I am writing a new "Tech Tips" section for the shop's Web site at www.kennedysdynotune.com and thought I'd post some excerpts here for your reading enjoyment. It is only excerpts (as the whole thing is a bit long) and a draft. So, if you want to see the final version look on the site in a few days.

Intro:
Two aspects of engine building that relate to nitrous use will be discussed. Those that allow the motor to survive under nitrous boost and those that enhance performance. General principles are discussed as definitive answers to such FAQ's as "will my motor survive with an xxx shot of nitrous" are surprisingly hard to answer. There are just too many variables involved to provide general answers to such questions.

Engine Block:
Factory blocks vary all over the map in terms of their basic strength. Different materials are used and designs vary from wimpy to beefy. And for certain motors, the aftermarket provides numerous alternative designs with the same basic architecture. The main areas to concentrate on are the strength of the cylinder walls and the design and materials used in the main bearing support areas; the caps and webs.

To illustrate these points, let's look a little bit more closely at the venerable small block Chevy, the big block Chevy, and the new Gen III small block.

The original SBC is not a strong design. Priorities of the design were light weight and low cost. The SBC was not designed as a race or even a high performance motor. Designed over 50 years ago the designers lacked the advanatges of modern CAD systems. And in addition, much has been learned since then about metallurgy and production techniques. Fortunately, by staying in production for more than 50 years and becoming the darling of the performance community, GM made many changes and the aftermarket became heavily involved. In fact, the performance aftermarket was in a sense created to address the deficiencies of the small block Chevy design!

The two areas of most concern, the cylinder walls and the main bearing support, are two that are compromised by the low weight/low cost design priorities for the SBC. Cylinder walls are thin to save weight (and to promote heat transfer). Nitrous use drastically increases peak cylinder pressures. This can lead to bore distortion with blow-by and loss of power. If the cylinder walls are even thinner due to boring and production tolerances and if a large nitrous shot is used, cylinder walls may split, which for practical purposes destroys the block. When building a nitrous SBC, this leads to a rule that really applies in priciple to all nitrous motors: overbore as little as possible to preserve cylinder wall thickness.

The newer castings (since ~1987) have even thinner cylinders than older motors. If building up a newer block, do not go beyond an 0.030" overbore and it is much preferred to stick with the smallest overbore possible. The huge variety of SBC parts makes it practical to obtain pistons and rings in overbores as small as 0.005", though 0.010" is the most common small overbore size. Older blocks may be ok with larger overbores of up to 0.060".

Cylinder block fill should be considered if a large overbore must be used or very heavy nitrous use is contemplated. A complete fill makes the block unsuited to anything other than drag strip use. But a 1/2 fill or less provides some added support for the cylinders and can be used on the street. A partially filled block will run hot though. Overheating may occur and an upgraded cooling system using parts such as an electric water pump, high capacity radiator, and a better fan may be needed. Agents that promote heat transfer such as "Water Wetter" are also helpful.

Before starting any expensive block modification, the block should be checked by a competent machine shop for cracks and casting defects such as core shift. Ultimately, if extra displacement is wanted, it should be attained by installing a stroker crank and not by excessive use of the boring bar.

Besdies keeping the cylinders as thick as possible, the main cap area also needs attention in the building of a nitrous engine......


More to follow, if people want to see it. So please give me some feedback. I am writing it anywway but don't want to waste bandwidth if no one cares.

Rich Krause

BTW: I am not trying to sell anything. The shop I referred to in the beginning of the post is a high-end tuner shop catering to a different (local and regional) crowd than generally hangs out here. In any case, I don't own it or work there, just help out when I can. But I will ask the other mods if they think this is advertising and will delete it or modify it as needed.

 

need more input....more input!!!!

/johnny five voice

 

Good start

 

keep it coming, thats what the forums are here for!

 

EXCELLENT!! Would like to see some more info.

 

 

Great reading, Rich. Thanks.

Thinner cylinder *walls* I presume...

Dave

 

Yes.

More to follow.

