2L OHC Turbo Head Modifications. - First Generation Forum

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2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 6:13 AM
Hi all,

I've been running a post on my car club in the UK on the modifications I've been making to my 2L OHC head.
I thought that I'd put the main body of the text and pics on here for people to look at.



I thought these pics of development work I've been doing may be of use to those who have turbocharged 2L 8v engines.
One of the key ways to get high power out these engines is with a good flowing cylinder head. The standard head is not too bad for it's class with reasonable valve sizes as standard and a good downdraft intake port. It's negative points are the dog leg exhaust port and it's emissions friendly open 'D' shaped chamber. The basic chamber is based on the 'bathtub' design which in terms of efficiency is worse than a 'wedge' chamber, which is worse than a 'hemi' head!

Starting with the chamber shape, we can't change the basic 'bathtub' arrangement. So we are limited on how much bigger the valves can go (not much - more on that later). However we can improve the chamber shape by making it a closed chamber. This gives us more squish which improves flame speed and knock resistance. In the US the factory GM turbo version of this engine used a different head casting that had a closed chamber as seen below.



Obviously this is going to be hard to get hold of in the UK. However we can modify the standard chamber and perhaps improve on the closed chamber design that GM used. To do this I looked at modern 2v per cylinder chamber designs. The best of these are to be found on Nascar/Pro-stock engines where considerable time is spent on their design. Most of these engines use 'wedge' chambers forming a figure 8. Some of these though are inclined at quite a shallow angle which then could be copied onto our head. One such design is shown below - a Yates Ford head.



To do this we need to add weld metal to the area above the spark plug and a little opposite. I've marked in pink where the main welding needs to be done above the plug on a stock head.



I have a few heads laying around for development so the above head was used to experiment with. I used MIG (4043 wire, 100% Argon) for the welding process so I could lay down a large amount of weld quickly so the head didn't get too hot. MIG welding aluminium can lead to porous welds though as can be seen from the pics. This is not a problem for just playing with chamber shapes. The final shape would be welded using TIG.
Below is two chambers done with the standard one on the far right.



It needs a little more work particularly opposite the plug - the wall could be brought closer to the valve on the intake side to incourage swirl more.
Once I'm happy with the chamber shapes I'll reproduce them on another head with TIG welding and post more pics. Then it's on to the valves/valve seats and ports!


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More

Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 6:14 AM
I managed to find time recently to do a bit more work on the heads. I've got a welding procedure ready for TIG welding which I'll get done on a head later this week. I also found that when using MIG to weld you can reduce porosity to almost zero by using a 60% Argon/40% Helium mix sheilding gas.
The chambers I have finalised in terms of shape, what I want to try in the next few days is moving the spark plug position. I feel it can be moved 3mm closer to the centre of the cylinder and twisted more towards the exhaust valve. We'll see, there's not much room there!
I've also been working on the exhaust port trying to remove the resrictions there without increasing the port area too much. I've been doing a lot of research into the design of turbo engines and one of the things that I discovered was that a bad exhaust port design can rob up to 20% of the exhaust gas energy available to the turbo. I feel that by getting the exhaust port to flow as much as possible without dropping velocity enough energy would be available at the turbine inlet to maybe go up an A/R size. The reduction in back pressure from a larger turbine housing/wheel would increase VE across the rpm range resulting in more power. A better flowing exhaust port would also decrease pumping losses during the exhaust stroke. Below is a picture of the standard exhaust port;



Here's the modified version with a slightly revised bowl area and a more streamlined valve guide boss. You have to be careful here, there's a water passage between both seats so not much material can be removed from there.



Here's a cross-section through the exhaust port;



Ideally I'd like to raise the port to get a larger short turn radius but there's a water jacket above the port as you can see. Port wall thickness seems to be around 5mm. I don't think there's much I can do here without the aid of a flowbench to take some velocity/pressure measurements so I can shape the port properly.

There's obviously some gains to be made with the seat angles and the profile of the back of the valve. I'll look at these areas later this week. I also feel that for a turbo engine there would be benefits in lengthening the exhaust valve guide. It's quite short as stock and with the higher exhaust temps associated with a turbo engine a longer guide would allow more heat to be removed from the valve helping it's durability. There would be a small penalty in flow but this could be minimised with a good taper profile on the guide.

That's all for now


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 6:15 AM
Small update...

Spark plug location.
Can be moved slightly towards towards the centre, but to twist it towards the exhaust means cutting into the head bolt boss significantly to get access with a socket. I don't know the structural effects of this on the head (it'll need to be done to four of the head bolt bosses) as yet so I won't pursue this further for now with standard plugs. I have yet however to try this using a motocycle type plug. It's smaller size may reduce the need to grind the head bolt boss so much. The next step I think is to get a motocycle plug and try it.
IIRC I think this was also tried out on the Pinto engine... Can anyone remember?

