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Re: Building high MPG Motor for a 93 Vhevy Van
racprops #325676 September 12th 2009 5:14 pm
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interesting article on the reason for the birth of the 4-7 swap cam. evidently they are a bit more than a high end cam. most common manufacturer is Lunati. they can seemingly make you anything you want. Interesting how this really came about due to factory design issues that were trying to be corrected for high performance use. I have always had excellent luck with calling Lunati or Manley and talking to a tech. explaining to them exactly what you have and what you want to do. They will give you excellent recommendations on cam specs to idealy suit your needs with the equipment you are working with. they will even recommend equipment to get you to your goal if what you have is not compatible with the result you are looking for.

http://forums.chevyhiperformance.co...on/4-7-lobe-swap-cam-question/index.html

Last edited by swimmster; September 12th 2009 5:15 pm. Reason: forgot the link.. der..

Yeah..... I know I know.... It's NOT a van... But if you squint, It could be a REALLY long van?

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Re: Building high MPG Motor for a 93 Vhevy Van
swimmster #325688 September 12th 2009 6:57 pm
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Oh I remember about the problem of the Rooads Lifters and knock sensors and that they really fade out at the low rpm I want to use.

What about the old adjustable cam timing gear set, they were spring loaded to change the cam timing ??

I am trying to have low RPM power and then run normal at higher RPMs...

Any one ever hear of Power valves?

I have a 305 TB in a 87 Van that needs an engine...heck I might just pull those heads and build them...

OR a wild idea, build the 305 with a 400 crank and end up with a strocked 342 (or something...)

Long strock small bore?


Rich

Re: Building high MPG Motor for a 93 Vhevy Van
racprops #325806 September 13th 2009 1:35 pm
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man.. I used to know all the bore/stroke combos out there.. what would work with what, etc.. lol..

I know if you go with 305 heads, forget anything above 4500 rpms.. power starts dropping like a rock.. I think you may be heading towards an excellent breathing 400 plus hp motor with good everything on thru to 6000 rpms, and going with a gear vendors over/underdrive unit and then throwin in some 3.08 rearend gears if you can find some beefed up enough to handle the strain. Lot of factors going against good economy. lots of parasitic losses in a drivetrain. most automatics can easily burn up 40-60 hp just turning everything and maintaining pump pressure. LOTS of compromises in a high horsepower yet economic engine drivetrain combo..


Yeah..... I know I know.... It's NOT a van... But if you squint, It could be a REALLY long van?

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Re: Building high MPG Motor for a 93 Vhevy Van
swimmster #325885 September 13th 2009 10:30 pm
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OK Have you done the 305 TBI trick adn have you done the 305 heads on a 350??

Rich

Re: Building high MPG Motor for a 93 Vhevy Van
racprops #325896 September 13th 2009 11:00 pm
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I have had 305 heads on a 350. you gotta clean up the sharp edges on the combustion chamber to get rid of potential hot spots for pre-ignition. I used bone stock 87 305 heads from a monte carlo application on my 94 GMC pickup. converted it to a Q-jet. I was getting 28 mpg on the highway at 70mph on long trips. MASSIVE amount of low end grunt. hard to not spin the tires with no load. used to haul the race car like it was invisible. would go up hills like they were flat open road. headers help with this setup too. course, they help with any setup.

the 305 TBI works as good or better with an adjustment of the pressure regulator. If i remember right, the friend who had that setup reduced the pressure and had more gains. the air intake velocity is sufficient to further atomize the fuel into the air and create a better mixture. you get more power with less fuel. the 305 TBI body has smaller diameter bores which effectively helps out in the air velocity department. Your vacuum level in the intake will go up a bit too. I never played with aftermarket cams for the truck. I am sure though that a call to a manufacturer will get you something that could make the setup work even better. If you're going to throw alot of money at this issue, find a set of vortec heads for a truck as they are cheaper, have the exhaust ports ported to flow better as the intakes are the same as the performance vortec heads. vortec heads have efficient intake runners ad high swirl combustion chambers that make them a pretty efficient head design. You can get some gains in economy with ignition parts too. get a high voltage coil and bump up your plug gap. get a shim kit for your distributor gear so you can have highly accurate timing.


