Front Plate, Mid Plate, No Plate topic

[Tim Corcoran]

This topic was touched on a bit in the girdle topic and I thought I would open one just on motor mounting. Some say don't run a front plate unless you also have a mid plate. Some say don't run a front plate, only a rear plate and motor mounts. I am curremtly running a front plate only and am wondering if this is a bad thing or not. I would like to see what some of you guys are doing and some opinnions on this subject. Thanks for your comments.

Tim C

[potentpontiac]

I would think you should run both.I personally run aluminum front with 1/8 inch steel mid plate.If you do not run the mid plate I would think some flexing issues could result in some serious consequenses.You would be lacking support because the front plate has to carry the load.Maybe some chassis guys can answer this question.Certainly my best guess is to have both for proper support.

[flamedabone]

Along that note.....I wonder if using side motor mounts contributed to my thin web 500557 block taking a big chunk out of the drivers side main web?

Yes, I know those blocks suck, but was my motor mount situation compounding the problem?

-Abone.

[Jagtec1]

OK...stupid questions: How exactly does a midplate m ount to both the motor/trans and frame? Pics anyone? Does it go between the motor and trans?? If so, how do you deal with the converter to flexplate spacing?

Hopefully I'll be knocking on low 10's this year, maybe into the 9's if I'm lucky. I'm still running stock type motor mounts with the Jim Hand deal on the PS. Am I asking for big trouble? Car is footbraked and will be around 3000# race weight.

[potentpontiac]

The mid plate is between motor and trans.I have 2 tabs welded on subframe and 2 bolts on each side to tie the mid plate in.As far as converter distance there is the 1/8 differencial,which you can use a washer in between the converter pad and flexplate.Basically my steel midplate is drilled for the trans,bolts to block and tied into the subframe.Very secure deal to tie everything together.Sorry no photos available.

[screamingchief]

Does it go between the motor and trans??
Yes.

If so, how do you deal with the converter to flexplate spacing?

You use spacers/washers that match the thickness of the mid-plate between the flexplate and convertor,also if the midplate is thick enough you may need a longer convertor pilot too,this often requires shipping the convertor to a convertor company for the mod,some high end convertors come with screw-in replaceable convertor pilots,and an assortment of various length pilots.

You'll likely also need longer rear trans dowels too.

My opinion says if your gonna run just one or the other in addition to the stock motor mounts,use the midplate,then the stock mounts are basically just there for locating purposes,and the mid plate controls the the situation mostly.

Using just a front plate places a lot of burden on those fasteners to handle the whole deal in check,and this palces the loads at the very end of the frame where the frame has less strength to limit movement unless the car has been "beefed up" with the J bars up there that are tied into the roll bar or such.

Best bet is both a front-plate tied into the J bars and the mid-plate,no stock mounts,along with a fore/aft limit strut tied to the frame.

JMO/FWIW.
Bret.

[Bill Eveland]

I think if your not running side mounts, I would be running a front and mid plate. I think a front plate and rear trans mount only is a long way to spread out the weight and torque of the engine. Imagine a 2"x4"x8" with 200lbs of bricks stacked right in the middle, I know the engine/trans is alot more ridged but more chance of flexing without the middle support.
I found this one the other day and wondering if it could be modified to fit a Pontiac, it was listed for a sbc. I suppose spacers would be required between the flexplate and converter.

[screamingchief]

Bill,that pic looks like it has both patterns (BOP/Chevy),the only problem I see is the starter pocket/notch is on the wrong side for the pontiac/olds starter,ours is on the drivers side,maybe they offer it that way as well.

Who makes that may I ask?

[GTO]

I'm running 3/16 front and mid with a rubber trany mount. My buddy ran a front plate with just a trany mount and had no problems. That was on a 70 Camaro with a 502. ... Eric Here's a couple of pictures I had on file. ... Eric

[Bill Eveland]

That was from Speedway motors. They actually called it a safety shield, with our without the mounting tabs. No other engines were listed.

http://www.speedwaymotors.com/p/6537,,_Chevy-Transmission-Safety-Shield.html?itemNo=910-27032

[v869tr6]

I used a TCI brand midplate that has a built in SFI shield but its made for a Chev bolt pattern. You need to redill two holes and cut a starter hole on the Pontiac sde. That kill the SFI rating but nobody has given me trouble in tech.
The rest of my mounts are side mounts and a rubber trans mount. Never any trouble yet.

