Intake Manifold, Throttle Body, & Injector Sizing + Selection

Hey Guys,

I am currently considering running a K20 for an Endurance Race. Specifically the K20-K330 built by 4PistonsRacing. I'm fairy new to the K20 so I've got a few questions in regards to it. I'll be running in the N/A class which limits us to a 65mm throttle body. Is this the OEM size the K20 comes with? If not what aftermarket throttle body would you recommend? Secondly, which intake manifold should I go with? It's difficult for me to decide which one would be best as there are so many brands and styles. Due to the size restriction of the throttle body going with a giant manifold/plenum would be a waste. ITB's will not be allowed. Finally, I plan on using DeatschWerks 550cc injectors. Would this be suitable? Too small? Too large? For my application extracting maximum horsepower is a plus however, reliability takes priority as it'll be running in 12hr and 25hr races. All comments and advice is greatly appreciated.

Thanks!

Hi.

1) I would choose intake manifold that gives you the highest air velocity since you are going NA. That should give you best cylinder filling and power.

2) Throttle body size should correspond with duration of the camshafts chosen. Any less and you are loosing cylinder filling quality and if it's too big you are loosing air velocity thus power.

3) Injector size depends on your target power level and type of fuel chosen...

Hey,

As for the specific specifications of the camshaft...

Intake Lift: 0.533"

Intake Duration: 260@0.050"

Exhaust Lift: 0.513"

Exhaust Duration: 260@0.050"

Do you think these specs correspond well with the 65mm throttle body? This will be the largest size we are allowed to use. For horsepower, I am targeting between 250-275HP. Not sure if 275HP is possible due to the restricted size of the throttle body. Do you think the 550cc injectors are a good choice for this level of HP or should I go with something larger? If so what size would you recommend?

Thanks!

Well, assuming that the throat diameter of intake valve seat in your engine is about 31 mm and total duration of your camshaft is about 270 ish degrees the throttle body size you need is about 60 to 61mm. 65 mm would be overkill...

550 cc/min fuel injectors are fine for your target power level as they should handle 300+ hp..

4PP should be able to give pretty accurate recommendations for the engine.

As Shota said, the TB is a little larger than what may be optimum - it shouldn't cost power/torque but may make small throttle opening driving a bit trickier.

What ECU are you planning to run, and what method?

An important (some would say most) part of deciding on engine configuration is what it's going to be used for - in this case the track(s) and their configuration - fast and open or tight and twisty with short straights, what is the expected engine power/torque range and how do the available gearboxes and diff' ratios work with the engines characteristics? Do you expect the engine to run a season between rebuilds or do you expect a rebuild after every race or what - it's important that 4PP know your expectations there for part selection?

If you're allowed sticky tyres or slicks, that can put a big side acceleration on the oil in the sump - do those engines have any known weakness in high "G" cornering that could cause oil stravation? If you have to use stock springs or, especially anti-roll bars, this will worsen it.

A good single TB and plenum manifold should act like an ITB in that the runner length should be optimised for the expected rpm range with that camshaft selection - again 4PP may be a good place to start, as they should have a lot of testing experience.

Give some serious thought to the filtration of the engine - some will run un-filtered in the mistaken belief it gives more power. While potentially true initially, the increase in ring and valve seat wear as track dust and dirt passed through will cost more in the long run, and require rebuilds after each race - and that's without the risk of debris, stones or whatever being flicked up into the intake. As a general rule, the bigger the better for the filter (within practical reason) and giving it cold air can be a definite advantage.

On a related subject, the exhaust dimensions can make a big (I know of 20% on different engines between best and worst) difference - I don't have a specific recommendation but there are numerous formulae on-line and I'd suggest averaging three or four for pipe diameter and lengths. On that, you may find a 4>1 the best option with around a 2 1/2" collector - most modern tracks have a sound limit, so a good muffler is critical to balancing flow against noise and the 2 1/2" exhaust size should give a good balance.

Then there are the other aspects - with longer races like that brake wear can become an issue - what are your options for managing pad/disc changes if needed, fuel and tyre stops should be syncronised - eg. every third/fourth/? fuel stop matches a tyre change.