Thread: Blower Expert Needed

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Well Pat,

I think I need to quit thinking for a little while and enjoy this set-up as is. I got more power with the blower than what I was shooting for initially. I had plans of a 500 horse engine with a like amount of torque. With 10:1 and a solid roller 252/258 @.050 .630 lift and 104 LSA, wouldn't have been nearly as streetable, really bad manners with stop lights. With the blower, I was able to drop my CR a little shorten my cam just a touch and open my LSA to make a better street engine and a gob more horses all at the same time. I think blowers are addicting, and one plus is I haven't been ridiculed once like the NOS boys (only babies need a bottle) The only mod I think I'm going to do is drop my stall to about 2200 because of traction on the street. I'm not whacking my car right now so that's about the best next thing. I wish I would have back-halfed it when I had it apart. I might try playing with front springs for now though.

bottle get's empty .but if the belts is on look out . i have said this many a time .and have proved it more than once

I'm no racer or enginge builder, but from what I've read about blower motors, is just get the exhaust gasses out, and let her BREATH! I would bet tuning for exhaust pulses would be benificial if you are looking for the last tidbit of power.

Since you run 9:1 static compression, which is high for a roots blower, you are getting into the realm of detonation on pump gas if you go with 6-7 lbs of boost unless you are running a boost retard unit. If you are running racing gas then it won't be an issue, either. Maybe since you are running a cam with a 112 degree lobe center, you are bleeding off a little more boost than if you were running a cam with a 114 degree lobe center like I was. But be careful when you lay on it with than much boost. Detonation with a blower can spell disaster.

Hey rumrumm, that's a VERY nice ride you have!
I hear you on the detonation problem, that's why I invested in a total overhaul of the 502. I actually considered running alcohol (blower motors love the stuff) but, after realizing that it would take another $6K investment to make it practical for a street car, I opted for a pump gas friendly rebuild. Detonation is THEE biggest bugaboo on a street driven blower motor. It took some time & cash but, the results were (IMO) worth it. Anyone want to buy a Hilborn Shotgun injector hat & BBC pump and kit cheap?

To try and stay away from detonation, I'm running a MSD 6 BTM
It seems to work pretty good. When I'm cruisin and in a vacuum, I leave it on about 3 degrees per pound because my timing is set at about 37 for cruise purpose and I don't want to make the mistake of forgetting and hitting it, but when I'm purposely running into my boost I only set it for 1 per 1 for about a 30-31 total.

What about vacuum advance hooked to the manifold for cruising. It would only come in when I'm under a vacuum. Would I have to run some type of one way check Do you run vacuum advance at all or leave it capped like I'm doing right now?

my car likes lots of timing and i run btm msd so it at 36 .i have tried less but it dose not like it and on vacuum advance i do not run any .i would not run the advance .but you would hook it at the base of the carb and would check it first. with a vacum gauge be for you hook it up to make shure it stop pulling in to boost to make shure the vacuum drops run it wot and check it. on my car at the carbs it dose

When running a vacuum advance, and a blower, you should pull the vacuum from on top of the blower. I'm under the impression that running some sort of one way check valve at the manifold could run into problems when under full boost. I would recommend running your advance from under the carb on the base plate, or from the top of the blower, there should be a plug somewhere on the top side or back of the case just below where the carb/s mount.

