My big cam is not letting the engine produce enough vacuum for my new Willwood discs. An accumulator tank did not help. Who has ideas for me? Thanks, Jim
Same problem here, thinking of checking out the system that uses the power steering pump to give power assist to the brakes. I'm not impressed with the lack of warning on this site about lack of vacuum with certain cams. My cam is said to be the largest you can get by with power brakes, well if you call one push of the pedal power brakes I guess it is true. As fast as my car gets going I need the security of knowing it will stop. :rant: Maybe rhoades lifters will help, I'm thinking of trying them but I hate ticking from the rockers. Steve
If you have good heads, there really is no reason to go over 230* or so of intake duration. You can make 500 HP or more with a smaller cam and good heads. My KB118 cam is 228/246, .490 lift, 118* LSA. It pulls all the way to 6000 RPM, it makes 16" of vacuum at a 750 RPM in gear idle. It's very responsive on the street especially with the Q-jet, and it is marketed as being very easy on the valvetrain. I am very happy with this cam, but with the 118* LSA, it doesn't build top end HP. My cam change will be the last thing I do to this engine as I am very satisfied with the way it runs. With my heads, I don't need all that split duration either. I will either go with the TA 288-92H (231/234, .525/.525 lift, 110 LSA) or have a cam custom ground. I haven't decided. The TA catalog will tell you if power brakes are OK with a cam. If you don't see "Power Brakes OK" in the cam description, your brakes will be marginal at best, and non existant at worst. Big cams are for race cars and mostly strip cars, not for a street car that you want to enjoy and cruise. Bigger is not always better, and if the rest of your combination is not matched to the bigger cam, it won't perform anyway. When you do match the rest of your combo to the cam, driveability suffers. You have to be honest with yourself when you decide what you really want from the car. I have a friend with a 70GS455. It has ported iron heads, Edelbrock manifold and Holley 850DP, full 3" exhaust, and SP4 cam (253/270, .548 lift, 110 LSA). He has 4.10 gears and a 3500 converter. The car turns heads and is beautiful. It sounds awesome and gets alot of attention at cruises. I'm sure the brakes are nothing to write home about. It has run a best of 11.90@110. But, I have never seen the car driven more than 10 miles from his home. Between the converter, gears and carb, it gets terrible gas mileage, and I bet it would run very hot if he ever got stuck in stop and go traffic on a long trip. He is reluctant to drive the car any greater distance, and I don't blame him. That is not what I want out of my car. Sure I would love to run 11's, but I'm not willing to give that much up. I could drive my car cross country if need be, race it, and drive it back. That is a true street car IMHO.
if any of you guys with brake problems are in my area I'd like for you to drive my car and try the brakes. I'm curious to get your opinion. I had a local guy that owns a 70 GS 455 Stg 1 conv drive my car and he told me the pedal effort was more than his. That was when I had the 350 and lots of vacuum. While the pedal effort may be a little more, the car stops good, and if you wanted to, could easily lock all 4 wheels. I haven't noticed a change in the braking with the big cam I run now. I've put 1000 miles on it with the 455 and they've always been there for me. You can ask anyone that knows me and they'll tell you I don't drive slow. In fact they all think I'm a bit wild behind the wheel. I installed front disks back in 1988 and the car didn't stop that great. I always thought it was because I never installed the disk brake proportioning valve. During my restoration in 2004 I changed from a 1.125" bore to a 1" bore master cylinder and the difference was dramatic. I never did change the proportioning valve because I was happy with the braking. The smaller bore translates into more pedal travel and less effort or more pressure with the same effort. Maybe this is why my brakes are fine with my cam o No: Think about this. A circle track race car does not have power brakes and I can tell you from experience that pedal effort and stopping was not an issue. In a 100 lap race I'd hit the brakes 200 times and my leg never got tired. This is achieved by proper design of the whole system and not fancy expensive parts. An exception would be Martinsville where you need some special stuff because of the heat but still no power boosters. My point is, you really don't need power brakes to begin with. I did drive a couple of old manual brake drum cars where pedal was like a rock and stopping was scary at times especially if you got the drums very hot. I don't know why they were designed that way but they were. Those cars needed power boosters. IMHO they use boosters today because people want to be able to stop an a dime using one toe.
