is there a specific reason? Just wanted to know.

 

You might try a search. There were some long threads about this a while back.

Short version: overlap bleeds off boost and isn't needed as it is on an NA motor for cylinder filling.

Rich Krause

 

LSA's are not always related to overlap in some cam profiles. I have seen zero overlap @ .050 with 226/226 duration (590/590 lift) on a 112. This would be a really good cam for a 6spd blower car.

 

Overlap is strictly a function of LSA and duration. Larger LSA = less overlap, more duration = more overlap. A 226/226 cam with a 112LSA has 2 degrees of overlap at 0.050". If the LSA were 113 degrees, there would be 0 overlap at 0.050". The way that overlap effects flow will also depend on the intake center line. If the cam is advanced, overlap will occur with the piston further down the bore as it approaches TDC on the exhaust stroke. The effects of this are subtle in the range we are talking about, so I won't elaborate further at this point.

A 226/226 cam would not be an optimal blower cam for a gen I or gen II SBC with a 23 degree head. The exhaust ports on these heads are barely adequate for optimal NA power, that's why even NA cams for these motors often have more exhaust than intake duration. Add a blower or nitrous and a "split pattern" is definitely needed to facilitate adequate exhaust flow with the greater volume of combustion gasses produced by the N2O or the forced induction. Most LT1 blower cams have 10-12 degrees more on the exhaust than the intake for this reason.

Rich Krause

 

Rich

Its been a long time since I have visited the board. Could you recommend a blower cam for me? My engine is a 355 with 8.50-1 JE pistons, LT4 heads and intake, a few other goodies and a D1 making 18lbs of boost. Currently it runs fine but I am getting tired of its ho hum existance. I would like something stronger than a LT4 hot cam and something milder than a CC306.

Thanks in advance
Joe

 

Joe: a lot of people have had good results with a setup like yours with the following two cams. You will need good springs to go with them, especially the second.

CC XE lobes 3190/3192 on a 114LSA. 214/224 @ 0.050" .530/.567" (1.5 rockers). I had good results with the cam ground on a 114 intake center line, though it's more typical to have 4 degrees of advance ground in (112 ICL). Running 1.6 rockers, especially on the intake was something I wanted to try but never got around to.

CC XE lobes 3192/3196 on a 116LSA. 224/236 .567/.585" on a 112 intake center line. This is the cam I am using now.

If you want spring recommendations, let me know.

Rich Krause

 

Rich:

Thanks for the reply. If I did the math right the first cam would end up as .565/.604 with 1.6 rockers. The second as .604/.624 lift with 1.6 rockers. I guess the question is... what are the street manors like? Having grown up with multi carb GTO's and Big block Ford Fairlane's I have had my share of the 1800 rpm trying to idle situations with zero torque until the rpm's hit 4500 or better. I would like to be able to feel the effects of the blower and the cam at around 2500-3000 rpm with a redline of 6800 or so. Your recommendations for spring height, open and closed pressure would be appreciated. Do the heads have to be machined for the correct height?

I do appreciate your time and information as I remember you are very knowledgeable with blowers and cam profiles and I value your opinion because of the facts it is based on.

Joe

 

Joe, I am pretty conservative on what I consider "streetable". On that basis, I use the somewhat arbitrary figure of 0.600" max lift for a "street" cam. Obviously, it's not an exact number based on sciene, just an opinion based on experience. When I was running the first cam, I was considering using the 1.6 rockers just on the intake side only to avoid "excessive" lift on the exhaust. But admittedly, .604" is only marginally bigger than my arbitrary 0.600" max. Anyway, I did have good results with the cam and 1.5 rockers.

The first cam will not be very effective over 6,000rpm. Revs for max hp will very with the rest of the setup, but 5,800 is typical. The second cam will make max hp in a typical combo at ~6,200 and be pretty effective up to 6,400-6,500. Sounds to me like you would prefer the larger 224/236 cam. I think that the best spring is something on the order of the CC #987 or the #977. It gives 123lbs of seat pressure installed at 1.850" and 368lbs at 1.250". Should work without any changes to the heads. If you want more rpm, the #977 spring or equivalent will be needed. It has a rate of 441lb/in vs. the 403lb/in of the #987. Installed at 1.850" the seat pressure is 155lbs and it's 419lbs at 1.250". This is high for a hydraulic cam, but a good choice for higher rpm.

With either you will need a HD 0.080" pushrod and good rockers.

Hope you find this helpful.

Rich Krause

With either

 

Does the 987 spring require machining???

What is the diameter?

is the part number 63-987-16???

 

CCA-987-16

If I remember right there wasn't any machining done on my heads.

Well....damn, maybe there was.....I think there may have been just a slight bit of machining on the seat.

Sorry...it's early morning for me and I'm now just getting my first cup of coffee.

 

Oops....and the ID is .697.

http://store.summitracing.com/defaul...art=cca-987-16

There ya go.

 

For stock heads, either the spring seat or the heads will neeed to be machined. I found it easier to have the springs seats machined for the 987 spings to work with my stock heads.

 

well.. as seen the 987 is not enough for the 224/236 high lift version

 

I want a cam with a HEAVY lope and the blower whine!

-B