AKS Racing

No response in C4 Tech / Performance, so maybe someone will respond here.

I have been doing some thinking about more stroke in an L-98 block. Looking at some of the combos that people have built, I am thinking that a 4.25 stroke crank can be put in an L-98 block. Anyone done this in a factory L-98 block? With a 0.040" overbore, that would be a 436 ci L-98. Lots have done this with aftermarket blocks, but that ruins the stealth factor.

I have the heads (18° Chevy) and intake (Bowtie converted to port fuel injection) to feed this sized motor, but am concerned about the viability in a factory type block. I'm thinking this might be a good motor for my '89. Currently 383 resides in '89 coupe.

Thoughts? I kinda like doing things that really haven't been done (or at least not a lot of times yet). Kinda like the people who say that running a 4" stroke in an L-98 WILL hit water.

Thanks,
Aaron

korvetkeith

I dunno, thats awful lot more stroke. I don't think 18* heads are much stealthier than an aftermarket block.

JAKE

I've read of some really exotic mods that ended up 454 CID using a small block. But it ain't easy and is probably outside the area of expertise of most machine shops.

Durability will be a question too because of the unfavorable rod/stroke ratio. A BB rod starts off at 6.135 and when you opt for 4.25 stroke, most go with a 6.535 rod - .400 long. Try stuffing that in a SB.

Even if you did get it in, you'd only have a BIG small block, with it's inherently inferior in-line valve cylinder head design. You'd really need a splayed valve or hemi arrangement in order to take full advantage of the cubes.

You're chances of stuffing a 4.25" stroke in a stock block are about nil. Even with new profiled rods, it ain't gonna clear. Also, even with a small base circle camshaft, you'd have a tough time getting the rods to clear the cam.

As I understand it, coolant passages run along the bottom of the bore, right in the area that has to be ground for clearance. In order to get the clearance you need, you hit water.

A Bow Tie block, however, has relocated coolant passages which allows for a greater amount of clearancing, but I suspect that 4.25 is even a stretch with a Bow Tie.

Now, I'm supposing that you're not considering an all-out banzi approach to this. I mean, maybe you could fill the lower portion of the bores with cement, relocate the camshat tunnel higher up, and do some other equally expensive and exotic mods. Afterall, we did fix the Hubel Telescope, right?

Jake

Monty

The most stroke I've ever run in a production block is 3.75", but I'd be VERY skeptical that you could run a 4.25" stroke in any production or even Bowtie block. I know you can in a GM Rocket Block/Dart Iron Eagle though. I'd be willing to bet money that you'd hit water in a production block, and probably a Bowtie too.

I understand the stealth factor, from outer appearances no one would know I have an SBC427 without rasing the hood. The car is all stock on the outside. Even looking at the motor, there's no way of knowing it's anything other than a 350/383 with some fancy parts. I run 18* heads, and unless you really know what you're looking at, most people don't know. Of course the custom Hogan's sheetmetal aluminum manifold and Jesel belt drive are obviously not stock.

Just my opinion, but if you're going to go through the effort and expense of running 18* heads, as well as the cost of a forged 4.00" plus crank, the only way they come, why short change yourself with a stock block. Even though my Dart/Rocket block is has a tall deck, raised cam, BBC cam bearings, etc, there's no way, from the outside, you can tell it's not a stock block, unless you really know what you're looking for. Even if you manage to fit a 4.00" crank in a production block, you're still going to have the weaknesses and limitation of a production block.

If you consider the inheerent benefits of one of the aftermarket blocks, plus factor in the cost of bringing a production block into shape, the aftermarket block are a good deal. The aftermarket blocks feature thicker cylinder walls, thicker decks, thicker bulkheads and main webs, plus splayed 4 bolt steel mains, raised cam location etc. You can take a Dart?Rocket block out to a 4.200" bore, and still have at least a .275"-.300" cylinder wall thickness. That's still thicker than most unbored production blocks. Also, the decks are thicker, and feature blicnd tapped bolt/stud holes, etc.

I can understand wanting to do something different. With enough effort and money, anything can be done, you just ahve to decide if it's worth it.

