Classic HorsePower Scratch GT40

[Devin]

If any of you have noticed on my front clamshell the absence of the center vent duct...it WAS there prior to my ownership but the previous guy filled it in for some reason. I’m leaning towards cleaning out the body filler and opening it back up again (hope it’s not a bear) for cockpit fresh air.

Any thoughts from those that use/don’t use it?

 

[Kyle]

I’ve been waiting to pull the trigger on plans from Chris until I have reasonable space to build. In the mean time, how heavy do you estimate the frame to be? I know he had it expertly designed. However when I compare it to something like the space frame of the FFR coupe this frame seems crazy robust. Are things such as all the steel plates on the front necessary? Would any sort of space frame design with aluminum skinning save weight?

 

[Devin]

I’ve been waiting to pull the trigger on plans from Chris until I have reasonable space to build. In the mean time, how heavy do you estimate the frame to be? I know he had it expertly designed. However when I compare it to something like the space frame of the FFR coupe this frame seems crazy robust. Are things such as all the steel plates on the front necessary? Would any sort of space frame design with aluminum skinning save weight?

Kyle

I’ve seen someone else’s variation of the AP chassis that did choose to make more of a space frame front box design. Doing that would certainly make it easier on the home builder as I had to source these panels out to a shop with CNC plasma cutter.

I chose to stick with the AP design due to 1) I had a good local machine shop that chose to take on my request and had confidence in them and 2) I think safety wise that I would trust the all steel box protecting my (and my passengers) legs in the event of an accident vs something of my own design and partly aluminum. If you have sat in one (I did many years ago) I don’t think I could safely get out if any portion of the area forward of my knees were to become even smaller...I have a difficult time getting in/out anyways at 6’1”.

To answer your question on overall weight...I don’t have a great estimate for you but am sure Chris can answer that with their standard built chassis. I do plan on weighing it at some future point as I am a bit mod’d from the standard plan with my wheelbase being 2” longer, a different rear bulkhead design, and some slightly different material thicknesses due to the materials that are available locally to me. Personally weight isn’t one of my primary concerns but understand the question. If one were to race this chassis design, I would count on a robust roll cage overhead to make up for a lighter material in the rest of the chassis structure.

 

[Devin]

Been working on the spider substructure. Since my spider pieces were skins supposedly taken from an original MK1, I felt they didn’t have enough rigidity on its own...especially being the roof panel and will be exposed to Texas heat (and possibly a dark color). I am making removable from the space frame in the event the spider ever needs to be removed.

The one question I have for anyone that has completed their windshield installations, what kind of spacing around the perimeter of the glass did you find you needed for a nice fit (not what the fiberglass molding gave you)? Since I’m just swimming in the dark here, I have left at least 1/4” around all edges but plan on using kitty hair body filler to even up some of the irregularities I have in the spacing prior to being satisfied with the fit and primer/paint.

 

[Devin]

Been working on the dash & steering shaft angles/supports. Pretty happy with the overall feel & space so far. Also welded in the seat support strips & seatbelt anchors as well as getting seat sliders mod’d and fitted to the seats themselves.

Had to make a stake in the sand (so to speak) and temp bolt down the rear part of the spider in prep for more body fitting and eventual fiberglass bonding of the sides of the spiders to the top now that I have a metal support structure to the roof and A pillars.

One question to anyone with experience in steering wheel location and can measure yours...what is the “ideal” distance between the dash top and the back of the steering wheel? I know it’s a personal preference but since my seat will be adjustable, I’m looking for a good location for several driver heights (I’ll be about the tallest at 6’1”).

Ol

 

[Devin]

More scratch building progress and lessons learned.

The main lesson learned was...you don’t know what you don’t know!
Again in an ideal world, you have all the parts ready and waiting so you can measure and make room for it all to work together but that isn’t realistic in any custom car building scenario. First off, I ordered the Wilwood 3 pedal assembly hoping I could make room around my steering shaft & rack but mainly selected it for the fact that it has an integrated throttle pedal and homogenous & high performance look. After initial mock up and measuring the assembly as well as the master cylinders, I realized that the steering rack needed to be raised all the way to the top of the pocket and suspended from the top versus the vertical face of the firewall. Once relocated, I realized that I needed to separate the clutch pedal from the rest of the assembly to gain space from the steering shaft & clearance from the rack gearing and masters on the front side of the firewall.

On another note, my new hydraulic hole punch paid off in saving so much work and made nice professional looking holes for the master cylinders. I did pretty much max out the capability of this model and had to take 3 bites/slices at each hole since it was working through 2.6mm/12 gauge mild steel. But I can see using it more in the future and may experiment with using it for dimpling as well.

