Renault 1108cc OHV questions

Road-race engines and ancillaries - general discussion
Post Reply
JK
Posts: 3
Joined: September 25th, 2006, 7:28 pm
Location: Poland
Contact:

Renault 1108cc OHV questions

Post by JK »

Hello, I run a 1988 Renault 5 in amateur rallies. Polish amateur rallies are somewhere between American autocross (cones, most of the time the car is in 2nd gear) and real rallies (using "natural" terrain to set up courses). Perhaps you will get a better idea about them by watching this movie (95MB):
http://www.gorzow.mm.pl/~skrzynka/rajd_poznanski_06.avi
What is needed in such an event is more torque in the low rev range I think. At the same time the car will be driven on the street so perhaps some compromise will be necessary.
The engine in my car is a C1 E-G750: 1100cc, iron block and light alloy head. The crankshaft rests on five bearings. Factory data claim this unit has a 9.5 compression ratio and performance figures of 47HP at 5250rpm and 79Nm at 2500rpm. The fuel is delivered by a 1 barrel Solex BIS carburettor.

My questions are:
1. Is it "worth" tuning such an engine? My budget is pretty limited and some of my friends say I'm better off swapping a 1400cc SOHC engine than trying to get anything out of an OHV. I'm reluctant to follow their advice however, as a 1400cc engine would put me in a higher class and could be more expensive (I'd have to swap pretty much all of the drive train and front suspension as well). Plus I've heard that 1200cc OHV Opel units used in C series Kadett were very good units that could safely rev up to 7000rpm. So perhaps OHVs aren't that "poor" after all?
2. My plan is to swap the stock carburettor with a 2 barrel Weber 32 DRT that was used on 1400cc engine and replace the stock header with a 4-2-1 design. What kind of results can I expect from these modifications?
Julian
Posts: 181
Joined: June 22nd, 2006, 6:45 pm
Location: Manchester, UK
Contact:

Post by Julian »

To answer your first question you need to decide what you want to achieve. If staying in your current class is the priority then you have already answered your own question. How much tuning you undertake would be down to your budget. The reality with small engines though is that it costs more to make significant gains (in terms of real horsepower).

The OHV layout is not ideal but there is always scope for tuning, more importantly the old Renault OHV has seen many years of development.

To answer your second question with any degree of accuracy would demand more imformation on exactly what you are going to do but as an outline you are going to make some gains provided you do the necessary research.

A 4-2-1 exhaust manifold will allow you to take advantage of a relatively broad range of revs but you will need to tune the header lengths to get what you want.

The carburettor is a bit harder to measure - you have the potential for good performance with one of the double choke webers. Reasonable economy on the first choke and performance on the second but it will take some fine tuning to get what you want and that means rejetting. Just bolting the 1400 carburettor onto your car will not give you what you want.

In order to make the most of these upgrades you will need to do more work. Ideally you need to look at using a different camshaft to optimise on both the new exhaust and carburettor. At the same time the cylinder head should at least be cleaned up and the valves reseated, matching the ports would be my next priority but I would also suggest you look into getting the inlet valves replaced with larger equivalents, match the combustion chambers and have the ports opened up to ease the gasflow. In short what your average headshop would refer to as a fast road head. Of course this may not be appropriate to your regulations so it is important that you plan out carefully what you can and cannot do and take advantage of what the rules do allow.
JK
Posts: 3
Joined: September 25th, 2006, 7:28 pm
Location: Poland
Contact:

Post by JK »

Thank you for your reply.
As far as class requirement go, you can do everything to you car and engine as long as you don't add forced induction. My friend ran a fuel injected Fiat 126 with an engine rated at 45-60hp (stock engine has 25hp) and the only thing that was left from the old engine was the block as far as I know.
I knew that simply bolting on different parts is not the way to go but I didn't realise there are so many factors to look at. This troubles me as tuning market in Poland is still pretty much in wild west (or wild east if you prefer) state. I have no idea where can I get a camshaft or the mentioned header for the my engine for example. This means there will be a lot of custom building and no guarantee of performance gains. So perhaps the swap will actually be cheaper, even though I'll end up in the 1300-1600cc class.
sumplug
Posts: 234
Joined: June 25th, 2006, 10:25 am
Location: Banned 4th Oct 07 by GC
Contact:

Post by sumplug »

Well you need to read up what Gordini did with Renault tuning. He was the man who got plenty of power from these OHV engines. Indeed, why not fit a 1300 OHV renault 5 gordini spec engine in to your 5. Should go straight in.

Andy.
JK
Posts: 3
Joined: September 25th, 2006, 7:28 pm
Location: Poland
Contact:

Post by JK »

Getting such and engine is one thing, fitting it into a Super 5 like mine is another. The first and second generation 5s are pretty much different cars.
Julian
Posts: 181
Joined: June 22nd, 2006, 6:45 pm
Location: Manchester, UK
Contact:

Post by Julian »

Rather than trying to get everything done locally I would suggest doing a bit of shopping around. There are companies out there in Eastern Europe that can help even if they aren't *in* Poland.

If you have an anything goes set of regulations (bar forced induction) then there is plenty of scope open to you.

Higher compression ratio, flow optimised head, balanced and lightened bottom end, lightweight valvetrain, etc are all possible.

The extent of the work is going to be down to budget of course and ultimately how far you want to go if the car is to be used on the road.

If you are going to do any work on the bottom end yourself I will give you just one word of warning - the bearings do not all wear at the same rate due to the way the journals were designed by Renault so it is not enough to measure the tolerances on just one of them. Make sure you do it on all of the bearings.

One more bottom end tip - check the pressure of the spring in the oil pump. We've had a few pumps on Renault OHVs that were hopelessly below specification leading to woefully inadequate oil pressure.
Post Reply

Who is online

Users browsing this forum: No registered users and 43 guests