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Discussion Starter · #1 ·
Been seeing discussions on 289 engines lately so let me know your thoughts. Engine runs great but no real power compared to my 302 I had in 89 mustang with about 350hp. That's my goal. I think I'm about 225-230hp right now.

Engine was rebuilt right before I bought car but no information on what was used In rebuild so I replaced heads, intake and cam. Definitely made a difference and runs better but want more. When pulled stock heads as shown below shows C code pistons and they are 0.030 in the hole, also appears to be 0.060 according to piston. So have about 8.5 compression, boo. So should I just replace pistons to bring me closer to 9.5 or higher? Look for a new 289 block? Save money and just get a short block 347 or supercharger since both about same price? Leaning toward supercharger since not something you see often. 🙂
 

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You mention getting a new 289 block. Is there anything wrong with the existing block? If not, this won’t really help.
If your block and everything is good, I think the low compression is good for a supercharger.
If you have a block problem or concerns with any of those components, then a fresh new stroker would be a better option imo.


67 coupe, 289, performer intake, 302 heads, Holley 570, Pertronix II dizzy, C4, 9” rear, 3.50, 17” wheels
 

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0.060 is pushing it to its end of usable life anyway sooo...I say go ahead and put a S/C on it as it is, a bit safer since it has low C/R. Then turn to boost up to 11. Drive it, wear it out, then you already have to S/C stuff paid for and can use it on another block someday.
 

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My, you stated that you replaced the heads, cam, and intake. What did you remove, and what did you install instead ? ? LSG
 

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Discussion Starter · #5 ·
My, you stated that you replaced the heads, cam, and intake. What did you remove, and what did you install instead ? ? LSG
Hi LSG, I replaced the stock heads 65 289 Heads, Peformer Intake and not sure what cam it had but it had a lope to it so not stock with Edelbrock Performer heads milled down to 58cc, Performer Air Gap intake and a Howards cam with 213/219 @0.050 and 0.517/0.523. When I saw the pistons I should have yanked the engine out and replaced stuff but I was already deep into just head removal that decided just to put the parts on and see what it did. It was an improvement but am hoping for more. I know that compression is killing this engine. It is dead reliable though and will get me anywhere but I know I am leaving alot on the table. Question is how much, if I pulled engine and replaced the pistons I figure at least another 20-30HP maybe more? Or just leave it as is and drop a supercharger or pull the whole thing and replace just the short block since the top end is good? Definitely one of the 3 options hopefully in the next couple of years.
 

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8.5 CR seems low for heads that are 58cc. The reliefs in your pistons don’t look to be more that 12-15 cc. What did you use to calculate your CR?


67 coupe, 289, performer intake, 302 heads, Holley 570, Pertronix II dizzy, C4, 9” rear, 3.50, 17” wheels
 

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Discussion Starter · #7 ·
I used the Summit Compression calculator. The 0.030 in the hole is hurting it instead of the 0.010-0.016. It seems they didn't use the right pistons when they rebuilt the engine before I purchased the vehicle.
 

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If you can't run out the rest of the lifespan of the 289 my vote is for a stroker but you will need good aftermarket heads to get the most out of it. It would also if built with the right parts make way more than 350 hp.
 

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My, do you still have the 65 289 heads ? What is the lobe spread on the cam you have ? Do all of the pistons say 060 on top ? And you are correct, they used wrong pistons. Most people do, unfourtunately.
LSG
 

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Discussion Starter · #10 ·
If you can't run out the rest of the lifespan of the 289 my vote is for a stroker but you will need good aftermarket heads to get the most out of it. It would also if built with the right parts make way more than 350 hp.
This engine easily has many years left in it. As mentioned it has great oil pressure and good compression 150psi average. Is just the lack of power that has me pondering new project.

My, do you still have the 65 289 heads ? What is the lobe spread on the cam you have ? Do all of the pistons say 060 on top ? And you are correct, they used wrong pistons. Most people do, unfourtunately.
LSG
Yes still have the 65 heads stored up in case wanted to go back to stock. LSA is 110. Yes all pistons showed the 060 on it. Yeah figured wrong pistons :( but so many choices and routes to go down for more performance. Just seeing what most folks would do.
 

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I used the Summit Compression calculator. The 0.030 in the hole is hurting it instead of the 0.010-0.016. It seems they didn't use the right pistons when they rebuilt the engine before I purchased the vehicle.
How many cc’s do they spec for the piston tops?


67 coupe, 289, performer intake, 302 heads, Holley 570, Pertronix II dizzy, C4, 9” rear, 3.50, 17” wheels
 

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Discussion Starter · #12 ·
How many cc’s do they spec for the piston tops?
I am not sure what they are. I just used 10cc as a guess in the calculator.
 

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That’s probably in the ballpark but it could be closer to 15. You should be able to look on the their website and get the correct number. It can make a difference.
I’m building a 390 and mine are 12.1 and yours look to be more.


67 coupe, 289, performer intake, 302 heads, Holley 570, Pertronix II dizzy, C4, 9” rear, 3.50, 17” wheels
 

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Discussion Starter · #14 ·
There is no markings though for me to know what pistons these are so not sure where to look to get exact cc of the pistons. The only markings is the 060 on them. But you are right, my compression could be worse then I think.
 

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Here are compression ratios with a piston .030 "in the hole. -15cc = 7.8 , -12 = 8-1 , -5 = 8.7 -1. NONE of those ratios are good with an aluminum head in a naturally aspirated engine. 9.5-1 will run with 87 octane and 10.5 for 91. that change will wake up engine performance VERY seriously. These were calculated for a 289 so a 302 would be a couple points higher.
Randy
 
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You could get your block decked to zero deck, get new pistons with only +5cc of valve reliefs and mill your heads to 54 cc from 58 cc (Would require about .020 taken off the heads) and this would get you to about 10:1. You would also have better quench to help with combustion and provide less chance of detonation. That being said, You probably won't gain much more than 20 HP which is good but it may still not be enough to get you what you're after. It's also a lot of work for just 20 HP. I'd say stroke it.
 

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Discussion Starter · #17 ·
So I guess I just need to decide if I want to go Stroker or Supercharger. I think the Edelbrock heads will be fine with stroker just not take full advantage of it and I think supercharger will work well with low compression and good intake tract. Hmm decisions decisions.
 

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Tracy,
If you do that much milling , the manifold faces will need to be machined and bolt holes slotted as well because it will be too wide. "I" would be tempted to get some proper pistons. Machining the block and heads could cost about the same money.
Randy
 

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Seems like it would make more sense & be more cost effective to put a supercharger on it . With a compression ratio that low it should take a good bit of boost.
 

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Tracy,
If you do that much milling , the manifold faces will need to be machined and bolt holes slotted as well because it will be too wide. "I" would be tempted to get some proper pistons. Machining the block and heads could cost about the same money.
Randy
I knew about it and should have included it also in my post. My point was mainly to say that a lot of work would be done to raise compression with very little gain. Now include manifold milling and it's really not worth it and the manifold will forever be non-standard.
 
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