[Runswithscissors]

Wouldn't that make the case for the larger injector ?

Not necessarily. We don't run as high as the PS, but our SS runs at 9,600. It performed better with the smaller injector/higher fuel pressure set up as does my Stocker that will turn 8,200.

I am not sure why this is the case. Both are sequentially tuned which I feel fades at the higher RPMs, but improves the harmonics on the way up. It may have to do with the higher fuel pressure keeping a more consistent fuel supply to the injectors.

 

[john marcella]

So you went smaller injector and uped the pressure, did your duty cycle end up similar? If so is your thoughts based on droplet size from the pressure? What i found was the injector wanted to be fired at a closed intake valve, and it was big! Lots of ideas why that was , but....

 

[Runswithscissors]

I ended up with a smaller injector and higher fuel pressure, but I also played with the larger injector at various fuel pressures and duty cycles. And I did the same with the smaller injector, fuel pressures, duty cycles...

It all ended up pointing the same direction for the best performance on the track, smaller injector/higher fuel pressure/duty cycles in the 70%-75% range. This is not first hand information about your droplet size question, but one of my closest friends and tuning confidant ran a dyno in the Wichita, KS area. He had an injected dragster motor on his dyno that the owner's primary goal was to test injector spray patterns.

One of the tests basically had the pattern a near single stream hitting the back of the intake valve. It made no difference on the dyno at all which really surprised me. I hesitated to mention that because I do not have all the parameters of the engine in question, but I would have thought it would have made a noticeable difference.

Maybe he will chime in here.

 

[Lobes]

Makes sense to me to have some known quantity of fuel laying on a closed intake valve rather than wetting all the surfaces from the plenum to the chamber..."poof" when the valve opens...

 

[john marcella]

I ended up with a smaller injector and higher fuel pressure, but I also played with the larger injector at various fuel pressures and duty cycles. And I did the same with the smaller injector, fuel pressures, duty cycles...

It all ended up pointing the same direction for the best performance on the track, smaller injector/higher fuel pressure/duty cycles in the 70%-75% range. This is not first hand information about your droplet size question, but one of my closest friends and tuning confidant ran a dyno in the Wichita, KS area. He had an injected dragster motor on his dyno that the owner's primary goal was to test injector spray patterns.

One of the tests basically had the pattern a near single stream hitting the back of the intake valve. It made no difference on the dyno at all which really surprised me. I hesitated to mention that because I do not have all the parameters of the engine in question, but I would have thought it would have made a noticeable difference.

Maybe he will chime in here.

I went through a lot of effort to try and break the fuel up more being that it was my first go with efi and i "had all these great ideas". But to further my EFI disappointment i found that , that to made no real difference , at least for me. So i would say that your friend and i found the same results.

 

[Runswithscissors]

I went through a lot of effort to try and break the fuel up more being that it was my first go with efi and i "had all these great ideas". But to further my EFI disappointment i found that , that to made no real difference , at least for me. So i would say that your friend and i found the same results.

Yes, it really surprised me also. Stuff like this is humbling in a hurry.

 

[deuceswild]

Nick do you and Jake Hairston split the duties on building the engines? I don't think he has been mentioned. Robert Freeman bought Ashton and I a beer at Carinos at the Ennis race. That was cool of him.

 

[BBF612]

I would think that you would want the fuel pooled up sitting on the valve so when the valve opened the fuel would be sprayed into the cyl by the rush of incoming air at low liftes and there would be "room" for more air flow without any fuel in it at the higher lifts. Some "sharp edged" valve angles might help spray the fuel into the cyl. Don't know, just a thought.

 

[Lobes]

I would think that you would want the fuel pooled up sitting on the valve so when the valve opened the fuel would be sprayed into the cyl by the rush of incoming air at low liftes and there would be "room" for more air flow without any fuel in it at the higher lifts. Some "sharp edged" valve angles might help spray the fuel into the cyl. Don't know, just a thought.

Latent heat of vaporization...post combustion temperature is your friend when the intake valve opens...Poof! Best power will be made with a consistent A/F ratio spread throughout the vaporization process. This is geometry related.

 

[Bigtime]

Are they going to be changing the fuel now also?

 

[rickseeman]

With the air now being pulled into the grille area instead of the opening in the hood scoop, will the opening now be bigger for direct air to the engine?


Regarding the removal of the huge scoop and the lowering of the hood overall (so it sounds) how will this effect the air flow going up and over the roof and on to the rear lay-down spoiler...

It seems to me that the areodynamics will not be so "confused" anymore around the windshield. Possible slightly smaller area needed of spoiler?

When I first looked at the 2011 Drag Pak Challenger and didn't see a hood scoop for fresh air I thought "How dumb, no cold/ram air, got to slow it down". Then I found out the entire grill (36" wide) is the air intake, funneling air straight to the throttle body. Not a bad idea.

 

[john marcella]

Nick,
What kind of valve life do you get out of intake valves and how thin of a margin do you guys go down to?

Do or have you guys use different intake manifolds (runner length) at different times of the season for drastic temp changes/ density differences. ?

 

[Festus]

Nick / Bob / George and anyone else who builds their own stuff...

It amazes me that year after year, you guys keep finding a few more horsepower. What mechanisms do you use to keep the fresh ideas flowing - FEA, brainstorming, trial and error, steal (just kidding)? Good grief, it's a push rod design. What has not been tried (yet apparently quite a bit).

 

[papawins1]

This might have already been talked about, are you allowed to use a 02 sensor on each cylinder and would you benefit for tuning purpose by doing so.

Jesse

 

[Runswithscissors]

They should be able to run them and it would help tremendously to see the readings going down the track as opposed to only on the dyno. Especially how it is effected at the top end of the track with the extra air pressure entering the manifold.

I will run all 8 on my car plus the 9th in the collector when I am trying to refine the sequential stagger. I won't run them all the time because they take a lot of electricity to run since they are heated.

 

[Chris Uratchko]

Most run 8 o2 today...

 

[papawins1]

Thank you, this is exactly why this thread is so great, you get honest answers, hope it last a long time.

 

[95gts5oh]

I'm not sure if you will be able to do that since the hp computer uses 1 o2 sensor...not sure about the ps spec ecu.

 

[clevo]

They use the Racepac Logger for their 8 O2 sensors.

 

[CalBoy101]

This is something I've always wondered about too. Even with a pretty basic Rimac spring tester and a dial indicator you see the difference in what I would call coil bind and solid height. I've always worked to the coil bind or soft bind number,but have always wondered if the solid or hard bind height would better control things in an engine with "heavy" valvetrain.

My preference is to always use the "soft bind" height in setups, this is the point at which the coils are just starting to stack up.

You can then use pretty tight clearances from that height, ie .050" or less and still be confident that you will never be operating the spring in a range where its coils will be partially stacked.

If you set your bind clearance from the "hard bind" point (coils totally stacked) there's no guarantee that you stay out of that partially stacked range, its a guessing game on what clearance will avoid that.

By the way there is a really good article covering PS engine tech written by Nick and Ian Bamsley in the issue of Race Engine Technology that just came out.

It has more details of what goes into PS engines than any article I've ever seen, and by a long shot, Nick thanks for taking the time to contribute to that article, its a great read.

This a magazine out of the UK so its not commonly on the shelf around here but it can be ordered at the link below. This same issue as has pretty good article on valve springs also.

https://www.highpowermedia.com/p/1201/race_engine_technology_-_issue_089