Okay, I currently am seriously considering a blower for my t/a. I have 8.5:1 compression due to my 76cc 487 casting 1971 heads. I was considering vortecs, but a roots style blower isnt made for them and my compression would end up being way to high to do it. That and playing with flow numbers in DD2000 did not make a serious gain in power with Vortec flow numbers, and doing them over with bigger valves said made more power than if I threw Vortecs on it. Yes, I realize its junk science. But my current heads (I dont know much about heads, I am learning and learning fast) had some huge ports on them in comparison to the other casting heads I had lying around, and look like they have the capability to support decent power. Here's my plan: 3 angle valve job with larger undercut stem valves (2.02/1.60's vs. 1.94/1.50's), new springs (my springs are from 1971 and have a 100,000 miles on them, dont ask), new valve seals, roller rockers, and some self porting of the intake and exhaust track. I have the capabilities (aka gearhead father willing to teach) to do most of this at home except for having the valve seats machined. What would I have to do in order to place larger valves into the heads besides having them machined? I was also thinking 1.6 rr, and I know those need other modifications. But the heads will be off, and when their off I might as well do everything right. Anything I should watch if I am planning to supercharge this motor in the next 2 years (money is in short supply for me right now).

Any superchargers suggested? I was looking at a 142 or a 177 weiand, smog legal, unless I dontn have to pass CT emmisions after this february, which I think is a definite possibility (2 year pass, then its too old to need it). Im only planning on running 7-8 lbs of boost. I want to end up with a car capable of running mid 12's easily.

I have all the time in the world right now, Id just like suggestions on what I should do as I am pulling the heads and doing them this christmas break.

 

My buddy runs a 177 with 10psi .. Car runs good..

The only problem Ih ave about roots blowers is the noise, and hood clearance.. I'd go with a centrifigul if you could.

Intake porting doesn't do crap on a blown motor, exhaust porting is priceless. If you can get your exhaust ports to flow like 50-60 cfm more, then you're sweet.



-- Joe

 

Noise, thats not necessarliy a bad things. And I am getting a spare hood specifically to cut for this project. I am gonna port the intake anyways, as the motor will still be driven unblown for a year or so anyways. The exhuast ports I will pay special attention to.

Any times on the car with the 177 or any detail on the setup? What did he need to do to the motor to get it to stand up to 10lbs of boost? I'm assuming on my stock internals it wouldnt be wise to run more than 7-8lbs.

 

Hi,

Motor is like 9:1 compression. Car runs high 11's @ 3200lbs..

Stock bottom end, holley heads, 700cfm holley carb, msd ignition, semi-rad cam. _NO_ porting..


I'm in a similar boat. Stock rods and crank, forged pistons, sportsman heads _NO_ porting. 6psi = 12.5-12.7, hopefully 10psi will be like 11.9..


-- Joe

 

I don't consider myself an expert on these things, but i've had alot of practice with them.

porting the intake side of the heads with a blower is actually very important, especially if its a daily driver. remember the car acts like it would without a blower anytime your not under boost, meaning anything less than half throttle you have a N/A car with a big fuel atomizer sitting on top... porting the intake will greatly reduce driving temps under boost as well. flowing better on intake side will also lower your boost and raise your dynamic compression ratio, provided your exhaust is setup to handle the boost.

Exhaust in general is very important, not just the porting of the heads... your exhaust should be as short as possible and Contrary to popular beleif, not as BIG as possible for a daily driver. Remember, anytime your not under boost, a super-huge exhaust will give you driveability / gas mileage issues especially at lower RPMS and on the highway. Theory wise, the best setup would be a dual 2.5" exhaust with 2 high flow mufflers. I've found that anytime a Y-pipe is used you generally see about 30-40 horsepower less at the flywheel, even though the exhaust backpressure may be the same. for a thirdgen, a single 4" mandrel bent pipe back or a 3.2" oval tube mandrel bent setup, and as short / big a "y-pipe" as possible. I say this instead of duals because this lets you keep your ground clearance and your low end torque on the street.

Blowers jack up volumetric efficiency well above 100% anytime your over 3/4's throttle, even at very low rpms. this is important because these times are the most critical for timing and cylinder pressure to do nasty things. 3-4 PSI of boost at 1000 RPMS with some engine load and 36* of timing is enough to blow a stock replacement felpro head gasket. gearing plays a huge role in your timing profile... the higher the gearings in your tranny / rear end (numerically lowers... 2.77 for example) the less timing you want right onto boost. the problem here is without fuel injection and a computers MAP sensor you can't set your timing back with a BTM instantly, you choose 1-3* of retard per PSI.

Example: part throttle acceleration from a stop light. 1-2 PSI of boost. if you have a total of 10 PSI then you want your BTM to retard your timing a total of 7-8* if your total timing advance is 36* which is common. that means about .6-.8* per PSI. at 1-2 PSI of boost your still around 35* of total timing, assuming roughly a 2400 rpm centrifugal advance and about the same stall, you <b>will</b> experience Detonation at this point if your static compression ratio is above 9:1 or your engine is above 180* but this is generally speaking... the point is you will have a LOT MORE fine tuning to drive a blown car on the street than on a track. your timing advance, BTM retard, Air/Fuel ratio, and engine components make a huge difference. also the type of induction, if you dont have a blower carb (i.e. Manifold referenced power valve) then you will not get good gas mileage at all.

I could go on all day, if you want specific help Email me:
Kingtal0n@aol.com
Cam280magnum@aol.com

Use a big subject like "ROOTS BLOWER HELP" I get alot of junk Email and delete it if I don't catch it.

Let me know what your doing, where you will drive it, how much power you plan on making etc... I will break it down from engine components to carb air bleed sizes for you to maximize performance.

My car: http://www.geocities.com/kingtaling
and check my sig for details.