As a side note, you can twist the standard plug round to the exhaust if you move the plug further from the centre of the chamber. As it is the plug is only ~15mm away from the centre which actually is pretty good for a 2 valve head (except a hemi of course).


Exhaust Port.
This can definately be raised 4-5mm by adding metal to the bottom of the port and also to the top of the outside of the port to keep the same size mounting flange area. I'll post pics of this once I get time to hog it to shape with the burr.





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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 6:16 AM
More updates;

Spark plug location.
Tried to fiddle around with the position using a smaller plug. Unfortunately there's just not enough meat in the casting to rotate the plug and keep it near the centre.
However, in disscussions with some V8 builders it seems an increase in knock resistance can be acheived by properly indexing the plugs towards the exhaust valve as shown below. To do this, washers need to be used to properly position the plugs when fully tightened.




Exhaust port.
Not much to report here, haven't done any porting of the welded port. Got this Thursday off so I should have pics then

Intake manifold.
The original intake I restored to the condition below...




The stock 43mm throttle body size being good for ~250hp. But, I wanted more
Flow testing of the manifold carried out in the USA shows that although the intake is generally a good design, with straight runners, decent plenum volume, etc. the position of the TB means that a lot of the flow goes straight down No.4 runner! I thought it was best to modify the position of the TB whilst increasing it's size. I also wanted to route the intercooler pipework around the engine, not over it. So I've modified it to take an Ecotec 57mm TB. Don't worry about the bright red paint, it'll get a fresh coat




The Ecotec throttle cable bracket is a horrid affair that will get binned as soon as I've made a nicer bracket.

That's all... Possibly more on Thursday...


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 1:39 PM
Righto, pics of the exhaust port now
I've welded the floor so the port could be raised 1/8" or more to form a D-shaped port. I've done some work around the valve guide area. So here you go...

D-shape port on left, square stock height port in middle (not finished yet) and stock port on right.








More soon



--------------------------
LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 3:34 PM
I'm not a turbo owner, but I appreciated the good detailed writeup of what you're doing.

I also like reading about what people are doing to foreign J's across the world. Great post,and keep us up to date on your project!



Re: 2L OHC Turbo Head Modifications.
Thursday, September 07, 2006 5:52 PM
So lets say you wanted to sell one of these reworked heads...

I guess the shipping would kill me.




Re: 2L OHC Turbo Head Modifications.
Saturday, September 09, 2006 9:27 AM
interested as well, and on the intake mani....


1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Saturday, September 09, 2006 10:40 AM
Paul94Z28 wrote:

So lets say you wanted to sell one of these reworked heads...

I guess the shipping would kill me.


You don't need to buy one off me The pics are here in the public domain so you can take them to your local head porter and copy it.

I've welded the chambers of another head, done all four, and machined it today. Should have some pics of that and dimensions etc. next week.


--------------------------
LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Thursday, September 14, 2006 5:57 PM
Well, Steph, some interesting work you're doing here. As far as the spark plug type, I don't know what a "motorcycle plug" equates to here in the US. The common plug here uses a 5/8 inch (16 mm) hex, tapered seat, and 14mm dia thread. The OHV Pontiac engines are actually somewhat of an oddball, as the 13/16 inch diameter hex and gasket went out of favor in the 60s in most of the GM vehicles. I can think of at least a couple of engines using gasketed plugs with the smaller hex which may have the right tip length and heat range for the 4V OHC head. I can also think of a tapered seat type plug with a 9/16" dia hex which could be checked into.

I'm curious. With what seems like an abundance of 4 valve/ cylinder heads available, why are you choosing the 2 valve cousin?

-->Slow
Re: 2L OHC Turbo Head Modifications.
Monday, September 18, 2006 3:47 PM
Slow,

By motocycle plug I ment the really small ones you get for the jap superbikes. Some seem to be a 10mm thread. But, I'm not going that route.

As for not using the 16v... Well I do have a 16v engine in the corner of my workshop. But, I like the little 8v. It's unloved over here and I'm enjoying seeing what I can do with it.

I have a head with all four chambers done now and this week it's having the exhaust ports TIG welded. Maybe at the weekend I'll have some more pics to post up. I need to get valves/seats/guides ordered soon also.

Stef


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More

Re: 2L OHC Turbo Head Modifications.
Tuesday, September 19, 2006 10:16 AM
stef where did you get that awesome looking adj cam gear and is that for the 8V head....