Also spent time reworking the drivers seat now that I have a “wet cement” location on the steering, dash, and pedals. What I found out was my plan to use a 7/8” thick seat slider was too high for my 34” inseam and knees were hitting the dash bottom. After some careful measuring and sweating in the Texas heat, I was able to make an offset bracket for installing the seat sliders on the sides of the seat! The AP chassis design has 20” wide floors between the tanks and center backbone...I used up 19.5” with this configuration, leaving plenty of room for paneling and installation. This bracket not only lowered the rear of the seat nearly an inch (now just fractions of an inch above the floor) but also added more seat back recline and boosted the thigh support! Works so much better now, is more comfortable, more leg room, headroom, and is adjustable for any shorter drivers (I’m 6’1”). It worked so well that I may even need to bring the seat forward a notch or two to reach the pedals comfortably! I will remind all those that haven’t been following from the start that I did plan and built my GT40 with a 2” stretch in the wheelbase of which I’m using about an inch in the cockpit and 1” in the engine compartment (hopefully making for a smooth rear firewall and not having to notch the cross support for the distributor).

Couple of side notes. 1) the lower control arm “floor humps” DO NOT need to be as large as the plans called for. They WILL require some cutting and re-Engineering to allow my size 12s to use the clutch without obstruction and better comfort. 2) my stock Boxster shifter assembly will fit nicely and will require the center console to be 5” wide. This was planned for and will intrude into the passenger seating area but I will keep the under seat mounted adjustable slider and incorporate a front riser to aid in headroom and seat back recline...why a passenger adjustment? I am thinking rather than removing the seats for rear bulkhead removal and access, I can just slide the seats forward approx 7” and have access the the panel an front of the engine. 3) I will have to widen the drivers seat actuator and possibly shorten its length as well to finish it all up.

 

[Neil]

More scratch building progress and lessons learned.

The main lesson learned was...you don’t know what you don’t know!
Again in an ideal world, you have all the parts ready and waiting so you can measure and make room for it all to work together but that isn’t realistic in any custom car building scenario. First off, I ordered the Wilwood 3 pedal assembly hoping I could make room around my steering shaft & rack but mainly selected it for the fact that it has an integrated throttle pedal and homogenous & high performance look. After initial mock up and measuring the assembly as well as the master cylinders, I realized that the steering rack needed to be raised all the way to the top of the pocket and suspended from the top versus the vertical face of the firewall. Once relocated, I realized that I needed to separate the clutch pedal from the rest of the assembly to gain space from the steering shaft & clearance from the rack gearing and masters on the front side of the firewall.

On another note, my new hydraulic hole punch paid off in saving so much work and made nice professional looking holes for the master cylinders. I did pretty much max out the capability of this model and had to take 3 bites/slices at each hole since it was working through 2.6mm/12 gauge mild steel. But I can see using it more in the future and may experiment with using it for dimpling as well.

Also spent time reworking the drivers seat now that I have a “wet cement” location on the steering, dash, and pedals. What I found out was my plan to use a 7/8” thick seat slider was too high for my 34” inseam and knees were hitting the dash bottom. After some careful measuring and sweating in the Texas heat, I was able to make an offset bracket for installing the seat sliders on the sides of the seat! The AP chassis design has 20” wide floors between the tanks and center backbone...I used up 19.5” with this configuration, leaving plenty of room for paneling and installation. This bracket not only lowered the rear of the seat nearly an inch (now just fractions of an inch above the floor) but also added more seat back recline and boosted the thigh support! Works so much better now, is more comfortable, more leg room, headroom, and is adjustable for any shorter drivers (I’m 6’1”). It worked so well that I may even need to bring the seat forward a notch or two to reach the pedals comfortably! I will remind all those that haven’t been following from the start that I did plan and built my GT40 with a 2” stretch in the wheelbase of which I’m using about an inch in the cockpit and 1” in the engine compartment (hopefully making for a smooth rear firewall and not having to notch the cross support for the distributor).

Couple of side notes. 1) the lower control arm “floor humps” DO NOT need to be as large as the plans called for. They WILL require some cutting and re-Engineering to allow my size 12s to use the clutch without obstruction and better comfort. 2) my stock Boxster shifter assembly will fit nicely and will require the center console to be 5” wide. This was planned for and will intrude into the passenger seating area but I will keep the under seat mounted adjustable slider and incorporate a front riser to aid in headroom and seat back recline...why a passenger adjustment? I am thinking rather than removing the seats for rear bulkhead removal and access, I can just slide the seats forward approx 7” and have access the the panel an front of the engine. 3) I will have to widen the drivers seat actuator and possibly shorten its length as well to finish it all up.
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My rule-of-thumb on steering wheel placement is, 1. Far enough forward to extend your arms but, 2. Not so close to the dash that you scrape your knuckles- i. e., it isn't critical. What is important is to make the steering wheel removable and use a quick-release adapter with as little "play" as possible. It appears that you are using Borgeson U-joints in the steering column- those are good.

