for inline six cylinder engines

We have a lot of feedback now from serious racers making seriously good power from our range of AussieSpeed manifolds, many had results straight out of the box and others had to work at it little and apply themselves. We also have had the guys who did not do so well and when I dig deeper with questions those guys have a common thread of a lack of pursuing it any further than a first bolt on, or they just have no idea at all really.  The guys that do well are just dam persistent, and the following info is what we have learnt, from what we have seen to date.
A baby engine with tall hwy gears and low max rpm demands, needs a small carbie and a small intake runner style manifold like the original factory units. Performance manifolds are for performance modified engines runnning at increased rpm, as a minimum you really need to raise comp and cam the engine up a bit, and get rid of the emissions compliant camshaft and timing chain and get rid of the retarded spark advance to feel any real results from a manifold change. 

This is also applicable for those just converting a stand EFI engine to run on a carburettor, the retarded spark advance and camshaft timing events is not the same as an earlier pre 1976 non EFI engines that you may be more familiar with tuning. So if you want to persist with the stock EFI engine and its existing OEM camshaft and dizzy then it may need some fineese and persistance on your part to work on dialing it in, if you call me and ask me what to do if you start having problems on a stock used engine, the first thing I will tell you is to change the cam, timing chain and dizzy to performance based units to eliminate any question that that will be the source of any carby tuning issues.
First up DO NOT PORT the manifold, ever. Most people stuff it up and ruin the manifold balance by porting them out.  Yes even self proclaimed professional engine builders have done it, so for best results just leave the dam thing alone.
A Performance Manifold is;
The AussieSpeed race manifolds are a large runner high air speed intake manifold and are designed to not restrict the engines air flow right up to 7000+rpm. For example with a big cam that will allow the engine to rev, [cams with durantion greater than 225deg @ .050 and > 290deg Total] a stock intake manifold starts to restrict airflow at about 4200+rpm, you can measure increased manifold vacuum at wide open throttle all the way up on a stock manifold. An AussisSpeed manifold will help greatly in the 4000+ rpm range to allow the eninge to breathe.

What is the purpose of a inlet manifold plenum filler?
AussieSpeed also make a range of plenum fillers for the various different intake manifolds that are shaped to increase air speed at low rpm and close the plenmum up a bit for the baby race engines operating in the lower rpm to increase the bottom end. This can help in for example the street stock clases where there is a really tight corner in the track and rpm drops real low, and you are still runnning what is essentially street gearing in the car. A stronger low end will improve your wining ability when it depends on how quickly you can pull out from these slow corners, even if it is detremental to the top end power on the straight.

AussieSpeed also has some smaller runner designs to help the baby race engines make power in the range they are operating in.
"I used an AussieSpeed manifold and it didn't work"
The small number of times I have heard a statement like this is in all cases so far where a racer goes from running a stock or modified OEM manifold, where they have experiemented and developed the car to a point where it will not make any more power with that manifold, or they want to make more power and they move to an AussieSpeed performance intake manifold and expect an instant power increase.  Most guys get the power increase straight out of the box and for some reason a small few don't, so the following paragraph and info is there to guide your thoughts when you don't.

Now the Aussie Speed manifolds will work in all applications but it can show up your mismatch of other parts and settings. For example in most cases you are going from a fairly restrictive intake manifold and that can be masking a problem or more likely a component miss match that may not have been apparent before. Typically engines that have been developed with restrictive manifolds end up being over cammed and when the breathing is opened up the cam is too big for the engine or it is now coming in at the rev range it is supposed to which is a lot higher than before, this may also result in it feeling doughy in the bottom end.  The camshaft lobe separation angle might be too close together to suit the shape of the intake ports and the turn into the intake valve or just the lift is way too high for that size port. Now a restrictive manifold will mask all these issues and more ...... it can give the novice tuner a false sense of expertise having made all these changes thinking they all worked.  Quite often on a race car or burn out car when an engine development program has progressed with a restictive manifold I have seen low 9s compression working ok with full advance spark timing, but when you open up the engines breathing it will show up the deficiencies with trying to hot up a low comp engine.  The driveline gearing that got this to work well over time and experimentation may now well be out when the engines breating is opened up too. 

Remember it is real easy to over cam a 186-250 cubic inch straight six, especially the Holden Red, blue and black motors with the 90 degree turn into the intake valve from a flat port floor.

