Best Exhaust To Add Torque To 283?

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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

This is critical.. If your "2500 stall" lockup converter for the th2004r trans was made from a stock GM converter core "298mm" then on these budget price high stalls when they bend the fins to raise the stall speed above stock the converter efficiencty and STALL TORQUE RATIO get WORSE. the STR is already lame on these.

You want a converter built on a small diameter "245mm"
9.5" GM lock up converter core. You want the true stall tweeked for the (modest) engine torque of a 283/305 cid sbc. (not the torque of a 350 cid sbc)
Ya these cost a bit more $$
You want a true 3000±++++++++ stall speed (when behind a lil 283 cid sbc AND a high STR (stall torque ratio) ( 2.2-2.5:1 ish)
And the lock up clutch for cruising.
Starting with the right converter core diameter and getting the true stall correct for the small CID engine AND getting the STR correct makes a HUGE DIFFERENCE.
A true verified 4000 flash stall lockup converter is NOT TOO MUCH for this 283 wirh that Voodoo camshaft.
Last edited by F-BIRD'88 on Thu Mar 02, 2023 6:51 pm, edited 2 times in total.
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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

If you are a EFI guy you should have stolen the WHOLE OEM GM TPI induction off a Camaro/ Firebird 305 TPI engine for your lil 283.
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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

Another thing that is VERY critical on building a high perf but small CID sbc like your 283 is getting the true engine compression ratio correct.
On your flat top piston 283 if the bkock was not "O decked" thus the piston s down some .025" (or more) at TDC then the real compression ratio is a lot lower than you think. Could be as low as say 8.9:1 cr if a .040" gasket + a stock block .025" deck clearance and 56cc chambers

Thats pump gas supercharger territory.
If so the N/A torque output will be low especially with a high perf camshaft.
It is CRITICAL THAT you get the true CR correct on a small CID sbc build. A small error makes a BIG DIFFERENCE on a small motor.
A error here really cuts into the small cid engine tirque output with a high perf cam like yours.
With your current Voodoo camshaft in your 283 I'd want a true 10.25-10.50:1 CR (92 octane pump gas)
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Re: Best Exhaust To Add Torque To 283?

Post by Tom68 »

327 crank would be the best torque adding exhaust.
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Re: Best Exhaust To Add Torque To 283?

Post by skinny z »

GMHTP wrote: Thu Mar 02, 2023 11:19 am
Here’s the card skinny, I gave wrong adv duration numbers above. The machine shop installed the cam, and all I know is they said they’d install based on Lunati’s recommendations.

A53BCE77-4987-4E8A-AB85-8198B4DBA2C3.jpeg
What strikes me as odd is that on the cam card, Lunati says IVC is 34.5°.
That's an .050" value and the valve certainly isn't closed at .050". IVC is really 58.5°. This is what I use for a DCR calculation.
That aside, I get about 9.55 SCR and 7.9 DCR.

283 SCR.jpg
283 DCR.jpg
283 DCR 2.jpg
Not torque monster numbers but from personal experience with SBC's (and this is SBC related) very workable street /pump gas values. Especially with aluminium heads. You could probably go another full point on SCR and a half point on the DCR although there are other areas that the torque you're after could be found.
Most notably the carb spacer and headers as pointed out earlier.
The converter has been touched on and this is an area I find one of the greatest bang for the bucks. The right convertor can really wake up a lazy engine. It was night and day in my streeter. This is off the shelf stuff too. The racer can find even greater gains with something specifically spec'd but the TCI 10" behind the 353 really changed things.
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Re: Best Exhaust To Add Torque To 283?

Post by Walter R. Malik »

GMHTP wrote: Thu Mar 02, 2023 12:18 pm Thanks for the replies. Interesting thoughts about the spacer. I’ll have to rewatch that episode, now I’m wondering if they were testing it on a single plane manifold. Probably.
Do you drive around at Wide Open Throttle ...? That is what the dyno tests will show ... driveability at throttle transitions during part throttles are a totally different ballgame.
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Re: Best Exhaust To Add Torque To 283?

Post by GMHTP »

Lol indeed mt-engines. We get spoiled with turbo torque for sure.

And Walter, I try to be WOT all the time. Of course I’m kidding, I do see your point.

Here are the specs I was given:
3 inch stroke
3.915 bore
1.805 installed height KB flat top pistons w 6cc reliefs
5.703 rods
.030 cometics
4.030 bore diameter
Machine shop said “deck block to 9” but didn’t elaborate on if exactly 9.000

Great point on the converter. I told Extreme Automatics about the low torque 283 and he did supply a 9 inch lockup, don’t know what STR his converters have. I think I just need more true stall speed, I was a little conservative with asking for 2500.
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Re: Best Exhaust To Add Torque To 283?

Post by GMHTP »

Wouldn’t be opposed to an EFI system in the future F bird, but trying to learn about carbs now. I knew just enough about the Buick’s FAST XFI to get me in trouble, and a friend of mine Ray Bohacz told me “try to learn carbs, because it will help you understand EFI.” Was good advice.
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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

My friend has a 57 chev w/ sbc and it has Mid Length off the shelf headers on it. They are either for GM truck or for GM B body, G Body , 70's F body cars. (2nd gen)
His car is changed to aftermarket rack and pinion steering... Don't know if thats a factor on these common popular Mid Length headers fitting this car.
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Re: Best Exhaust To Add Torque To 283?

Post by GMHTP »

Yep there are so many variations for tri 5s regarding aftermarket steering box/R&P, straight/angle plug, pwr brake, clutch or column shift obstacles, removing bell housing mounts, LS swaps etc that someone on tri five put together a great chart:
https://www.trifive.com/threads/headers ... rt.226192/
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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

What is the observed max flash stall speed rpm on launch with that torque converter in your car , now?
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Re: Best Exhaust To Add Torque To 283?

Post by F-BIRD'88 »

I am going to suggest that the mid length headers my friend has on his sbc 57 is Flowtech #31108FLT
Or something real close.
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Re: Best Exhaust To Add Torque To 283?

Post by Stan Weiss »

What psi do you get when you do a cranking compression?

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Re: Best Exhaust To Add Torque To 283?

Post by Tom68 »

F-BIRD'88 wrote: Thu Mar 02, 2023 11:54 pm I am going to suggest that the mid length headers my friend has on his sbc 57 is Flowtech #31108FLT
Or something real close.
Curious why you'd go to something that whilst free flowing isn't tuned for any useable rev range ?
I'd have thought he'd need 40 odd inch primaries to give it a kick in the middle.
You won't get much from exhaust, but if you're spending money you might as well get some of what you want.
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Re: Best Exhaust To Add Torque To 283?

Post by skinny z »

wrote: I am going to suggest that the mid length headers my friend has on his sbc 57 is Flowtech #31108FLT
Or something real close.
Those are 1 5/8" aren't they?
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