 

[Devin]

My rule-of-thumb on steering wheel placement is, 1. Far enough forward to extend your arms but, 2. Not so close to the dash that you scrape your knuckles- i. e., it isn't critical. What is important is to make the steering wheel removable and use a quick-release adapter with as little "play" as possible. It appears that you are using Borgeson U-joints in the steering column- those are good.

Thanks for the feedback Neil, that’s what I’ve generally done by on my other builds but just didn’t want my ‘40 to look odd with it being too long or short.

 

[Brian]

I've dithered back and forth on the steering as well. I ended up rotating the rack so the shaft comes down to meet it with it hitting near the 90, placing the shaft higher. I also have the 4" stretch and ended up putting the MCs fully in the cabin unlike everyone else. Made a nice closure and intermediate bearing support I need to post pictures of. I've been waiting on big tubing benders for refrigerant lines to final mock up all of the plumbing minus brake lines.

 

[Jac Mac]

I saw the photo of the FE on pallet & then the photo of the Coupe it came out of, then had to read whole thread to work out if the 40 was going to be FE powered.... Still with all the scratch build parts I'll keep watching..... close but no cigar.

 

[Fred W Ballinger]

Hi there

You say "steering rack needed to be raised ". If you have changed the vertical position height of the rack away from that intended by the suspension design you may get severe bump steer. Apologies if you have considered this

 

[Devin]

I've dithered back and forth on the steering as well. I ended up rotating the rack so the shaft comes down to meet it with it hitting near the 90, placing the shaft higher. I also have the 4" stretch and ended up putting the MCs fully in the cabin unlike everyone else. Made a nice closure and intermediate bearing support I need to post pictures of. I've been waiting on big tubing benders for refrigerant lines to final mock up all of the plumbing minus brake lines.

I was back and forth on moving the pedals further into the cabin but instead reworked the position of the seat first and seems all has worked itself out once I cut down the drivers floor hump (so to speak).

Next I’m looking at the AC units and plumbing as well, leaning towards Old Air Products 800 series system since it’s compact and they are only a couple hours from me here in TX.

 

[Devin]

I saw the photo of the FE on pallet & then the photo of the Coupe it came out of, then had to read whole thread to work out if the 40 was going to be FE powered.... Still with all the scratch build parts I'll keep watching..... close but no cigar.

Jac Mac, I had thoughts of an FE build (not too in depth) since I do have another block and stuff to build one up but the whole trans axle expense and extra $$ to support the build made me lean SBF for this one . Maybe next time?!? LOL. I do think there would be room in the Active Power platform and especially making it from scratch.

 

[Devin]

Hi there

You say "steering rack needed to be raised ". If you have changed the vertical position height of the rack away from that intended by the suspension design you may get severe bump steer. Apologies if you have considered this

Fred, I did/am considering that and thanks for the reminder and will easily take any input or critiques. Being retired military, I know I can’t possibly know or see everything nor have the best solution to a problem but at some point we all have to dive in with a decision and adjust course as required from there!

I ended up raising the rack only 1/2” and the end-link height (tie rods) are adjustable with the right amount of spacers and length of bolt. I’ll start out by making the steering rack arms level at ride height and make adjustments as necessary once I have some experience with it on the road. I do have an advantage over most other builders by having my own alignment system so correcting any changes in alignment will be quick and easy.

I’m finding that scratch building has one advantage… I’m building adjustability into the things I may need to change once I get it in a “go-cart” stage…I.e steering shaft angles/height, seat, suspension, etc. I’ll have no one to blame but myself for bad design LOL and won’t be “stuck” with a certain manufacturer’s product as I’m building around the parts I want or need (good or bad). Now that there is a “foundation” I’m seemingly happy with most other things can be welded, riveted, or bolted into the space allowed.

 

[Devin]

Just wanted to share that I’m using the Mazda Miata ball vents. They were pretty easy fit and made a couple notches in the pocket hole as well as a relief cut in the vent housing to be able to do a clockwise twist to lock them place.

 

[Devin]

Another update from Classic Horsepower garage...

Despite the triple digit heat, getting my Cobra replica into a running go-cart stage (man that 427 side oiler sounds sweet!) and starting a new job, I have managed to make a little progress. The mock up of the 289 block to the Boxster transaxle (with a Kennedy Engineering adapter) went fairly smoothly and even test fit the Aviaid oil pan and tried the starter too. This identified that I need to clearance the Boxster bellhousing for the KEP supplied starter in order for it to engage the flywheel properly.

Another lesson learned will be for the chassis to be on the floor (or my 2 post lift) when it comes time to install the final motor & trans as my engine hoist boom can be shorter and lower than working with my 4 post lift.

