Inliners International Forums General Discussion Hi Performance Cam duration question

As a very interested spectator, I've always wondered about racing flow benches and/or dynos. I see there can be so many variables introduced (on purpose or otherwise)that comparing data from one to another is pointless. But I see tremendous value in looking at torque curves and valve lift vs crankshaft position plots.

Anyone have any insight as to valve lift beyond peak flow? Particularly, is there power to be gained by lifting the valve beyond peak flow numbers to gain more area under the curve. The valve spends so little time there that it would seem that it the flow would not be stalled.

Dynamics at 5-6000 rpm must be way different than steady state flow. I have opinions but no real data to back-up my suspicions.

Anyone?
Panic?

If I understand correctly, you are saying that having a higher peak lift would allow for a longer duration at let's say .200 lift and have the same or almost the same .050 duration. From looking at Crane's and Comps lobe chart,that seems like what happens.I of course have no data to back me up other what I read.Oneof the advances in cam design seems to be fast opening and closing rates along with higher total lift for a larger "curve" but keeping total duration low to help with low speed torque for a given duration. For myself I am looking for low speed cylinder pressure to make the engine seem bigger in normal driving. I still want some improvement in top end,which should be easy to do given the specs for the stock cams. Jay

The reason this (faster ramps, accel/velo for the same or even shorter events to conserve cranking pressure and duty cycle) is not more commonly used is that it:
1. requires a harder, finer finish on parts, especially those with scrubbing contact (lobe/tappet, stem/rocker)
2. requires higher spring tension for the same RPM
3. requires stiffer pushrods (anticipating pushrod as the weakest link, in some cases it will be the rocker)
4. reduces service life

Which would lead me to believe:
1. Steel Roller camshaft (Hydraulic?)Steel Roller rockers
2. Limit RPM with reasonable spring rates
3. Increase pushrod diameter
4. Expect shorter service life, offset by fun factor, 'cuz that's why we do it.

Good recipe for a strong street combination. Basic parameters for my next 292 based engine.

I believe that 1. Crower camsaver HYD lifters. 2.I allready have valve springs that are in the process of getting measured if they don't work out because they are too strong I will use sbc stock or Z28 springs. 3.Max rpm will not be high enough to cause problems.(4800-5000) 4.X2 big time! I also have more info to share. Got a responce from Kevin at Schneider and the specs are:Part 02527 252-56H IN 252@ .006, 198@.050 ,166 @.100 100@.200.
EX 256@ .006 ,204@.050,172@100,105@.200 Cam lift IN .265/EX.268. The reason this is different than what is published on their website is these were ACTUAL measurements taken from the master. I see why evervone has such good things to say about Schneider! Jay





0

I have the z28 350 springs, brand new. They measured EXACTLY the same as my old springs in every way. Length, stiffness (LBS at same compression test heights compared to my old springs) and so on. No difference. So maybe someone already replaced my stock springs with those. Nevertheless, it's not enough for bigger cams.

Did the springs that you took off the engine have a flat coil damper inside? All sbc stock springs have them but from what I have seen the factory stock 6cyl springs don't. (Maybe someone who has tore down a lot of engines can confurm this) Someone could have put in sbc springs in before you got the car. I just tried to look inside the oil fill holes in both the engines that I have, can't see inside well enough. I ran the Crane 203901 cam (.530EX lift) with sbc springs and did not have problems. I foolishly did not check for coil bind and just got lucky. Truth be known it had to be dang close if not barely touching! That was when I was young and dumb. Now that I am old and dunb I'll make different mistakes. Jay

Yes the old springs had the flat profile secondary springs inside. Just like the new set has. I just wanted NEW springs because I didn't know the age or history of the old ones. Installed pressures were all over the place, all way too low. I could easily open the valves with my thumb. Maybe installed wrong or maybe a result of seats and valves wearing, or valves stretching...? I didn't care, everything is new now. Head had hardened seat inserts before so they just got machined true.

Ditto CNC Dude.

I don't know how one could pick out a cam for a performance engine with out the flow numbers. You need flow numbers at all lifts, and it helps to have reverse flow numbers at the lower lift for intake reversion. You can get 200 cfm @28" on the 235 chevy which makes 300 hp possible. GMC racer that have dynos are claiming 350-400 hp (on gas). I know one racer is welding in the GMC combustion chamber to help out the short side port radius. Yes this is the 21st century and more hp is coming.

