Different day ,different car .................same shit !!!!

Mr Law junior is porting a pair of 2.5 12V heads as we speak so one of the Laws should be able to advise re: proximity to water galleries etc.

From what I saw there wasn't too much scope for opening things up (probably good as this is now considered to potentially be a bad thing these due to reduced port velocity) but there were a lot of lumps and bumps in the casting that could be 'softened' or removed.

Tony L also has penny on a stick valves and higher lift cams in his new engine build but he's binned the original manifolds so there won't be a direct comparison.

AFAIK it's all pretty interchangeable but others can advise better.

Indeed, by distance correspondence course, should give note to the source of the original information & work. Thanks.

All heads fit all engines but you need to make choices about external hardware. But you better go ask a friend

... bad day, had my medication now

[stephendell]

Indeed, by distance correspondence course, should give note to the source of the original information & work. Thanks.

Indeed the senior lecturer on the correspondence course is as I understand Mr Faullks!

That may be the case but things like inlet manifolds are not always interchangeable, the head castings can be very different. there is a massive difference between the port positions - 2.5 inlet won't fit a 3.0 head for instance

After pulling apart a Volvo B280F and an R25 V6 Turbo motors to build up a 2975cc turbo motor for my GTA I have some info. The heads on the Renault have nicer inlet and exhaust ports, but the valves are about 3mm less in diameter than the Volvo ones.

The inlet ports are of a good size and shape, the exhausts I believe are a bit small. I did port these out a little and hit water jacketing and needed to get this welded. I really didn't take out more than a couple of mms. Perhaps there was some core shift in my casting causing the ports to be closer than normal to the water jacket. There was no corrosion in the heads.

I got bigger valve seats fitted to the Renault head and used the Volvo valves. The V6 Turbo cams are where I believe the biggest gains are to be made as they are tiny. Without boost you are flatout getting the engine to pull over 4000 rpm.

I have fitted the Volvo B280 cams, but have not assembled the engine, but will be using the 10mm longer stroke even fire Volvo crank and block, and a set of A610 pistons and sleeves, giving a 2mm overbore over the GTA. The conrods are both the same, with the pistons having 5mm less gudgeon the crown height.

Don't know what Hp this new engine it will make with the std manifolds and a GT30/71R ball bearing turbo .63 AR turbine, .5 AR compressor. Looking to run 1.2 bar. Currently running this turbo with 3" exhaust on the std engine, making it somewhat laggy, but it certainly doesn't run out of puff at the top end like the std one.

Maybe this year I will get around to building it and fitting it to the GTA. Of course this will lead to the rear cradle being blasted and painted, and the gearbox being rebuilt, and new radiator pipes being made up in stainless, so I have been putting this off as the car is likely to be off the road for a while.

Tony, correct that's why I mentioned you need to make decisions about the external hardware. But all is possible just down to whether it's worth it. I've built a 2.5ltr bottom end with 3ltr n/a heads and done the necessary messing around, and actually on reflection wouldn't consider it today given the grief involved (turbo build). Obviously cheap availability of 610 hardware would have been a different matter though..

Alan, I assume that's the 46mm inlet valve, if so then this is the same as the 3ltr Renault heads. Have you checked your inlet valve clearance with the 280 cams? When I dry built the above - bare in mind this is the 3ltr head casting and 46mm inlet valve - I had issue with clearance on the 280E cams around 10 deg ATDC. The total clearance at TDC from seat to piston with the 46mm valve was 3.8mm.

What size exhaust valve are you using?

Sounds like you were a little bit unlucky with the castings on your heads, but the variation and quality is so mixed that it doesn't surprise me - much rather Fiat / Lancia of the same generation any day.

Sounds to me like you're one step away from simply fitting the 610 pistons and B280E cams to a 3 litre laguna engine (which is the version with under piston cooling).

610 pistons have a crown height some 2mm lower than a Z7U, more than enough to make up for the pocketing on the original NA pistons.

Hi Martin, contact point was on the flat land area outside the raised crown. I assume the 610 pistons still come to the top of the liners, and not 2mm down the bore? Are the 610 pistons the same as the 24V? I could check with those.

I've only had one block with oil squirters, and didn't check to see if they squirt at the inlet side of the piston under crown (or just generally everywhere) to heat the end gases, but judging when this was all designed in, think it's more to do with emission controls and fast warm up than any potential for detonation control. Comments, anyone know?

