Irmschers. What's the difference?

[philcav]

I recently picked up a pair of Irmschers and a thermostat housing and have a couple of questions.

1. What's the difference between the two in the photo's below?(the first one is a pic I found here on the site) They are shaped different and the flange where it bolts to the head is different

2. The pair I received has been ported slightly on the carb side, and is not perfectly round. Is this any concern?

3. The thermostat housing has rust damage where it mounts to the head, is this going to be a problem? Should anything be done to correct the pitting?

Thanks,

Phil

[philcav]

photos of thermostat housing

[spdkilz02]

ur manifolds are the shorties, that will work on the gt with modification of the heater box...

[nobody]

Irmsher shorties don't need heater box changes you will just have to do a minor few things for them to fit.

[greensmurf20]

i dont think the ports not being perfectly round would be a large worry. the thermostat housing would PROBABLY be ok, but it is pitted pretty badly. i'd try to lay a fine grit sandpaper over a piece of glass or other true, flat hard object and slide the thermostat housing over it, to see if the pits will clean up some, if they wont clean up that well maybe it'd be a good idea to have a machinist surface the mating side of the thermostat housing.

[spdkilz02]

totally sorry, i meant will work with no modification of the heater box...

[yellaopelgt]

So, your the one that got those! They should slide right in with a little bit of perssuasion with a hammer. Wouldnt worry about the intakes being ported. Thermostat should be milled flat, wouldnt want any small leaks that could be a bit annoying.
Joe

[soybean]

This brings up a question I was going to ask later, but I think I already know the answer to. Mine look just like philcavs, with one exception. Only 1 intake has the hole tapped for the vacuum line. I probably need to tap the one without the hole to achieve proper vacuum balance. Correct? I know I'm going to have to tap it in order to synchronize the carbs. Thanks, Jarrell

[yellaopelgt]

good question, I won a set of dbilas intakes and only one port is tapped as well. But why is this? If your set is a used set like mine is, why werent they set up properly?
Joe

[baz]

better to tap all 4 runners and do a bridge pipe to get a smoother vac for the dizzy and even pull for the servo

[soybean]

Originally Posted by baz better to tap all 4 runners and do a bridge pipe to get a smoother vac for the dizzy and even pull for the servo

The same size hole in all 4, as the original or is that an obvious answer? Jarrell

[yellaopelgt]

So,if its better to tap and connect them, whitch makes perfect sense to me, why is it that I see quite a few used sets of intakes with only 1 side being tapped? Unless they originally had some type of set-up that I've never seen before? I guess I dont understand how they could be synchronized if its only pulling vacum off one side.
Joe

[yellaopelgt]

So, for example:say the first port is 1 inch(its not but bear with me) would they all need to be 1 inch or should you reduce the first one to 1/4 and drill the other 3 accordingly? When does too much or not enough flow come into play with these intakes??
Joe

[GTJIM]

Only one runner is drilled because when you apply the brakes you usually lift your foot off the gas - the butterflies close and the vacuum drawn by one cylinder is enough to work the booster.
The dissy vacuum comes from a port in the carb itself and also is only needed in over-run stiuations when off the gas. That is why Dell'Ortos & DOCMs are better than DOCEs - they have the port for distributor vacuum, again on only one throttle body.
With twin side drafts keeping the individual runners separated is the whole point - 'balance' tubes just mess up the whole operation of the individual bores.
'Balance' tubes come from the SU constant depression types of carb where they keep the slides from pulsing up and down.

