Downdraft Sri Head Vs 205gti Head

[veloce200 3]

Only questions here for now - sorry !I will at some point this year be rebuilding the 8v motor and was considering the Sri piston and then I thought what about the head. I've read a few posts but can't seem to find any real data on the downdraft head. Does anyone have any ideas or info they can share. Engine will be using a hot cam and high compression.

 

thanks !

[DrSeuss 0]

isn't the main issue the inlet manifold poking through the bonnet on a 205? Dom9 is the person to ask, but i doubt anyones done much real flow work with it.

[veloce200 3]

isn't the main issue the inlet manifold poking through the bonnet on a 205? Dom9 is the person to ask, but i doubt anyones done much real flow work with it.

a little more info. Assuming bespoke manifolds and bike tb's with 4 injectors. Tgt compression is circa 12:1

[littlemike 0]

isn't the main issue the inlet manifold poking through the bonnet on a 205? Dom9 is the person to ask, but i doubt anyones done much real flow work with it.

 

The whole 405 sri engine fitted fine in one of my 205's, not sure if an sri head on a gti engine would be any different, but I wouldn't have thought so??

[Anthony 1,000]

The whole 405 sri engine fitted fine in one of my 205's, not sure if an sri head on a gti engine would be any different, but I wouldn't have thought so??

The block is identical on all XU 1.6/1.9 8v's, so would be fine. I'm guessing the compression ratio would be all wrong if you used GTi pistons though, as the SRi ones are flat top and the GTi ones dished.

[Dom9 2]

Yeah, the two blocks are identical apart from the pistons. As the others have said, GTI pistons are dished and the SRi pistons have flat tops... The combustion chamber of the SRi is all in the head, as opposed to the GTI, where some happens in the piston bowl.

 

If you are going to build an engine using the SRi head, then you might as well start with the SRi engine. If you used GTI pistons, or drop the SRi head on a GTI block, then the compression would be horribly low. It might work if you were going to turbocharge the thing, but not if you are staying NA.

 

I believe Mattsav flow tested the SRi head years back, when I first started looking at maybe using that head... It flowed very well indeed as standard, a fair bit better than the GTI head if I recall. The engine produces a lot of torque as standard, possibly due to the fairly tame camshaft and long inlet manifold, but also due to the fairly narrow, yet efficient inlet ports.

 

This is something of a double edged sword. The narrow, downdraft inlet ports appear to be pretty efficient compared to some of the other heads Peugeot has produced with a sharp corners to turn before the valves. The big problem is that these narrow ports strangle the flow at high rpm and the engine cannot get enough air to produce the same sort of power as a tuned GTI engine.

 

Normally we could just port and open up the inlet to get some more flow, but this is very difficult on this particular head as the inlet ports on 1&2 are VERY close together and then again on 3&4. I highly doubt that the ports would require much, if any, re-shaping so it may be possible to take each one out by 2-3mm using a bore bar, which would be cheap and easy... Whether that is even enough to challenge a good spec GTI 8v though, we never found out.

 

The other big problem is the inlet manifold. Apparently the engine does fit under the GTI bonnet, although I have only ever seen one myself. It maybe one of those things where it depends how well built your car was as to whether you get any clearance, but I'd say an auto bonnet was a safe bet, even if it is not required. If you have ported the inlets heavily then it maybe difficult to then port the original manifold to fit, in which case you are into bespoke manifolds. I doubt one exists off the shelf so I guess your best bet would be to have a go yourself or throw someone like the Bogg Brothers some money and get them to build you one. The only problem is the angle of the ports and the sharp corner that would be required to get carbs under the bonnet. It would also be interesting to know whether you could shorten the standard inlet manifold like Maxi and others do to the Mi16, however I don't think you can...

