304 budget rebuild - guaranteed to make you cringe

[afstruct]

There is one for sale for $25,000. The price has gone up from around $14,000 last time I looked.

Holy shxt , last time I sore people were going $8000 to $10000 = why better options.
Obviously someone pays.

A trick shift manifold would be great but I don't think they're making anymore and they're still quite expensive.

 

[Immortality]

No if you watch Steve Burle do it you can see he actually adjusts all the AFR's to with in a few percent and picks up 60hp.

I also read a small article from HP academy on EGT sensors vs O2 sensors. He said after tuning an engine with the wideband O2 sensors they checked the EGT sensors and had an ES of 28deg C so they're not as accurate and apprantely have a slower response. But any way back to manifolds.

Yes, on a down draught manifold with twin carbs (so one barrel for each runner) you can tune very well but on a more common single plane manifold with single carb you have all the runners sharing a common plenum or with a duel plane where the engine is divided in half there isn't much of a chance. Steve is a clever guy and has spent his whole life doing this ****. David Vizard has a good explanation and graphs of airflow distribution in some of his books, the early duel plane stuff has huge variation between the different ports and depending on port arrangement and engine firing order one port scavenges from another making it leaner too. It's all very interesting when you get into the nitty gritty of it all.

I do agree that O2 sensors in each runner is ideal but EGT is much cheaper and will get very similar results.

 

[keith reed]

I have been in contact with come racing regarding their twin throttle body manifold running lean at the front and rich at the rear and this is the response from Sam Blumenstein.

This is rubbish.

The people who have had rich rear and lean front cylinders in 99% of cases are using the wrong size injectors. Injectors that are TOO large and being pulsed slowly so that there is no actual fuel spray mist but rather puddling and droplets.

The incorrect atomisation of air and fuel in circumstances like this create issues like what you describe and frankly it doesn't matter what manifold you use. Ours is more susceptible to this because it is so efficient. The runners are high and out of the heat and we require far less fuel to make big power figures.

We personally built over 500 street and race engines using our manifold since their introduction in the early 2000's and never had issues the so called experts describe.

A simple rule of thumb is to forget traditional formulas for injector size versus engine capacity and rpm when it comes to our manifold.

For example a typical 383 engine with 600 heads, 11.8:1 compression, solid roller bracket cam with 253/261 @ .050" 112 LCA and .591" net lift will make 580 BHP @ 6500 using a 24lb Bosch injector

If you do your calculations with all the online injector sizing problems there is no way this is possible, yet we did this with engines like this all day long. Plugs remained clean, consistency from cylinder to cylinder was always excellent.

The only problem with our manifold is that so called tuners and engine builders have no clue about the unique nature of it's design and they simply go ahead and apply the generic formulas to something that requires a smarter approach.

Sam

 

[Immortality]

Unique design.....

Trouble with his answer is that most efi engines use a single O2 sensor in the collector so if indeed there were lean/rich cylinders you wouldn't see it as the O2 sensor gives you an average of the 4 cylinders on that bank.

I'd like to see a link to said 383 engine with full dyno graphs and parts used/tune info or I'm inclined to not believe.

The other problem with that answer is that if you have lean and rich cylinders (but have the same size injector in each hole) than it simple does not add up that the injector is fine on one cylinder but not on another.

Now is that clean or lean plugs?

 

[keith reed]

Unique design.....

Trouble with his answer is that most efi engines use a single O2 sensor in the collector so if indeed there were lean/rich cylinders you wouldn't see it as the O2 sensor gives you an average of the 4 cylinders on that bank.

I'd like to see a link to said 383 engine with full dyno graphs and parts used/tune info or I'm inclined to not believe.

The other problem with that answer is that if you have lean and rich cylinders (but have the same size injector in each hole) than it simple does not add up that the injector is fine on one cylinder but not on another.

Now is that clean or lean plugs?

I can only suggest that you contact them.

 

[Immortality]

No need. A 24lbs injector simply does not support 580hp unless the bitch is lean as **** or he has 16 fitted instead of 8.

Those pesky online fuel injector calculators he rubbishes in his answer use Brake Specific Fuel Consumption (BSFC) to determine fuel flow requirements and it is widely accepted that with gasoline you need .45-.50 BSFC to make X number of HP.

 

[shane_3800]

Most quality injectors have a wide window of operation. Plus duty cycle does not make as much difference to spray pattern as pressure. I have some old injectors laying around some where I can throw them on the test bench at work if anyone wants proof.

 

[Deuce]

Sounds like my 36lb injectors are too big for my 355.

 

[keith reed]

Sounds like my 36lb injectors are too big for my 355.

If you look at their site you will see that they only mention the blue top injectors for any of their fuel injection motors up to 383.

 

[EYY]

If you look at their site you will see that they only mention the blue top injectors for any of their fuel injection motors up to 383.

But what operating pressure do they recommend?

I think the come manifold was probably more developed with the twin carb config in mind, and the front facing throttlebodies were probably more an afterthought which would allow them to be fitted to later model efi cars without the need for any serious bonnet mods.

Some very interesting discussion.