[baz]

you need only match the bore of your vac pipe to the servo when all 4 are added up as thats the most you can pull so 4 x1/4"bore into a collector manifold would be great this way everything is in harmony (take all vac hoses off the manifold for best average vac
one must balance the ying and the yang grasshopper

they build a vacume in the servo after going through a check valve and loose only a little each time when you brake ,the only other need is for the advace and retard can and that is changing all the time in driving and the extra in a 4x1/4" would be covered

[soybean]

So then, I can use a regular servo hookup from a regular manifold for the servo vacuum and to pull the vacuum for the advance off of the one runner? Then the 4 holes needed to synchronize the carbs could be used for the retard at the distributor? Or am I way off base? At this point I am totally confused. How do I get the vacuum advance and retard lines into this equation? Totally lost now. Jarrell

[GTJIM]

With DOCEs just plug the servo into the one hole that is there using the standard check valve. Don't use the vacuum advance/retard on the dissy bolt the plates together and use mechanical advance only.
With the Dell'Ortos or DCOMs that are fitted with a dissy vacuum port just use the vacuum advance if you must.
FORGET 'balance' pipes.......

[nobody]

Joe and Jarrell the thing to do is order or find on Ebay one of the mercury style manometers. They come with 4 adapter pipes in brass. Tap them into each runner of the intakes. Ok now you can set your twins in a heartbeat and equalize your vacuum all in one simple step. I do it with every set of twins I do.

Jim you also have a vacuum issue with the brake booster if it's run off of just one.

Oh and Jarrell just skip the retard line.

[GTJIM]

The 1500cc Cortina motor, with twins, I had in my Fiat Topolino worked OK with just one port - but it had a "street" cam in it with not too much overlap.
Lumpy cams reduce vacuum the worst. It had manometer holes in each runner but they were just plugged with 1/8" pipe plugs when not being used for tuning

[opeldean]

I did mine like dave said. I have since tied the balance tubes together,seems a very common thing on English cars. I tied it together because I thought it would help the brakes a bit.

My brakes worked fine running off one big line. I used the motorycle manometer,fast and easy. Dont spill your mercury, do it outside.

To answer opelenvy's question. It has now been over a year and I have not needed to adjust them.Car runs great. I drove it most weekends through this dry warm winter. Although last night was lower 30's..she runs great.

I got photos and videos in my gallery of the twins. Carbs are now dirty and 6000 miles or so later.

Again, Thank you Dave, for sourcing me parts and telling me how to jet,link and install.

[nobody]

Jim I'm building Joes motor complete and supplying the head and slightly lumpy cam for Jarrells. Having a bit of inside info into what is being used I'd equalize the vacuum. I've set up 4 twin sets and always use them on my motors and had problems if I didn't do it. The advance becomes erratic off of just one and you get hardly any brake booster help.

Keep the advance unless you are running a really big cam and extreme compression is my advice. Since neither of you are, but will be looking at 10:1 you just need to watch your octane levels you put in it.

Dean I was glad to help out

[baz]

Originally Posted by GTJIM The 1500cc Cortina motor, with twins, I had in my Fiat Topolino worked OK with just one port - but it had a "street" cam in it with not too much overlap. Lumpy cams reduce vacuum the worst. It had manometer holes in each runner but they were just plugged with 1/8" pipe plugs when not being used for tuning

jim theres enough talk of mice in dashes without bringing more on the site

and i though car makers always use the cheapest way to do things. ford tap from the top most of the time as do vauxhall/opel so its easyto hook up on the production line .the cih seams to be an odd ball by taking the tap from the back of the manifold plenumn so they get an even pull ,i can only think because the machining jig must have been a freak setup or because they had a lot of room to the side (such a rare thing these days


btw did you ever see the crossbread 1500 with a crossflow 1600 head on and the head/block spacer ? what a motor , low drag from the 3 bearing block and good air flow

[nobody]

Here's a nice one to finish off your twins.

http://cgi.ebay.com/ebaymotors/MOTIO...08457385QQrdZ1

[spdkilz02]

so my intakes are good for having each side tapped already?

http://www.opelgt.com/forums/showpos...&postcount=123

that has the pics of my intakes, it wouldnt load them since they have already been uploaded....

[nobody]

Adam you will be fine with those, Don't forget the synchroniser and soft mounts on sale right now at OGTS. Part # 9065 for 22.50. Or contact David and see if his price is better. You will need them for twins.