 

If I was to build a road engine I would be very tempted to get a standard SRi engine, skim the BLOCK AND LINERS, not the head, to get the squish area improved as I believe the pistons sit a little way down the bores, then port the inlets out as much as you can, whilst still retaining the ability to use and port-match the standard inlet manifold... Add a GTI cam, vernier pulley, set it up to run on Megasquirt and I don't really see why you couldn't get around 150bhp, but excellent road manners, torque and driveability. I have heard of one in a 205 GTI producing 160bhp, not sure how true that was, but I do believe it's possible... The problem might be trying to produce more than this figure, hence why I say it would make a great road engine, but may be rubbish as a rally/race engine.

 

Alternatively I'd quite like to throw a set of SRi, flat-top pistons into a GTI engine and see what compression they give. If you could skim the liners and block to maximise the squish I reckon you would have some serious compression and be able to run quite a lairy cam. The problems then might be that the pistons need machining for valve reliefs on a high lift cam, and they are un-tested at high power outputs, so maybe they wouldn't take it? Then again, they are probably the same grade material as GTI pistons that seem to take some abuse.

 

There are other ways of building these engines, obviously, but, despite my interest in pissing money up the wall, I'm always trying to see ways of building the best budget engine... I actually think the SRi would provide a good base for a cheap but torquey engine, or some of its parts could be butchered to build a rather saucy hybrid. I bet you can get whole engines from the breakers or eBay for next to nothing, whole cars even! Maybe after I move house I might try and build a hybrid monster (he says for 94th time in 4yrs!).

[veloce200 3]

thanks Dom. I was thinking initially 1.6 pistons and GTI head with light skim and then I thought flat top pistons with heavily skimmed SRI head. Good points about squish. I guess without a comparison of both heads well modified and tested at all lifts it's almost impossible for me to get the answer without doing both! My thoughts were maybe the SRI head offered a better lift/vs flow curve than the GTI and maybe better as a race spec option. I'm aiming for 180+ HP so I guess the catch here would be how much could you skim off the SRI head as I'd need to run 12:1 to make the cam work and as you say then may need to work the crown of the piston for clearance.

 

Thats the only problem with the MI16 being so available this path has not been trodden at least from ultimate power on a budget perspective.

[Dom9 2]

I reckon that a GTI head with SRi pistons would give you in the order of 12:1 CR. That might include decking the liners/block, I did do the calcs a long time ago but f*** knows what I have done with tem. You could probably do a search on here for the volume of the piston bowl in a 1.9 and how far it sits down the bore at TDC, then just change the numbers for a lack of bowl and a decked block.

 

My concern is getting the inlet ports large enough to flow 180bhp... I simply don't think you can do it. Induction would also be difficult as you would need at least carbs if not TB's for that and I think it would be tricky to build a suitable manifold, although not impossible. The lift Vs. flow curve for the SRi head is better, but I don't think that tells the whole story as I don't think flow benches generally pull enough vacuum to simulate exactly what is happening when the head is actually on the car.

 

Dave Baker will probably read this at some point and he may be in a better position to comment, but he may not have seen one of these heads. Despite the valve sizes being the same as the GTI, the ports are a lot smaller and if you use the calculation on the Puma racing site, I think you will see that the head is limited to around the 160-170bhp mark, if memory serves correct. You could use a big valve, but I don't think you could open up the throats enough to make any use of it.

 

Now, I'm not saying that it's pointless trying as I think you could put an engine together quite cheaply and if it doesn't work just strip off the the vernier, cam, springs, whatever else you used and transfer them to a GTI head, so the only money lost would be in porting the SRi head and getting the manifold made. However, that might be the point that tips it from being 'budget' to fairly expensive as starting with a GTI head may have been the cheaper and more well-trodden path.

 

Having said that, I would love someone to have a go! It wouldn't lose you anything getting the bottom end built up as that could be re-used with aGTI head, so maybe just a trial fit of all the pieces with the SRi head might be fun just to see what the valve clearances are and to see how much you could port the inlets.

