2.5 question

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Re: 2.5 question

Postby Greybeard » Tue Mar 01, 2016 3:04 pm

I used to be involved in hydros, and built or assisted in building everything from Crosleys to Merlins. I see that you aren't unafraid of building or rebuilding. One of the engines you mention is the 3.0 Merc. The original motor was the 153 Chevy ll. It was used a lot in the 2.5 liter hydro class as well as in Sprint cars. The architecture of the 153 is the same as the Chevy six minus two holes, and bore and stroke was 1/2 of a 307 v8. Connecting rods same as the 6, and Pistons the same as the 6 and v8. They were cheep to build and robust enough for hydro racing, the equal to a 3 1/2 min Dyno run, except when you bounced the prop free. Although we only dyno'd 230 hp, others claimed power near 300. The 3.0 is built to run wide open, all day long, at 4800 rpm. Say "Robust". With cam,induction,and headers it is easily capable of the power of most of the v6 you mention and there would be a fun part of using an old pushrod motor that dates back to 1962.
An engine you might consider is the 215 Buick and Olds, as well as the Rover variants up to 4.6 liter. Lighter than all the v6 engines you mention, and easily modified. Because of Rover building them for years, parts are not unobtainable. The 215s were used in the 225 hydro class. Running astronomical rpm, the 215s were by far the sweetest engines to hear out on the lakes. Another: a Chevy power book of the '90s was dedicated to racing with the 2.8/3.1/3.4 engines. A 60 degree motor which is way more compact than the 90degree v6s. you can stroke the 2.8 and 3.1 to 3.4, and production alloy heads were on some. Last, the 5.3ls motor with the alloy block is lighter than a 4.3,and much, much, more powerful.
Have fun!
Mike
1937 Chev 2dr sedan
1966 Chevy El Camino (daily driver w/300K miles)
1966 Chevy V8 Corvair https://greybeard.shutterfly.com
1972 Vega GT
1985 Corvette
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Re: 2.5 question

Postby philip1 » Sun Mar 06, 2016 1:16 pm

interesting you mention the 3.0. I just came across a 3.0 crank rods and pistons on CL and have contacted the seller. if the interwebs are correct I can swap the 3.0 parts into my 2.5 block and have close to the marine power with stock fitment.
Phil
Charlotte NC
1980 Monza Coupe
2.5l Automatic 2.73:1
white over tan
second owner
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Re: 2.5 question

Postby philip1 » Wed Aug 03, 2016 2:49 pm

I'm back,
lots of things have happened since I last posted, biggest of which is moving house, so nothing has happened with the Monza. this coming weekend I will be pulling the broken 2.5 and start the rebuild process. The stock block will get S-10 pistons but very little else. I need this to run for inspection so I can get the title. As far as power I'm going to stick with the 2.5 but do what I can to improve it (possibly mpfi if I get a wild hair) higher compression, weber dgav, maybe a header and possibly a camshaft. The only option I'm even allowing into my thought process isan OMC 3.0 and that is only if i can make ALL the accessories work with it.
Phil
Charlotte NC
1980 Monza Coupe
2.5l Automatic 2.73:1
white over tan
second owner
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Re: 2.5 question

Postby res0o7eb » Sun Oct 09, 2016 11:20 pm

Philip,

Glad you are choosing to stick to the 151(2.5) Pontiac.
Check out the '181 I-4 Stroker' link in my sig below for lots of information on performance parts for the 151 cu. in. (2.5 l) Pontiac I-4 and using marine parts to increase it to 181 cu. in. (3.0 l).
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Re: 2.5 question

Postby kgroombr » Sun Oct 30, 2016 12:08 pm

I am now the owner of this car, Unfortunately the previous owner was unable to get a title for it. For me it is not a problem as Georgia is a no-title state so can register and drive older cars without a title.

It is a very nice car except for some of the interior like door panels and a-pillar trim, and possible more, but still inspecting it. I am going to stick with the 151 but I don't want to sink a bunch of money into it, but I want to do it right. I will be pulling the engine and going through it.

Since the one piston is bad, I would like to replace all the pistons at once. The compression on this engine is anaemic. Will flat top pistons with no valve relief work in this? I am guessing it should increase the compression to about 9.5 to 1, and if this is correct, that is a realistic nice compression that should help performance some. Other than that, and some minor head porting, I plan to leave it as is. Before I buy anything, I have to pull the engine and verify the condition and possible get it bored if it is out of tolerance for standard pistons.

Thanks,
Ken
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Re: 2.5 question

Postby res0o7eb » Mon Oct 31, 2016 10:04 pm

kgroombr wrote:I am now the owner of this car, ...

It is a very nice car except for some of the interior like door panels and a-pillar trim, and possible more, but still inspecting it. I am going to stick with the 151 but I don't want to sink a bunch of money into it, but I want to do it right. I will be pulling the engine and going through it.

... Will flat top pistons with no valve relief work in this? I am guessing it should increase the compression to about 9.5 to 1 ...

Thanks,
Ken

Congrats Ken.
I haven't seen a pic of the Monza.
I think I will be pulling the motor in my 77 Sunbird (avatar) due to a suspected cracked block. I have a complete spare engine that will go in its place.

Yes, flat tops are your best friend.
See link below for flat tops made specifically for the 151 - CR depends on the cc of the CC. Price of $231.35, not too bad.
https://www.uempistons.com/index.php?main_page=product_piston_info&cPath=3_4_22&products_id=577&zenid=fbe834343a60d69fc90c711c0caa7a0f
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Re: 2.5 question

Postby kgroombr » Wed Nov 02, 2016 8:14 pm

Thanks Tom,

It is a very solid car, but needs a lot of TLC. Brakes don't work, interior is rough, and of course the hole in the piston. Here is a pic:

1980Monza.jpg
1980Monza.jpg (100.85 KiB) Viewed 89 times


Ken
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