Rich

 

WOW, great job Rich. Keep it coming

 

Looks good, and I'm looking forward to the information about the rotating assembly and associated parts for nitrous use.

 

Here's more. We ended our last installment with:

Besides keeping the cylinders as thick as possible, the main cap area also needs attention in the building of a nitrous engine. Stock SBC with 2-bolt caps are adequate for basically stock motors with small amounts of nitrous (in the 100-150hp range). As noted above, block filler will help here also, keeping in mind the potential for overheating that relates to using fill. Block filler will stabilize the crankcase webs and help prevent main cap "movement" under load. The term "movement" refers to a consequence of block flexing and if excessive this will quickly destroy the main bearings and then the crank. Highly modified small blocks will need 4-bolt main bearing caps. The stock iron 4-bolt main caps are a significant upgrade compared to stock 2-bolt caps. They are all that will be needed for typical street or street/strip use. Very highly stressed engines (250+hp nitrous) will need 4-bolt steel caps. Caps with splayed outer bolts offer only a small advantage on stock blocks. Aftermarket blocks, with reinforced webs, will benefit most from the 4-bolt splayed outer bolt steel caps.

The deficiencies of the stock SBC block have been addressed by both GM and the aftermarket. An analogous situation exists with respect to the SB Ford. For both, the factory and the aftermarket produce a variety of heavy duty "race" blocks. These typically are made of stronger alloys, offer thicker cylinder walls, strengthened crankcase webs, upgraded main caps, and thicker deck surfaces. All are quite advantageous when a max-effort motor is being built. In addition to accomodating larger bores, these blocks are often designed to also allow use of longer stroke cranks than their OEM counterparts. The primary downside is cost. Typically, from $1,500 and up depending upon the model chosen. However, these blocks are stronger than even a maximally prepped OEM case. And compared to the cost of fully prepping a production block, the total cost may actually be less if a factory machined race block is selected. Having a stock block fully "blueprinted" is not cheap by any means and no amount of machine work can compensate for the basic deficiencies of the OEM design.

The "new generation" of small block motors are the future of the domestic performance market. Both the gen III Chevy and the Ford "modular" motor offer significant advances over their traditional predecessors. While most of the advancement has been in the cylinder head area, the "bottom end" and cylinder blocks of these motors also have been improved. These stronger blocks have increased potential for handling high power without resorting to extensive modifications compared to the earliet models.

Besides the ubiquitous SBC and SBF, there are a huge number of other engines that may be modified by the enthusiast. Each has it's own strengths and weaknesses. Especially in the import market, many seemingly similar car models will have different cylinder blocks, depending on the exact model and year of production. The number of possibilities is so large that it is not possible to generalize in an article of this length. Small domestics also cover a wide range. We suggest you consult us further if you need information about a specific model. The same applies to "exotic" motors such as the Viper and "Triton" V-10's and European models.

Before leaving the subject of cylinder blocks, domestic big blocks deserve a few words. These motors are not currently used as original equipment in cars though they may still be found in light trucks. The big block Chevy in particular is a much stronger piece than its' small block counterpart. The stock BBC can withstand nitrous boost in the 300+hp range with no difficulties due to thick cylinder walls, larger main bearings with thick crankcase webs and strong 4-bolt main caps. As with the small block, both GM and the aftermarket offer "race" versions that are immensely strong though also very expensive. It would be very unusual for any street or street/strip big block setup to require a replacement block. But if you want to experiment with huge amounts of nitrous boost (500hp range) they will be necessary.

Next installment: crankshafts and pistons.

Rich Krause

 

So...which is the best catback?

Looking forward to the complete article.

Side note: I am coming up to NY in a couple weeks (26-30th). Hopefully, I'll finally get to meet you, Rich. I am staying with J Short.

Ryan

 

Excellent! I haven't seen J since the fall, people tend to hibernate in the winter up. My car should be ready by then, with any luck.

Rich

 

Oh man...a ride in your car would be too much . Lunch for a ride in your car sound fair?

Ryan

 

keep the articles coming!!! really appreciate it , good reading!

Charles