Guest Locutus Posted April 2, 2001 Share Posted April 2, 2001 My neighbor is one of those guys who thinks he knows a little about everything. Anyway he was telling me that I should use 305 heads since it will raise my compression ration way up. My question is, what will it take to get them to flow really well. I realize that buying aftermarket heads may still be the much better deal, but I would still like to know what would be involved to at least understand why its not a good venture. Mike Quote Link to comment Share on other sites More sharing options...
DavyZ Posted April 2, 2001 Share Posted April 2, 2001 Mike, assuming you are talking about factory 305 heads, this is the ultra-cheap way to bump compression. If you have a smog job motor with 8.0:1 compression, the 305 heads will bump compression a minimum of 2 points! Reason? They have a chamber volume of something like 53cc or close to that. This is in contrast with the smog heads of about 76cc. Compression goes WAY up, but flow does not necessarily go up by the same amount. The valves are smaller then the 1.94" x 1.5" valves you most likely have on your 350 heads. CarCraft likes these 305 heads because they can come practically free. If you are on a very limited budget as I am, they are worth looking at if you already have them or if they are practically free. They have small runners, which is good for a fast responding small block, but top end horsepower is where the engine may suffer--it depends on what the top rpm will be. If you will run 5000rpm or less, then its no biggie, but if you are trying to build a motor that will spin upwards of 6500rpm, you should look at better (more expensive) heads. You can always do some "pocket" porting and get some results, but only put money into 305 heads if you are doing the work. Otherwise you are probably better off buying some aftermarket heads. If, however, the 305 heads you are talking about are already aftermarket heads, then forget all the above, becuase they will outflow the stock heads anyway. HTH David Quote Link to comment Share on other sites More sharing options...
Guest Locutus Posted April 3, 2001 Share Posted April 3, 2001 I am going with TPI so my top end is kinda of limited by that as well, they say at about 5000 rpm the TPI engine loses power. What if say I had bigger vavles and a port and polish done on them with a 383 bottom end(this is what the neighbor said would make a awesome TPI motor). You think this would be a strong motor about 400HP? The only thing I am afraid of is going to high on the compression and not being able to use pump gas. Mike Quote Link to comment Share on other sites More sharing options...
fl327 Posted April 3, 2001 Share Posted April 3, 2001 i think thats the best part about tpi on a mildly modified motor with alright compression ( less than 10-1 or 9-1 or so) you can run 87 all dang day! man i should have never sold that tpi harness, and you can chip it rather cheaply to get power across the whole rpm range!!!! and reliable yes!!!! but i hear nothing but bad news about the 305 and i agree with davy, if youre doing headwork by yourself or with a friend or something, by all means go into those 305 heads, but if not, go aluminum aftermarket with that tpi and run em... Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted April 3, 2001 Share Posted April 3, 2001 The 305 head's combustion chamber is so small that the valves themselves are shrouded w/out much wiggle-room/thus airflow suffers. Airflow is not always the only thing to consider; most airflow benches dont test for "Swirl" which an important factor when considering efficiency w/airflow! A head my have great flow #'s & still be a dog because of its "lack" of swirl at a cirtain RPM! Be sure you know your cyl.head; those "Smog" years are known for having thin castings-if you go grinding in the wrong place you may thin the casting to a diminishing level where it cant disipate the heat quick enough-AKA..."Cracked Cyl.Head". Read about porting/or ask a lot of questions from knowledgable people before grinding on thin castings. (I hate tight budgets-I'm on one as well). Just FYI! Kevin, Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 10, 2001 Share Posted April 10, 2001 Mike, I put a set of stock '84 305 heads on my 355 rebuild and have been very satisfied. To knock down the compression I used dished pistons. My observation is that my old 280Z pulls like a mule at 125 mph in overdrive and it runs fine on 87 octane. The transmission is a TH2004R. David has the right idea; this combination is not ideal or even desirable for racing, but it is an economical and effective approach for a street car if you don't feel like throwing $ at it. Paul Quote Link to comment Share on other sites More sharing options...
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