 

Out of interest, why do you need 12:1 CR? How lairy is the cam you want to use? If you are only going for 180bhp, I would have thought you wouldn't be a long way off with a well ported head and something of the order of 285-290° duration, which wouldn't necessarily require a CR that high, or would it?

 

This is an interesting topic!

[veloce200 3]

Out of interest, why do you need 12:1 CR? How lairy is the cam you want to use? If you are only going for 180bhp, I would have thought you wouldn't be a long way off with a well ported head and something of the order of 285-290° duration, which wouldn't necessarily require a CR that high, or would it?

 

This is an interesting topic!

 

are the ports really that small? Normally they are the bit thats easy to mod but doesn't need modding - what a refreshing change! Depends how you measure the cam. It is PT28 Kent 309 inlet 314 exhaust at .25mm. I'm told it's 283 @1mm. So yeah it's about as hot as you can get and I've calculated that it needs 13:1 but then that is really stretching reliability. Given a big valve race spec head then over 190 hp would be possible I guess, but the plan is cast piston, std valve head and possibly a simple water injection system so the thing can be run on Optimax if octane boost is not available and to prevent high speed detonation. Bike TB's but 4 injectors. IMO With std valves it will still have a good broad spread of power being that the engine is so undervalved. I did initially want to keep plenum but from recent experience know that idling will be out with the lift at TDC (5mm IIRC)

[Dom9 2]

The ports really are that small lI'm afraid! It would make a nice change if you could actually take them out a lot bigger but I really don't think you can! Find one on eBay or in the scrappy for a few quid and see what you think. It woul dbe money well spent before investing too much in the project!

 

That also sounds like a hell of a lot of cam! It is certainly one that would require a high CR but it woul dalso work best at high rpm, which won't happen with the SRi inlets strangling the flow. Some people have seen close to 160bhp on the 279° CatCam that Matt sells and yours is a fair bit wilder than that. You would be better, IMHO, to go for something in that order or maybe the next cam up (which requires new springs etc I believe) and getting a better spread of power throughout the rev range!

 

Your cam will be very peaky, but you might not be able to ever reach that peak, even with a GTI head, on a cast bottom end. Although, having said that, I believe Miles has a race engine on a standard bottom end!

 

You could keep the plenum and run any cam you like with good management, but whether it's worth doing is up to you. As you say, bike TB's are so cheap that they would be the way forward. I think I posted a picture of the SRi ports some time ago, I will post it again if I can find it and you can't find it on here, although I'm guessing it will have popped up when you did your search!

 

If I was you I'd give Matt at QEP a call and see what he advises... You may be better eBaying that cam and sorting yourself out something that will give you a broader powerband and one that won't push the bottom end to it's limit!

[veloce200 3]

If I was you I'd give Matt at QEP a call and see what he advises... You may be better eBaying that cam and sorting yourself out something that will give you a broader powerband and one that won't push the bottom end to it's limit!

 

well being a catcams dealer I've spoken to matt about this already. I was a Kent Dealer b4 Cat though hence the lovely mountain lobes are sitting in their box in my workshop! The 279 catcam is 254 deg at 1mm so a lot less than the Kent which measures 283 at 1mm. You are probably right about broader powerband but don't forget these engines are way undervalved. Also Kents cams according to Dave Baker don't always measure up as advertised. I built an A-series 1000cc with a 286 kent cam (prob about 255 @1mm) and it pulled from low rpm no problem and ticked over fine. Hotter cams in bigger engines are less noticeable. If I were to put this cam in a 1.6 then you could certainly call for me to be locked up !

 

In an undervalved long stroke engine like the 8v I reckon you need a wild cam to get past 170hp. Certainly all the 100 hp per litre 8v's are not doing it on a cam as mild as the 279/254 catcam. Charge robbing will make idle unacceptable on plenum - nothing ECU can do about that hence my desire to change to TB's.

