How much can a Lotus head be milled?

[ShelGame]

How much can the Lotus head be milled?

I'm thinking (once again) about an NA Lotus headed engine for NHRA Super Stock for my Daytona. The stock Lotus head has way too much volume to get the compression ratio I'm looking for. But, it also looks like it has quite a deep chamber.

I used to have a Lotus head I was keeping for this reason, but I sold it a while back when I needed the cash. Now, I seem to have all the necessary parts for the bottom end I want - 2.5 TIII flat top JE's, 3.500" bore, 1.555 CH, 6.180" Aluminum rods, 2.5 crank stroked 0.5mm, all stuffed into a tall deck block (that's a 2.6l for those counting). Before I get too deep, I want to understand if the CR I want is even possible with this proposed bastardized collection of parts.

The Lotus head has a ~58cc chamber. By my calculations, the head would need to be milled 0.05" to get that down to ~51cc. Which should give me a 12:1 CR. If I want to go 12.5:1, then I need to take off another 0.015" (0.065" total). From the pics I've seen, I think the chamber can take this. But, I don't know about the deck. Is it thick enough? I've looked for TIII head sections but haven't seen any yet.

I did find a pic of the chamber area, and it looks like the deck is maybe 1/4" thick at the water holes near the chamber. So, 0.065 off might be OK?

Anyone know for sure? Ken?

[iTurbo]

I don't have the knowledge to answer you question, but I'm wondering if you plan to run this with fuel injection and the stock TIII intake manifold? I've always thought a n/a Lotus head would be awesome to run with high compression and the dual Weber DCOE carbs...and a distributor of course.

[ShelGame]

I don't have the knowledge to answer you question, but I'm wondering if you plan to run this with fuel injection and the stock TIII intake manifold? I've always thought a n/a Lotus head would be awesome to run with high compression and the dual Weber DCOE carbs...and a distributor of course.

Probably stock intake and EFI to start with. Maybe go to ITB's in the future...

[wheming]

Would you not be better off with custom pistons, so you can leave the head alone?
I'm not a TIII guy, but aren't those heads prone to cracking? Less meat might worsen that.

[ShelGame]

Would you not be better off with custom pistons, so you can leave the head alone?
I'm not a TIII guy, but aren't those heads prone to cracking? Less meat might worsen that.

I don't think so. The TII chamber is 58cc; the SRT-4, for reference, is 48cc, and the Masi ~29cc (from something Alan posted). The cracking issue they have is in the water jacket plugs between the spark plugs. I've never heard of them cracking the camber or deck surface.

Here's a pic of the Lotus chamber. You can see that it is a pretty 'deep' chamber compared to most DOHC chambers. I think to make a piston that would fill that up would not be a very nice piston. It would have to have quite a bit of a crown, and even then would be difficult to fill the space. (I don't know who's pic this is, just one I've collected...)

[Lotashelbys]

Milling a TIII head that far should not effect its strength. The weak part of that head is the top side between the core and spark plug holes. The only thing that it will effect is the cam timing. What are the rules on cam gears? If you can get the cam timing corrected than I dont see a problem.

[ShelGame]

Milling a TIII head that far should not effect its strength. The weak part of that head is the top side between the core and spark plug holes. The only thing that it will effect is the cam timing. What are the rules on cam gears? If you can get the cam timing corrected than I dont see a problem.

Thanks, Jackson.

Cam timing is a whole other issue; with the tall deck block, I'll have to source a special timing belt (no ideas there yet). So, custom adjustable cam gears, tensioner, etc. will probably be in order just to get it all together.

For Super Stock SSGS, basically anything goes (except for forced induction). It's a pump-class. So, the car weight is based on the engine displacement. The only tech or teardown it gets is to pump the motor for displacement.

There are 2 other cars in the country that regularly run SSGS - Tim Kish's 2.0 DCR engined Neon, and Art Leong's 2.4L Neon. They both run in the 12's. So, I'll need to make near 300hp NA to catch them. It's not going to be easy.

[Lotashelbys]

Ok. I have never had a tall deck block so how much taller really is it than the std blocks?

[ShelGame]

Ok. I have never had a tall deck block so how much taller really is it than the std blocks?

12mm taller. It's quite a bit.

Plus, due to the longer stroke, the TD has a ticker cylinder wall. That's the other reason I wanted to use that block. These pistons I picked up (quite a while back) are 3.5" bore. Most CB can't go that big (0.055" over)...

[ShadowFromHell]

Sounds like a lot of work and $$$. I know you have raced that daytona for a LONG time, but if you want to run in that class its time for a upgrade. To me it looks like a knife to a gunfight situation. You're going to be going up against motors that have had a ton of development on them, and be running a heavier car. 300hp NA on pump with a neon motor, I dont even know if I have seen it done. Starting from scratch would be even harder.

That said it sounds like a cool project! Here is a tip that might help you. A few years ago I was moving some T3 and DOHC 2.0 parts around the garage and noticed that the T3 exhaust ports are almost identical in shape, and are identical in spacing. Bolt pattern is different but you should be able to run a off the shelf neon header by just redrilling the flange.