[Elarson]

The optimum setup can be built easily on a tube frame car. A stock chassis takes a bit more thought. Sorry for the long post, but here goes:

Tube chassis
Mid plate needs to be mounted strong enough to take all torque reactions and locate the engine fore & aft. You do not want the torque reaction from the transmission (in 1st gear especially) to be transferred into side motor mounts that can flex the side of the block. Get them into the frame before they get to the block. The fore/aft bracing needs to take 1st gear "G" loads of the whole engine/trans assembly (weight of engine & trans x 2.5 , in our case). The mid plate should be braced to send all of these loads into the main cage and/or double-framerail on a tube car.

The front motor plate should suupport the engine vertically to keep it from pitching up & down and should support it laterally to keep it from yawing side-to-side. It needs to be a little bit flexible fore/aft since the engine gets longer when it's hot. The forward part of the frame is not nearly as stiff as it is around the midplate, so you can't count on this location to take much torque (and you don't really want it to..).

The transmission tail should either hang free or it needs to have a soft mount, so that none of the chassis twist tries to bind the gears or break the case. Our Lenco is mounted to rails, but they are very wimpy and are mainly there to slide the trans back& forth during disassembly.

Stock chassis:
The factory mounts are designed to avoid binding the engine & trans during chassis flex. 3 point mount (2 motor sides and 1 trans tail) with soft mounts is ideal for a flexible stock chassis and streetable horsepower. For a stock chassis, the following combos wouldn't be bad:

1) solid side motor mounts and a soft trans mount

2) solid midplate with soft mounts at engine sides and soft mount at trans

3) solid midplate, soft mounted (like on rubber shock mounts) front plate, no side mounts, soft trans mount

4) roll cage welded to stock frame to reduce flex, solid midplate, fairly solid front plate, soft trans mount, no side mounts

Note that none of these suggested combos has a hard trans mount. It's asking for trouble to put loads into the trans case. Our funny car will not have any trans mount at all, since the 2-speed Lenco is light enough to remove without slide rails.

Overall, the things to remember: any chassis flexes and a stock chassis is all over the place. You do not want to have the engine & trans trying to resist chassis flex. And remember that the engine gets bigger when it's hot.

If you're still not convinced about flex of a stock chassis, follow a pickup truck over a bumpy road and watch how much the bed moves relative to the cab. Then imagine adding a good load of drag racing torque reaction!!

Hope that helps stir some thoughts.

Eric

[pmd428lms]

I've got mine set up with a front plate between the water pump housing and block with no leaking issues, both solid motor mounts and a poly trans mount. Haven't been to the track yet, just street miles, but it sure does stiffen up the chassis. I jacked the car up on one side and the whole front end came up perfectly level. Will post pictures in my PY garage soon. Course I wonder what torsional loads that is putting on the block, if any?????????????????

[Elarson]

If the solid mounts add so much chassis stiffness, then the engine/trans have to be taking torsional loads. You've illustrated my discussion pretty well.

[Brian Baker]

My mid plate has a hole only large enough for the crank. Has anyone else deployed this type of plate, that uses a spacer between the crank and flexplate? This is going in the funny car and I'm running an automatic so there's no clutch can to take up the open space left behind from such a large hole in the plate. In a funny car, this plate also serves as a firewall.

[tempest455]

You should also be using a F-B limiter, w/ adjustable rod ends is ideal control F-B movement.

[janderson]

Best bet is both a front-plate tied into the J bars and the mid-plate,no stock mounts,along with a fore/aft limit strut tied to the frame.

JMO/FWIW.
Bret.

