Hi Norm, DrRansom442, all,




I haven't called you a name, I just ask you do not act like Norom




82 Vette + offy, yes OK I jumped to the Crossfire as its the only thing that closely matches those perimeters...as for a "dualport" vette intake we still haven't established this



OK but this is not how the LT5 operates, there are no primary and secondary butterflies, there is but one throttle body with 2 butterflies sharing the same pivot. the 16 intake plenums supply air constantly to all 16 intake valves, which do not remain closed at any point the engine is running (well atleast without catastrophic results). the "valet mode" is handled by the ECM recalculating spark and fuel delivery. Sort of like GMs electronic speed governors -- once a vehicle hits a certain speed, the timing and fuel are readjusted by the ECM to prevent the vehicle from travelling faster <---easily undone by most power reprogrammers.




See above, this is already a moot point, no need to go on about it.



and when his assertation that the LT5 has secondary and primary runners is flawed?


moot point but it gets back to my challenging the existance of an OEM dualport Vette intake



the dualport design, I fail to see any need for separate intake runners for the primaries and secondaries, since the intake seems to have a spreadbore vacuum secondary like a Q-jet in mind. What is the purpose? The secondaries don't supply air/fuel unless there IS a demand, that is the whole point of a vacuum operated secondary circuit. It allows a lesser air/fuel charge under low and part throttle for economy and low end. When the engine develops enough demand it opens the secondaries air horn allowing as much air/fuel as the engine can handle (since overall CFM meant a Qjet was larger then most engines it was bolted to could handle). Using runners from the primaries and runners from the secondaries seems not only redundant but detrimental by adding weight and restrictions to the size of the intake ports. I could see this intake used with a mechanical secondary carb but then wouldn't it be a squarebore?


well that's 2 of 3, can we get Norm to agree, is the question




black toes = bad strut/no steel toed shoes related memory

........ So I guess this is sorry Norm for dogging the Crossfire. ........

OK but this is not how the LT5 operates, there are no primary and secondary butterflies, there is but one throttle body with 2 butterflies sharing the same pivot. the 16 intake plenums supply air constantly to all 16 intake valves, which do not remain closed at any point the engine is running (well atleast without catastrophic results). the "valet mode" is handled by the ECM recalculating spark and fuel delivery. Sort of like GMs electronic speed governors -- once a vehicle hits a certain speed, the timing and fuel are readjusted by the ECM to prevent the vehicle from travelling faster <---easily undone by most power reprogrammers.

the dualport design, I fail to see any need for separate intake runners for the primaries and secondaries, since the intake seems to have a spreadbore vacuum secondary like a Q-jet in mind. What is the purpose? The secondaries don't supply air/fuel unless there IS a demand, that is the whole point of a vacuum operated secondary circuit. It allows a lesser air/fuel charge under low and part throttle for economy and low end. When the engine develops enough demand it opens the secondaries air horn allowing as much air/fuel as the engine can handle (since overall CFM meant a Qjet was larger then most engines it was bolted to could handle). Using runners from the primaries and runners from the secondaries seems not only redundant but detrimental by adding weight and restrictions to the size of the intake ports. I could see this intake used with a mechanical secondary carb but then wouldn't it be a squarebore?

the dualport design, I fail to see any need for separate intake runners for the primaries and secondaries, since the intake seems to have a spreadbore vacuum secondary like a Q-jet in mind. What is the purpose? The secondaries don't supply air/fuel unless there IS a demand, that is the whole point of a vacuum operated secondary circuit. It allows a lesser air/fuel charge under low and part throttle for economy and low end. When the engine develops enough demand it opens the secondaries air horn allowing as much air/fuel as the engine can handle (since overall CFM meant a Qjet was larger then most engines it was bolted to could handle). Using runners from the primaries and runners from the secondaries seems not only redundant but detrimental by adding weight and restrictions to the size of the intake ports. I could see this intake used with a mechanical secondary carb but then wouldn't it be a squarebore?

There are two intake ports and two exhaust ports per cylinder. Intakes are individual but subdivided into primary (front) and secondary (rear) ports. The secondaries are all slightly larger in diameter and each contains an auxiliary throttle plate. The exhaust ports are all the same diameter, are individual for most of their lengths but pair-up just at the port exit. The four camshafts ride on bearing surfaces machined in the head and are retained by the cam covers. Each cam has two different intake profiles, mild (252°) for the primary valves and aggressive (272°) for the "secondary" units. All exhaust durations are identical (252°) and valve lift of all lobes is the same (.390"). Direct-acting hydraulic lifters work the valves and dual valve springs are used.

OK but this is not how the LT5 operates, there are no primary and secondary butterflies, there is but one throttle body with 2 butterflies sharing the same pivot. the 16 intake plenums supply air constantly to all 16 intake valves, which do not remain closed at any point the engine is running (well atleast without catastrophic results). the "valet mode" is handled by the ECM recalculating spark and fuel delivery.

The induction system is described as "three-phase" and looks like a sci-fi version of the tuned port injection we've known since 1985. There are three throttle bores, 16 runners and 16 Multech injectors. The smallest throttle plate, 22mm, supplies air at idle and very low speeds. Next, the two main throttle bores, 59mm each, open. Below half-throttle and 3500 rpm, the engine runs with the auxiliary throttle plates in the secondary ports closed and on eight of the injectors.

Once the driver gets his boot into a LT5 V8, things begin to happen. When both 3500 rpm and 1/2 throttle are exceeded, the auxiliary throttle plates pop open and the second set of injectors come on line. The extra punch of the secondaries is further augmented by their more aggressive intake valve timing. This three-phase TPI maintains high intake flow velocity and turbulence along with tight control of air/fuel ratio over a wide range of engine speeds. The result of this is a flat torque-curve and that, along with digital engine controls, is responsible for the engine meeting Schaafsma's goal of smooth down low and real nasty on the top end.

They achieved a significant improvement with the use of the computer

A most interesting feature of the LT5 TPI is the power key, or "valet switch" mounted inside the car. Turning it off, disables the secondaries and protects Its Royal Highness from the abuses of valet parking services, children trying to impress their peers or detail shops who aggressively "road test" each job.

........ After more thinking on the subject and more research, I have a couple comments regarding DrRansom442's latest posting, seen here: ........

I believe that I can clear up some of the misinformation regarding the LT5........

........ Earlier (possibly '82) Corvettes used a manifold with two runners to each intake port. One was used for normal driving, both for max power. It was a variation of an early '50s street/strip design by Offenhauser. They achieved a significant improvement with the use of the computer ........

Unless DrRansom442 objects, we have one down and three to go.