If funds permit, this is the best way of course. Computerized self adjusting system that compensates for temperature, altitude, and weather conditions. If you want to drive it every day and have less maintenance, this is the only way to go. Adding in a roller cam would complete it (and as large of valves as you can, so that you need less cam lift--another feature with modern engines and their multi-valve setups that require very little valve lift. It gives a very wide powerband and camshaft longevity is much improved with an overhead design, since there's no extra valvetrain weight to add to it and so spring pressures are very light in addition to the low lobe lift--then there's variable valve timing on the camshaft(s) themselves, spark knock sensor, etc.). These older engines are super, super simple when compared to modern engines! As far as what happens, you don't have to worry about wet flow anymore, and so velocity isn't AS important. Fuel atomization occurs right there before it goes into the head, so what happens before that isn't as crucial to keeping the fuel charge in the air, since there's no fuel charge to worry about. You still want a nice flow of air past the injectors of course, but getting the velocity/volume of flow matched to your CFM demand based on RPM powerband and CID is still important. Tuning would be much simpler and efficiency would be optimized. You can expect more power AND fuel economy with port injection vs a carburetor system. Notice on modern engines how there's usually one large throttle blade that controls the air, with an air mass flow sensor before that. Then there's the throttle position sensor, and oxygen sensors on exhaust to regulate how much fuel needs to be mixed with the air. Point is, velocity of airflow isn't nearly as important for port injection. Anyone else have more to add feel free to do so. Gary
do a leakdown test then you know what % the engine is at. my compression test was at 190+ leak down was at 90-97%
I'd like to see more multi port systems on high swirl Buicks. Multi port fueled engines with lesser swirl characteristics have had to incorporate methods to increase mixture motion (that continues and often accelerates as the piston rises) to make up for lost atomization naturally happening from introducing fuel into a long, fast-moving airstream.
Hey Guy, I did a leakdown last week, IIRC, leakdown was around 3-5% on all cylinders, no leakage heard past intake, or exhaust valves, all was past rings into crankcase. I will check again since I still have the plugs out AND I CRACKED ONEou:
That sounds good at least you know now that everything is tight. I have been using NGK YR 5 plugs now and they are burning good. These are not extended tip, this plug is more for a stock 350 from 1970 and they work real good with the nitrous. If you broke a plug they are in too tight. I do not give them much of a turn after seating.
I use an impact to run 'em in:laugh: Actually its the #8, damn AC box makes it a bear Im using NGK UR4, seem to be doing good
I forgot to add two more things to this thought process: reversion and potential lean cylinders in #5 and #7 from single plane usage. This was one of the main problems with using a single plane intake at lower RPMs (with v8's--v6 doesn't have this problem), and using port injection would alleviate if not totally eliminate this issue since the fuel is being delivered directly to the ports and so each one gets adequate supply without any worries about one or the other being starved due to sequential side-by-side firing order. Seems fuel injection would solve more than just a couple of issues that carburetors have! Addressing your comment, it seems that finding that optimized velocity/flow is still important with a dry flow system eh? Gary
The issues with MPFI intake manifold tuning is creating a large enough plenum behind the throttle body and matching runner length to cam profile and powerband. Most SP intakes converted to EFI have too little plenum volume and too short runner length, making narrow, peaky powerbands.
You are on the right track. A street/strip manifold built for a 4 bbl carburetor has runners that originate from a plenum under the carb which restricts design. MPFI adapted to such a manifold is a compromise at best and should be free from this type of design restriction. Per Keith's description Example of a non-restricted design with large plenum with long runners. This type of design should offer wide power bands and work with a wider range of cam profiles. https://dl.dropboxusercontent.com/u/39382077/Manifold.jpg However this thread is about the SP3 and if MPFI is added it should be in sequential mode where adjustments can be made to individual cylinders. Paul
So please lets keep it that way and not hijack this thread like other threads have been. Please start a new one if you guys want to talk about this. It's not that hard to do. :rant:
Talk about what? Fuel injection on the SP3? I figured it was relevant enough, as did the others. The bosses are even there for it on the manifold, so shuddup lol. Gary