Nice motor.
I think you have a pretty good handle on tuning this motor or you would have toasted something by now. The msd is the way to go.
Here are few things:
The blower is about maxed out but it is ok for this. Concealed so this is your trade off. Yes you can overdrive it some more. this will help boost at the low end and up the range a bit but as you go faster with the blower speed it reaches a point where it becomes less and less efficient and take a lot more power to drive and give you less back. It creats a lot more heat in the intake and makes detonation control more difficult. Keep in mind that the motor is making more power but it is using the power to drive the blower and not the wheels. thus the motor is working a lot harder than it would appear. enough about this.
exhaust. some was said about tuning etc. bull... on supercharged motors bigger is better. You should be using the largest pipes you can get on the headers even larger is better. from there , as big as this motor is I would have nothing less than 4 inch anywhere in the system. Ironically if you do open up the pipes you may lose boost!! This is good because you have more mixture being able to flow into the motor and better scavanging. You will make more hp or rather release more more hp. Also reduce the hp required to drive the blower. complicated but true. open those pipes up. my 6 cyl diesel 350 cu in only revs to 3000 and has 4 inch pipe and no muffler and well over 25 pounds boost and 600 ft lbs torque at 1500 rpm and over. other guys run a 5 in pipe and double the boost.
o-ring the heads or block. you may have already done that. If you use solid copper gaskets you can reuse them if you use sealant. Felpro's I don't know. I don't think so. We used our copper gaskets over many times on our old gas dragsters. even the alcohol FC. often annealing them before reuse.
As I recall on the gas dragster early hemi we ran about 20 psi boost maybe a little more. this cost us at least one piston a run sometimes a lot more.
My t-Bird SC ran 14 psi max with computer control so it couldn't kill it self. If pushed hard you could blow the head gaskets and cause a lot of trouble. This was a motor that if you increased the overdrive on the blower by 5 % (pulleys were avail) you could guarantee loosing a head gasket a lot sooner than later.
You could add a water/alcohol injection. I think Summit has them and it will help with the mixture. I wouldn't expect to make more power but it will enable you to use power you can't now.
Running dual 650 or 750 might help but at what cost?? You already have a real killer now. They might help some on the top end but you only have 6500 to 7000 to run with so do you need top end???? only you can decide.
There is a really good book out called guide to superchargers I think. It in all the hotrod magazines. It a basic green cover with a blown motor on the cover. In this book it explains how to fix a holley carb to take the vacuum/pressure reference from below the blower. Summit sells holley carb for blowers with this feature. This is a big help for tuning. I have only seen one run but it ran very well. 6-71 however. Taking vacuum from under the carb is risky as you can get vacuum much higher that you would think from a blower and cause the power valve to close (seeing more vac) and lean it out. A lot of guy take the PV out and compensate for it with jets and kill the gas mileage. It works but...... is it worth it??

you haven't killed it yet so good job.
good luck

I think I'm going to have to add MSD's knock alert system. It's an audible and warning light type of system. The cool weather today had me running dang good, but It leaned me just to the point that I could every now and then hear a little ping. My engine is loud and I don't know how long it might've been going on before I noticed it, and turned on some more retard. Does any one know of a system that automatically retards the ignition as it picks up detonation. I'm talking of a small system sort of like the BTM now. Not no big lap top ecm programmable system. Just something a bit simple. I would love to have something that would work with the BTM. Let me know what yall know....

Originally posted by camaro_fever68
I think I'm going to have to add MSD's knock alert system. It's an audible and warning light type of system. The cool weather today had me running dang good, but It leaned me just to the point that I could every now and then hear a little ping. My engine is loud and I don't know how long it might've been going on before I noticed it, and turned on some more retard. Does any one know of a system that automatically retards the ignition as it picks up detonation. I'm talking of a small system sort of like the BTM now. Not no big lap top ecm programmable system. Just something a bit simple. I would love to have something that would work with the BTM. Let me know what yall know....

UPDATE: Found a company called J&S Electronics that makes a complete system. It is a ignition box, boost retard, rev limiter, and knock sensor that retards timing to individual cylinders automatically. It's all completely adjustable and seems to be almost as simple to operate a the MSD 6 BTM.


Never ran this system as it was not found to be needed.

Originally posted by pat mccarthy
my engine some people say should of not worked. but it works great and i have 10to1 and run 10 of boost i have the msd btm on mine and it all work and this been this way for 5 years and i am not easy on it. the cam this big and is on 110 this kills some static cr and at idle at the intake my vacuum is 2 inchs but when it runs in to boost hang on .but it sound like your on the edge. like i am to but it will work. i think i would of used the multi-layer steel head gaskets but that what i would have done .O rings are out the new head gaskets work good unless you run top fuel

This was a very good informational thread. Lot's of great advice and experiences shared.

Pat, I had to go searching for the info you gave me on the head gaskets for the blower set up. I'm running pre-flattened steel fire rings at this time, but will be going with the MLS now. I'm going to add the water injection kit to my engine and even if I don't raise the boost, I can still add some timing and get the power back that my BTM kills with the retard under boost. I haven't busted a gasket but the tracks are starting up so I may as well fix it before it breaks and if I decide to go to the 210% pulley for 10lbs, my head gaskets should be safe.

One question on the Fel-Pro MLS gasket: On the Hi-perf. 400 gasket, the water passages are restricted to cure the overheating problem. It works very well as I have had no issues with running hot. Do you know if the MLS is the same? I did a search at the Federal-Mogul web site and various others but, couldn't find anything about the modification.

look at the mls cometic gaskets (800)752-9850 i would run them. i was looking at a knock sensor to but was told it would not work with the blower with gear case noise and the soild roller cam they told me the knock ear would go nuts and pull out the timing all the time