I think I’m happy with the initial height (actual pics are 1/2” higher than what it is now) of the motor and what will be sticking up in the rear deck & window. It actually can’t get any lower due to the rear of the transaxle sitting above the rear chassis of the AP designed rear structure. At this height, the max driveline angle shouldn’t exceed 11-12 degrees and normal resting angle in the 5-6 degree range (upward angle) with a 4.75” ride height. As it sits, the motor will be level and oil pan will have about 1” clearance above the lower frame rail with the 6.5” Aviaid pan. Next sourcing research and procurement challenge will be to decide on a 331 vs 347 stroker internals and what intake & carburation to use. Still back and forth on Weber induction or simple 4 barrel/ dual quads.

Just finished fabricating the rear transaxle mount yesterday (still need to tac to the frame) and used 2x BMW E46 poly transmission mount bushings. I felt their compact size, simple design and popularity made it and easy choice buy &to integrate into a proper mount. After using a piece of wire bent to a proper shape, I made the transaxle mount bracket out of 1.5” angle iron and will weld tabs and gussets to the frame for the lower mount/support. Next will be tackling the motor mounts.

 

[Devin]

Dug into the drive axles today to take a look at the conversion from C5 Corvette hubs to a Boxster transaxle.

After removing the boot retainers and pulling back the C5 boot, the joint almost fell off in my hand due to the ball retainer ring being dislodged at some point prior to my ownership (used axles came with the rear suspension parts). Then I removed the snap ring and used a 3 jaw puller to take off the cv inner “race” from the axle splined shaft.

To remove the Boxster joint, I knocked off the dust cap, removed the boot retainers, snap ring (virtually the same as the C5) and pulled the entire joint assembly with a 3 jaw puller as well.

After cleaning up the grease and exposing both sets of splines, I was able measure the spline diameters and length…nearly same for both!
I haven’t totally cleaned up the joint assembly but did trial fit the end of the shaft and looks like it should slip on there with a little pressing and/or freezer time for the shaft prior to final fitting.
So final conversion unit will use the C5 outer CV and shaft plus the marriage of using the Porsche inner boot and CV assembly (just reinstalled on the splines).

I’ll post another entry once I do the final reassembly and measurements to see if the overall length is as planned/expected for my current transaxle placement.

 

[Devin]

Ok…looks like American (left) meets German (right).

Everything went together as planned. I did freeze the axle shaft overnight and ended up pressing on the Boxster CV and reusing the C5 snap ring. Also added some fresh bearing grease before tapping on the Porsche dust cap (far right).

I did trial fit the axle and looks like the length will be just as expected but need to rework the lower A-arm bracket supports but should be easy to do and shouldn’t affect it’s structural integrity. This is mainly due to how much lower the Boxster transaxle sits compared to a flipped 911 transaxle and drives the axle shafts to be angled upwards instead of downwards.

 

[Neil]

Another update from Classic Horsepower garage...

Despite the triple digit heat, getting my Cobra replica into a running go-cart stage (man that 427 side oiler sounds sweet!) and starting a new job, I have managed to make a little progress. The mock up of the 289 block to the Boxster transaxle (with a Kennedy Engineering adapter) went fairly smoothly and even test fit the Aviaid oil pan and tried the starter too. This identified that I need to clearance the Boxster bellhousing for the KEP supplied starter in order for it to engage the flywheel properly.

Another lesson learned will be for the chassis to be on the floor (or my 2 post lift) when it comes time to install the final motor & trans as my engine hoist boom can be shorter and lower than working with my 4 post lift.

I think I’m happy with the initial height (actual pics are 1/2” higher than what it is now) of the motor and what will be sticking up in the rear deck & window. It actually can’t get any lower due to the rear of the transaxle sitting above the rear chassis of the AP designed rear structure. At this height, the max driveline angle shouldn’t exceed 11-12 degrees and normal resting angle in the 5-6 degree range (upward angle) with a 4.75” ride height. As it sits, the motor will be level and oil pan will have about 1” clearance above the lower frame rail with the 6.5” Aviaid pan. Next sourcing research and procurement challenge will be to decide on a 331 vs 347 stroker internals and what intake & carburation to use. Still back and forth on Weber induction or simple 4 barrel/ dual quads.

Just finished fabricating the rear transaxle mount yesterday (still need to tac to the frame) and used 2x BMW E46 poly transmission mount bushings. I felt their compact size, simple design and popularity made it and easy choice buy &to integrate into a proper mount. After using a piece of wire bent to a proper shape, I made the transaxle mount bracket out of 1.5” angle iron and will weld tabs and gussets to the frame for the lower mount/support. Next will be tackling the motor mounts.

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All those notches in your transaxle support bracket are good places for fatigue cracks to develop. Another approach might be a good idea.

 

[Devin]

Motor mounts fab’d and tacked in place. I mimicked the AP mounts I’ve seen in pics but of my own dimensions and form from what I had available.

Sorry but the forum auto turned the pic sideways