Engine & Exhaust / Tech / Tech Articles

Blower Basics (Part 3): Recommended Upgrades, Mods & Tuning

Supercharger Intro

Image/Summit Racing

In Blower Basics (Part 1), we debunked the myth that a supercharger is an exotic upgrade. We even gave you basic boost and compression ratio guidelines for safely adding a supercharger to your stock or mild engine in Blower Basics (Part 2).

But what if you want to take your engine beyond stock or mild?

If you want to take your boost and/or engine rpm past Weiand’s recommended threshold for stock engines, you’ll need to make some modifications to your induction, ignition, and engine. The extent of these modifications will depend entirely on how the engine is to be used. Let’s first review Weiand’s recommendations for stock engines to see if upgrades will be necessary:

Supercharger Guidelines for Stock Engines

  1. 7.0:1 to 9.0:1 static compression ratio, with an effective compression ratio below 12.0:1 (review Boost Basics Part 2 to learn more about effective compression ratio): The optimum static compression ratio is 8.0:1.
  2. 3-5 psi boost level: This range of boost has proven to be the best compromise for power and reliability for engines using cast pistons, cast crank, and small cam, according to Weiand.
  3. Engine rpm: When using stock cast pistons, the engine should be limited to a maximum of 4,500-5,000 rpm. Exceeding this limit may over-stress the cast pistons causing failure. Blueprinting an engine using the proper components will allow higher rpm reliability and will maximize a supercharged engine’s potential.
  4. Detonation (pinging): Detonation is the single most destructive force in a supercharged engine and steps must be taken to eliminate it. This may include lowering boost level, retarding timing, installing a boost timing master, increasing fuel flow to prevent leanout, and/or using a fuel additive to raise octane level. The cooling system also needs to be in good condition to prevent overheating, which may lead to detonation.

If you’re going beyond the guidelines above, you’ll to start making some modifications.

Guidelines for Higher-Boost Applications

To run boost levels from 6 to 10 pounds, Weiand recommends the following:

For maximum boost and horsepower applications (12 pounds or more), Weiand recommends the following engine specifications:

  • High-quality forged or billet double keyed crankshaft
  • Four-bolt main caps with quality bolts or studs
  • Steel double keyed harmonic balancer or crank hub
  • High-quality steel connecting rods (H- or I-beam)
  • Forged blower pistons and stainless steel piston rings
  • O-ringing the block (mandatory)
  • Severe duty stainless steel valves or iconel
  • Fully ported and polished heads
  • Solid or roller camshaft designed for high boost
  • Roller rocker arms
  • Chromoly push rods
  • High-output ignition management system or magneto
  • Blueprinted carburetors or fuel injection
  • High octane race fuel (112+ rating)
  • Minimum of a 3-incn diameter dual exhaust with free flowing street/race mufflers and large tube headers
  • Maximum effective compression ratio on gas not to exceed 24:1

Cylinder Head and Valvetrain Preparation

HeadsWeak valve springs or burned valves can lead to backfires. When an engine has more than 50,000 miles on it, it’s a good idea to inspect the entire valvetrain. If the valve springs require replacement, factory heavy-duty springs should be used.

For higher boost applications, consider a three-angle, “street-type” valve grind to promote better cooling. With the additional combustion temperatures normally generated in a supercharged engine, the wider valve seats will provide better cooling of the valves, and the three-angle valve grind will provide better sealing of the valves.

When any port work is being done to your cylinder heads, most of the effort should be directed to the exhaust ports. The supercharger will overcome most minor restrictions on the intake side of the cylinder head. The use of O-ring head gaskets requires receiver grooves in the heads and block milled by a competent machine shop.

CarbCarburetor and Induction Considerations

At full throttle a blown engine can require 50 percent more air than an unblown engine and as a result needs a larger carburetor(s) in order to make maximum power and boost. If your blown engine is primarily driven on the street at moderate engine speeds (under 4,000 rpm) you won’t need a larger carburetor(s).

Typically the carburetors(s) will need to be enriched by 5 to 10 percent on the primaries and 10 to 20 percent on the secondaries. The idle mixture screws may need to be enriched by one or two turns. In either case, the carburetors need to be jetted properly to prevent a lean condition. A lean condition can lead to overheating and detonation.

For initial start-up, it’s better to have a slightly rich condition to help prevent the engine from overheating. After initial start-up, check the spark plugs for proper reading (color) and adjust the carburetor(s) accordingly. You want to see a medium to dark tan color.

If you’re installing a supercharger on a fuel-injected application, you may need to upgrade to larger fuel injectors and fuel rails to deliver the added fuel you may need based on BSFC (brake-specific fuel consumption). Contact your supercharger manufacturer to calculate your fuel needs or see our fuel injector post to learn more about BSFC. You should also make sure you have a good-flowing air cleaner and exhaust system to allow your supercharged engine to breath easily.

CamsCamshaft Selection

A supercharger can overcome inadequacies in a stock cam up to about 4,500-5,000 rpm. You will typically find that performance with a blower will not be significantly enhanced below these speeds with a cam change. However for optimum performance at higher rpms, a more aggressive camshaft will provide substantial power increases.

For best performance with a blower, you should look for a cam that has higher lift and longer duration on the exhaust side. Street performance with a blown engine is usually best with a cam that is ground with a 112- to 114-degree lobe separation. With the use of an aftermarket camshaft, follow the camshaft manufacturer’s recommendations for valve springs. Blower cams can typically be run “straight up.” Note that a blower has tendency to lessen the rough idle of radical cams.

