Too good to be true?

[RPMS]

Okay, I'm a cynical bastard at heart. Tell me there's a free lunch, and I'll ask "What's the catch?" every time. So Pete came out with this link to a buildup article detailing a 400+ hp 350 engine using a 400 block w/ F*rd rods and a 327 crank.

http://www.airflowresearch.com/Articles/A3-P1.htm

 

This just seems too good to be true. If this is up to snuff, why haven't more folks on this list gone this route? I'm seriously considering going the 400/327 route, and I'd like some opinions please?

 

Also, Lingenfelter says that Aluminum heads are good for an additional compression ratio mark over cast iron. If I used 58cc iron smog heads and a thick gasket instead of 56cc aluminum, would the compression ratio drop to a low-octane-friendly 10:1? I'm guessing power output would drop by 10-15% by going from 11:1 to 10:1. A valid guess?

 

Any and all comments are appreciated!

 

Scott Ferguson

1974 260Z - Awaiting heart transplant

[Kevin Shasteen]

Scott (hope its your car that you're referring to about the heart transplant! and not you)

 

I'ld really enjoy having a destroked 400. I get a kick out of reading that article "The 350 Chevy Should've Built" everytime it surfaces.

 

I've been doing a little research ever since that article came up as well as our Octane/Compression -vs- Camshaft thread occurred also. I've discovered quite a lot-mostly just theory & some fact.

 

What I've come up with besides the Rod/Stroke ratio is the Piston Top in Sq.In. to Stroke Ratio & the Int/Exh Valve's to Max.HP ratio. I've completed a handwritten spreadsheet on Fords Factory Displancements & Included some Popular Ford Stroker's using these ratios. Currently working on the Chevy's SBC/BBC displacements & their ratios.

 

From this article alone I've noted:

1)352 cu.in.

2)4.155 x 3.25 Bore/Stroke

3)1.91 Stroke to Rod Ratio

4)13.559 Piston Deck in Sq.In.

5)4.1:1 Piston Deck Sq.In to Stroke Ratio

6)4.87 sq.in Window on Combustion Chamber

7)721cc's Swept Volum per Cylinder

8)145cc's minimum required to run this engine

 

Comparing this engine to my list on Ford's; the Stroke to Rod Ratio equates to Ford's 292 V8 and the Piston Deck Sq.In to Stroke Ratio of this engine equates to Fords 351W & 429.....just Numbers? Maybe-until you begin playing w/their Redline figures-then the tell-tale numbers come to life/fun!

 

How I understand the article in quesiton is this: The combustion in an engine occurs like a grass fire. The grass burns outward away from the point of ignitoin-just like a flame front in a cyl. after the spark plug fires.

 

From what I've read "High Perf.Auto Fuels & Fluids" at WOT, heat transfer amounts to @ 15% of fuels thermal energy. The heat transfer is maximized at perfect air-fuel ratio (stoichiometric) and decreases when richened (too much fuel or too little air). In the absence of Leaded Fuels-This has lead to two main stay mind sets of thinking regarding the maximizing the performance of an engine 1) To add a compressor (Supercharger/Turbo) 2) To search for a fuel w/a higher Specific Energy or "SE".

 

SE is a rating which indicates a fuels ability on how much heat energy a given amount of fuel can deliever for a given amount of air being drawn into the engine. (In the absence of Leaded Fuels-this seams to have been the Mfg's choices a)Turbo/Supercharging for Perf.Cars and/or b)Different fuel SE's for the lessor perf.eng.

 

Why is the SE important-well, the fuels performance is closely related to the release of energy during the combustion process. This is affected by the eng's reactants & its products of combustion; and by heat transfer in the cyl.walls.

 

Back to Compression issue; How do we hot rodders get the most "simple" power from an engine-by dumping as much "Cooler Air" into our engines as possible. This brings in more colder air which gives a more "Dense" air fuel ratio. The result of an A.I.R system is identical to the result of a higher comp.engine during the burning after combustion-but for different reasons. As the spark is ignited-a higher compression allows the air-fuel mixture to give off more energy & results in better burning; in other words-that Grass Fire burns quicker & more efficiently instead of slower.

 

The lower comp.ratio will raise the fuel requirements at idle because there is more clearance volume in the combustion chamber which dilutes the intake charge-thus, fuel is still burning longer as the piston descends'lower comp.ratio's raise the exh.temperatures and increase stress on the cooling system.

 

Now back to the article in question: the longer rod allows for the piston to "Hang" around the TDC area for a longer time-this is called "Dwell". This increased "Dwell" time holds the maximum comp.ratio in the higher spectrum of its maximum comp.ratio for a longer perior of time-thus allowing for a quicker/more efficient combustion. As this article proved-w/a longer rod you can also increase the comp.ratio w/out fear of detonation.

 

As for me-well my committee is still out on their fact finding mission; but the facts tend to speak for themselves.

 

All the books I've read about Stroke/Rod Length Ratio's indicate that it is a big debate between big name engine builders.

 

What I'm not sure about and this may be pure paranoia:

 

1) The smaller piston skirts of the custom piston-will this reduce engine durability due to the piston wobbling in the cyl; the purpose for a longer/wider piston skirt is to keep the piston as square in the bore as possible.

 

Other than that-I like the idea of running an engine w/11.1:1 comp.ration on 87 Ocatane!

 

Sorry for the long post-just some interesting facts.

 

Kevin,

(Yea,Still an Inliner)

[DavyZ]

I'm one of those people who thinks that engine combo is the "best." Let me put it this way, it is the one I want to build and I think it would be most effective in a Z-car. I thought about the 383 route, which would most likely be cheaper since this is an extremely popular motor with a host suppliers for it, but the other one seems like it would suit a lighter car more, at least in theory anyway. Perhaps someone can correct me if I'm wrong, but the chief obstacle to doing a destroked 400 is mainly cost and the lack of suitable blocks? That's the only real kicker as far as I know. The 383 is cheap in comparison, or at least one can build a 383 on an tight budget. When I looked at parts for the 383, it made me think why even question it? The cranks are cheap, so are pistons...I have yet to do serious research on the destroked 400, but it looks really good to me too. I think Kevin Shasteen is a lover of the same motor, so maybe he'll chime in!

 

David