A couple more ideas/thoughts on this: the Buick 350 has a natural advantage in this regard with its super wide stature, having long runners by nature of its dimensions alone, and the already large plenum could be increased by adding a larger open spacer before putting the throttle blades on top of that. I think it would certainly alleviate the issues you speak of, which would be common problems on narrower engines. Was this design intentional when they engineered the SP3? I've said that they put a lot of thought into it already, perhaps even more so than anyone had previously thought... Next is a statement not aimed at the originator of this post, but to all it may concern: All the 'design flaws' are simply engineering that people do not understand yet. As time goes by, maybe people will finally see there's more than one way to skin a cat, and sometimes the old paradigms become defunct and are in need of rethinking and new processes. The computers you guys use to read and type inside this forum, the internet itself, and the newer cars you may or may not drive are all results of things like this. To all you negative nancy's trying to derail advancement on the progress of this thread: If you can't add valuable input to the thread/forum and only have insults or negative things to say about others presenting ideas, then you are nothing more than stumbling blocks to progress. Even so, we will overcome that too. Understand that we're not a threat to you personally (as it seems to be taken), but to the knuckle dragging mindset that keeps things stagnant. Once this can be understood and accepted, we can all be friends again. I'm not your enemy. Let's work together, shall we? I've always said the Buick engineers back in the 60's must have been from another planet or from the future or something... Gary
:TU: I agree Gary, Reading all these ideas and theories, even tho some are not directly related to my issue, are enlightening! I myself do not understand all the engineering that goes into and went into then SP3 and the 350 Buick, But I did read awhile back that the Buick powertrain engineers were ahead of their time, maybe at that "time" they're ideas weren't embraced by the masses. "Ok, Buick engines work, they move the car, ok good" Like I said Im not an. engineer, or an engine builder, but when I bolted on my 750 Vac. Sec. Holley, my car felt stronger ON THE PRIMARIES, compared to the Q-Jet, The Holley has larger primaries than the Q-Jet, hmmmmmmmmmmmmm. Maybe a 650 cfm is not the way to go. Being an internal combustion engine is always referred to as an air pump, MAYBE the smaller primaries on the Q-Jet are restricting air intake compared to the larger primaries on the Holley. Another thing I noticed while driving with the Holley, there is a definite bog ON THE PRIMARIES when slowly increasing the throttle while cruising, once past the bog, it did pull stronger than the Q-Jet. My thinking on this, the Q-Jet with the smaller primaries, had the proper air/fuel ratio, BUT not enough of either one for my engine Im not going 650 cfm, Im for sure going mechanical secondaries, minimum Im going is 750, probably 850 cfm more likely. Would a 950 work:eek2: Geeeez, I have all winter to sort this out:eek2:
The reason it bogs on the primaries of the 750 is it's showing you your velocity isn't what it needs to be until RPMs raise a bit and the 'bog' goes away because velocity increases. This also points to it needing a smaller total size carb for a single plane. You wouldn't feel that same bog on the dual plane, as I described earlier in the thread (or was it the other thread?) before my ideas were slapped down. You will feel stronger on larger primaries once the air/fuel mixture is properly atomized, and supports my claims made in another thread about how large 2 barrel carbs rock on a dual plane vs 4 barrels at partial throttle, or vs their primaries. Sigh. I don't care who's right or wrong, I just want this figured out, and as long as we all keep talking, it'll get there. The primaries on the Qjet will keep velocity up and so won't bog while it's using those, but won't provide enough air/fuel when RPMs raise. The secondaries opening are what provides this, but at the same time, may be too much too fast, or not enough fuel to go with the air, as was originally stated with the idea of a secondary accelerator pump. Then came the idea of even fuel/air distribution that a square bore carb would give, and it's been etc. etc. from then on. Reread my ideas of dual plane vs single plane and CFM/velocity. Gary
My suggestion is a 650 DP with a 4 hole 1 inch spacer, ill almost guarantee you'll get some low end torque back and the car should pick up a couple of tenths !! That's my prediction.....
The bog when just running on the primaries can be tuned out with either a different pump cam and or swapping to a 50cc pump shot diaphragm from the 30cc one that is probably in there now, the squirters can even be changed on some models. Holley carbs have a lot of adjustments for tuning that's why they're so popular, you just need to learn how to adjust one and you'll be hooked. GL Derek
I had a previous car with the same cubes(albeit not a Buick) run mid elevens with just a 650 Dp carb I still say you need to see what happened between manifold changes, as a good working Qjet and or 750DP shouldn't be more than a 1/10's difference in et You still have another issue I believe Ill beat this dead horse some more,but................ the SP3 has run low 11s using a Qjet so far,so the carb style is not the problem
You don't even have the carb figured out yet and you want to talk about fuel injection. Maybe you should do more research. What you now own this section where's your 350 at, and where's that physics equation on velocity mr math. Don't forget to do it both ways and don't forget the fuel or is that too much for ya. Forgot to tell ya, shuddup. lol :bla:
When running only 2 barrels at light throttle it isn't just velocity, it's vaporization and how vacuum helps achieve that. Vacuum is one of the biggest contributors to vaporization. The fuel curve is basically goofed up. A big thing to remember is that any one cylinder is drawing the rest of the intake and all of the available throttle bores rather than half, with a dual plane. Transitionary enrichment needs changed from the previous tuning. SP's require a bit more enrichment to make up for the reduced draw when previously tuned for a similar DP installation. PV and accelerator pump, maybe primary jetting. It's not so much the CFM rating, it's the fuel curve and how the carb draws...booster type, air bleeds, etc. You can MAKE all of these carbs work, with various levels of difficulty and skill. Easier to start with a carb set up for SP combos.