The one thing I will say, is that with that much of a stroke in a standard 9.030" deck block, you will have a bad rod/stroke ratio. That is the main reason I went with a taller 9.325" deck block. even with a 4.00" stroke, I am running 6.125" rods, which equals a 1.53 rod/stroke ratio. For comparison purposes, a 5.7" rod 383 has a 1.52 rod/stroke ratio. My motor has been up to 7500rpm on the dyno, and could go up to 8500+ according to the ratings of the parts I've used. It also revs very quickly. I would be concerned that with the rod length you'll end up using, and subsequently the rod/stroke ratio, that with a standard deck height block, your motor will have a limited rpm range and won't rev quite as fast. Additionally, with the resulting rod/stroke ratio, you'll end up with alot of sdie thrust loading, resulting in increased cylinder wall/ring/piston wear. I don't think any of us beleives our modified, stroker motors are going to go 100K miles like a Honda, but I would be concerned.

Just my opinion from someone who has built or helped build a few of these SBC427+ motors.

AKS Racing

Thanks for the comments guys.

As a side, I am already running a 4" stroke in a production L-98 block (no cement or block fill here). Based on the clearancing that was required, and the additional 0.125" (1/2 of the additional stroke), I am thinking that water passages may not be an issue. I currently run a lightweight forged crank (lots of heavy metal due to internal balance that I wanted; remember stealth), Oliver billet stroker rods (5.85"), and custom J&E pistons. I run this with an ATI ProCharger, and it does rev very quickly.

The main question here is: Does this seem reasonable to pursue in the late model L98 block. When I started the 408 project, I looked at one of my 18° sets of heads, and was turned off by the fact of the sheetmetal intake. I no longer hold those same reservations.

I do however still hold the same approach toward stealth combos. My motors look like factory TPI motors with bolt-ons. Remember all the work I went through to maintain the factory centerbolt valvecovers on the AFR210CPs (several posts on the forum)? That is how far I will go to look like a bolt on only project.

Thanks for the input.
Aaron

Monty

Like I said earlier, I've never put more than a 3.75" stroke in a production block, but admittedly, I am surprised that a 4.00" will fit without hitting water.

There's nothing worng with filling the block, I know of several street motors that are filled to the bottom of the freeze plugs. If your goal is to run production block with a 4.25" stroke, go for it. If you break into the jackets, just fill it, no big deal.

There are several sources of affodable cart aluminum intake manifolds for 18* heads - Dart, Edelbrock, GM and others make maifolds that will fit, but they are simgle plane style, which you could convert to EFI, but that wouldn't look stock obviously.

I spent alot of time and effort researching the options when I decide to build my SBC427. I really think the Dart/Rocket block is the way to go. The only external difference is the Dart/Bowtie logo next to the the right water pump holes. I suppose you could easily grind it off and no one would be the wiser.

JAKE

Interesting. You sig shows you're running a 350, but you say that you have a 4" stroke; give us a rundown on your combo.

Jake

gkull

4 inch is considered the max for chevy deck height. Even 4 inch requires very short piston skirts. The bigger blocks is the only real way to go. You can use your crank/rods/heads on a 4.125 bore. I would attain more cubes from a bigger bore. Or since you have an ATI just pull your motor down. thermal coat your entire chambers and run more boost on the same octane.

AKS Racing

Monty,
Am, I to understand that with the taller block, the only external difference is the casting insignia? From the top this would look like any other small block?

Components I have identified at this point:
- 18° heads Chevy ported by Rons (exceptional flow, but I think the intakes are like 245cc). Titanium valves, retainers, Jesel shafts. I have these already, with several sets in various stages.
- 18° valve covers (the discontinued Chevrolet covers with the kick out for the Jesel shafts). I have these as well.
- Matching BowTie intake. Ported by Rons as well. One has been converted to fuel injection. Square bore throttle opening. Have this already.
- SS step headers for 18° heads and C4 chassis (4" collectors). Have these already.
- complete short block (of the appropriate size)
- offset solid roller lifters (required for the heads)

Would like to have all of this internally balanced. Would like engine size to be in excess of 430ci. Compression will be in the 9.5 range, and everything will be coated for thermo reasons. The motor will run a supercharger. Combo will be mated to a ZF tranny.

Thoughts?

Jake,
As for the question of my 350ci motor with a 4" stroke, if I could just figure out how to change my siggy, it would reflect the current combo. The nice 350ci motor that ran in the very low 11s at high 120s sits on the stand in the corner. This has been replaced with the 408 L98 block with supercharger. The '87 runs good as is. I am thinking of upgrading my 383 in my '89.