1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Tuesday, September 19, 2006 3:14 PM
It came from Kent Cams here in the UK. If you want an adjustable cam pulley it's best to look on www.ebay.co.uk under "vauxhall OHC". Be careful as over here there is smaller versions of the OHC i.e. 1.3L in which the pulley won't fit.
Any worries about shipping from the UK ask me or 2litreturbo.

Stef


--------------------------
LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Tuesday, September 19, 2006 11:33 PM
nothin available. if i were to paypal you the $ would you possibly purchase it and send it over to me?


1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Thursday, September 21, 2006 5:32 PM
I understand your motivations completely. I was worried that you'd say there's some type of fundamental flaw in the 16V heads.

I know of another individual who is using modified computer code from the 1227749 Sunbird ecm in a naturally aspirated mode. The code is running in a 1227730 ecm, with an 8V engine which makes decent power in a little race car. Despite the complaints of his peers, he's ditched the carby and distributor for some "high tech" parts.

Good luck. Don't hesitate to ask if you need parts. I'm not that far from Tony's place and there are quite a few 8V engines at the wreckers here.

-->Slow
Re: 2L OHC Turbo Head Modifications.
Friday, September 22, 2006 4:26 PM
Justin,
I may be able to get you a second hand pulley for you after this weekend. If not, I'll let you know the price of a new one.

Slow,
Thanks for the comments and the offer of parts, much appreciated. BTW I've seen these engines with 230hp N/A used on the street. Needs a lot of work to acheive that but it's possible.

Stef


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Saturday, September 23, 2006 6:00 PM
thanks stef! appreciate it!


1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Tuesday, September 26, 2006 11:06 PM
Stef any updates?



1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Friday, September 29, 2006 5:09 AM
Justin, I can't get a second hand pulley after all. I can get a new pulley from either Kent Cams or Piper for around 100, hopefully less. Shipping shouldn't be expensive because they're quite light.
Check the current exchange rate and let me know if you still want one. It may be worth waiting for a low /$ exchange rate etc.

Stef


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LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Wednesday, October 11, 2006 1:07 PM
Well some bad news... After welding the exhaust ports I found three chambers had cracked between the valve seat areas. It's really hard to control temps between the preheat and whilst welding and I guess it got over-cooked.

Still I've got two more heads left and ones going in a cleaning tank tomorrow until the weekend when I'll remove all the guides, seats, etc. again. I need to get some temp monitoring equipment this time too lol.

All good fun though


--------------------------
LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
Re: 2L OHC Turbo Head Modifications.
Wednesday, October 11, 2006 6:58 PM
you may already know about doing this, but try heating the head in an oven before welding it, and keep putting it back in and reheating it to keep the temps up. this will keep the head from heating up unequally and helps keep it from cracking. its a trick that we use when welding up the blocks on the dragster i work on.

sucks to hear how all your hard work ends up in the scrap.




Re: 2L OHC Turbo Head Modifications.
Thursday, October 12, 2006 1:24 PM
Sorry to hear Stef! thought you really should post these things in the 2ndgen forum.....


1st 1st gen on air.....
Re: 2L OHC Turbo Head Modifications.
Friday, October 13, 2006 8:33 PM
Wow Stef that head looks awesome! Nice job mate.
By the way our crazy friend picked up some Jaffa cakes thanks to you and she's quite happy now. She bought me a box for my birthday the other day too. Yummy!

Tony


Tony
1987 Sunbird GT turbo convert
Ported intake, Fiero 53 MM TB, 52 lb inj, ported and flowed head, tube header, Mitsu TD06, ARP rod
bolts/head studs, adj cam sprocket, 4" x 12" x 31" FMIC, Paxton AFPR, modified 125 trans/LSD
unit/3.42's, custom chip tuning, Alky Control Methanol injection
13.61 ET at 101.44 mph, 262 WHP/350WTQ

2009 Pontiac Solstice GXP roadster, 2.0 turbo w/GMPP exh, CAI and turbo upgrade, 290 hp/325 ft lbs

1969 Olds 442 convert
400 Eng, 200-4R trans, 3.73 posi, power everything, OAI


Re: 2L OHC Turbo Head Modifications.
Monday, October 16, 2006 4:20 PM
Tony, glad you like it. So you got some jaffa cakes huh? They are indeed yummy and I hope you didn't share them to your kids 'cos they'll only want more!!

Justin. I guess I should of posted it there. Can the moderators move the thread over?


Stef


--------------------------
LT3 Powered Vauxhall Astra.
Intercooler, Mopar Super 60 Injectors, SDS Stand Alone EFI, Ported Big Valve Head, Cast T3 Manifold With External Wastegate + More
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