"290HP" GM crate 350 details?

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DaveMcLain
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Re: "290HP" GM crate 350 details?

Post by DaveMcLain » Thu Oct 19, 2017 10:40 am

i dyno tested the engine I built for the customer which was a replacement for the replacement for a 260 horsepower boat engine. It made 259 horsepower on my dyno with the water manifolds, flame arrestor etc. I used a set of the World Products SR heads and a cam with 205 at .050 duration.

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Re: "290HP" GM crate 350 details?

Post by novadude » Thu Oct 19, 2017 10:43 am

autogear wrote:
Thu Oct 19, 2017 10:07 am
The 260hp crate engine has a smaller cam (essentially the 300-horse cam) and is usually cheaper than the 290hp crate. Something to think about perhaps.
Exactly what he said! It also makes more torque and would likely work better in a ski-boat.

You can always swap cams later with something more appropriate for low compression. To me, the L82 cam GM puts in those engines should be paired with 11:1 (as in 1970 350hp/350), and it's a terrible mis-match in a low CR engine.

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Re: "290HP" GM crate 350 details?

Post by DaveMcLain » Thu Oct 19, 2017 11:11 am

The cam I used was a flat tappet hydraulic "Torque Master" ground by Demos' Cams HL 18-9A1.

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Re: "290HP" GM crate 350 details?

Post by F-BIRD'88 » Fri Oct 20, 2017 3:02 am

This is why if using the .450 .460 "L82" L46 cam in the 350-290hp crate motor you advance it a good 7-8 degrees for the boat motor. Really improves the torque curve where it matters.
115-113 centers stock move to 107-121 or 109-119 centers 114 LSA

Do you not have 305 SBC's there you can buy? for 4416 or 081 heads ( which you can port) for this?

Do they not have chevy pickup trucks there? 1996 2001

The real compression ratio on that 350-290hp crate motor is 7.8:1
It has -15cc dish pistons.

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Re: "290HP" GM crate 350 details?

Post by steve316 » Fri Oct 20, 2017 8:09 am

F-bird88 did you read what questions the original post was asking? I didn't read anything anything about needing a cam specked.

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Re: "290HP" GM crate 350 details?

Post by KnightEngines » Fri Oct 20, 2017 7:13 pm

Yeah, new glasses required there Fbird.
I don't need to know what to put in it, I just want a better idea of some basic dimensions such as typical deck height & surface finish, valve job crappiness, piston weight etc.
Just want to be able to formulate a plan to knock this one through quick smart with minimal delays & head scratching so I can get back to more interesting jobs!

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Re: "290HP" GM crate 350 details?

Post by pamotorman » Fri Oct 20, 2017 7:31 pm

why go to all that trouble, why not just move up to a higher performance crate engine ??

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Re: "290HP" GM crate 350 details?

Post by KnightEngines » Fri Oct 20, 2017 8:36 pm

Options are limited this side of the pacific, next step up is a fully dressed engine with intake, carb, dissy etc in a much higher price bracket, so we'd be paying a lot of extra $ for parts that are sitting on a bench here & owe the customer nothing. I'm pretty sure I can tweak the cheap crate 350 to be a better social ski boat engine for less $ than a higher spec fully dressed crate.
Customer gets a better engine for less $ that has been looked through & is know good & I get a quick & easy job - everyone wins.

I know the heads are pretty weak, but I've run the calipers over the cracked ones from the old motor & sizing is pretty good for an engine that'll be used between 2000-4500rpm most of the time, a few hours with the grinder will make for better suited heads than a larger out the box head with no grinding.

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Re: "290HP" GM crate 350 details?

Post by Carnut1 » Fri Oct 20, 2017 9:00 pm

Last time I did one of those crate engines it came with 993 Mexico heads 76cc 1.94" / 1.5" valves. To me the Mexico heads are cast thicker than USA castings. The machining is pretty poor on the Mexico castings as well. With some easy bowl work and pinch open a bit they will easily cover your goals. Thanks, Charlie
Servedio Cylinder Head Development
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9:00am - 9:00pm EST

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Re: "290HP" GM crate 350 details?

Post by pdq67 » Sat Oct 21, 2017 8:56 am

Did one of these crate engines have the great old -929 cam in it?

It was used in everything from the 283 to the big 400 if not mistaken.

pdq67

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Re: "290HP" GM crate 350 details?

Post by Keith Morganstein » Sat Oct 21, 2017 10:48 am

The 260 HP might still have the 929 cam. Nothing special or good about that stock cam.

The 290 HP has the the old corvette l-82 cam, bad choice for a marine engine, esp with water-cooled exhaust. It's a crappy cam period.

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Re: "290HP" GM crate 350 details?

Post by pdq67 » Sat Oct 21, 2017 1:31 pm

All I am going to say is that ALL of the Chevy cams bigger than the old -929 cam really need something like at least 10.5 and preferably 11 to 1 CR like Chevy put them in engines that are of this CR back then!

And fwiw, my 350SS, L-48 engine had the old -929 cam in it and it was rated at 10.25 to 1 CR and I really figure it was more like 10 to 1 CR and it ran great. The old L-48 engine is the 295hp and 380 T, 350 engine!

Now to up my new 67SS Camaro's 350 engine, I installed the old -151, 350hp/327 cam in it and it really came alive for a cheap $18 cam back then. Early summer of '67 here!

I gave my good Buddy, "Nuts", a $20 and he gave me back change along with the new -151 cam and a cam install gasket set.

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Re: "290HP" GM crate 350 details?

Post by KnightEngines » Mon Oct 23, 2017 1:28 am

Got the crate motor.
Pulled down the top end - it has those rockers that are guided on the tip, was expecting the pushrod holes to be slots to guide the rockers, but these are like the vortech rockers.
So I guess I have to machine for screw in studs to be able to use the 1.6/1.5 roller rockers on it - no biggie since the heads are off anyway.

Deck face looks pretty decent, it'll hold a .015" metal shim gasket no probs.
Deck height is .029-.031" on the left bank & .024-.026" on the right bank.
.015" head gasket will close up the quench to .039-.046", that'll do I guess.

Looks like I can chop about .050" off the face of the heads before I gotta worry about getting in to the valve job, haven't CC'd the heads yet, but if they are 76cc then .050" off should take them down to about 68cc.
That'll get comp to around 9:1, which will do. A lot better than 7.9:1 which is what it had!

So I won't touch the rotating assembly, I'll just change the cam, tweak the heads & throw it back together with .015" head gaskets.

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Re: "290HP" GM crate 350 details?

Post by KnightEngines » Mon Oct 23, 2017 2:25 am

Looking at a Howards cam - 213/213 on 111 centres, .450/.450" lift (will be .480/.450" with 1.6/1.5 rockers).

Crane 99848 springs - will drop in if I use machined locks, with pressed locks installed height was 1.72", machined locks drop that to 1.7" to give 114lb on the seat. I'll leave the exhaust slow rotors in, can't see a reason to eliminate them.
I'll have to machine the intake guide bosses down about .060" to get enough retainer to seal clearance, they'll be on the seat & guide machine anyway to do the screw in studs, so easy enough.

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Re: "290HP" GM crate 350 details?

Post by DaveMcLain » Mon Oct 23, 2017 7:41 am

That's exactly how the heads were on the one I saw too. They used the Vortec style valves and the tip guided rockers with round pushrod holes. I think I'd go very easy on the spring loads. Does it really need more than 100 on the seat to run reliably at boat rpm levels? What's the open load going to be?

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