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How much of a power increase?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by vdubbin86, Jun 2, 2002.

  1. vdubbin86

    vdubbin86 Registered Member

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    My Blazer has the 305 in it. The engine seems to be nice and tight, Doesn't burn oil, etc.. Although it does run a little rich. (I think the carb may need to be rebuilt.) On the 350 I have in my S10 I have a near new edelbrock performer intake and 600cfm carb (man. choke) with a 360* aircleaner on it. This will bolt up to the 305, correct? And will putting this on the old 305 give me a bit more ooomph? The blazer already has a dual exhaust with no cats and flowmasters.

    Thanks
     
  2. 91K5

    91K5 1/2 ton status

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    Yeah the manifold will bolt right up to the 305. I'd guess you'll see around 15-20 more hp or so from the better manifold.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    If the Q-jets worn, and not "tuned" for performance, then yes, you might see some gain. It will likely come at the cost of lost economy though, if thats a concern. Again, if its having problems already though, then its not a fair comparison. I posted it before, tuned correctly, and of the same basic design, I'm still kind of at a loss how two carburetors rated at teh same CFM, equally well tuned, can perform significantly, if at all, better than one another. Going from a worn carb to a new carb though, will obviously make some difference, which may later be "attributed" to a "better" carb, when in fact, its just not worn out, or it started out tuned better.

    IMO, an air cleaner mod is worthless (how much CFM can the carb feed vs stock air inlet snorkel CFM capability) and seeing as the Q-jet is (at least on CK5) pretty much hailed as the end all off-road carb, (personally my favorite for a daily driver too besides fuel Injection) I probably wouldn't swap it in your case.

    Whoops..you said intake lol. Sorry, tired. The stock one is likely designed for low end torque and a swap probably won't do much on the crappy headed/valved 305, with the stock cam. If the stock one is not aluminum, you could maybe console yourself that the truck would be a few pounds lighter.

    The Q-jets are pretty easy to play around with once you understand them, and a rebuild would give you that understanding.
     
  4. BorregoK5

    BorregoK5 1/2 ton status

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    If your 305 intake manifold is cast iron, then moving to an aluminum manifold can help in keeping the air/fuel cooler. Cooler air has a higher density and results in a little more power. I think the Performer manifold has slightly longer runners and sits a little taller as well, so you will have a little more vacuum and bottom end (stored vacuum with more volume between the valve and the carb) and a smoother shot to the valve. This results in better bottom end and better fuel mileage. They should both be dual plane manifolds unless you have the Performer RPM which will do better at higher RPM at the sacrafice of bottom end, so not much would have been gained there. If both carbs are spread bores and the same cfm then nothing would be gained other than the cleaner working carb would make an improvement. Going from a spreadbore to a square bore might be a little dissapointing though if that were the case. While the power numbers would be relativley the same at peak rpm, the botom end / primary to secondary transition / and fuel mileage would be very different. Good luck.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Aluminum dissipates heat faster than cast iron. It also absorbs it more readily. Since the water ports still run through the AL intake, and the heads are still bolted to it, I doubt if an AL intake swap will result in any noticeable temperature change.

    If you cool off the intake air charge, fuel has more of a chance to drop out of suspension as well. When not striving for a 14.7:1 mix ratio, (racing, etc) thats not a problem, however, when striving for economy or low end power, that can obviously be a problem, and cost you on the street. (in performance)

    Small intake runners build velocity, and for low end torque, small valves and small runners are a plus. LONGER runners won't hurt, but about half the stock 305 intake manifolds I've seen are AL, and appear to be fairly "tall". Don't think my trucks 305 had an AL intake stock, but the '85 SS I pulled apart did.
     
  6. DesertDueler

    DesertDueler 1/2 ton status

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    The only reason I can see a carb perform better than another and have the same CFM rating is like a holley compared to a q-jet.The reason being is beacuse the secondaries on a q-jet are alot bigger than the front ones, and the holley they are all equal. So at high RPMs the holley will work better. But for city driving, The Q-jet will get better gas milage, and they perform better on angles. I stick holleys on street rods and race cars. Daily drivers get Q-jets, and so do rockcrawlers.

    Dan
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    If a Q-jet primary flows 250CFM, and the secondary flows 550CFM, (give or take a few) while a Holley Squarebore flows 400 on each side, if the fuel metering (per CFM) is the same, the end result is the same also, right? If anything, the Q-jet would have better low end throttle response (intake charge velocity)and the Holley could only equal the Q-jet at WOT.

    Again, IMO tuning and carb condition make all the difference in the world. I just don't think Q-jets are as common racing because people don't spend the time tuning them, and that there are no "mechanical" secondary models. I really don't see how they can be much different to play with...all adjustments/changes (primary rods, jets, float level, needle/seat, secondary rods/hangars) can be made by taking the air horn off, which is at most like 9 screws and a pin, plus the air horn gasket.
     
  8. BorregoK5

    BorregoK5 1/2 ton status

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    Your right on the shorter runners vs longer runners where the port diameters are the same, I was thinking along the lines of MPFI and throttle response based on stored vacuum with larger diameter and longer runners. But in a carburated instance, that doesn't apply the same as the runners are typically 1/4 the length and width.
    As for the aluminum VS cast iron, the temp difference has always been very noticable. Take a q-mile run on both and then hop out and put your hand on the manifold, the cast iron will give you a 3rd degree burn, the aluminum would be hot but not nearly as bad. I converted a 924 porsche from FI to dual hitachi side draft carbs once, we used screens at the carb to atomize the fuel before the runner. The aluminum intake runners would internally/externally ice over from prolonged WOT, but the steel one (Yamaha 850 Special exhaust manifold modified as a side draft intake, hahah, dont ask) didn't ice over and concequently ran a little better on top end with less overall power. It was an interesting experiment, and a free porsche so it went well, except the tranny which we eventually blew! Sold the car for more than we invested in play parts too!
     

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