I just got a set of Stg 1 conversion heads back from the flowbench and the numbers seem low... .100 68.74 53.96 .200 127.93 98.23 .300 189.01 135.21 .400 241.75 165.31 .500 247.97 184.95 .600 237.84 196.74 It turns out the shop didn't unshoud the valves like I asked for and it's being done now... This is a street engine and the port work was pretty basic, but what I'm asking about here is cam selection. I'd like to see around 450 with 10inches of vaccum (fond of my brakes) What's a good cam for this combo? I've researched & simulated more than a few and have it down to these three choices: 288-94H 288-96H 286-08H ...I've got a rough idea of the HP involved, but not the vaccum. The rest of the combo: 38 over SRP conical dish pistons polished & peened rods 1 7/8 headers - 2.5" mandrel dual SP-1 intake 800 Q-jet (secondaries drilled, englarges idle & primar circuits) SP torque converter 3.42 gears 29" drag radials 3100lbs car & driver So am I likely to make my numbers here or should I be thinking of another cam choice? Any help is appreciated. Thanks!
I would go with the 286-08H. Since your ratio of exh. to intake is not the best in the .300 to .400 area, the extra exhaust duration will help you out. The somewhat short intake duration should keep the torque up there. Looks like a good choice to me! Since the cam is about the same as a 290-08H with only a little less intake duration and the same lobe center, you should be able to run power brakes. What size are the chambers in those heads? You should be around 9.8-9.9:1 with that cam for the right dynamic compression with pump gas. I was told that unshrouding the valves is extremely important, so your flow numbers should pick up quite a bit after you do that.
Thanks Steve, The heads are 59 cc, though I have not had them matched. I put the dynamic right at 9.4. I was thinking about having the heads re-flowed after the unshroud work is done, I'll decide on that in a bit. Given that the exhaust is a bit better than the intake I wonder if I should go with more of a split in the cam??
YES, i would like to see the flow #s after un shrouding, i recently pulled my S1 heads off and unshrouded them, when i originaly ported them, due to lack of knowledge i didnt do it. now i wish i would of had them flow tested, but o well im not pulling them off for that, they are 70 heads, stainless S1 valves, 3 angle, dual springs 300lbs at 520lift, portmatched, most work in bowl blending, and runner clean up, i wonder what they flow and if going from a 113a cam to the 290-08-hl will help E.T.
...and the winner is... Well, I've decided to order up the 286-08H. I don't know if the vacuum will be streetable enough for my tastes, but liked the curve best. I considered the 413, but I wanted a split profile to cover the old irons... Kelly, Unless I'm mistaken the drop in flow I'm seeing at the 500-600 range is due to the lack of unshrouding. I'm also told by a couple of Buick guys that back cuting the valves 28-30* will help out. I have no flow numbers yet to back this up, but I think I'll get them re-flowed once the work is complete if only to have some conclusive evidence to show future shops!
The local machine shop that did my heads didi the same thing to me. They installed the larger valves but failed to unshroud them. I was surprised to see that it wasn't done but I didn't want them to do it after the fact because of other issues with them. They said they knew Buicks, but it ended up being a lie. Be careful of who does ANY of your machine work. Buicks are not chevy's and some shops just can't understand that! Brian
Clint, Are you sure those heads are 59cc? Did you have them cut quite a bit? It seems like those chambers are really small. Also, are you having the block decked? How far in the hole are those pistons going to end up? I was trying to run some numbers on your combo, but I don't have enough info.
Steve, Bit of a typo there, it's 69cc. The piston to deck is -0.005? Wha? Maybe I'm reading this clearance sheet wrong but shouldn't that be 0.030 in the hole? Guess I'd better check my numbers again here.
Drat... I've heard from another local guy that the duration on the 286-08H makes lousy vacuum...7-8 Inches and idles fairly poor. Can anyone confirm this?
Well, I would be surprised if you couldn't run power brakes with it. Weise seems to do it with the 290-08H cam, which has the same exhaust duration, and more intake duration on the same lobe center. Maybe you should search for the posts on that cam, or contact Jim for the info on how he does it. I'm sure that the idle won't be really mild, but it shouldn't be all that rough, I would think???