Boost ControllerIgnition System Settings

Blown engines make great power in the low-and mid-rpm range. That means most late model OEM electronic ignition systems have the capability of working well with a supercharger and will be fine if you keep your driving under 5,500 rpm.

Some distributors with computer controlled advance curve and timing may not be compatible with a supercharger because of the preset timing and sensors they require. However, any of the aftermarket high performance standard or electronic distributors should function well when properly calibrated. A quality electronic unit would be the preferred choice for best all around performance and reliability.

Set initial ignition timing at 6 to 10 degrees BTDC. The distributor advance curve should be calibrated to give a total advance of 28 to 34 degrees by 2,500 rpm. If detonation is encountered, a boost/retard system that works with manifold vacuum and pressure is recommended. It is also a good idea to run your spark plugs one or two heat ranges colder than normal with a blower to reduce the chances of detonation.

Keep in mind, these are general suggestions–there are no hard and fast rules. Bottom line is you can benefit from supercharging a stock, mild, or wild engine with the right tuning and modifications.

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  1. I wish someone would really detail supercharger performance. For instance, why does everyone focus on pressure (psi)? It is not directly related to air density, which is the real factor controlling output. Maybe I’m missing something here. It seams to me that pressure is more an indication of a restrictive intake/bad cam timing than it is supercharger output.
    I also find it interesting when people remark that a supercharger doesn’t perform better with aftermarket heads. This does not make since to me. Obviously the optimum intake to exhaust ratio is very different NA vs boosted and every head designed for NA has to be modified for good results for boost. Maybe I’m way off here, but it seems to me that it could be explained by relating a smaller engine with forced induction to a larger NA motor in terms of intake/carburetor/exhaust. Then relate that to temperature because if forced induction.
    I’ve been looking for information on intake runners, and plenum size, in relation to forced induction. I can’t find a reason why I shouldn’t apply intake valve pulse wave tuning with the intake runners. Also the low lift air flow and overlap scavenging principal still seem to apply. The intake charge probably moves a little faster in total, but from what I’ve read overlap and low lift at the valves move air around the speed of sound. So that should be just as important boosted or NA.
    The second to last issue I’ve come across is LCA. Everything I’ve read references using cams ground at 112-114 LCA. I’ve seen several cams that still have 25* or more overlap while others have 1-5 degrees of overlap. Just mentioning LCA seems very incomplete.
    The last one. I can’t find anywhere that details carburetor function for a roots supercharger. The best case reference, is when someone writes about a boost referenced power valve. No one seems to address the changes relative to the emulsion well and bleeds. I know, a person does not have to make these changes to make the engine run, but most of us are not ok with just bolting on a carb and leaving it to run like junk when running NA, why do that with a supercharger? ‘Because it is not as obvious,’ seems like a crap excuse to me. No one seems to want to divulge how to do it right. I just want people who feel that way to know, that mindset is the type of ignorance that created the middle ages. The carburetor’s days are numbered, share the information before it is largely lost.

  2. What you need is the inside scoop on the size numbers inside a Holley Blower Carb. I don’t have them myself. The 112-114 LCA is for a low boost motor, when the boost goes up higher a 110 LCA . The Boost Reference of the carbs to the lower manifold gives you the true engine vacuum reading and stops blower roll up and down idle speeds because under the carbs there is always a vacuum messing up the power valve. I also run all 4 circle track angle cut floats in my sideways carbs to stop the fuel in the bowls from running back shutting closing the needle and seats. Good heads less restrictions = more power, Remember its easy to move the air but to keep the fuel mixed with the air going in the engine it will stick to any walls in can find and drip. I called cam cams the other day to compare a stock bbc solid flat cam 11-106-3 which was getting 12mpg on the highway to a small hyd blower cam 11-404-4 they said they think I would get even better mpg with the blower cam, and I could run solid lifters on it with .012″ lash clearance. I myself just don’t trust hyd lifters. You Never what to hang a intake valve open= back fire into intake and up ! No one knows all the facts of why things work on one car better then another too many variables, its always trade off of different things to learn what works for you !

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  5. Thanks for the article, helpful to many and I shared it…by the time I realized that it was meant for guys who were using V8’s built prior to the the LT1 or so…or whatever ford and mopar guys ran back then it was too late…then the recommendations from Weiand….I was like…OH MAN…rip van winkle. Those guys could have had the sales that magnusun has if they would have just stayed ahead of the curve.

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  7. Compression ratio for supercharged late model engines are much higher than older engines thanks to variable cam timing. 11:1 compression ratio is common these days with forced induction.

  8. William Rhodes says:

    In High School, I started building an Olds 442 with the 455 engine. This was in 1979 when you could still find Ethyl High Test at some stations. I used a Dyers 6-71 under driven 12 %. The pistons were TRW 0.030 Forged. Sig Erson provided the cam with a max lift of 530 exhaust 500 intake 112-degree lob centers. tourbo 4oo trans, long story short I drove that car back and forth to work, ran it all over the place for 5 years and only lost one head gasket the entire time.

  9. I have a tko600, most people run automatic transmissions. I love my manual. I am building a blown 454, 8 pounds boost, 750hp range. Anyone running manual transmissions?

  10. Hello.

    I’m wanting to supercharge my Gen III Eagle Hemi, but according to your helpful article that listed the specs on it, it already had a 10.5:1 compression ratio. In this series of articles, you mention the max safe boost would be the kind that gives a 12.0:1 ratio, meaning I only have 1.5 PSI to work with on a stock engine.

    Is this correct? The Edelbrock one I was looking at lists a maximum boost of 5. Does this mean I need to upgrade the internals?

    Just making sure I interpreted your information correctly.

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