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Discussion Starter · #1 ·
How long do you think a unibody car would last (before warpage) using an engine no greater than 320 hp/ 450 tq (gmpp 383ht) if not using subframe connectors?


Or perhaps the car wouldn't be affected with "only" 320 hp?




i'm not copping out:


1) i'm not convinced that subframe connectors alone really do the trick---need more such as roll cage etc. to really stiffen things up?


2) plus, it seems overly complex----the car i want to use doesn't have commercially available connectors.



3) i only want to run 11's in the 1/4 mile with this car, then move on to a different project.


Again, i'm not afraid of work and i really believe in doing things the right way, but it seems to be too much trouble for questionable benefit?
 

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I put a lot of stock in the factory engineers. If the car was produced at the factory as a unibody with a strong V8, even if it was another brand under the same Corporate name (Buick, Olds, Pontiac, Chevy, Cadillac, all under General Motors), I would be OK with using a V8 without mods. If the car was only produced with a I-4 or V-6, then I'd probably not use a V8 in it without mods. But then you have to understand that I spent the last 20 of my working years doing technical inspection on drag race cars, so I have probably seen some stuff that you have not.
 

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It will be fine, that level of horse power will not affect anything. If you get into the 500-600 hp range and have good gearing and traction, you may start to tweak rhings some. Remember, some big block cars only had front subframes and easily 500 hp....

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depends on the design.

Some unibody cars were not strong enough with stock V 8 's. Take the early fox body Mustang-Capri from the early 80's. Highway patrol cars had some additional bracing. but most
V8 cars that have been driven hard had cracks under the driver's seat and in the rocker to floor pan. . I have 4 of then, a couple are parts cars The Capri T Top had cracks in the quarter panel to belt line at the rear of the door opening. I bought the tubular single tube for each side then added 1 X 2 tubing under the rockers. and added crosspieces making a ladder for each side, the cross pieces support the seats and mount the roll bar. additional gussets and a cowl to shock tower brace. I added more bracing around the radiator support. and a cross brace under the rear seat. I remember when I was an engineer at ford , they put wide wheels -tires on a prototype and ran an autocross course and the metal bent. de cambering the front wheels. The last time I was under the capri I saw some distortion where the upper rear suspension attaches to the floor pan. Time for some more 10 gage steel.
 

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Think it would be helpful to know what unibody you are talking about. Some as mentioned can handle it without major issues but certainly others could be a death trap of sorts. I also question the whole 11 second project, then moving on to something else - faster I suppose, so why bother with this one to start with?
 

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What car? 450 ft lbs is more then a lot of these cars came with.

Even if a specific car was produced with a v8 or big block, some of the high power cars had additional reinforcements that the lesser models didn't get. Ie, high hp Mopars.

Unibodies are predominately spot welded. They loosen up from flexing over time. As stated there can be damage. Cracked quarter panels, permanent twist, crack a windshield, etc from flexing. There is a tremendous benefit whether drag car or g-machine to installing them. Even better if they are tied into the floor pan in at least a few places. They'll take a lot of the squeaks and rattles out of a car and help the suspension work. Welded is the key. Bolt on ones just tend to wallow out the holes you drilled to install them so they don't do much.

If you don't think you car is flexing jack one front wheel up under the control arm and see if the door still opens and closes as nice. Some cars the door won't close if you can even get it open.
 

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Discussion Starter · #7 ·
Sorry for the slow reply. The weekend is really the only true time i can respond and even that is not guaranteed.


Chevette.


And i forgot to emphasize the 444tq that the 383HT makes. Really from 2000rpm and above. That may affect the car even more than the HP?


Drag only, no street use.


i want to gear enough to run in the 11 sec bracket, but not so much to risk wheelspin---so maybe 3.73? With 11.5 x 29 slicks. Likely a custom aftermarket 12 bolt as the stock rear can't handle it. Front suspension "generally" will remain stock.




My original plan was to take two 1/4"(or thicker if necessary) metal plates, about at least 35" inches wide by about 12-14" long(or longer) and bolt or weld one to the bottom of the floor and one to the top----thus forming a "sandwich." This sandwich would be located where the rear seats would normally be. Then weld the ladder bar brackets to the bottom one. i could then use the stock floor for the coilover mounts (?).


i think have seen this setup(or similar) before on a fast nova, so i think the concept has merit. (i believe Joe Sherman's son?)



However, i'm into doing things the right way, the first time. So, if the above concept is stupid, then please indicate why so.


It may seem like i'm trying to skip steps, but for this project i just want to go bracket racing without getting too complicated.
 

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Discussion Starter · #8 ·
What car? 450 ft lbs is more then a lot of these cars came with.

Even if a specific car was produced with a v8 or big block, some of the high power cars had additional reinforcements that the lesser models didn't get. Ie, high hp Mopars.

Unibodies are predominately spot welded. They loosen up from flexing over time. As stated there can be damage. Cracked quarter panels, permanent twist, crack a windshield, etc from flexing. There is a tremendous benefit whether drag car or g-machine to installing them. Even better if they are tied into the floor pan in at least a few places. They'll take a lot of the squeaks and rattles out of a car and help the suspension work. Welded is the key. Bolt on ones just tend to wallow out the holes you drilled to install them so they don't do much.

If you don't think you car is flexing jack one front wheel up under the control arm and see if the door still opens and closes as nice. Some cars the door won't close if you can even get it open.

Yes, i have a 29 yr old GM j-body and one of the doors doesn't work---and i've never raced it. So yes, they do flex.....
 

