I've searched for info on this, with some degree of success, but I haven't found anything addressing a concern like this.

From what I gather, siamesing lets one cylinder scavenge air from the one beside it, i.e. 1&3 scavenge from each other, 2&4, 5&7, and 6&8. The big question I have about siamesing the manifold base is this; firing order being 1-8-4-3-6-5-7-2, since 5&7 fire one immediately after the other, then logically the valves open one right after the other. Wouldn't that starve number 7?

I hope you TPI gurus can help me out on this, If it's going to starve number 7 then I'm just going to port the ever living crap out of it, but if you folks who have already ported your base haven't had any adverse effects, then I'm going to siamese away.

BTW, if it helps any, It's going to go on top of a 283 ( i know a 350 will make more power, but it was cheap as free, ran well when removed, and it's tradition in my circle of friends to run the 283 at least once) ported 896 casting (power pack?) heads, .510" lift camshaft, 244° @.050"

 

I can't ever remember seeing a siamesed base. You can siamese the plenum and upper runners and just port the base. I am no expert at this but have been researching for my own porting job I am trying to figure out and so far have not run across anything on siamesing the intake manifold base. I haven't particularly read not to do this for any reason but the prodessional jobs I have seen done do not siamese the base.

 

Same here. I had my intake ported but not siamesed. I dont think siamesing is functional, otherwise my machinist would have suggested it to me.

 

Try a search here guys.

I wouldnt do it on a 283, its not looking for a bunch of air.

 

I did it and from reading the plugs the cylinders are getting a good mix of fuel/air and are all even colored. It helps a bunch and will make your stock runners do a much better job of supplying air.

 

244 @ .050? isn't that kinda big? Especially on a 283??? That would be big for my 383, and I run a 234/242 on 1.6's! I'm afraid to ask what the LSA is...

Not to mention the LTR setup would be a real big mismatch, siamesed or not...but siamesing would help a little though by effectively shortening the runner length.

Dont forget a bigger motor needs more cam...likewise a smaller motor needs less. I think the rule is add roughly 5 degrees duration for every 25 cubes for the same effect...?

 

Dont siamese the base! a friend of mine did it last winter and the engine lasted 6 month.............

from another topic....

Siamese base

Question:
-Would siamesing the base manifold show any gains on a superram(plenum, base, runners) engine? This engine would have been treated to cam, heads, headers, etc. I recall seeing a gentleman's website (Mike Davis) where he was using non siamese LTR's and a siamese base with incredible results.

MAX:
-Mike Davis blew that engine up twice and figures it was teh intakes fault. His theory was that 5 was stealing the fuel from 7 since they are next to each other in teh firing order. Both times the engine blew 5 was dark and rich looking and 7 is the one that popped (ringlands). His theory makes alot of sense. Extreme siameseing is probably a bad idea, especially if you are going to run the tune on the edge. He doesn't even own the intake anymore, another member here bought it.

Mike:
-Yep, MAX basically has the story.. My Exh valve on #7 was leaking and was blowing the intake charge back into the siamesed area of 5&7, which #5 was getting most of because of the firing order...

When the motor was rebuilt, I had to scrape 1/8" of carbon off of #5 because it was so rich, and #7 actually melted a forged piston it was so lean..

I don't tout siameseing the base any longer, but mostly because I hate pulling motors twice in 1 year.. 8-)

mike

Jimmy:
-My friends motor did the same thing after siameseing his base way into the intake

he siamesed the whole thing and i dont remember what cylinder went.....but he took it to the track and it didn't go any faster, said the car wasn't running right

then the car just "exploded" while cruising.....just driving along (lol, this sounds like a lie already) and KABOOM

I can ask him to post to this thread when i see him online

Answer#3
-I'm the guy Jimmy was talking about . #7 piston ate itself on mine . Honestly I did'nt give it a whole lot of though after it blew up other than the fact that a N/A stock shortblock , heads , cam runners and plenum car has no business blowing up like it did . That piston had a hole the size of half dollar in it . In the back of my head I was concered about air or fuel distribution problems and I guess that concer had mertit . Prior to the intake I never had a problem with the car . The engine wasnt a tired motor either , my Iroc had 55K miles at the time .

Interpret what u want from that . The intake ( siamesed almost al the way thru ) was on my car for one month before the carnage .
I improved from a 13.11 to a 13.10 and mph stayed the same right about 102 , which tells me I really want making anymore power .

 

Thanks guys, I appreciate that. You may have just saved me a motor!
Yeah, the cam is probably a bit much, but it's actually smaller than what my friend had in it before I got it.
I have read where siamesing did provide some benefit, is it a matter of how far down you siamese it? The ones that self-destructed sound like they were siamesed pretty far down... I do want to try to take advantage of the 283's higher rpm capabilities, I know it's going to turn higher than say a comparable 350, but is it going to fall flat on it's face a few hundred rpm higher or what?

 

FYI, I've been running this base for 3 years now, still waiting to burn up my engine. Something tells me its not coming.

And Ed Maher said that, not me. Go read the post. https://www.thirdgen.org/techbb2/sho...hreadid=140646