SBC 421 combo advice

[cjperformance]

The wider LSA for an n2o cam has real advantages for higher n2o use, the wider lsa effectively retards the intake events and advances the exhaust events ( decreases overlap figure) and the real advantages here for more n2o are, the retarded intake giving a lower cylinder pressure at the beginning of the n2o pull making the engine less detonation prone, the advanced exhaust events open the exhaust valve earlier in the exh cycle to start getting the much increased volime of exhaust gas out early to reduce pumping loss later in the exhaust cycle, and the resultant reduction in overlap leaves less in/ex valve open time and flow area to reduce overscavenging (unless your exhaust is extremely restrictive) caused by the higher gas velocity thru the header pipes due to the increased gas volume created from using n2o.

According to Billy Goldbold, Comp Cams lobe designer, the reason for wide LSA on higher N2O set-ups is strictly about knocking down the mid range, when the car may not be able to put it down, and shift the power curve up a little where the car can.

That makes no sense.
The mid-range power actually picks up on the wider LSA with NO2.
It does flatten out the torque curve, but it makes more power above peak torque.

Beat me to it ^^

[Frankshaft]

Not to mention reduced chances of a back fire out the carb. Pull a bunch of timing with tight centers, and jam it with a big shot of nitrous, and get ready for a big boom and some fireworks.

[rfoll]

The reality of 5000+ converters is that you are always turning lots of rpm. Every stoplight means leaving with the engine rpm way up until you hit the next stop, which could be 2 blocks or less. With a really loose converter, engine braking becomes a thing of the past. If your not careful, the tires will go up in smoke under acceleration, at anything under 60 mph, and that tends to get the attention of people you would rather avoid. Did I mention how incredibly loud things get with the engine rpm always over 3000? The novelty wears off really quick.

Sounds like you need to find a new converter company.
[/quote]

I thought the same thing when I read it......get a better converter, sounds 30 years out of date technologically.
[/quote]
The converter is from TCI, recently freshened. I believe it is a spragless design, I'm sure high stall converters are not all the same.

[user-17438]

421SBC

11.7:1
23 degree heads hand ported
Single 950 4150

[hoffman900]

According to Billy Goldbold, Comp Cams lobe designer, the reason for wide LSA on higher N2O set-ups is strictly about knocking down the mid range, when the car may not be able to put it down, and shift the power curve up a little where the car can.

That makes no sense.
The mid-range power actually picks up on the wider LSA with NO2.
It does flatten out the torque curve, but it makes more power above peak torque.

Beat me to it ^^

Mike, I might have misquoted, he said in combination with duration increase on the exhaust. Listen here for yourself: https://www.youtube.com/watch?v=whmOxK4XDYQ&t=6058s (go to about 1:30:00)

[cjperformance]

Not to mention reduced chances of a back fire out the carb. Pull a bunch of timing with tight centers, and jam it with a big shot of nitrous, and get ready for a big boom and some fireworks.

Yes, and even moreso when combined with high EGT and a restrictive exhaust!

[raynman1969]

So I am going with the AFR 235 heads, going to try the 4000 rpm converter. Not sure if this cam will work or turn my motor into a roman candle with the nos. I would like to run nos so if i have to change the cam i will. I would like to run a 150 maybe 200 shot. I did learn from this posting that i would love to party with the Aussies. If someone has a cam recommendation for this i would love to hear it.

[MadBill]

A major effect of nitrous usage is more exhaust gas to process. Absent NOS-specific head porting and valve sizes, a much earlier EVO ( maybe 15° or more) can be a big benefit. All other events equal, this results in a perhaps 5° wider LCA and 5° more cam advance.

[CamKing]

So I am going with the AFR 235 heads, going to try the 4000 rpm converter. Not sure if this cam will work or turn my motor into a roman candle with the nos. I would like to run nos so if i have to change the cam i will. I would like to run a 150 maybe 200 shot. I did learn from this posting that i would love to party with the Aussies. If someone has a cam recommendation for this i would love to hear it.

Fill this out, when you have time
http://jonescams.com/street-performance/

[cjperformance]

Definetly fill out Mikes form if you want a custom cam.
For a shelf cam with your 235 heads and conservative stall you would not go wrong with Howards Cams 110613-12 (or -12S for small base circle)
Adv - 291/307
@.050" - 259/275
Lift/1.5 rr - .640/.630
LSA-112
ICL- 108
Lash - .022

You will find that will cope with the lower stall and work with your 250hp n2o.

[raynman1969]

Not to mention reduced chances of a back fire out the carb. Pull a bunch of timing with tight centers, and jam it with a big shot of nitrous, and get ready for a big boom and some fireworks.

What is considered a big shot of nitrous ?

[user-17438]

Not to mention reduced chances of a back fire out the carb. Pull a bunch of timing with tight centers, and jam it with a big shot of nitrous, and get ready for a big boom and some fireworks.

What is considered a big shot of nitrous ?

A small shot is up to 250hp and often time a regular N/A cam is effective
A large shot would be 3-500hp single kit
A big shot 600+ per kit

[randy331]

421SBC

11.7:1
23 degree heads hand ported
Single 950 4150

What heads you use ?

Cam size.

Workin on a 421 sbc now, so just wonderin.

Randy

[raynman1969]

So I am going with the AFR 235 heads, going to try the 4000 rpm converter. Not sure if this cam will work or turn my motor into a roman candle with the nos. I would like to run nos so if i have to change the cam i will. I would like to run a 150 maybe 200 shot. I did learn from this posting that i would love to party with the Aussies. If someone has a cam recommendation for this i would love to hear it.

So i can't get a definite answer if the afr 235 heads will work with the flap top pistons i have, instead of having to tear it down i will be using the afr220 heads. Is anyone on this board using a progressive controller with their NOS? Is the a hp level where a person should use a controller? I plan on using a 150 shot.

[n2xlr8n]

Is anyone on this board using a progressive controller with their NOS? Is the a hp level where a person should use a controller? I plan on using a 150 shot.

If the car doesn't hook, it won't matter what you use, honestly.

On my fun street car, I used a cheap timer (not progressive per se, but it worked flawlessly) to enable first the 100 hp "power shot" off the transbrake, then 1.4 seconds (iirc) the "cheater" system. About 275 total. This was on a 406 with a 25x/26x @ .050" solid roller on 108 LC. PTC provided the 8" 4400 converter.

http://www.galco.com/buy/SSAC/TDM120AL? ... 1ZEALw_wcB