Thanks for everyone's input.
Aaron

korvetkeith

A 4" stroke crank in a 400 will yeild a kickin 434 cubic inches.

Monty

Aaron,

The only external difference bewteen a production block, and a Dart/Rocket block is the casting insignia's and the outer side of the block has very slight curves where the cylinder bores are, but his is hardly noticeable. I doubt very many people could tell that the deck is .300" taller, and the pan rails are spread .400" on each side. Maybe if you had both bare engine blocks side by side on an engine stand, but not when it's a complete engine and in the car. World Products' Motown block is similar to the Dart/Rocket block except the pan rails are not spread, the cam is in the stock location, theres are no tall deck options, and there are no BBC or 50m roller cam bearing options. World claims they didn't offer the spread pan rails and rasied cam to avoid requiring th euse of expensive racing parts, but in reality that's not true. A Cloyes Tru-riller timing chan for a rasied cam block is about $95, and you can use a standard timing cover. You can get oil pans for the blocks ofr as low as $200, I saw one in the latest Summit catalog for $250. In my opinion, the additional cost is worth it. Not only does the spread pan rails mean you can run the longer stroke crank without having to noth them, but the wider pan means you keep the oil farther away from the spinning crank, reducing windage - whichs frees up a little power. The raised cam locaiton means you don't have to run a weaker small base circle cam, not that cam breakage is typically a problem, but you can also run shorter pushrods which reduces valvetrain weight, and adds rigidity. The reduction in weight, and the improved rigidity leads to improved high rpm stability, and allows you to run a little bit lighter valvespring.

18* heads are the way to go if you can afford them. Really, that's where all the power is. Don't be afraid of a 245cc intake runner either, my Dart 18* heads have CNC ported intake runners that are 254cc's. Throttle response is intantaneous, and it makes good low end torque, 425 ft lbs at 2000 rpm, and 500+ ft lbs from 3000-7000 ropm, peaking at 580ft lbs@ 5100rpm.

You can pretty much run any tall valve cover on the 18* heads. The cast aluminum GMPP valve covers that say "CHEVROLET" fit really well. Be aware though that if you run less than a 1.7 ratio rocker, you'll probably have to noth the vlave cover rail, the valve cover gasket, and maybe the pushrod slot in the head. The valecover gasket for 18* heads already come slotted to some extent, but I had to slot them a little more.

Sounds like you already have about everything you need. Be aware that the the head stud between the two center exhaust valves on each head requires a 3/8" diameter stud, rather than the typical 7/16". You also need a 3/8" washer and 12 point(they are all 12 pt) nut for each. Alot of people will say you have to remove the twwo center exhaust valve springs from each head to intall the head, but I've worked around it. What I do is prior to sliding the head over the studs, put the 3/8" washer and nut in the pocket between the two springs, then start sliding the head over the studs. When the head is about 1/2" or so above the block, the 3/8" stud whould start coming up through the head, make sure the washer went over the stud, and then start threading the nut onto the stud. Lower the head onto the block as you keep threading the 3/8" nut down. When it is seated on the dowels, just install the rest of the washers and nuts, and torque as usual, folloing the rotating sequence and incremental steps.

Sounds like you'll have a very nice motor. I guess you're going to go with a .30" over 4.155" bore then, if you want something bigger than 430, which is a 434. If you decide to go with the Dart/Rocket block, one really good thing about them is that the cylinder walls are so thick, that you could broe it out to 4.200" and still have a minimum of .300" thick cylinder walls. Even then, the walls are much thicker than most any unbored production block, and significantly thicker than a production SBC 400 - which can get as thin as .100" or less.

I've built or helped build 3 SBC 427/434's now, and each has made over 600hp. It's all in the heads. With those 18* heads you have, plus the supercharger, you should probably be well over 800hp depending on how much boost you run. All from a streetable, pump gas small block - pretty impressive!

JAKE

One more point. If stealth is really your game it's gonna be really hard to hide what you're running from a sharp eyed SB guy.

In addition to the things that Monty and KorvetKeith mentioned, the 18 degree head angle will jump right out at a SB guru. Freeze plug number and location are a giveaway too as is starter snout, oil dip stick location, etc.

BTW I think you change your sig under "My Profile"

Take care,

Jake

korvetkeith

Hey monty, do the aftermarket blocks have to 2 or 3 freezeplugs?

Monty

2 on each side, plus the two on the back of the engine block.