64U Iv'e wanted to flow test my 2bbl intergrated head with both the stock 1.72 intake and the 1.84 valve that I plan to install. How much will it cost to have it done? Is there a place in Central Ohio that does this kind of work? Thought about calling Jegs in Columbus but I haven't got around to it yet. Jay

The integral heads are bad about being cracked, so have it magnafluxed and pressure tested before you get too deep into it.

intergrated j 78

I only flow test my own heads and have not dealt with any of the porting shop. I am sorry I have not had your cylinder head on the flow bench. Of the six cylinder heads that I have tested SISSELLS AUTOMOTIVE stuff is the class of the field. They may have the flow numbers you seek. 805 499 7077 They have the experience and a lot of Bonneville racers are using their stuff.
GOOD LUCK

Thank you 64U. CNC Dude is there a common place that these heads crack? I can't remember where the head on my 79 GMC broke but it did not leak oil or antifreeze. Had to buy a brand new head because no one had any good ones used This was in 1987 or 1988. The Chevy dealer had one in stock. The headgasket seeped down the side of the block for 50k+ miles, when I got apart one of the head bolts had broken and the bolt head was laying beside the bolt hole. IIRC I read that you took care of a fleet of trucks with this head? Jay

Hi Jay, yes we had a fleet of phone company vans that their service tech brought us the engines to machine as they needed to be serviced, and he had the same problem with cracked and broken castings. They typically were cracked in the exhaust seats, but also externally between the head bolt bosses and other high stress areas. They also had to go to the Chevy dealer to get replacement heads because all of the used castings they found were also cracked and unserviceable.

Were these hardened seats? If so, it sounds like they weren't properly heat treated.

It was mostly due to a poor design with the intake and exhaust all being made as one casting with the head.

I find it hard to believe that GM somehow saved money by creating a single (but more complicated) casting - versus just casting individual parts and machining them to mate. But I guess the cost of hardware/gaskets and labor to mate them is in the mix too . . .

I wonder if GM changed/ improved the later or replacement castings. They had to know that there was a problem based on warranty claims and replacement head sales. I do remember that my 79 was very lean mixture possibly helping to crack heads. When I put on the new head I also adapted an autolite 2bbl from a 400 Ford station wagon that was richer than stock but not too rich. (Light brown plugs ect.) Do you remember if any replacement heads cracked also? Jay

I think by the time they came due to be replaced again they had already swapped over their fleet to the Chevy minivan with the V6's and phased out the earlier big body van with the inline powerplants.

Thanks CNC Dude for the reply. Possible cracks and not having to put in new seats is why I will stick with the 1.5 ex valve size. Going bigger on the Intake valve only, 1.84 to avoid problems with breaking into water and possible Intake seat cracks. The plan for the head is a extreamly close inspection by me then a pressure test and mag test. If it passes all that then bigger Intakes and at least a small cut to flatten the surface. Will back cut the Intakes and front cut the exhausts. I am afraid to even cut the seats any extra angles for fear of cracks. Jay

I agree that the 1.5 exhaust valve should be fine, but do not be afraid to do three angle cuts on the seats as the amount of material removed is nil and the benefits of having a correctly placed seat of the proper width and with gentle lead-in and lead-out angles are great.

I agree that the 1.5 exhaust valve should be fine, but do not be afraid to do three angle cuts on the seats as the amount of material removed is nil and the benefits of having a correctly placed seat of the proper width and with gentle lead-in and lead-out angles are great.

Frenchtown Flyer, I will take your advice and do 3 angles on the valve seats. I work in a truck shop and all we do is swap complete heads.(CAT reman ect.) Couple that with the fact that until recently I had no need to build an engine,(Grandson changed that) the polite way of putting it is I am a "little"rusty at best. One thing I do know from user experence: There is big difference between vortec (good flowing)and non-vortec heads. (305). A lump ported,ported head is out of the budget,plus I want to try something different. I also hope to contrubuite some information and not just take info that you and others have worked so hard to get. Who knows maybe someday I will be king of "The land of misfit cylinder heads" LOL Jay
'


ec

I think it was Sissel that used to sell a complete modified head called the "Lions Share Head", meaning that an economy port job was done that got you 80% of the way to a completely ported and polished head. Unstated in the ad was that the "lions share" of the benefits can be attained with only minimal work - deburring, minor blending, gasket trimming and a good 3-angle valve job.

Food for thought.

There must be a lot of "easy" gains with a 3 angle valve job. With the cams that I have under consideration, the valve spends a lot of time at low lift, meaning that the valve and seat are fairly close together. I will also match the exhaust gasket to the head and manifold. Thank you for the advice. Jay

Update. Have cam in hand. (Christmas present). Part # CS-1033R from Sealed Power. Bought at Summitt Racing for $119.95. If you drill down their cams by engine this part will not show up as one of the cams offered for the 194-250 6cyl. Also can be bought at NAPA for a higher price. Specs are: .006 duration I272 E282.At .050 duration I194/E204 Max intake lift @105ATC. 110 degree lobe seperation angle. Lift I.464, E.490. Not very much "Hydraulic Intensity", but I am OK with that. This cam is almost an exact copy of the Clevite 229-1878 that is no longer made. For all I know both cams ARE the same. Can the cam list be updated? I "helped" my Grandson measure the lift to make sure that we got the right part.(We did). Next thing to arrive will be the "Camsaver" lifters. Jay