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how much HP can a stock 240z frame take?


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Since i'm planning to do a SBC swap into my 240z; thought i would ask the question before i twisted my car into a pretzel.

 

How much power can the stock 240z frame/monocogue take without addition reinforcement?

 

 

I'm currently planning a SBC 350 putting bout somewhere between 300 to 350 hp at the wheels. I have yet to buy the cam and heads; but i have the block and the rotating assm. complete.

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I have a '72 with a small-block in it, somewhere in the 400 hp range, t56, runs in the upper 12's, original r180. Traction, what's that? Put about 10,000 miles on it like that, haven't done any chassis stiffening yet, though I hope to soon. Nothing has bent, twisted, crooked, warped, contorted, deformed, bowed, arched, curved, angled, hooked, or kinked yet. If it's a pretzel, it's a rather tasty one...

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Wouldn't a pretzel be better than a noodle? 150hp might be a little conservative. I guarantee there are a lot of people here that throw in ludicrous speed engines without doing crap to the chassis. I'd wish to think I'm one of them... :rolleyes:

 

 

Although I trust the chassis wont fast-and-the-furious on you, performance probably takes a big hit. I bet most people start stiffening for the performance first rather than necessity. Even with my little scooter I think it's time to start investing in at least strut braces and of course a better diff mount because I get wheel hop and apparently diff hop like crazy. Still not getting any of this traction you speak of though.

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Funny that pretzel comment got so much air time. Anyway, the problem I have had with my z-car is cracks in the paint and metal at the spot weld/lap joint locations I referred to-the rest of the paint is beautiful, so I don't want to screw it up to fix the cracks-paint work is such a drag. However, once the paint cracks, rust starts on the raw steel, and now I am afraid to park my car outside for fear of rust in those weakened areas. I got all those cracks with a stock L24 motor, alas I have no chassis reinforcement. I have no idea how many miles my car actually has-probably a million (it had 5 coats of paint on it when I bought it). My springs and sway bars are stiff enough to lift a wheel everytime I go in and out of my driveway-had to get a posi just to get in the garage! I am putting an LS2/T56 in it right now and will drag race it with slicks. I have autocrossed it with BFG R1s, so I ask a lot of the old, tired sheetmetal. The driver side door won't shut well with the tires on the ground, but it shuts fine if I put it on jackstands positioned on the frame rails close to the middle of the car, so I must have some amount of chassis flex. I'm planning on continuing to beat the tar out of it inspite of the chassis damage I have. Anybody ever had a chassis snap catastrophically-I don't really know? I don't expect to lift the front tires with only 400hp and no nitrous, so I should be fine. Next major component to be replaced WILL BE the chassis tub, and I plan to do some serious strengthening with an integrated non-SCCA-legal cage before swapping all my components over. The windshield frame is just so frail-that is where I plan to concentrated. I won't be reinforcing to improve performance, rather I just hope to keep the paint from cracking and compromising my tin due to rust in stress areas. That's my 75-cents on the need for chassis strengthening. Good luck.

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Here's a list I just sent a prospective customer of the mods I did to my old road race car and one of my street cars:

 

1. Welded in subframe connectors.

2. Welded in roll bar.

3. Welded in rear strut tower bar.

4. Custom triangulated front strut tower bars.

5. Front anti-roll bar reinforcement.

6. TC rod mount reinforcement.

 

That worked well for 325 hp, 275 width Hoosiers, and over 1.2G sustained lateral.

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I think just as much consideration (maybe more) should be made to how modifications to the suspension can cause twisting of the uni-body. Stiff springs and anti-roll bars coupled with hard bushings can put a lot more strain on the car than big bags of housepower on soft motor mounts. With the wheels mounted at the four corners of the car they have a leverage advantage.

 

Either way I would follow johnc's list. Saves a lot of future headaches. Take it from a guy who put the cart before the horse and had to deal with the headaches.

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My car currently has upgraded brakes, coilover suspension, thicker front and rear sway bars, strut bars front and rear, 275/4017 tires on the rear and 255/45/17 on the front.

 

Are there any shop drawings with measurements/instructions for all the stuff John C mentioned?

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Logan1:

 

It is doubtful there are drawings for the stuff the John C. mentioned. It would be interesting to conduct tests of torsional stiffness. One test prior to each of the modifications recommended by John C. The one that may be the most significant is Custom triangulated front strut tower bars. It would be interesting if there were a FEA computer analysis of the structure of the Datsuns to see which mods have the most impact on torsional stiffness. It would appear that more than a roll bar is needed to increase torsional stiffness. It would take a properly designed Roll Cage with diagonal torsion stiffners not only at the main roll bar but also further forward.

 

Comments on these aspects are welcomed.

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Logan 1

 

What are you primarily looking to do with the car once complete? I think it is very important to ask yourself that question with a build in order to determine direction with regards to suspension, engine components, "frame or chassis upgrades" etc. For example: I wish my car was more of a driver now that it is complete but the direction I chose engine,suspension and even fuel type wise is drag racing specific. At the end of the day I wanted to go Drag racing. That is not everyones goal. That is not to say you can't take a piece of knowledge from a drag car, a piece of knowledge from a road course car and some what arrive at a finish product that accomplishes your goal. Most people will agree that for every gain in one aspect you generally compromise in another so determining a cars primary function is key. Hope this helps a bit.

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It would be interesting if there were a FEA computer analysis of the structure of the Datsuns to see which mods have the most impact on torsional stiffness.

 

There is (or was). The triangulated STB, TC rod, frame rail, and rocker front and rear clips on my Rusty Old Datsun race car was designed via FEA that was done by Bill Savage of T-Mag (currently SPD Products): http://www.spdproducts.com/nisson_gto.htm

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Johnc:

 

I would imagine that you paid to have the FEA computer analysis done for the Rusty Old Datsun. Don't understand what the triangulated STB is. Would you be so kind as to spell out this acronym and any further suggestions you might have in increasing the torsional stiffness of the Datsun. Thanks for all your help.

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About 150 hp/150 tq. The Z-chassis is a noodle. Add 40 years and it is a pretzel. If you drive it hard or soup it up, it will crack at the a-pilar and b-pilar and at the weld between the rockers and the quarter panels. I just let it crack.

 

I had to weld the cracks in mine and it was STOCK!! Not anymore :P

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