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COMPRESSION RATIO/NITROUS OXIDE

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COMPRESSION RATIO/NITROUS OXIDE

Postby Old School » Sun Feb 13, 2005 11:27 pm

First let me say this is a most informative and exciting site. Thanks to everyone for the sharing of knowledge and experience. After reading Darin Morgan's post on nitrous oxide and the need to reduce compression with increasing amounts of nitrous I would appreciate any advice concerning nitrous/compression relationships. If an engine has 14:1 static compression, pumping compression 220 with an 288-304 at .050 camshaft, 1000 ft elevation, 300 hp fogger system that has never lifted ring lands, burned pistons, or caused damage of any kind should compression be reduced if another 150 nitrous hp is added? If a second nitrous system worth 200 more hp is added how much further should the static compression be reduced? I am taking into account that with each increase of nitrous the timing will be increasingly retarded. If more camshaft exhaust duration is added to compensate for each nitrous stage will compression still need to be reduced more and more for each addition? I realize that a lot of answers rests with the tuner but is there a rule of thumb or generalization that might apply? Is there a difference for an aluminum block compared to a steel block, rod ratio's, or chamber types? Thanks in advance for any help.
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Postby Ben » Tue Feb 15, 2005 10:41 am

You can take this for what it's worth, but we sprayed 600 on a 406 CID 18* SBC. Static compression ratio was 14:1. We ran straight 116 Octane and never had a problem with detonation. The car ran 8.22 with a 1.26 60' time on a true 10" tire @ 3150 lbs.
Crew Chief - Outlaw 10.5 #4033
1992 Mustang Coupe, 25.2 Chassis, 406 CID 18* SBC, 'Glide, 106mm Turbo.
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COMPRESSION RATIO/NITROUS OXIDE

Postby Old School » Thu Feb 17, 2005 11:10 pm

Thanks Ben for sharing your experience. I am trying to run a Quick 8 dragster but have failed to qualify a couple of times. I am currently running 4.40-4.46 et in the 1/8 mile. It is going to take a 4.25-4.30 to quality most all of the time. Adding another stage of nitrous should do this if I can get it right. If I miss the combination and damage the engine then my season will be cut short. Thanks again, I need all the advice and experience I can get. Billy
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Postby Doug Schriefer » Thu Feb 24, 2005 8:26 am

Even on most Pro-Mod cars we’re running 14+ compression, and at least 3 if not 4 stages of nitrous. Being a Quick-8 dragster, you’re most likely going to be doing some racing other than just your Quick-8 stuff. I’d stick with the compression ratio you have since it’s going to make the engine run more consistently when bracket racing. Depending on how you’re adding the nitrous (time wise, and amount) this will vary as to what is your best method. Normally in a Quick-8 Car we’ll set the first stage to come on as quickly as your chassis can handle it (the quicker it comes on the more benefit you will see), but shutting it off before the finish line. This will allow you to finish line race without damaging the engine. Now setup your second stage on a manual override button for qualifying.
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Re: COMPRESSION RATIO/NITROUS OXIDE

Postby Jay Allen » Thu Feb 24, 2005 12:13 pm

Old School wrote:If an engine has 14:1 static compression, pumping compression 220 with an 288-304 at .050 camshaft

What intake center and LSA is the camshaft?

The 288 @ .050 and 220 psi of cranking does not add up. Also at what lash?
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COMPRESSION RATIO/NITROUS OXIDE

Postby Old School » Thu Feb 24, 2005 11:04 pm

Lobe separation angle is 112 degrees. Intake lobe is on 107. Intake lobe is on 71 ATDC at .050. Seat duration.020 is 320. Valve lash is .032 hot. Possibly advanced 2-3 degrees to much. This cam is too large for the engine NA without nitrous, maybe to much even with nitrous. One advantage with the larger duration is the nitrous can be activated sooner and the car is not so violent, leaves much smoother than with a smaller cam. I am thinking something about 284 at .050, .510 intake lobe, 308 at .050, .480 exhaust lobe on a 114-115 lobe separation might be a better choice with another 200 HP stage of nitrous? Any thoughts?
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Postby Jay Allen » Fri Feb 25, 2005 11:02 pm

I am not a fan of running very loose lash such as you are. It appears as though you are success with it so who am I to refute that?

I would run something in middle 270's and design a lobe or find a lobe that has about .008" to .010" of lash at the cam so lash HOT at the valve is .016" to .022". I would try to obtain as much duration at .200 as possible. I would also (more than likely) have the LSA 116'ish with an IC in the 111 to 113 ATDC neighborhood.

290 to 295 on the exhaust with again a tigher lash, big at .200.

I have designed these types of lobes before for guys running NOS and they work well.

If you run a cam such as you describe, let us know how it turns out!

Good Luck!
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