I have installed the 290-08H cam in 3 cars now.. and a variation of it is the standard cam in the Level 2A motor. Not one made less than 11" of vacuum, not one would not operate the power brakes. I also have heard the stories of guys who could not get this cam to behave, but without being personally involved in the projects, I could not give you an answer why they feel this way. That being said, this is the "max" cam that you would want in a street car, as your build has to be right on the nuts to make it work. Sealed, round cylinders, good valve jobs, proper intake and carb selection, and correct cam and ignition timing are all very important factors here. If there is even a shadow of a doubt about your engine machine work accuracy, your building and tuning ability, I recommend you select a smaller camshaft, and sacrifice the 15-20 HP for the sake of having an engine that will be more "forgiving", to slight but important variations and factors in this type of build up. Now the 286 is 4 degrees smaller on the intake, and I would expect to see 12" of vacuum with that cam. JW
Thanks guys, something smelled fishy about 7-8 inches. The 290 is looks like a good cam, but I probably don't have the combo (or experience) to support it. I was actually considering the 288-96H over the 286-08H because it semeed to have a little more room for error. I'm afraid I'm not enough of an expert in the dark art of cam selction. I picked the 286-08H based on the split pattern, a bit of additional exhaust duration for cooling, mild overlap, lift that supported my head flow, and reasonable results on the sim with the SP-1/800QJ combo. That number crunching doesn't show me the "real" results and I've typically under estimated my cams. Did I miss something in the selection and if so would the 288-96H be a better choice?
I'm no expert by any stretch of the imagination, but I think it's a good choice for what you're doing. I would still like to have more information on your combination. If I had the piston to deck clearance, which head gasket you're using, and how much of a dish your piston has, I could run the dynamic compression and it would tell a lot about how this cam will work for you. You are going to want an actual static compression of right around 10:1 with this cam run straight up. If you have a 25cc dished piston, .010 in the hole, a .040 thick head gasket, and your 69cc heads, you will be right there. There' s a good article on real olds power, on the front page, about cam choice. John Zerucha told me to read it. You might want to check that out. One thing that is noted in the article is to choose a cam with an intake duration that puts you in the RPM range you want, and then adjust the exhaust duration to get the horsepower you want for what your heads will flow. The TA413 is a great cam for a street motor because it makes great torque and good hp too. I think your 286--08h might be even better, because it's helping you out more with your exhaust flow. You might not need the extra exhaust duration when you unshroud the valves (maybe your exhaust flow will pick up a little) but I would be willing to bet that it's not going to hurt you either. Anyway... my point is that you could go down to the 288-96H, but what would you gain? With your car as light as it is, you don't need more torque. Seems like the best choice for what you want to do, in my opinion.
Reading through this thread got me to wondering: has anyone out there experimented with 30 degree valve seats to get more flow moving quicker? Might could get by with less cam for streetability? Just a thought!
Could you run one of these cams with the Rhoads variable duration lifters? Seems to me that they might help on the getting to much cam issue?
He could probably run the Rhoads, but I really don't think it's that big of a cam. He should be able to get it to work without those.
Steve, Here's what I used for my sims: 0.005 in the hole 0.040 gasket 25CC est. (JE/SRP's new conical dish) One thing to consider, Calgary air is at 3500' and rather chilly. I used the following air: 26.00inHg 74.0*F 20% Humidity Any results would be great man, please let me know what you think! If you need any more info on the buildup I can send everything from basic numbers to a spreadsheet containing the entire combo. I read over the ROP article, it ties the engine events to cam selection very well. I unwittingly used a similar technique when guesstimating a cam, so it might not be too far off. Here's the thinking: I selected a 5000-5500 power peak range initially based on the expected lifetime I want out of the engine given the reconditioned/polished/arp'd rods and the lack of a girdle. Desired overlap was backtracked to a 114* LC. I then looked for as much exhaust duration as possible while maintaining that intake & LC. The thinking at the time was to crutch the low exhaust ports, and increase the exhaust flow velocity to reduce the cylinder temp. Again, a very amatuer attempt so the more eyes the better, and I'm open to ANY ideas for improvement! You bring up a very good point that the extra torque supplied by the 288 probably won't help given the cars light weight! I've already got a bagged, prosquat, 3.42 rear with Wagon weight over it and the thing still spins with the Buick torque. With torque out of the picture, the only gain might be a bit more idle quality with the 116 Lobe Centre, only valuable in terms of the sleeper appearance. Solving the high end horsepower problem might be worth more than the idle. Bob, Staying with stock rockers at 1.55 ratio I'm trying to keep the lift lower, so the rhoads are being left out. It's proably the way to go with the 286-08HL though...
Clint, I'd like to see the spreadsheet. It sounds to me like you're right on the money and know what you want. If it were me, I would go for as much HP as possible, but only you really understand what your priorities are. Idle quality would definitely be better, but is it worth giving up hp? I can't wait to see what results you get! Should be really cool! I decided to go fairly radical on mine. It's going to be a 464 with 10.25:1 compression, ported iron heads, and a 210S solid cam. I just started buying parts for it- can't wait to get it together! Steve
Clint, Here's another good article. Download the free calculator after you read it- great free tool! Steve http://members.uia.net/pkelley2/DynamicCR.html
