Race Engine Forum UK

Hi Guy,
I have a 128 circuit car that I have been putting a little time and effort into, Whilst I am pleased with the progress I have been making with the car I feel there is something not quite right with the engine. I was hoping for a better result on the dyno with the setup I have.

I am trying to make the most of what the car came with when I brought it, before I get carried away changing things.
Not being an expert I could quite easily head of in the wrong direction and wast time and money.

I will try to give you as much information as I can. Can you please have a look and let me know what you think.

The engine has the following setup

1500 Strada Bottom end (Std as far as I can tell)
Std Flat top pistons
Lightened Flywheel

Cylinder head
Originally 1100 or 1300 I think it has the 12mm head bolt holes
Exhaught Valves 31mm
Inlet Valves 40mm
The head has been extensively ported, Unfortunitly I did not measure the size of the ports before I but it back togeather but I can tell you that I had to enlarge a Tipo inlet/ex gasket by 5mm on the inlet ports and match port on the ex port.
Most of the material has been removed from the top of the ports as they flow around the corner before the valve seat.

Double valve springs (Unknown origin.)

I have cc ed the head and block and found the Compression ratio to by 10.5/1

As for the valve seat all I have done here was to give them a lap in, they all ended up with a land about 1.5mm wide. Unsure of angles I left well enough alone until I learn more.

Have shimed all the valves to run a clearance of 0.3 on the cam shaft after you explained the reasons for the clearance to me previously. (thank you)

I have sent the camshaft away to a local company to find out the specs and also managed to find out where it came from, The company that ground it is no longer trading and I believe the owner has passed on.

It has been discribed to me as circuit only

I have CNC machined a Vernier cam timing pulley and dialed the cam shaft in at 106 degs and moved slightly on the dyno to 108 degs which helped slightly.

Carbs

2x 40mm DCNF's

32mm Chocks
160 Mains
70 Idiels



Now for the interesting bit , this is where I think my problems may be, I will be interested to see if I am way of the mark.

THE HEADERS

4 into 1

Primaries 44mm 1.75 inch 800mm Long

Collecting into a 2.5inch pipe to the first muffler the reducing down to 1 7/8 to exit the side of the car.

He is a copy of the Dyno sheet, I had hoped to see somewhere around the 110 hp.
Also just out of interest a 5/1 final drive and Limited slip diff made from scratch. I think this has had the biggest effect so far on improving the car


I look forward to your constructive criticism and I hope this comes out all right, A bit unsure of photo size!

Regards, Andew D

If the cam is a regrind, that will never produce any decent torque or power whatever figures are stated on the Audie Tech cam map, and yes it looks familiar, 45/75 10mm lift, I might know its origin but I'm not stating it here, would be breaking my own Protocols because I wouldn't have much good to say. Numbers mean nothing when it comes to cams, unless those numbers relate to a billet design of proven performance. That cam, I reckon, has to go for a start.

Your carbs at 40DCNF are OK, ignoring that if you put a billet cam in there, from me, Kent, Piper/whoever_u_like rejetting/rechoking will be needed. Likewise I don't see much wrong with your 4-1 31.5" header.

As far as the head goes, looks like a fair bit of work has gone into it eg: deshrouding, but if the ports are way big (my dimension for 37.5mm valve is shown on the graph, with a 40mm inlet I'd go parallel 33mm); standard inlet port is about 29.5mm at smallest section, + 5mm thru would be too big really. I used 32-21mm port with a 42mm valve on one of them, got 90 cfm at 11mm lift - see second 'KM SOHC' graph) and that head developed 175bhp or so on a 1600 SOHC Tipo block.

The short side radius is utterly crucial, get it wrong and you get turbulence coming off it that disrupts the whole flow regime - badly. Good closeup photo from you would help me ID that. The valve back angle and seat angles are pretty critical, more so than the contact width actually - although they don't like anything much under 1.5mm wide - and here is a graph of an X19 1500 head I'm doing for another member showing what happens if you don't get the angles right.

Hope this helps in the first instance.

G

Hi Guy,

Ok so the cams for the bin, Id rather replace it than make headers which I thought I was going to have to do.

I don't know if it is a reground one or even how to tell, as a rule are all regrinds a no-no or is it just the poor profile on this one which makes it even worse?
Of the different cams you have which one do you think would suit my engine bearing in mind that I am into circuit work and what sort of caracteristics will it give the engine.

I have found the old inlet manifold gasket which I matched to the head and the inlet ports range from 33-35mm, I know this isnt a very accurate way to go about it but I will measure properly and take some close up pics of the ports to post when I take the head of to replace the cam.

thank you,
Andy D

Cams photos - with good closeups and any markings?

GC

Hi Guy,
I have been informed the cam came from a company here in New Zealand , hense the first three letters on the cam , The company is long since gone so no conflicts of interest here, as for wheather it is there profile or just one they copied I dont know.
I would be interested to know how the caracteristics of the engine will change with your camshaft.

Regards,
Andy D

Thanks for doing your best with cam ID.

I have looked at the pdf cam data and unfortunately it's not clear to me what clearance if any was used for checked duraiton and cam 'area'. If it was measured at true running clearance of 12 thou the area of 36 inch degrees would indicate a billet grind.

However looking at the lifts (and assuming the figures are true, ie: with clearance allowed for) we have inlet and ex peak lift of around 10.4mm. LATDC inlet is 4.2mm and ex 3.3mm. That's too much inlet lift at TDC for a cam of realtively short duration and low-ish lift really. Certainly for this motor, in my exp anyhow. That's full race LATC and I'd be looking for much higher peak lift. The problem with a lot of LATDC is you need a lot of charge momentum to get it to work.

The cam data indicates inlet set at 101 deg FL and the ex 109. Being a single cam of course you can't move the inlet and ex lobes relative to each other, but you can move the inlet to 105 deg ATDC FL and this will reduce the inlet lift at TDC, and it will naturally shift the ex FL from 109 BTDC to 105 before. This might be a more stable combination, but you'd have to check the ex piston to valve clearance before running because it will be more than 3.3mm.

Some other comments>
Your valve combo (if stated correctly at 40mm/31mm is no good, because that only yields an E/I ratio of 60% - in other words ratio of valve area ex-inlet). You need at least 65% and preferably 75% or more or you're risking serious pumping loss (ex gas pressure in the cylinder doesn't drop to atmospheric fast enough and has too be pumped out by the piston) and diminished ex wave pressure wave effects. That's by way of saying the cross-scavenge you need on a race engine isn't working. Plus that big inlet valve, coupled with high LATDC is going to develop serious reverse flow problems 'off cam' (if it ever comes 'on' cam, that is ..) IAdd to this the cam configuration coupled with your low CR (flat top pistons) and you've got a mismatch really.

This is what I recommend:
35mm ex valve
Piper BP300 cam
GC 3VSR springs
Forged pistons to around 10.5-11/1 CR

Hope this helps for now, sorry for delay due to workshop load,

GC