Yeah..... I know I know.... It's NOT a van... But if you squint, It could be a REALLY long van?

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Re: Building high MPG Motor for a 93 Vhevy Van
racprops #325961 September 14th 2009 11:17 am
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Hey hey.. I apologize for not totally comprehending your first post.. i fully read it the first time, then promtly forgot what you were using for a setup. the TPI intake may be a waste on the vortec heads. the runners will be far too long and your D pistons will just be a waste. yes, looong runners will increase velocity, but that length of runner will cause the fuel droplets to start pooling together by the time they reach the cylinder and this pretty much negates the swirl heads as you're back to OEM efficiency and not burning as much of the mixture as you could be. the short yet small intake ports on the 305 heads makes for a nice quick burst of airflow into the cylinder without the fuel droplets having time to come back together. Leaving a very rough, as cast finish on the intake ports helps with keeping the air moving with turbulence to help keep the mixture as atomized as possible. smooth ports only really helps when you're in the 6-8,000 RPM range making TONS of power.


Yeah..... I know I know.... It's NOT a van... But if you squint, It could be a REALLY long van?

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Re: Building high MPG Motor for a 93 Vhevy Van
swimmster #326022 September 14th 2009 2:37 pm
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I am unsure what your thinking...

But I am still stuck runming a TBI unit so I am looking to tighten it a little before I swap out the old motor and switch to a TPI unit.

So I am working on both.

I have a 87 305 in a another Chevy Van that is knocking...So it is a dead motor.

So I have a 305 TBI unit and a pair of 78 Heads if I want them.

Did they ever make a Vortec 305?

A stock TPI is port injected so the runners run dry...

So how will it work with the 305 heads?

Rich



Originally Posted by swimmster
Hey hey.. I apologize for not totally comprehending your first post.. i fully read it the first time, then promtly forgot what you were using for a setup. the TPI intake may be a waste on the vortec heads. the runners will be far too long and your D pistons will just be a waste. yes, looong runners will increase velocity, but that length of runner will cause the fuel droplets to start pooling together by the time they reach the cylinder and this pretty much negates the swirl heads as you're back to OEM efficiency and not burning as much of the mixture as you could be. the short yet small intake ports on the 305 heads makes for a nice quick burst of airflow into the cylinder without the fuel droplets having time to come back together. Leaving a very rough, as cast finish on the intake ports helps with keeping the air moving with turbulence to help keep the mixture as atomized as possible. smooth ports only really helps when you're in the 6-8,000 RPM range making TONS of power.

Last edited by racprops; September 14th 2009 5:23 pm.
Re: Building high MPG Motor for a 93 Vhevy Van
racprops #326044 September 14th 2009 3:56 pm
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MOST TPI systems were on 305 engines.. make sure yours matches. if you install a 305 TPI on a 350, you will need a custom burned EPROM. For what you want to do, in the RPM range you want to use, the 305 TBI will work excellent. use that and the 305 heads and you'll have tons of low end torque. the shorter runners of the TBI manifold will let you breath better. than the TPI. your 350 suckin thru long ass 305 TPI runners will cause more harm than good. 305 vortec heads.. hmmmm.. I don;t THINK they made them, but i could be wrong. if you plan to use vortec heads, make sure your piston domes don't hit. even 350 vortec heads with so much as flat top pistons generates 9 to 1 compression. if you have a slight dome, then you're lookin at 92 octane MIN.. there goes your gas savings.. lol.. There's alot of ways to do this.. you just have trade offs on most of them.


Yeah..... I know I know.... It's NOT a van... But if you squint, It could be a REALLY long van?

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Re: Building high MPG Motor for a 93 Vhevy Van
swimmster #326122 September 14th 2009 11:02 pm
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Please show my the front of your engine so I can see if I can use my stock belt set up..

Rich

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