 

However Catcams do a cam even hotter than the PT28 - it's a beast -

310 / 310°

283 / 283°

13.90 / 13.90mm

Lift TDC 6.50 / 6.55mm

 

check out the lift at TDC ! I intend to run it to max 8000rpm. By then it's revs for revs sake - with std valves I reckon powerband will be 3500-7500

[veloce200 3]

from what I have read about hemi heads with downdraft ports I think the advantage the Sri head has over the std head is at mid lift flow efficiency. From what I can glean downdraft ports flow better at the kind of lifts we are dealing with. Also as the valves are relatively big the port efficiency of the downdraft head is at it's maximum when the valve of 41.6mm is lifted 12.5mm it represents 30% lift of diameter. The std port would probably flow better at higher lifts but then if you can't lift the valve much more than 12.5mm this explains the possible advantage of the downdraft head. In the SRi application with a std cam of much less than 12.5mm this probably explains the 9 lb of torque. (from carfolio - they say sri 128lb torque and gtii 119lb torque) although I think I have read 122lb somewhere.

 

What I need to know if I am to give this a go (I think based on the above a bigger valve would work better in the downdraft head rather than the gti head) is the port to valve size - does anyone know what size port should be in relation to valve eg - 80% roughly to get 100hp per litre? Then I can get an inlet gasket and see what the std sizes are. 2mm ought to be achieveable. More to the point this might be an easier head to modify for a novice head modifier!

[pug_ham 240 3 Cars]

405 SRi engine & inlet manifold will fit under a 205 bonnet with no clearance problems imo. There is someone on the PSOOC forums that has this fitted with no trouble afaik. (205_Sunderland)

 

The 405 SRi head is basically the same design as the XU10 head & will probably be similar in design for a high spec engine which Sean (smckeown) looked into last year & he's chosen the XU9 head route instead because it out-performed the XU10 head with the same amount of work.

 

A search of Dave's posts should bring the results of Seans head for the work Dave looked at doing as a comparison which I think will yield similar results to the SRi downdraft head.

 

Graham.

[veloce200 3]

405 SRi engine & inlet manifold will fit under a 205 bonnet with no clearance problems imo. There is someone on the PSOOC forums that has this fitted with no trouble afaik. (205_Sunderland)

 

The 405 SRi head is basically the same design as the XU10 head & will probably be similar in design for a high spec engine which Sean (smckeown) looked into last year & he's chosen the XU9 head route instead because it out-performed the XU10 head with the same amount of work.

 

A search of Dave's posts should bring the results of Seans head for the work Dave looked at doing as a comparison which I think will yield similar results to the SRi downdraft head.

 

Graham.

 

I was reading an old thread where Dom posted a link - it no longer works but I do remember the SRi head being markedly different to Xu9 and Xu10. The XU10 problem was in it being designed for a larger bore so the sealing problems seemed to be the issue and this put me off Xu10. I guess I'm just going to have to get one and construct a basic flow bench (inches water only) and see whats what. I might see if I can persuade Matt to pop it on the flow bench too!

[Dom9 2]

No, there appear to be two different SRi heads and the one we are talking about G is VERY different to the XU10J2's that we have used in the past. When I built that XU10 head all those years ago now, I also had an SRi head and was looking into all of these issues, but I really didn't see a way of extracting the power I wanted out of it. Now days I am less concerned with headline figures, so it might be interesting to look at doing an SRi again...

 

Veloce200 - That's kinda my point about the CatCam. The 279° actually measures up as being relatively mild but can still produce in the region of 160bhp... I just don't see how you need a 2 point compression hike and 30° more duration to gain another 20bhp or so. Also, I'm not convinced that the heads are under-valved. Well, certainly not for a budget build anyway. Dave Baker wrote a lot of interesting stuff about big valves in that pinned topic and it certainly seems like you can get away with a milder cam and bigger valves if you want, but that will be up to you.

