mygasser
Well-Known Member
yep, those formulas don't always work out. ford 289/302's like a 3310 too.
neil.
273 commando HELP!!!
- Thread starter bamacuda
- Start date
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neil.
Charrlie_S
Well-Known Member
I did a 273 for a 65 Valiant 4drsdn, way back in the late '70's or early '80's. I don't remember all the specs (would had to find my old notes) but it ran 12.80's-12'90's in the quarter.
I do remember it had Jahns 12.5 pistons. I did try a set of 360 heads but saw no improvement over the 273 heads. I think it was a case of what was gained in flow (bigger valves/ports) I lost in compression (open chamber vs closed chamber). Cam was a Crane with about .520 lift, dur ?, intake ?, carb Holley 750 DP, Fender well headers, dual point dist. 904 with a good (at that time) converter, RMVB, 8 3/4 (don't remember ratio) rear.
I do remember it had Jahns 12.5 pistons. I did try a set of 360 heads but saw no improvement over the 273 heads. I think it was a case of what was gained in flow (bigger valves/ports) I lost in compression (open chamber vs closed chamber). Cam was a Crane with about .520 lift, dur ?, intake ?, carb Holley 750 DP, Fender well headers, dual point dist. 904 with a good (at that time) converter, RMVB, 8 3/4 (don't remember ratio) rear.
I'd look at Chevy 4.8l and ford 4.6l builds obviously it's not gonna be apples to apples comparison, but there very little 273 info out there, similar head flow and cams should workabout the same in all 3.
0.9-1:1 hp per cid shouldn't all that hard to get and be reasonably streetable, cam cr and 4bbl headers should be more than enough, cam my guess somewhere around 220-225 110-112 .475-.500 9-9.5:1 cr 650 carb
1-1.1:1 hp per cid just got to step up the cam 225-230 and pocket port the heads, but your starting to leaving a street friendly package for most.
If I was looking to make good power and streetability I'd think about going with magnum heads and probably do a little pocket porting, that's how modern engines make good power is with head flow and mild cams. and go with fast ramp 220 ish cam and .500 + lift. Probably get you well into 350 ish hp with decent streetability.
Here's some videos might help
He's doing a bunch of Chevy 4.3l v8 right now might help.
https://www.youtube.com/channel/UC8uf_zVTV63l1-uRSx6XbnQ
there's a lot of 4.8l LS in this playlist got to search through it though.
He's doing a bunch of Chevy 4.3l v8 right now might help.
https://www.youtube.com/channel/UC8uf_zVTV63l1-uRSx6XbnQ
there's a lot of 4.8l LS in this playlist got to search through it though.
Agree. Magnum heads are pretty nice but not too much of an upgrade from stock 273 heads. The chambers/compression are almost the same and they do flow a bit better but if you are building a 1:1 273 you will need to do some head work. The Magnum rocker gear is strong enough but the shaft/adjustables are already there on stock heads. Don't discount stock 273 heads. I wish I would have flowed mine. If I ever take one off. I will get them flowed just to see what they will do. They have been milled .030 to minimum, polished chambers,Serdi seats, bronze guides, stock valves (damn) Gasket matched and ported. Gasket matched intake and stock manifolds as well. (exhaust is a bottle neck but I didn't want headers) I also didn't want to build a high performance 273. Just a good running stocker. Probably 250 horse as a guess.
I agree the stock 273 head is more than enough for up to 300 ish hp, but magnum allows you to go over 300 hp and even if you don't care about more than 300 hp, you can get away with a lot less cam to reach whatever power level your looking for, more head flow and smaller cam is more streetable than larger cam and less head flow.
5.9L magnum heads makes about 300-320 hp with stock non performance cam, 360 LA heads makes about 250 hp with similar cam and 273/318 heads on a stock 360 LA would probably be about 200-220 hp . That should be a least a 100 hp difference from 273/318 heads to magnum. all with super mild cams.
Wow, that's a stretch. I'd like to see some dyno sheets for that comparison. I wouldn't compare HP numbers between a stock 273 and a 318 Magnum without some dyno time it's skewed numbers just to guess what a 273 with Magnum heads would do. The Magnum heads are not that much more and not superior to a 273/318 head. Not much different than a #302 head which isn't much different than a say #920 head. There are flow numbers floating around here somewhere. If I didn't have anything better to do I would look for them. What ever you think.
Not saying if you put Magnum heads on a 273 your gonna gain 100 hp, but couldn't see less than 50-60 . There is dyno numbers for 5.9l Magnum and LA 360 both with 4 bbl and LA 360 exhaust manifolds, LA 360 made 266 hp @ 4300 rpm and magnum made 314 hp @ 4600 rpm. The only one I'm guesstimating is a 360 with 273/318 heads.
Installing Exhaust Headers Into 300hp Crate Engine - Mopar Muscle Magazine
https://www.hotrod.com/articles/mopp-0105-dyno-test-360-smog-motor/
ChargerKG
Active Member
Here is the ISKY T-3 sheet. Toolman, I found a thread where you ran this grind on your software. I want to shift at 5000 max. Ron Iskenderian told me I would be fine with 3:23s and stock converter. Maybe you want to consider this cam. Please run simulation again with headers, dual plane and a 625cfm on the 273 Charger. Thanks KG
That was almost 12 years ago. I hope bamacuda has his 273 built by now.
He hasn't been online here since March 2020. I hope he's ok.
I noticed that right after I posted. LOL
I'll check it out tomorrow. Thanks
Looking at how cams and heads flow effects other similar displacement V8 is helpful.
With those specs I get
ChargerKG
Active Member
Thank You Mike. Just what I was hoping for. Building a Road Course car not a dragster. Think I'll go with a Holley 600 with Vacuum Secondaries. Hey do you drive a tool truck? Saw a glimpse in soundtrack video. Cool.
You bet. Ya, I was a MAC dealer for 28 years before I retired.
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