273 guys..Heads up!!!!

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omahamoparguy said:
I would not worry about blocking the heat riser. You gain very little form it really, AND, it makes it hard for the engine to warm up. I mean the intake is goin to warm up eventually anyway. The heat riser is there to make some vapors out of the fuel when the engine is cold. After the heat riser thermostat in the exhaust (if you have one) open up the heat riser has little effect on the intake manifold. You waste a lot of fuel by blocking the heat riser and cause some oil wash in the cylinder walls. I know everyone does it and I have done this in the past but now I have changed my mind on this after careful thought.
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I upgraded my car to a factory 4bbl manifold and 500 cfm AFB carb. Since then I've had the heat soak problem. I have to hold the throttle wide open and crank for a while to get it started when hot.

I have heard of two solutions. One is to partially block the heat rise passage with just a 1/4" hole to allow some gas to get through for warm up. The other solution is to install an insulating gasket (phenolic?) between the carb and intake.

I prefer the second solution for all the reasons you described. But I'm just wondering if it's enough to fix the problem. I would prefer not to have to pull the intake manifold back off if the carb insulator doesn't fix the problem.

Also, I have read that if you don't block this passage, the heat will burn the paint off the intake manifold. Don't want that!
 
Yes it will burn or dis color the paint for sure in time if left open,they all did back then. & the best thing ive found is the 1/4 to 3/8 thick carb base gasket (paper) ,worked great on my old 3/4 ton pickup with a mild 360.
 
Yes a working heat riser will ruin the paint on your intake and yes fuel boiling will be a hot start problem. Next time my intake is off I will block the passage and make sure the valve doesn't close. Here's a cool carb heat sink I need to try.
http://www.coolcarb.com/ tmm
 
Hipo65 said:
I called cometic there gonna send me one new head gasket for 30 bucks cheaper to help a guy out!
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What happened to the head gasket that you need to replace it ??
 
Update.... i got the new headgasket from cometic yesterday (they tod me they didnt wanna say to me just run it again & then have a problom so they sent me a new one for 60 bucks shipped! good deal for a 90 dollar gasket to begin with!) & got er buttoned up last night & fired it! runs f#$&en AWSOME! took it for a 50 mile 65mph drive after work today & ran great! (even though it was 17 deg here today!:wack:) worked just fine. & so far the felpro 1243's are holding. had to egg shape the bolt holes to make them work with my small bolt intake heads but seems good to go. So hopefuly im done with the motor for a very long time!!
 
Hipo65 said:
Update.... i got the new headgasket from cometic yesterday (they tod me they didnt wanna say to me just run it again & then have a problom so they sent me a new one for 60 bucks shipped! good deal for a 90 dollar gasket to begin with!) & got er buttoned up last night & fired it! runs f#$&en AWSOME! took it for a 50 mile 65mph drive after work today & ran great! (even though it was 17 deg here today!:wack:) worked just fine. & so far the felpro 1243's are holding. had to egg shape the bolt holes to make them work with my small bolt intake heads but seems good to go. So hopefuly im done with the motor for a very long time!!
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Good news!
 
Thanks mike! im very happy with it!!! fyi what would yer setup with 1.6 rockers give for power? ish. It has alot more torque than i thought it would for a little motor! our builds are very close to each other other than the 1.6 rockers. worthy up grade imop if you were evr thinken about it.
 
I used to use a dyno program on my computer but it won't work with my new 64 bit machine. Although it wasn't 100% accurate, you could at least compare modifications and see if they were worth the expense. I'm sure your rockers made a difference. The 273 chambers are small but efficient. The valves are small too and if they open farther it has to help make things more efficient. A comparrison on a dyno or a few trips down the drag strip would tell the tale. tmm
 
Very cool thanks, no plans for a "leagle"trip down the strip the closest 1/4 mile track to me is in kearney ne. but i promise it will sure test the holding power of the 904 in it & suprise a few in the way! Thease little motors are so under rated in there lite A-body plat form & shouldnt be over looked so much. They will superise poeple!:-D its BEER time!
 
Hipo65 glad you got it back together and all is well.

What kind of hp can be had switching to 1.6 rockers and do you do intake and exhaust?
 
Im honestly not sure of the increase just the 1.6 rockers themselfs made. Trying to compare a tired hipo 273 with ring end gaps @ .080 of an inch & 1.5 stock rockers to a fresh hipo 273 is night & day as it is. id guess i was losen 20-30 h.p. in blow by alone! But i will say this little 273 would put my o.e. 318 in my old 76 dart to shame,even after it was rebuilt & had the common bolt on goddies hands down! (R.I.P little 318!) Killed that 318 due to oil slosh back becouse we all know smallblock center sump pans had '0' baffleing in them & good hard accelration keept all oil away from pickup & fryed every bearing & crank in the bottom end! almost killed the 340 that replaced it too! until i wised up with a better pan. I made baffles in the 273 pan but looks bone stock from the outside! crafty eh?:D
 

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Hipo65 said:
Im honestly not sure of the increase just the 1.6 rockers themselfs made. Trying to compare a tired hipo 273 with ring end gaps @ .080 of an inch & 1.5 stock rockers to a fresh hipo 273 is night & day as it is. id guess i was losen 20-30 h.p. in blow by alone! But i will say this little 273 would put my o.e. 318 in my old 76 dart to shame,even after it was rebuilt & had the common bolt on goddies hands down! (R.I.P little 318!) Killed that 318 due to oil slosh back becouse we all know smallblock center sump pans had '0' baffleing in them & good hard accelration keept all oil away from pickup & fryed every bearing & crank in the bottom end! almost killed the 340 that replaced it too! until i wised up with a better pan. I made baffles in the 273 pan but looks bone stock from the outside! crafty eh?:D
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You are running a windage tray also, aren't you?
 
Nice to know I might just as well cut a hole in them, thanks. I have been cutting the gaskets for the heat cross over anyway. How is your 273 coming along?
 
66fs said:
Nice to know I might just as well cut a hole in them, thanks. I have been cutting the gaskets for the heat cross over anyway. How is your 273 coming along?
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my commando engine is coming along fine .. I'm using a different 273 commando block this time around.. block is all cleaned and prepped. going to check the main bearing clearances today ( plastigage ) and then torque the main crank caps down to spec.
today is the last nice 60* day to wrench on the 273 .. It's going to be in the 40's the rest of the week and then some.
I'll be updating my posts as I continue on my build 66fs.
66fs said:
Nice to know I might just as well cut a hole in them, thanks. I have been cutting the gaskets for the heat cross over anyway. How is your 273 coming along?
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