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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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You can't go wrong getting something custom from these guys. I have no personal experience, but the folks in real life and on this forum are 100% happy with their recommendations. This option will almost certainly yield you the best results.
 

· Registered
1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
Joined
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491 Posts
I have a Straub hydraulic roller in the 496 in my G-Body. I didn't talk to anyone there, it's an off the sheft "semi-custom" and is exactly the spec I was after.

I did notice by the custom specs specs others have posted that they do differ a little in how they get the job done. The folks I knew when I was drag racing swore by them both.

To the original poster, I remember your inquiring about installing this cam. If the budget allows for a custom cam, that's the best option. The latter of the 2 cams you're considering makes sense and checks a few boxes for a supercharged application. It's probably available in a 112 LSA too.
 

· Registered
1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
Joined
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491 Posts
The old saying was "the sweet spot" is at 2.3 overdrive ratio. Beyond that would be strong consideration for an intercooler or methanol. I'm thinking your 2.45 is crowding up on, but not over, where you're safe running methanol. I'm going on memory and it's been a number of years since my "trying to go fast" days. I could be mistaken and new information changes things all the time, but I'm in the ballpark.

Roots style superchargers (like your Weiand) cause higher temperatures than centrifugal ProCharger style superchargers. The centrifugal style and turbochargers are more compressors. The roots style are more "air movers" and that's the underlying cause for the increase in temperature.

With regard to the information you are getting from a trusted source(s). The tighter lobe separation CAN be beneficial to what you're doing. The overlap does push air through with both valves open and it helps to cool the cylinder. As far as how much that impacts performance, I haven't any idea. The "it's not as bad as you think" information you're getting could be true. Someone with more experience is a better judge of that than I would be.

Thoughts on your current cam. The 238/240 @.050" numbers (and some others as Johnsongrass noted) only tell a small part of the story. If the engine is "underheaded" (poor flow or too small intake runner) it takes a longer cam and everything that goes with it to make power in the usable range desired. The "overheaded" engine is the opposite, if you're trying for the same usable range. You're good with what you have in the 200cc area. Forced induction, in general, is increasing displacement without changing the dimensions of the cylinder due to the pressure behind the intake charge. It ends up with more to go out the exhaust, like a larger cylinder. Displacement tames the duration numbers. Your cam will peak at a lower RPM than it would if you were naturally aspirated, but it's not a surprise the pros are recommending shorter ones. Your shift RPM and desire to avoid spinning the blower point to that as well.

The recommendations in the 114 lobe separation angle are expected as well. A number of factors contribute to that. Limiting overlap is only a part of it. Wider lobe separation benefits you by allowing for an earlier exhaust valve opening and a later intake valve opening in relation to one another. The earlier exhaust valve opening helps the cylinder empty better in "blow down" where the cylinder pressure helps in evacuation. It's also a reason for many to consider, based on the cylinder head flow, more lift and duration on the exhaust valve (somewhat similar to nitrous). The aim is for less pressure left when the intake valve opens to reduce reversion into the intake.

The wider lobe separation also allows for the later opening of the intake valve. Opening the intake valve early and relying more on overlap to help the intake charge "get a head start" is far more important in a naturally aspirated application. It also helps the valve arrive at a higher lift (farther up the intake lobe in degrees) to coincide with the area ATDC where you're getting the most "pull" into the cylinder. To some degree this helps any kind of induction, it just doesn't matter as much to a forced induction system.

Forced induction can actually act a little opposite with regard to opening the intake valve early. Your cam on a 110 with 4 degrees advance in the grind installed on a 106 intake centerline seemed like it could be a hinderance. With the forced induction, you can end up fighting more against the piston coming up BTDC because it doesn't need the same "head start" as naturally aspirated. I wouldn't be surprised to see the recommended cams at 114 with little or no advance ground in. Your question on where to install your current cam a while back had me thinking the 110 would be better. Maybe even 112 with the additional information now. The dilemma there is causing the exhaust valve to open later might not blowdown to empty as well and possibly increase intake reversion. Given the 110 LSA and the durations, I thought the overlap would help to mitigate the risk of increasing intake reversion.

My head hurts if I get into these things any further. I hope it makes sense and I hope I'm correct in my thinking. I'm a hobbyist and not a pro by any means. Most of the folks here know more than I do and may correct anything I have as bad information. I thought it may be of use to our members with input and to you in correspondence with the trusted source you have. Would trying your current cam around 112 intake centerline would be worth the effort?

Getting a custom cam is by far the best choice. I think the noncommittal answers on "more power" you're getting from the custom folks is a consequence of the situation. Wanting to limit blower and shift RPM along with anything else currently unsettled would make an estimate difficult. The pros mentioned in this discussion are top of their game. Investing in their input seems like money well spent.
 
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