 

As for running on a plenum, it can be done... Remember a lot of the Formula 2 or whatever they are called, rally cars run on plenums and put out substantial power! However, there is no doubt with the spec you are talking about that you will want to use carbs/TB's... I reckon the inlet manifold will be a tricky one though... Lots of measuring and trial fitting methinks! Unless you can find a way to chop down the standard manifold and use that, like DreamWeaver did for his Mi16!

 

The downdraft port is better, IN THEORY! But, you need to go and buy yourself one and have a look as the ports are something like HALF the size of the GTI ports and I'm not joking! When you take into account the fact that the valve is the same size in both heads, you can see how you are a LONG way from having the ideal port:valve ratio in the Sri head... The chances of you getting close on a standard valve are poor, the chances of you getting close with an even bigger valve are next to none I would guess!! I can do the calcs for you, but it's all a bit arbitrary until you have a head in front of you... Go find one!

 

I would love you to have a go at this though and get it built just to see what can be done and if the theory does work! Even porting a head as heavily as possible and putting it on Matt's flow bench would be interesting!

 

How about an iron block with an Mi16 cranks, taking it to 2045cc with an SRi head, so now it has monster compression... I bet that would produce some torque and rev like a beast?! Hmmm... You would need an XU10 with flat top pistons though, which exist but may be the turbo versions, check the recent turbo threads for details of those, it would also be a lot easier to deck the iron block to sort squich and compression!

 

I can't find that photo of the head I had on my computer so I think it may be lost, but if you pick up a head, take some photos and add it to this thread along with any other findings and progress!

[veloce200 3]

From Dave's site 80% for a race engine. I'm trying to get hold of an inlet gasket to measure but 80% would mean 33mm.- sound like they are way smaller than that !The crossflow interestingly enough suffers the same problem! If the ports are indeed half the size it would sound tricky. I shall have to get hold of one as you say !

i couldn't run an iron block in sprints and although there are numerous advantages it is heavier also and the weight is right where you don't want it - 20kg more but I don't know this for a fact.

 

the plenum issue is more for emissions. I've seen 300 deg cams sail through MOT on TB's but getting a hot cam on plenum will be much harder I think - i'd need a very friendly mot tester to agree the natural idle was 1800 rpm! Piper make a cam specifically for the std plenum and it has less duration so i suspect the rally engines would too to prevent charge robbing. they probably get their power from brilliant head design and trick bottom ends - not stuff that the budget build can warrant. The cam and high compression would be the path you would take if say regs stated you had to use std valves, as I am self imposing std valves then that is more why this path is being followed. If I am honest as well I just love the noise and power delivery of a race cammed engine!

[pug_ham 240 3 Cars]

Wasn't aware of there being two styles of SRi head.

 

The SRi head I had from my donor car for the MP3.1 loom had the same style of inlet ports as the XU10 heads I've had since.

 

I think I still have this head downstairs somewhere so I'lll have a look for it & post a picture if I have.

 

If it is the same head as used on the BX GTi which uses the same engine then the inlet ports are round & they use an Mi style inlet manifold.

 

Graham.

[KRISKARRERA 2 1 Cars]

Yeah actually just to call it "XU9J2 head" is better because it was in the GTX and GRI 405 as well as the SRi.

[Dom9 2]

Yeah, I can't remember the dimensions off the top of my head but I'm staring at my ruler and I don't have a compass to hand but 33mm does sound larger than standard, but it may not be beyond the possibility of porting... I want to say they were 28mm but don't quote me until you have seen one... If they are 28mm though, you may be able to get away with enlargement to 33mm, but I'm pretty sure it will be tight... You certainly won't get the benefits you would from a GTI head with big valves...

 

Maybe I haven't read the other posts thoroughly enough, I didn't realise it was for sprints, so I guess the iron block is out as you say! Still, it leaves you scope to play with the flat-topped pistons in the standard block and there may be some safety margin for revving it if you find an Mi16 crank, which seems to be a bit tricky as I'm finding out at the moment!