"I bolted on the AussieSpeed manifold and is seems like it is getting too much fuel ..... it is boggy out of the corners ..... feels doughy under acceleration ..... and I have to rev the shit out of it"
When I get a phone call and hear this I can gaurantee the carburettor is not set up right. YOU MUST USE A POWER VALVE BLOCK OFF TO TUNE YOUR HOLLEY PROPERLY. Follow this link for a comprehensive Holley performance tuning guide for the AussieSpeed six cylinder intakes. click here
In this case what is happening is the power valve in the mettering block is staying open when it is not needed and it over enrichens the fuel mixture, we have noticed that quite often it is not significant enough to show up on the mixtures when dyno tuning with the sniffer in the tail pipe, yet it is easy to pick when you pull the carby off the manifold because the manifold floor is excessively wet. Follow our "Holley tuning for performance and the AussieSpeed intake manifolds" guide here under the intake manifolds section of this website and if you follow it thoroughly I am certain you will get great results.

When moving to a free flowing intake you need to be more conservative in camshaft selection so it will work in the rev range you want it to and for the gear ratios you have in the car, but you need to be more aggressive on compression ratio to make it pop.
Static timing and spark advance become more critical that they are set right for what that engine needs.  Each engine can be different; it only needs what it needs, nothing more and nothing less.  Note a lot of people overlook timing issues, especially with the modern premium pump fuels, I have advanced static timing and pulled total timing back to 25deg in a 10:1 comp engine and made more power and torque, before that it was running like a pig and felt doughy, but unless I worked at it I would never have found out how exciting an engine it is to drive.
Big pipe headers that appear to work with the restrictive manifold maybe too big for midrange torque gains, especially if the comp is down in the low 9s there is not enough pop to get it revving through the bottom end. I have seen this in some speedway engines when all the development to date has been with the restrictive intake, low comp and a lot of timing advance and then when they get rid of the intake restriction and it throws out how the other components were working together, and how they work with the way the car is geared. It is not that the manifold did not work it was that it made such a dramatic change to the engine’s breathing capacity that you may now have a mismatch of other parts and settings in the engine and driveline that you need to rework and dial in to suit the engine change.
Main thing to remember here is that nothing changes your base line tune more than letting the engine breathe better. A free breathing engine will really test your knowledge and understanding of parts selection, carbie set up, fuels, spark timing and driveline gearing.

A few examples of what to expect when it all comes together and works
We have seen rear wheel kW figures as high as 225kW for 250ci straight six engines naturally aspirated race engines with a 4 barrel Holley and AussieSpeed intake manifold.

We have seen 25hp gains on a flat track tarmack race car at the rear wheels straight out of the box.

We have seen street cars running in the mid 13s at the drags drop into the low 12s with just a manifold change and re-jetting of the carby.

Typically when moving from one of our competitiors manifolds to an AussieSpeed manifold I have seen they can run up to 5 or 6 jets leaner in the carb than the customer was running before.  What was happening here is that the previous other brand manifold was not even in its air fuel distribution so the carby had to be jetted for the leanest cylinder, which also leads to more fuel drop out and typically causes the regular fouling of #6 spark plug. This was all corrected by changing to the AussieSpeed intlet manifold and re-tuning the carbie jets.
Clarification: I have refered to a baby engine a few times here in the text and I know the ego in some of the punters think becasue they have a race car they have a race engine but in reality more often than not it is just a hotted up strong engine in a race car. So the reality is that a baby race engine has to work from lowish 2500 rpm corners or rolling starts on a tight track and have strong low to mid range with street gears in the drivetrain even though it may rev out on the straights. Our idea of a race engine when you say to us you have a race engine is that is starts to pull from say about 3800rpm and comes in strong from 4200 rpm and requires a gear change at about 6500-6800+rpm to keep it in the max torque band. Typically an engine like this will require the gears in the drive train and tyre diameters to be dialled in for each track to keep the engine operating at maximum torque, these are usually those hand full of guys at any race that are out the front with the sweet sounding engines on full song and absolutely nailing the others to the wall. 

Now I am the first to admit I am no expert, I only know what I have seen and I feel if I share what I have seen then it may help some of you.  Quite often my knowledge is of a general nature becasue when the customers are doing well they are reluctanct to pass on the sercrets for their set up becasue that is their racing edge over their competition, so I will juast keep adding info as we go and when I am confident it it will apply in some applications I will put it up, so stay tuned.

Random Tuning Tips for AussieSpeed equipped engines

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