Front plate from All Pontiac, mid plate from Chris Alston, "Fore/aft limit" struts with mis-alignment bushings. Transmission crossmember fabbed for clearance and floor support, TCI mount. With the forward tubes (J bars )coming off of the down tubes of the cage, its all tied together very well. While we were cutting, made the crossmember center section removeable also. 2" supercomps come out with engine bolted in.

[twooldgoats]

BOP front plate, All-Pontiac mid-plate and polyurethane trans mount.

Jim

[Jack Gifford]

I endorse post#12.

[FBNRacing]

Not that anybody can use this info unless bulding a new car from scratch, we make the mid plate part of the firewall. The section in the center is 10 guage steel. we ran two 11/4 pipes up each side and to the crossbar. We welded a flange around the outer perimiter of the tranny to act as a scatter shield (not SFI approved)
http://home.adelphia.net/~fbnr/images/fbn-racecars/fbnracecars%20pic%2027.jpg

this stiffens the whole deal up and also acts as a flange for the tunnel


http://home.adelphia.net/~fbnr/images/fbn-racecars/fbnracecars%20pic%2039.jpg

Over built for a car that will never see more then 900 hp?
So far nothing has cracked or broke in two years of serious racing at the 600 HP level.


Rex

[taff2]

I made my own midplate out of 1/4" T6 ali.

[Tim Corcoran]

Where do you get the long dowl pins for the TH-400 trans?

Tim C

[Bruce Meyer]

Tim-Butler sells them. They are in the catalog. They also sell midplates.

[Brian Baker]

No comments from anyone that has run a plate only large enough for the crank? Anyone ever run a spacer between the crank and flexplate?

[twooldgoats]

No comments from anyone that has run a plate only large enough for the crank? Anyone ever run a spacer between the crank and flexplate?

I've got one like that (All-Pontiac), but I'm ashamed to say I haven't gotten to the point of figuring out how it all goes together yet. I was hoping someone would answer your question, too. I was just looking at it the other day while I was doing something else and I started wondering how it would all fit together--starter alignment, flexplate, torque converter, etc.).

Jim

[screamingchief]

I dont see any big concerns with that style midplate guys,that is other than the fact that I'd want the spacer mounted,along with the flexplate to be used,when any balancing is done to the reciprocating assembly,just to be thorough.

Where do you get the long dowl pins for the TH-400 trans?
Pretty sure lakewood,moroso,TCI,and tavia all offer long dowels for GM applications.

HTH.
Bret.

[Brian Baker]

I've gotten 3 answers from 3 different people on the CFC board...two with BBC's and one with a SBC. The BBC owners said no spacer needed between crank and flexplate to clear 1/4" midplate. The SBC owner advised he needed a spacer.

[Tom Vaught]

Quote:

"No comments from anyone that has run a plate only large enough for the crank? Anyone ever run a spacer between the crank and flexplate?

The Lakewood scattershield I use has the "barely clears the crank flywheel flange" hole in the plate. The plate is .125" thick. I easily have enough room for an additional .125" of plate thickness if I ever wanted to use thicker material and
use that as a mid plate. If I went that way, I would have a custom bronze input shaft bushing made that would be .250" longer to support the input shaft properly.

I have to believe that the full plate is stronger and safer vs the "hollowed out" typical plate.

JMO

Tom V.

[GTO]

Just remember, when using the motor plates and a Fore/Aft limiting rod, mount the rod high enough so you can fit that darn diaper! ... Eric.

[84TA400]

Question:::::....if i am using solid engine mounts, what should the trans mount be, solid or soft?..i'm not using a front or mid plate,thanks, Billy

[GTO]

I don't like solid trans mounts, but that's me. Rubber or Poly. ... Eric.

[Brian Baker]

I'm running s solid tranny mount in the funny car. Can't speak for door cars, but they're all done like this in a funny car. Of course floppers run a midplate and a front plate.

[potentpontiac]

Stick to a rubber trans mount,it is more forgiving than steel.I run an aluminum front motor plate 1/4 inch 6061,1/8 steel mid plate with rubber trans mount.No issues at all.

