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Discussion Starter · #1 ·
Hello everyone, I'm trying to help another friend with a small Weiand blower on a SBC with a TH350 and 4.11 gears. It is either a 142 or a 177, he doesn't know as he bought it that way. It is in a 1st gen Camaro. At full throttle, off the line launches, the car melts the rubber with no problem. As the tires start to find traction, he shifts into second. The rpms drop and the car struggles and feels sluggish until the rpms build up, then he shifts to third and it feels sluggish again as the rpms climb slowly. It feels as though the motor is struggling to build up rpms. Why so sluggish at mid to high rpm?

The fuel pressure is a steady 6 pounds. The carb is a Holley 750 double pumper with 77 primary and 88 secondary jets. 31 primary squirter and 35 secondary squirter. The front pump is 50cc and the sec pump is 50cc. The pump cams are brown and came with the 50cc pumps. The timing is set at 33 total, all in before 3000rpm. All the header tubes burnt the paint off the first turn out of the heads.The fuel is 100 unleaded from 76.

Around the town cruising is fine, no hesitation and instant throttle response!! No black exhaust smoke, just tire smoke. It'll light the tires at will!!
 

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471A
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running out of supply

I ran, and loved, a 144 Weiand on a mild SBC that ran 11.30s in a 3,200 pound Model A with a single 750 AFB and 3:50 gears. The 144 is, however, in all of its configurations overdriven to where it violates NHRA standards, so I have move to a Weiand 250 to stay within NHRA rules. As for the particular problem you describe, small volume blowers like the 144 run out of "oompf" early in the rpm cycle. Typically, small blowers start dropping like a rock not far north of 4,500 rpm. It may be that, in the particular combination you describe, the 144 blower simply is running up against its' limits.
 

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WFO
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5,030 Posts
I tend to agree w/the post by 471A- the engine's "outrunning" the blower. It's probably a 142/144, but if you posted some good photos, this might be determined for sure.

in the meantime, I would crutch thing up by going to a tighter converter and gears no steeper than 3.4-3.5's. Shift points may well need to be lower (aka "short-shift) to suit the powerband as well. If he's shifting at anything above 4500-5000, he might be already past the power peak.

To ET w/this combo, a good 60 foot is really important, so anything that can be done to get GOOD traction off the line will be very helpful.

Be sure he stays out of detonation- which he's likely doing if the engine hasn't burned any pistons. But monitor the plugs carefully, just the same.

Be aware that a boost gage can show really high numbers, but w/o the performance that should come w/them. A small blower can "choke" at the top; pressure increases but does no work. Poor heads can cause the same thing. Combine them both, and you can guess the results.

Is the cam ground w/a fairly wide LSA, like 112 degrees or more? Just selecting the right cam for that small blower can help a lot.
 

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bentwings
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2,608 Posts
You really should look at a much larger exhaust if you haven't already. 3 inch is not too big. Even with marginal heads you still need to have no restriction after the heads. You will probably notice a drop in boost as you go larger in exhaust system but that is because there is a cleaner path. The T-Bird super coupe was a classic as far as the exhaust went. It wasn't untill someone came up with a 3 inch ex for the 3.8 motor that they really started to wake up. Typically the boost would drop 2-3 pounds with the big exh but the performance went up quite a bit.
 

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Discussion Starter · #7 ·
I guess we will have to re-think the combination and go with the cheapest route first. I relayed to him what everyone suggested. He will save for the 3-inch exhaust first. Then save in the future for a ring and pinion change and finally, if "funds" permit, a new convertor will be in the works. As of now, I guess he'll have to live with the combination and "table" the fix until more "funds" are available. :thumbup:
 

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Discussion Starter · #8 ·
We got it figured out. :thumbup: He purchased a dual three inch exhaust but the car was still sluggish from mid to high rpm. So I upped his primary jets three sizes and his secondary jets three sizes and went for a ride. It now pulls like crazy from mid to high rpm. Thanks for everyone's input! :mwink:
 
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