Author Topic: 250 inline 6, different power  (Read 3164 times)

Offline ChrisD

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250 inline 6, different power
« on: September 14, 2020, 01:33:18 PM »
Hi,
I have a 1978 c10 with 250 LD4 engine.
It‘s a engine with non integrated head (don‘t know if it‘s normal for this special engine, i find nothing about the LD4)
In 1970 the engine had more hp and more torque and a compression ratio 8,5:1
Don’t know which compression ratio my engine has, but can someone tell me, what GM changed to lower the compression ratio?
I had a look to the pistons an rods of 1978 and 1970 engine at rockauto, but they‘re the same (must not be original.

Then the 250 mercruiser marine, if I understand it right, it has 165hp, also more than the 1970 250.
I know it has a different camshaft, to lower down the max torque at another rpm
What‘s also different?

I‘m looking forward to your replies!

Regards
Chris
1978 Chevy C10 short bed with 250i6 and manual 3speed Saginaw
German us-car/truck newbie

Offline 1980K20

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Re: 250 inline 6, different power
« Reply #1 on: December 07, 2020, 09:24:29 PM »
Hey, I've got a l6 on my 67 camaro. Did lots of work to get more performance from it. If you replace pistons, there's a flat top that will get you more compression. Non-integrated is the best option.

Inliners.org has a bunch of people dedicated to these types of engines. Anything you want to know, they'll help you out. There's a guy in Iowa specializing in these, lots of inventory from a retired hot rodder business in Michigan.

I will say, though, the new 350 build for my 1980 k20 looked awfully tempting to put into the camaro....

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1952 International L112 - waiting for EV conversion
1967 Camaro - 250 six cyl, 200-4R
1980 K20 4x4 Fleetside - 350 SBC roller Cam, TH350

Offline ChrisD

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Re: 250 inline 6, different power
« Reply #2 on: January 05, 2021, 03:15:56 AM »
Hi,
sorry, I've just seen your answer.
Thanks for your tip with the inliners-forum, I‘ll see what ideas I can find there!
I also will search for the guy in Iowa.

Regards
Chris
1978 Chevy C10 short bed with 250i6 and manual 3speed Saginaw
German us-car/truck newbie

Online ehjorten

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Re: 250 inline 6, different power
« Reply #3 on: January 05, 2021, 10:02:22 AM »
The higher compression pistons for these engines were propane pistons if that helps you find them. The stock 8.5:1 pistons had a significant dish in the piston. The higher compression pistons have a smaller dish. I would also go with a 4-barrel intake manifold or if you want to get fancy, there are fuel injection manifolds. Clifford Performance is another source for parts and information. Jack Clifford passed away many years ago, but they are still going, although it looks like fairly pared down now.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline 1980K20

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Re: 250 inline 6, different power
« Reply #4 on: January 05, 2021, 10:41:19 AM »
Things I did with my engine

1) pistons - you can get pistons from a V8 also
2) Clifford intake
3) 4Bbl Holley - considering efi
4) ported and larger exhaust valves, a big Mistake - destroyed low end torque. So big, I'm thinking about undoing that.
5) truck cam
6) headers

So I'm thinking about 3&4. The car isn't as fun as it should be. These sixes are really nice engines.

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1952 International L112 - waiting for EV conversion
1967 Camaro - 250 six cyl, 200-4R
1980 K20 4x4 Fleetside - 350 SBC roller Cam, TH350

Online ehjorten

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Re: 250 inline 6, different power
« Reply #5 on: January 05, 2021, 01:53:57 PM »
My personal opinion is: don't get too romanticized over the straight 6. Is it a cool engine? Yeah! Is it different? Yeah! Is it inherently, perfectly balanced? Yeah! Will it sound totally different than a V8? Yeah! But...performance parts for these engines aren't exactly cheap, because the volumes are way down. It is going to be awfully hard to beat the bang for the buck of a SBC or even an LS engine. If you want to be different and have people give you weird looks and grins when you pop open the hood, then go for it!

One of the biggest changes you can make to the engine...that isn't an easy DIY project is modifying the head to put in a lump port intake in the head. Do an internet search and you will find lots of information. Basically the stock, siamesed intake ports have a big, head bolt, boss right in the middle of the port that really hurts flow. If you cut that out, it flows a ton!, but you need to build the floor of the port back up with a "lump" to increase the flow velocity so that the flow doesn't go all turbulent.

The one that I have been dreaming about for years is the old Sissell Automotive, 12-port head! They are still around and Sissell can provide you one, but they want $3,500 for a Street head and then you have all the accessories. This version moves the exhaust to the opposite side of the head and provides you with 6 separate intake ports! Sissell also does the Lump Port head work.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline Shifty

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Re: 250 inline 6, different power
« Reply #6 on: January 05, 2021, 04:12:10 PM »
What about forced induction, whether turbo or supercharging...(no experience with either on a 6, just spitballing)
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline 1980K20

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Re: 250 inline 6, different power
« Reply #7 on: January 05, 2021, 11:03:16 PM »
Here's my build thread, complete with my blunders and triumphs.

https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=86877&page=1

Here's the link to Tom lowe in Iowa. http://www.12bolt.com/

Mark

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1952 International L112 - waiting for EV conversion
1967 Camaro - 250 six cyl, 200-4R
1980 K20 4x4 Fleetside - 350 SBC roller Cam, TH350

Online ehjorten

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Re: 250 inline 6, different power
« Reply #8 on: January 06, 2021, 08:58:39 AM »
What about forced induction, whether turbo or supercharging...(no experience with either on a 6, just spitballing)

I saw a supercharged one at a car show many years ago! The supercharger was sitting off to the left where the intake manifold resides on support brackets braced off of the engine. Pretty dang cool!
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline Shifty

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Re: 250 inline 6, different power
« Reply #9 on: January 06, 2021, 12:54:48 PM »
What about forced induction, whether turbo or supercharging...(no experience with either on a 6, just spitballing)

I saw a supercharged one at a car show many years ago! The supercharger was sitting off to the left where the intake manifold resides on support brackets braced off of the engine. Pretty dang cool!
I've seen one with a B&M mini-blower back in the 90's (I think, might have been late 80's), and it sounded weird as heck, but it scooted.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline ChrisD

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Re: 250 inline 6, different power
« Reply #10 on: January 07, 2021, 02:06:48 PM »
Hi,
I‘ve read from port lumps and when mrhotrod switched his to a newer version, I bought an old lump port kit.
12bolt.com, I already know this site and the exhaust headers looks really nice. I really think of buying it, and perhaps split the exhaust 'til the end for a more interesting sound :D
For the intake, don‘t know if its true but I‘ve read, that the Offenhauser 4bbl is better for street cars than the cliffort or aussispeed. Think, it's the length of the intake pipes.
But I heared, that if if want more torque at lower rpm, the carburetor doesn‘t have to be too large, so i play with the idea to put a 350cfm 2bbl whit an adapter onto the original intake - or a 390cfm 4bbl with offenhauser. What do you mean?

A supercharged car isn't possible for me because of very strict rules in germany. If i modify my truck too much and too visible, I don‘t get a special oldtimer label and then this „little“ engine will cost more than 1000,- tax per year.

So I‘ll increase the compression and compression ratio, help the engine to breath better and thats all.
I‘ll definitly have a look for propane pistons, thanks for that info!
With the head down for port lump install perhaps i also put little bigger intake valves and put some mm away from head.
« Last Edit: January 07, 2021, 02:11:04 PM by ChrisD »
1978 Chevy C10 short bed with 250i6 and manual 3speed Saginaw
German us-car/truck newbie