 

I still think an iron block, 1.9 crank engine with an SRi head, maybe running the GTI cam, even with the standard inlet manifold would make for a lovely, torquey road engine and you ought to be able to put one together with spare parts from the for sale forum and a head from the scrappy for next to nothing!

Edited April 5, 2006 by Dom9

[Guest andy309goodwood]

hi all

i have just recived a phone call from mr shilliber ref my sri head

he has done a s*it load of work to it hevily modded the ports biggist valves he could shoe horn in and wasted valve stems

my biggiest concern was getting maximum use of all this work and have looked and messured the std sri manifold and i think it was a 28 mm bore at the cyl head end and 31mm at the plenum end how ever i can get more accurate messures if needed as i have one stripped down in my garage

but having spoken to sandy we dont think i will beable to get the flow i need thro the std throttle body so i will be hacking up the manifold and finding a way of mounting a set of lotus throttle bodys

as for spec it will be used for im aiming for around 300bhp via a 2L xm engine and 1.9 crank modded sri head custom grind high lift cam turbo tec manifold and a gt28r running thro a charge cooler and full megasquirt and a pile of other bits and bobs

so itll eather be f ing quick or it will go bang quite spectaculely lol

andy

 

How about an iron block with an Mi16 cranks, taking it to 2045cc with an SRi head, so now it has monster compression... I bet that would produce some torque and rev like a beast?! Hmmm... You would need an XU10 with flat top pistons though, which exist but may be the turbo versions, check the recent turbo threads for details of those, it would also be a lot easier to deck the iron block to sort squich and compression!

 

 

only prom with this is that the pistons on the turbo app sit .5 mm proud of the block deck at tdc

trust me

Edited April 5, 2006 by andy309goodwood

[pug_ham 240 3 Cars]

Some pictures for comparison of the XU9J2 & XU10 heads attached.

 

I measured the inlet ports on each earlier with some digital vernier calipers;

• XU9J2 inlet = 31mm
  
  
  Exhaust = 32mm
  
  
   
  
  
   
  
  
• XU10 inlet = 34.9mm
  
  
  Exhaust = 33.5mm
  
  

 

Each measurement was made at the manifold face of the head.

 

On the XU9J2 head the head to manifold face is cut at an angle for the inlet manifold face where the XU10's are vertical just like the XU9JA head.

 

Graham.

[veloce200 3]

Some pictures for comparison of the XU9J2 & XU10 heads attached.

 

I measured the inlet ports on each earlier with some digital vernier calipers;

• XU9J2 inlet = 31mm
  
  
  Exhaust = 32mm
  
  
• XU10 inlet = 34.9mm
  
  
  Exhaust = 33.5mm
  
  

 

Each measurement was made at the manifold face of the head.

 

On the XU9J2 head the head to manifold face is cut at an angle for the inlet manifold face where the XU10's are vertical just like the XU9JA head.

 

Graham.

 

excellent work Graham! so seems the ports are not that small after all. I'm definitely going to give it a go. thanks

[Dom9 2]

only prom with this is that the pistons on the turbo app sit .5 mm proud of the block deck at tdc

trust me

 

You could quite merrily lop 0.5mm off the piston... But I presume the head gasket is more than 0.5mm thick though anyway, so it wouldn't really be a problem?!

 

So, you have big valves in your downdraft head? What size are they and how big did he manage to get the inlet ports? This sounds like an interesting project indeed!

 

I wasn't surprised you saw 28mm, I thought that was the number in my head... I believe that G has measured his correctly but I really didn't think they were as big as 31mm, but if so, that's good if you only want to take them out another couple of mm!

[smckeown 1]

isn't there gojng to be the same block to head fitting issue as with the XU10 head onto the XU9 block ?

[rich_w 0]

No, Andy is having the cumbustion chambers opened on the head.