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81 280ZX SBC 400 V8 conversion questions


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New to the forum. Starting a new project with the following stuff. Need advice and any info. that would help me get this going.

Car:

1973 240Z with 3.34 factory gear ratio-rear end.

Engine:

SBC 400 standard bore 2 bolt main block

SBC 400 standard crank

Sterling Dome Top Pistons-Hypeurectic

350 5.7 Rods/ARP bolts

Edelbrock 750 carb

Performer Air Gap Alum. Intake

Double Roller Chain and Gears

High Volume Oil Pump

Alum. Water Pump

Cam Style:

Hydraulic flat tappet

Basic Operating RPM Range:

2,500-6,800 RPM

Intake Duration at 050 inch Lift:

232

Exhaust Duration at 050 inch Lift:

232

Duration at 050 inch Lift:

232 int./232 exh.

Advertised Intake Duration:

280

Advertised Exhaust Duration:

280

Advertised Duration:

280 int./280 exh.

Intake Valve Lift with Factory Rocker Arm Ratio:

0.485 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio:

0.485 in.

Valve Lift with Factory Rocker Arm Ratio:

0.485 int./0.485 exh. lift

Lobe Separation (degrees):

106

Intake Valve Lash:

0.000 in.

Exhaust Valve Lash:

0.000 in.

Computer Controlled Compatible:

No

Grind Number:

280 Mega

 

 

Will be running the cam with -4 deg. retard to help bleed off compression.

76cc Chamber Heads.

Hooker block hugger headers

 

Tranny:

Turbo 350 with HD race clutches and shift kit. Stock converter.

 

WIth all this listed, what can I expect to have to modify on the car to hold up to this engine/tranny setup? I want to keep it a streetable vehicle with good gripping street tires. Not really planning on running drag slicks on the car cause I want to try to keep the stock rear end under the car as long as possible.

Any advice, or suggestions on the car body, suspension, frame modifications is greatly appreciated. I am going to be doing all this work myself.

 

Jim C.

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That tranny is not ideal for a street car unless all the driving you do is in town. No overdrive is a real downer on the highway and you'll be reving the motor in the 3500 RPM range while cruising at 65-70MPH.

I would go with a 200R4 built up or even a 700R4 built up. The 200 has better gearing from what I have read from other members.

 

I don't know if you'll need to modify/beat the transmission tunel with a TH350 tranny but you will have cut the ears off the tunel.

 

Are you going to make your own mounts or buy them? The MSA ones are overpriced if you ask me. You can build mounts for a 280ZX V8 pretty easy....all you have to do is make a mount that adapts the chevy 3 bolt pattern on the block to the 2 bolt pattern on the datsun mount and bingo your done. Just have to add the right amount of space on each side. I have the rough dimensions on my website for how high then need to be.

 

Welcome aboard by the way!

 

Guy

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I actually believe the ideal way to go if you're using that transmission is to leave the stock mounts and use some sort of strap bolted TO the stock mounts for somewhat of a crossmember. I wouldn't beat on the tunnel to begin with because after I put my transmission in I really didn't see that it would have made that big of a difference. Someone makes a mount for the th350 in a ZX (I believe) that uses the stock transmission mounts. You might look at MSA but I'm not sure.

 

If your diff seems pretty tight I wouldn't do anything to the car. I'm still running my 383 on the stock rearend. I don't get any traction in 1st if I don't want to so I'm not stressing the rearend that much but I think it would take some mild street slicks without any problem.

 

Good luck!

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Thanks guys for all your info. I plan to run the Turbo 350 though because I will be running it at the Drag Strip and just on Rural roads most of the time, so the low gear ratio is not going to bother me any. Plus its already built and the money is already invested in it.

 

I do plan to build all my own mounts and stuff. I am really curious about how well the bodies hold up to the V8's. I am expecting to have to really beef up the underside of the car to prevent it from flexing and twisting. Is this been a problem on either or your cars, or are you both running the factory bodies without any extra subframe connections underneath?

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I would not recommend using the MSA tranny mount. You have to cut part of the stock ears to fit the MSA mount in anyways and still are limited on how far back you can put the tranny because it hits the ears. I would highly recommend using the kit from JTR. It requires cutting the ears completely off and making a whole new bracket. This allows much more optimal position of the engine and tranny, at least in my case with the LT1. I have alot more room to push the engine back toward the firewall if I wasn't limited by the MSA mount and the need for the stock ears to mount it. I had to beat the passenger side transmission tunnel a little to clear the transmission cooler lines. I plan on pulling my engine/tranny this summer and using JTR's setup.

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Probably going to make my own engine and tranny mounts. I plan to do all the work on my car myself, so I am going to style my tranny mount after the JTR mount brackets.

 

No one has ever gave me a straight up answer on how these 280ZX car bodies do with the V8 swaps. Mine is a 2+2 hard top version and I am just trying to find out if there is any extra stuff you have to actually do to the underside, or if they will hold up to a 300 to 350HP engine without any frame rail or body pan reinforments?

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What did you have to do underneath your car? Any special subframe connectors and body stiffeners? I am just trying to find out if the stock ZX body will hold up to my 400 sbc setup without having to do a lot of stuff under the car. You can shoot me any pics you got of the setup of your car at JimmyC@Hired-Hand.com.

I appreciate all the help you guys have offered me so far. It goes a long way to saving a lot of killed time when you got other people willing to help a guy out thats never done this type of swap before.

I actually believe the ideal way to go if you're using that transmission is to leave the stock mounts and use some sort of strap bolted TO the stock mounts for somewhat of a crossmember. I wouldn't beat on the tunnel to begin with because after I put my transmission in I really didn't see that it would have made that big of a difference. Someone makes a mount for the th350 in a ZX (I believe) that uses the stock transmission mounts. You might look at MSA but I'm not sure.

 

If your diff seems pretty tight I wouldn't do anything to the car. I'm still running my 383 on the stock rearend. I don't get any traction in 1st if I don't want to so I'm not stressing the rearend that much but I think it would take some mild street slicks without any problem.

 

Good luck!

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Well, lets shift gears here and try again. I just inspected the underside of my 81 2+2 and its officially now a basket case. Frame is rotted out on driver side from firewall back to behind the front seat. Passenger side is starting to show signs of rot around the area right past the firewall also.

Frame on both sides is crushed from people trying to lift the car with the rails. After today, its now just a doner car for parts in my book.

Its time to pull out my 73 240Z now and yank its stock motor/tranny to begin the V8 Conversion.

Any help on total frame replacement and tube front ends would be greatly appreciated. My 240Z front frame sections has been clipped at the firewall at some point in time, so I want to go ahead and do this up right the first time. Eventually, this car may become a Drag Car, so I want to do what it will take to make it hold up to 450 to 500 HP if necessary. Excluding rear end swaps for now though cause my current engine setup is probably only going to get me around 300 HP. Probably still have a good bit of torque though, since it is a 400 small block.

Links to pics, dimensions, drawings and stuff would be appreciated, along with any advice while doing this build.

I will also probably go ahead and look at installing a cage also.

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