 rpm would be the limit. So when choosing a stroke length, you have to pay attention to rpm and that may be a limitation.”
Another consideration is rod angle: often referred to as rod to stroke ratio, he explains. When the crankshaft is rotated 45 degrees and the piston is halfway down the cylinder traveling at maximum speed just before it begins to decelerate as it nears the bottom, the rod tips over on an angle. As you increase the stroke length the rod angle is increased. So it’s desirable to increase the rod length to take some of that angle out of the rod, because it is transferred to side load or thrust against the piston.
“It’s pushing the piston harder and harder against the cylinder wall as the stroke is increased. Once again, that’s friction and wear. So we want to increase the rod length when we increase the stroke length,” Nijssen says. “The limitation of that becomes the block deck height. Basically it all has to fit in the block.
“Custom pistons provide the solution to many combinations and we want to use the longest rod length we can. We have some discretion with the piston compression height. The question is whether there is enough material on the piston to fit the rings in and allow the valve pockets to be strong enough?” he says.
“We’re limited by two factors when it comes to piston compression heights: we have to fit all three rings between the wrist pin and the top of the piston and have enough thickness between them for the ring lands to be strong enough to support them all. We can raise the wrist pin up into the oil ring groove almost to the top of the oil ring groove. We can compensate for the cut by putting in a steel rail that covers the wrist pin area that was cut out. The steel spacer ring helps support the area that was cut out.”
Nijssen suggests that when there are concerns about negative side effects or effectiveness of a working component it simply comes down to a debate over which is more important: making more power or endurance?
“The other consideration with pistons is valve pocket depth. This is not usually a concern with a Windsor but if you have a Cleveland, which tips the valve over on an angle, now the valve pocket is extended over into the side of the piston where the top ring is. So you have to have enough material in the top of the piston to put the valve pocket in place without touching the top ring,” he says.
“Typically you could perhaps get a Windsor piston with a shorter compression height than a Cleveland piston. Custom pistons allow you to minimize the piston squish height, allowing the piston to reach the top of the cylinder bore.” says Nijssen.
“Typically when we’re building street engines we’re going for the big power increases. We’re not chasing 3 horsepower, that’s for racing applications where everything is on the line,” he says.
From a stroking point of view one of the most significant differences in deciding to build a Ford over Chevy comes to block construction. “A Ford 302 can’t be as large as a small block Chevy (SBC) stroker but a Windsor motor can be substantially larger than a SBC stroker. The Windsor is a taller block, so you can put a longer stroke crankshaft in it,” explains Nijssen.
“Typically, a factory Chevy can be stroked to a 383. You can take them to 396 and 408 although you’ll be pouring block fill in the bottom of the block so you can grind clearances into the bottom of the block into the water jacket and not have water pouring out. This isn’t as big a problem for Ford because of the way the blocks are cast you can cut a fairly substantial groove in the bottom of the cylinder and still not be near the water jacket,” he says.
In addition, the Windsor block has a higher camshaft height than the comparable Chevrolet. “When you’re building a Chevy you first have to consider adding the extra clearance for the rod when it comes around (otherwise, when the rod comes around, the nut will collide with the bottom of the cylinder; then you have to grind the corner off the other end of the bolt on the other side so it won’t collide with the camshaft. You hear about small base circle camshafts this provides more clearance for the rod on the cam lobe rather than on the connecting rod.”
Nijssen suggests that when using a connecting rod with a cap screw bolt on it, you have more clearance room for the camshaft and you’re not compromising the bolt by grinding part of it away. “On a Ford this is almost no problem at all because the camshaft is so high up that you won’t get interference even with a very long stroke you can put in a Ford block.”
Limitations to a stroker include striking the oil pan. You can’t go out through the oil pan rail, but Nijssen says sometimes he can cut into the oil pan rail as long as there’s not a bolt there. In addition, aftermarket oil pan makers often form additional clearance into the side of the oil pan.
He cautions, however, that you need to be careful about how far you’ll pull the piston down the bottom of the cylinder. If your connecting rod is too short, even if it doesn’t hit the counterweight, you may find you’re pulling the piston out the bottom of the cylinder further than you want to. And the piston may rock and as it comes back into the cylinder and it can scrape the piston skirt and thereby damage it.
An example is with Clevelands. A 4.000˝ stroke 6.000˝ rod does not clear the counterweight on all brands of crankshafts. Often the part number reflects the rod length. …4006200.. indicates a 6.200˝ long rod. Using a 6.000˝ will not work.
When choosing cranks, particularly longer stroke cranks, you run into the balancing issue. Ford typically has external balanced cranks in all of its motors, Nijssen explains. “When you go to an aftermarket crank and increase the stroke, it makes the crankshaft inherently heavier on the connecting rod side of the crank since you have more metal going out in that direction. Therefore as the stroke increases you start to find the weight of the counterweight is inadequate.
According to Nijssen, with an aftermarket crankshaft you might want to have it internally balanced even though the factory crankshaft was externally balanced. “You decide whether you’ll want to take advantage of that or just go ahead and use the factory harmonic balancer and flexplate and drill the counterweight like Swiss cheese,” he says.
“As you increase the cubic inch displacement,” he says, “not only do you want to increase the rod length, you want to change the camshaft duration. Because the engine is larger it needs a bigger gulp of air to produce power at the same rpm than a standard stroke engine. And a bigger engine wants bigger ports to feed it, so once again, if you use the same head as on the stock engine, you’ll want to increase the camshaft duration. If you can put a larger cylinder head you might be able to keep the same duration.”
“I started out in this field as an apprentice automotive machinist in New Zealand in 1977. I graduated first in my class 1980 and moved to the U.S. in 1982,” Nijssen explains. “I worked in various machine shops for many years until 2001 when I decided to start building custom high performance engines for those who where looking for something more than the typical crate engine combination.”
Nijssen suggests that stroker engine builders caution their customers that replacing an engine with a more powerful stroker engine may require increasing the strength of related components, such as the transmission, U-joints, driveshaft, differential and axles. It may also be a good idea to improve the brakes, and if you add enough extra power, you may need to stiffen the chassis frame rails.
In addition, traction may become a problem. Slicks increase stress, where as smoking street tires ease this load on the drive train.
“Long duration camshafts may require a higher stall torque converter, and high compression ratios will require racing gas or octane boasters. Be sure you plan your engine combination carefully,” he says.
“High compression ratios, long duration camshafts high speed torque converters work well when racing, but can just waste gas, and be a pain to drive in stop and go commuting to work traffic,” he says. “Sometimes, the best thing is to explain to a customer that a modestly powerful engine may be all he needs.”
Today’s cars and trucks use electronic fuel injection (EFI) which require ECU reprogramming, and States with smog regulations limit engine modification, but these are subjects of another discussion.
Finally Nijssen suggests you do your math, consider the application and enjoy building more power.
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