[twooldgoats]

Stick to a rubber trans mount,it is more forgiving than steel.I run an aluminum front motor plate 1/4 inch 6061,1/8 steel mid plate with rubber trans mount.No issues at all.


Do you run a front-to-rear limiter with them? I didn't make any provision for one and I'm wondering if I should have. I've heard conflicting opinions.

Jim

[jm455ho]

At what point in a stock chassis car is it recommended to run a mid-plate? High 10's, mid 10's, low 10's or only if into the nines?

[potentpontiac]

Jim.No I do not have the lateral bar,just the front,and steel mid plate.My car wheelstands pretty good,and have thought about adding the lateral tube from engine block to frame.But honestly have not had any issues.

[Tim Corcoran]

OK guys you convinced me I need a mid-plate. I ordered one from All Pontiac and the dowel pins from Butler this morning. Thanks for all your responses.

Tim C

[Robert C.]

As we see where we can make changes to improve our products, we do them.

This is just a update: If you have a front plate and it is not installed, we will bend the plate and sent it back to you if you pay UPS in we will cover the UPS back out at no charge.

http://allpontiac.com/steelfrontmotor.html

P.S. More to come in the next few weeks.

[Probird]

Bob, I just got it mounted to the frame and I see now why you are putting a bend in it. If I send you my plate back can you bend it the same on both sides? If not I atleast will send it back to have it done to the one side to clear the radiator hose. I'd like the offset to be the same on the left and the right. That way I would have the motorplate on the same side of the mounts on the frame. It would just make installation easier. Thanks.

[Robert C.]

Bob, I just got it mounted to the frame and I see now why you are putting a bend in it. If I send you my plate back can you bend it the same on both sides? If not I atleast will send it back to have it done to the one side to clear the radiator hose. I'd like the offset to be the same on the left and the right. That way I would have the motorplate on the same side of the mounts on the frame. It would just make installation easier. Thanks.


No problem on doing one side for free. I feel that doing both would look cool but making the cost go up for nothing gained but looks.

Customer service is # 1 @ AllPontiac.com

[60man]

As we see where we can make changes to improve our products, we do them.

This is just a update: If you have a front plate and it is not installed, we will bend the plate and sent it back to you if you pay UPS in we will cover the UPS back out at no charge.

http://allpontiac.com/steelfrontmotor.html

P.S. More to come in the next few weeks.

Cool Bob. I considered doing that to mine but couldn't figure out where to have it done locally..
I'll just order another one (with the bend) later..
Maybe with two bends...would be practical for me...need to move motor back about 14-3/8" for front space clearance...for electric fan..Easier than re-doing frame tabs..!!
That looks a lot more professional than my "grind' job and one off lower hose ..;) :rolleyes:

[janderson]

No problem on doing one side for free. I feel that doing both would look cool but making the cost go up for nothing gained but looks.

Customer service is # 1 @ AllPontiac.com


When we bent my front plate, moved the bends further outward to allow more surface area for the crank trigger mount, still chamfered the edge also. Didn't bend the drivers side because of mounting alternator. Shortened overall length to reduce flex.

Troy, if you need some help, PM me, or drop a note. My shop is in Alexandria.

[John Bailey (GTOKID)]

solid motor and trans mounts,stiff cage....no plate. the car is stiff .It sits on 3 jack stands. no plans to change.

[60man]

When we bent my front plate, moved the bends further outward to allow more surface area for the crank trigger mount, still chamfered the edge also. Didn't bend the drivers side because of mounting alternator. Shortened overall length to reduce flex.

Troy, if you need some help, PM me, or drop a note. My shop is in Alexandria.


Hey Jesse...how are ya..
...haven't had an excuse to go to Alexandria,
guess I'll have to invent one...
See you at VMP ??

[janderson]

Hey Jesse...how are ya..
...haven't had an excuse to go to Alexandria,
guess I'll have to invent one...
See you at VMP ??

Troy,
We are all fine, and glad to see you are also. And yes, the gang will be at VMP in May. Hope you plan on being part of the group.

If you do need help with your plate, just let me know, or if you want I drive though Richmond every week and I could drop it off at Bob and Franks shop.