Once apon a time a myth propagated that the Lagune engine was a 610 engine with no turbo, and the Safrane engine was higher compression but ran less advance (!). This came from the quoted engine codes in the PRV engine book, but was erroneous. However the link remains and I wonder if Renault pressed some turbo blocks (with the oil cooling) into service in a more mundane form.

Anyway, to get a static CR of 7.6:1, you end up with a crown height around 2mm (can't remember exactly) below the top of the liner. Certainly this matches up with the works Venturi 24v piston Kevin leant me



24v's have a taller crown than the 12v's, but only the 12v pistons are pocketed. not sure what the quoted 24v CR is. I think Steve still has my set of 24v pistons.

I know a few people have been saying the heads are restrictive but as the only person to have made more than 300 bhp (dyno proven) on a single turbo Z7U I would suggest the exhaust manifolds are definitely an issue to look at. The way they heat up once you get past 250 bhp is staggering and worrying. If you want to reliably run much over 300 bhp then new manifolds or twin turbos is definitely the way to go. The Venturi's make loads more power from their twin turbo engine with a not mahoosively different head/cam to the A610. Tony Law's new engine will have this set up with a lumpier cam (i'e not with round lobes ) on a 2.5 so it'll be interesting to compare.

All the really powerful PRV's I've read about seem to be based round odd fires - are they better?

2.5 = Z7U
3.0 = Z7X

Venturi twin turbos are 24v and the heads and cams are -very- different. AFAIK the bottom end of the 400hp cars is standard A610, the top end is standard Citroen/Peugeot 24v with their own cam profile, though there is talk that Venturi re-worked the valvetrain and those awful pushrod thingummies

The use of odd-fire on really high power PRVs comes from the lack of strength in the split crank pins in the even fires. Engine management systems that support odd fire are expensive.

Engine management systems that support odd fire are expensive.

I've just purchased an Emerald ECU to run my twin turbo set up that came via Tony. They could set up the ECU for even or odd fire and the price is comparable with Adaptronic.

Oops less beer when using the quote might help next time but hey it's my birthday !!

Yes the Venturi LM etc bottom end is std 73mm stroke crank, straight from the even-fire parts bin. Venturi went through more than one stage of development with the valve train mods from the components I have seen first hand, and have an early version of the modified setup. The later generation solution is very nice indeed and worth a fortune if you can get hold of it. I have sketched these up, and may one-day machine up, but loads of work, and then still have to make the solid follower adjusters etc.

The factory ceramic insert solution wasn't much better than the OE followers that got chewed up in short order. They suffered from cracking in racing conditions, and the smaller area restricted valve acceleration rates.

I have had a set of turbo profile cams (hydraulic) made for a 24V, but practicality is dictating it will be unlikely I will build now – my original intention was to go twin turbo, and have nearly everything to do it, time is my biggest factor now. There’s nearly as much fun to be had in easier ways… and from what I hear, Ireland has something to do with it, unfortunately it wasn’t me!

Hi Martin, contact point was on the flat land area outside the raised crown. I assume the 610 pistons still come to the top of the liners, and not 2mm down the bore? Are the 610 pistons the same as the 24V?

The A610 pistons don't come to the top of the bore. Approx 2-3mm below, I don't remember exactly, but if they did in my case the comp ratio with the 3L crank would be 8.6 to 1, but end up with 7.6 because of the distance down the bore.

The chambers of the Volvo B280F and Renault R25 V6 T heads were the same.

I know a few people have been saying the heads are restrictive but as the only person to have made more than 300 bhp (dyno proven) on a single turbo Z7U I would suggest the exhaust manifolds are definitely an issue to look at. The way they heat up once you get past 250 bhp is staggering and worrying. If you want to reliably run much over 300 bhp then new manifolds or twin turbos is definitely the way to go. The Venturi's make loads more power from their twin turbo engine with a not mahoosively different head/cam to the A610. Tony Law's new engine will have this set up with a lumpier cam (i'e not with round lobes ) on a 2.5 so it'll be interesting to compare.

All the really powerful PRV's I've read about seem to be based round odd fires - are they better?

As Ive always stated, the manifolds/turbo are and always have been the problem.

Simple comparison - Safrane, and A610, identical engines.

One has biturbo manifolds and runs 7psi and makes 268bhp

The other has the single collector manifold setup and only makes 250bhp at 11psi.

Now compressor flow are both equal, as they are both still running into the same 55mm throttle body, thus the only change is the exhaust side.

No point do anything to the engine mechanically untill you rectify that issue. But then you have two drawbacks, either the extreme cost of putting a DECENT biturbo setup on, or the extreme lag of a large bore single collector turbo setup.