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Discussion Starter · #9 · (Edited)
Think it would be helpful to know what unibody you are talking about. Some as mentioned can handle it without major issues but certainly others could be a death trap of sorts. I also question the whole 11 second project, then moving on to something else - faster I suppose, so why bother with this one to start with?



With me, i generally look at cars as projects. If i want to go faster, then it will get too complicated for this project---likely needing tube frame, struts etc. etc. etc. So i'll just start another project. Plus, i'm thinking if i want to go faster i would want to go with an altered anyways.


Why not just go tube frame now?


It's a money/time thing. Mostly time.
 

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Sorry for the slow reply. The weekend is really the only true time i can respond and even that is not guaranteed.


Chevette.


And i forgot to emphasize the 444tq that the 383HT makes. Really from 2000rpm and above. That may affect the car even more than the HP?


Drag only, no street use.


i want to gear enough to run in the 11 sec bracket, but not so much to risk wheelspin---so maybe 3.73? With 11.5 x 29 slicks. Likely a custom aftermarket 12 bolt as the stock rear can't handle it. Front suspension "generally" will remain stock.




My original plan was to take two 1/4"(or thicker if necessary) metal plates, about at least 35" inches wide by about 12-14" long(or longer) and bolt or weld one to the bottom of the floor and one to the top----thus forming a "sandwich." This sandwich would be located where the rear seats would normally be. Then weld the ladder bar brackets to the bottom one. i could then use the stock floor for the coilover mounts (?).


i think have seen this setup(or similar) before on a fast nova, so i think the concept has merit. (i believe Joe Sherman's son?)



However, i'm into doing things the right way, the first time. So, if the above concept is stupid, then please indicate why so.


It may seem like i'm trying to skip steps, but for this project i just want to go bracket racing without getting too complicated.
I really can't picture your idea. Normally you use box tubing as frame ties and this gives you a place to mount a proper crossmember for the ladder bars. A lot of these unibody frame rails are little more then 10-12 gauge
sheet metal so when you start moving attachments points reinforcement needs to be done. Chevette's are tin cans. I would be considering a cage.

Somewhere in all of this your safety and the safety of those around you needs to be considered. You don't want stuff ripping out of the car at 100mph.
 

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If that Chevette's too much work, how about switching platforms?

'79-'85 Mazda RX-7 can be found cheap and has exactly the same wheelbase as a 2dr Chevette. RX-7 has a very strong unibody that does not need strengthening, and has a far larger engine bay and transmission tunnel than the Chevette. The RX-7 did have a heavier curb weight from the factory, but bear in mind that the RX-7 doesn't need added strengthening to handle V8 power and came from the factory with sheetmetal subframe connectors. Did I mention that the stock RX-7 wheelwells are big enough to fit 275/60 radials? And the tunnel is big enough to fit a T56 without modification.

I have a sbc powered '85 RX-7 that weighs 2325 with no added chassis stiffening at all. It's been V8 powered since the early '90's, had 275/60 drag radials on it since 2007, been above 700whp since 2011 when it ran it's 1st 5.70 with a 1.30 60'. No cracks or buckling in the body, doors still open/close like new, original windshield still in the car.

Grant
 

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I have a 68 camaro that was bought just for racing by the original owner. I know because I bought it from him.
he did some mods to the 396/375 and bumped it to about 400+
when I did the restoration of the car in 2011 I found the floor behind the drivers seat was buckled slightly
he had no frame connectors or cage
 

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Age of the car and rust will have a lot to do with this too. That said, a Chevette wasn't built for this abuse. I would think you would want more than frame connectors and a cage to stiffen it.
 

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When my mom passed, I was tasked with selling her Chevette. I was checking it over to see what it was worth and the wheels were loose on the drums. I got out my 4-way to tighten them, only to discover that the fellows at the tire store, with their rat-a-tat-tat air guns had tightened the wheel until the nuts went through the wheel material and bottomed on the drums. You couldn't tighten the nuts any more, and the wheels were loose. That told me all I needed to know about the integrity of a Chevette. Build a 2" x 3" chassis for it, turn the Chevette into a backyard go-kart and take Grant's advice.
 

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Discussion Starter · #15 ·
i mean the easy thing to do would be to get a g-body, doesn't have to be monte carlo or cutlass--even a 4 door would work.


zz454 big block
ATI or equivalent quality TH-350
Bolt in aftermarket 12-bolt, 3.73 or lower
11.5 x 29 inch slicks
Driveshaft and u joints, hoop, not a big deal to get off the net these days.


This combo is 100% bolt in, no need to mess with "subframe connectors" for obvious reasons and should run in the 11 sec bracket fairly easily.


But i've fallen in love with the chevette and am not giving up on it despite better logic.
 

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If it matters, at the time I had a 68 Camaro, T-400, 12 bolt with 4.11 gears, 4 speed muncie and a 283 with a 4" bore to make a 302. It had 12.5:1 pistons, off road cam, 780 Holley. I shifted at 6000 rpm and ran a best of 13.2 in the quarter.
I wrinkled the driver side quarter in the front. Then I decided to install frame connectors.
 

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If it matters, at the time I had a 68 Camaro, T-400, 12 bolt with 4.11 gears, 4 speed muncie and a 283 with a 4" bore to make a 302. It had 12.5:1 pistons, off road cam, 780 Holley. I shifted at 6000 rpm and ran a best of 13.2 in the quarter.
I wrinkled the driver side quarter in the front. Then I decided to install frame connectors.
T400 and a Muncie?

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