Attached is a pic of how mine is done, car is not all back together, buy you will get the idea. Went though alot of radiator hoses to find one that would make the bend that I wanted.

[60man]

Looks good Jesse..
I wound up using one of those stainless steel "U-bend" hose kits.
My Griffin radiator has a funky lower hose angle on it.
It worked but damn it was pricy for a radiator hose..:eek: :rolleyes:
Thanks for offer of hitting Bob & Frank's place for me..
Think I'll wait until 505 swap before trying another front plate

Whoee!! you travel a lot on week ends.....
Take care.....
Troy

[6567GTO]

I have an All Pontiac front plate and mid plate and a rubber trans mount. the mid plate is 3/16" thick. The torque converter i have has a ring for a mount area. Doesn't seem right to put washer style spacers only at the bolt area. Should i be using a spacer shaped like a ring? Do I really need spacers? Already installed longer trans/block pins. The torque converter measures 6.190 from pad to snout of converter?

[Probird]

I have an All Pontiac front plate and mid plate and a rubber trans mount. the mid plate is 3/16" thick. The torque converter i have has a ring for a mount area. Doesn't seem right to put washer style spacers only at the bolt area. Should i be using a spacer shaped like a ring? Do I really need spacers? Already installed longer trans/block pins. The torque converter measures 6.190 from pad to snout of converter?

Yes washers are fine to use as spacers. You will need to lengthen the snout that goes into the back of the crank 3/16" so it will reach into the crank. A lot of converters have a ring that screws on there and can be swapped to a longer one to make up for a midplate. If yours doesn't have the screw on deal on it you'll have to send it in to have it installed and at the same time they can add 3/16" to the mounting pad.

[6567GTO]

Thanks!

[PrimeredPontiac]

Coan makes a shim kit for using a midplate. Washers for the pads, and a spacer for the center.

[6567GTO]

I've been researching that and can't seem to find much info or dimensions of these spacers. Are slip on spacers safe to use? V's a threaded version? I'll look into the coan spacer, thanks for the help. I'm debating whether to even use a midplate.

[PrimeredPontiac]

I've used one of the coan spacer kits with a .250 aluminum midplate for a couple years, forgot it was behind a bbc though. I think I still have it somewhere, if I find it, I'll measure it and see if it would work behind a pontiac.

[6567GTO]

great thx.

[PrimeredPontiac]

Sorry, the coan chevy spacer will not work for a pontiac. Unless they make one I don't know about.
Any one with a lathe could make one though.
This one measures around 2.584 where it goes over the back of the crank. A pontiac crank measures around 2.750

[6567GTO]

okay thanks very much Primered Pontiac. I actually work at a machine shop and am a machinist by trade. I have another engine and transmission in the shop and will put them together and check clearances. My worry is that there isn't enough clearance to go from the boss on the torque converter when transitioning to the ID of the crank. I have to also remember to allow for radii in all Corners to add strength.

[PrimeredPontiac]

This spacer goes around the outside of the crank, almost against the heads of the flex plate bolts, and basically makes the recess in the crank deeper.
Sounds like you're thinking going in the crank then to the outside of the converter.
Just trying to clarify and make sure we're on the same page. Good luck with whatever you decide to go with.

[6567GTO]

yes you're correct I'm thinking of going to the inside of the crankshaft because that's how the original pilot of the torque converter located itself. that's what was confusing me with the adapters I saw pictures of online it wasn't the same design that I was thinking about. I'll have to look at it when I'm down at the shop and see about that style you have.

[taff2]

A push on converter spigot spacer is fine, I make my own out of a length of ali bar.

[6567GTO]

Thx taff2. I haven't had a chance to take measurements. A friend has been helping me with bodywork on the car. Gotta take full advantage of that when he has the opportunity to help me. My thought was to use some 2 part molding putty to get some sort of idea of my clearances when everything was assembled. Are your spacers like what primeredpontiac showed or like this in my picture?

[taff2]

Like your pic but solid,no hole bored through the centre.

[6567GTO]

Got it, thanks