[5DIGITS]

Rob,
The head will handle the milling your looking to do, as Jackson also indicated, but please also consider the following items.
The chamber on most 16v engines does not support having sufficient squish area to suppress knock and is why many engines use the 'ski-slope' piston dome to compensate for this short-coming.
If you plan on running 12.5:1 with a flat top piston, the engine will be extremely sensitive to detonation and with or without high octane fuel the amount of usable spark advance will be limited.
To address what you can without expensive 1-off pistons, mill the block to use the little workable squish band on the front and rear of the chamber and mill the remaining amount from the cylinder head.
Combining these two together will reduce the over-all amount to be milled due to a greater reduction of volume when machining the block vs the head, improve squish, reduce knock sensitivity, and improve over-all performance.
Note: If broken belt clearance is desired, please also consider the need for deeper valve reliefs in the piston when performing this level of machining and the impact it has on compression ratio.

A thought for the belt:
I'm not sure this will completely address the belt issue but with the block and/or head milling, a de-shrouded 8V tensioner may provide enough belt to work with due to its smaller diameter.
You'll need to determine whether this will work with your hardware combination after all of the machining has been completed.

Interesting project!

[ShelGame]

Sounds like a lot of work and $$$. I know you have raced that daytona for a LONG time, but if you want to run in that class its time for a upgrade. To me it looks like a knife to a gunfight situation. You're going to be going up against motors that have had a ton of development on them, and be running a heavier car. 300hp NA on pump with a neon motor, I dont even know if I have seen it done. Starting from scratch would be even harder.

That said it sounds like a cool project! Here is a tip that might help you. A few years ago I was moving some T3 and DOHC 2.0 parts around the garage and noticed that the T3 exhaust ports are almost identical in shape, and are identical in spacing. Bolt pattern is different but you should be able to run a off the shelf neon header by just redrilling the flange.

Well, heavy is relative. All the cars in SSGS run the same lbs/cu in ratio. At 158 cu in, the Daytona will need to weigh 2705lb. I'm currently about 50lbs over that. Sure, a 2.0l Neon only needs to weigh like 2200lbs, but the 2.0l gives up a lot of torque.

Of course, 300hp is the eventual goal. 250 would get me in the ballpark (I think) compared to the current competition.

At one point I thought I would just do a 2.4, but I'm fixated on an NA TIII for some reason...

[ShelGame]

Rob,
The head will handle the milling your looking to do, as Jackson also indicated, but please also consider the following items.
The chamber on most 16v engines does not support having sufficient squish area to suppress knock and is why many engines use the 'ski-slope' piston dome to compensate for this short-coming.
If you plan on running 12.5:1 with a flat top piston, the engine will be extremely sensitive to detonation and with or without high octane fuel the amount of usable spark advance will be limited.
To address what you can without expensive 1-off pistons, mill the block to use the little workable squish band on the front and rear of the chamber and mill the remaining amount from the cylinder head.
Combining these two together will reduce the over-all amount to be milled due to a greater reduction of volume when machining the block vs the head, improve squish, reduce knock sensitivity, and improve over-all performance.
Note: If broken belt clearance is desired, please also consider the need for deeper valve reliefs in the piston when performing this level of machining and the impact it has on compression ratio.

A thought for the belt:
I'm not sure this will completely address the belt issue but with the block and/or head milling, a de-shrouded 8V tensioner may provide enough belt to work with due to its smaller diameter.
You'll need to determine whether this will work with your hardware combination after all of the machining has been completed.

Interesting project!

Thanks, Ken.

I had planned to deck the block as well. At this point, I'm thinking the pistons will be about 0.01 above the deck. The head gasket is thicker than I was planning for. I intend to keep the squish area on the front and rear of the chamber, too.

Almost certainly the pistons will require the valve pockets enlarged. But how much will depend on the can profile. That will require some work too. Nobody makes NA cams for a TIII.

This definitely is not a running-next-summer kind of project...

[2.216VTurbo]

Thanks, Ken.

I had planned to deck the block as well. At this point, I'm thinking the pistons will be about 0.01 above the deck. The head gasket is thicker than I was planning for. I intend to keep the squish area on the front and rear of the chamber, too.

Almost certainly the pistons will require the valve pockets enlarged. But how much will depend on the can profile. That will require some work too. Nobody makes NA cams for a TIII.

This definitely is not a running-next-summer kind of project...

How about some raw casting unmachined TIII cams, set ANY lift ANY duration you and your grinder can dream up. I'll sell them at a loss to help this project along for a good guy or maybe trade for custome cals for life?

[ShelGame]

How about some raw casting unmachined TIII cams, set ANY lift ANY duration you and your grinder can dream up. I'll sell them at a loss to help this project along for a good guy or maybe trade for custome cals for life?

I'd take that trade. Wait, exactly how many cars/vans do you have again?

[5DIGITS]

Thanks, Ken.
...I had planned to deck the block as well. At this point, I'm thinking the pistons will be about 0.01 above the deck. The head gasket is thicker than I was planning for...

With NA, run them tight !!
.015"-.020" clearance if possible, depending on the material of the piston and its thermal expansion/stability.

If your budget supports new exhaust valves, spec a valve with a wider margin and taller tulip, to pick up measurable exhaust flow.
This can be worth a 15-20 cfm gain (per valve/port) over the stock units, especially if you include higher lift.

On the contrary, we all look forward to this running next summer !!!

[johnl]

Good stuff.

[Aries_Turbo]

rob are you allowed to weld up the head any in that class? ie to add more quench pads?

Brian

[ShelGame]

rob are you allowed to weld up the head any in that class? ie to add more quench pads?

Brian

Anything goes. Maximum displacement is 165cu in; car must weigh 16lb/cuin...

[johnl]

Yeah, maybe leave more room for tumble/swirl/whatever with quench pads in addition to their contribution to same.