I was sure to check for power brakes compatability the first thing before choosing a cam. Stopping is a good thing. Wanted the performance without going to far over board so I chose the TA290-94H cam and keeping it respectable with 3:23 gears and a small stall.
Doesn't seem like we have enough info from your original post to have more than a general conversation about the pluses and minuses of different cam/intake/carb and brake combos here. Seems like there are lot's of ways to crutch a 'too big' cam to get enough vacuum to run power brakes. Among them are 'bleeder' lifters, advance/retard the existing cam, vacuum cans that store vacuum, the tune up itself, electric vacuum pumps, smaller carbs, etc., etc. There is always the hydro-boost system. Not a good option if you don't want the extra plumbing underhood. Changing over to a manual set-up is one answer, though that doesn't really address the problem. Bucks up guys/gals can go to a full manual disk system as described by the dirt track racer. I think I have to go with "The Wiz" on this one. Build it as a complete package to start with, keeping the final use of the car in mind. If you didn't build it originally, perhaps your use of the car is different than was intended by whomever actually put it together? That person didn't necessarily do a "bad" build, they just likely had different goals and were willing to sacrifice certain things you don't want to live without in your street car. This is the place to be to get the best advice available for building a Buick engine. Tell us more about what you want the car to do, how you want it to perform and then we can go from there. What is the complete combo now? From the carb to the cam, heads, intake, ignition timing etc. Convertor, auto or manual trans, gears. The folks on this board love to help guys out.
The brake system I was talking about was in a pavement stock car I once raced and the whole post was for the reason you said, to help. I believe that sometimes there are solutions to problems that are not complicated or expensive and allow you to have your cake and eat it too. I also believe that if something works for me it can work for someone else and if I can share information that will help someone I want to do that. Changing a master cylinder is a lot cheaper and easier than any of the normal "crutches" and IMHO worth a try if you're currently running a 1.125" bore master cylinder. PS. With the dirt car, the brakes were for the pits and cautions only.
The engine was built by Andresen in Woodstock Il, 2002. I have everything except the cam so far and will post all soon. This weekend I'll check how much vacuum I actually have. Thanks for all the help - you guys are GOOD! Jim
Hey Andy, I didn't mean to say your post was in error or part of the crutch thing. Changing the master is actually a good idea. If I were to do this, how could I tell that I had the smaller bore vs the larger?
GS464, I don't know of a way you could check other than if you could read a part number and look it up or actually taking it apart and measuring it. My last post wasn't aimed only at you and I wasn't offened by yours. I just feel that some of the stuff I post is kind of out of the ordinary and people think I'm nuts. :laugh: I was just trying to explain myself. I know the M/C made a difference for me. I'm not sure why my brakes work so good with my big cam. I went and bought a used vacuum pump and fully intended to use it but now I don't see the need. IMHO the electric vacuum pump is the easiest way to solve a low vacuum problem. I like it because it's always on with the ignition, even if the engine was to stall and it will help the engine make more power. I was planning on mounting it below the horns and running the hoses inside the fender to hide them. It would still be visible but not too bad.
Here's what I could find on my engine - Resurfaced cast iron heads with stage 1 conversion and port job. Bored to 462 CI. Edelbrock 800 cfm carb with performer intake. HEI distributor, LUN 33303 Hydr camshaft (DON'T KNOW WHAT THAT IS). TA headers with 3" x-pipes and TA 273 rear. Max dyno was 425 HP and 485 TQ. I tested the vacuum at 750 rpm 9" up to 25" at 2000. I think I'll try the vacuum accumulator again. Thanks, Jim
Lunati 33303 235* intake, 245* exhaust duration at .050, 113* LSA, .517/.517 lift with 1.6 rockers You should have more like 13" of vacuum, not 9" You may have a vacuum leak.
First connect the vacuum gauge with the engine running. Pinch off the vacuum hoses one at a time, and watch the gauge. You can spray some WD-40 around the carb base gasket, and intake manifold flange. You'll see a rise in vacuum and probably a change in idle speed when you find the leak.
