Race Engine Forum UK

Hello Guy!

We prepare motor and vehicle for the avtocross. It is Zastava Yugo 65. The car is a few years ago already drive in the state championship, since then the car does not drive. The engine was
already prepare before, but some thing is not good.
I am interested in a good preparation of the engine.

The engine has the following setup:

1300cc Lancia Delta botom,
STD flat top Pistons 86.77 mm, make-Motins
crank 55mm, lightened slihtly to 9,3kg
original rods, lightned to 591g
flywheel 6,4kg (all done before)

Cylinder head:

original Zastava 1300cc
original valve size (31mm exaust, 36mm inlet)
ports already modifided by previous owner:
- exaust port was enlarded from original valve seat throat to 30mm on exit
- inlet port was also original on diameter of valve seat, only material form iron valve guides was removed and some material on port under valve seat, the diameter of inlet was from 28mm to 26mm with same sizes iron tubes


Other:

Weber 34 DCMP from Polonez with 24/24 venturies
modifided intake manifold with matching 28mm on intake port
regrind original camshaft (unknown duration) but I measure, that valve could not open more than 9,6mm if I calculated 0,30mm tolerance betven cam and shims.
original ignition
exaust form Fiat 4-2-1, with cast iron manifold


The engine bottom is already complete. But like I read on your site, all power is in the head, so I was wondering, what we could do with this head, because ex. exaust port is too enlarged for original valves if I look your advices, witch I found on forum.
What is the best way if we use original valves and Weber 34DCMP carb? I think, is possible some correcting ports on this head? What is the higher safest CR with original pistons and use of 100 octane gasoline? The old pistons are damaged (I think because too high CC-around 11:1 and uncorect ignition timing).
Please, any advice for some good cam, or information for 4-2-1 exaust for 1300cc Fiat engine.

I was already remove some material on ports under valve seat ( I read that this is not good way, but shape of existing port is very bad).
If is some other information need, I will write here or take picture.

Best regards, and many thanks for some good advice and help.

Some pictures:

MODEL POST!

Thank you for your first-class first post! I look forward to replying asap,

GC

I'm really sorry for the long delay. Sometimes I just do the easiest posts first I guess because I have so little time to read much detail some weeks.

1. Get rid of the regrind cam. You need a good billet profile and I would recommend a Piper BP300. You will never get decent power out of the 8v SOHC (or TC) on reprofiled cams, plus they will knock the valvetrain to bits too.
2. The piston damage is certainly detonation - it often fractures the top land on cast pistons and in this case it's probably overheating inlet charge.
3. I just don't understand the tubes in the inlet at all.

The best way to prep those heads - whatever the valve size is just to port them GC style. Bigger on the ports, careful attention to valve angles, deshrouding. I've written a lot on this in the GC Virtual Workshop. Check the flowtest and dyno test result at:
http://guy-croft.com/viewtopic.php?f=9&t=1712

(Also reproduced below)

You can see that the 36mm inlet valve on the X19 head (pale blue) gives 123bhp on OE FI inlet setup at 12/1 CR - with std CR (or lower due to valve seat work) you will struggle to get over 105bhp even with with the cam and right carb.

What you're doing in the 'well' region of the inlet port below the seat is OK, always port with guides out, but I would be concerned about the transition from steel tube to the rest of the port and I'm not sure what the tube diameter is anyway! If they were trying to make the port completely parallel - it doesn't matter so long as the 'included angle' of the port taper is 15 deg or less. When enlarging on those ports more needs to come off the port roof and sides than the port floor. If you take too much off the port floor it really messes up the short side radius and thus the low and medium lift flow.

To be honest I'd get another head and maybe convert the valve seats to the bigger Tempra 1600 SOHC 37.5mm inlet valve (see flow graph) and that should take you to 120bhp or over. The ex port prepping is so easy, just open it out around the valve guide region by about 1mm each side, shape the curve of the short side rad carefully, finish off at 80 grit or finer and and do a good 45 x 70 seat grind and leave it at that. Those heads really don't have a flow problem. If the ex manifold does not match the head - open out the ex manifold. That is not a general rule but it is true here if I have interpreted your photo right.

Think very hard about GC forged pistons. You are wasting your time running cast and in racing when you fabulous power they will break up at high rpm. I can design the dome any way you want. The useable CR depends on the octane rating of the gasoline.

Feel free to write again, I hope I've covered some of the things you want to know about.

G

Guy, what about fitting a 39.5mm tipo/tempra inlet valve? Any gain there?

Sure, that will work fine.

Go port size 32 to 31mm. The new big valve seat insert needs to be at least 1mm bigger on dia than the valve.

Remember the VRs (valve reliefs) need clearance:

Vertical 2.5mm (closest valve to piston proximity will be somewhere between tdc and 20 deg after for the inlet and 20 deg before tdc to tdc for the ex)
Radial 1.5mm


GC

Thanks Guy. But what about exhaust valves? Are the 31mm valves big enough or one should go with 33mm valves vhen fitting big inlets? 33mm ex valves are also found on tipo/tempra 1.6 sohc engines. They go in combinations 37.5/33 and 39.5/31mm (in/ex)

OK - do the maths!

Work out the valve areas. If the ratio of ex valve area to inlet valve area is less than 70% go bigger. 75% E/I is ideal.

G

Hello Guy.

Sory for delay with pictures.

Many thanks for a lot of answers. Yes, I also see, that is better to get another head, but for first time I use this one.
The tubes in inlet port are 28.5-26.5. I see that you say that 32-31 tapper port is good for 1600cc engine. Is this also good for 1300cc
engine. I see that smaler than 29mm is not good-for inlet port.

In last days I work on:

I reshaped bad surface under inlet valve seat, instaled new valve guides and new 36mm inlet valves from Ritmo 1500.
The valve throat diameter was enlarged to 32mm, on valve was made 30deg back cut. The diameter of exaust port was 30mm, so I instaled bigger 33,5mm valves from Fiat Tipo 1.6. First I enlarged ex. throat to 28,5mm,
then mill 45deg angle so long, that exaust valve come so deep, that valve steam look on other side 39,9mm out of head. So I could used
old shims. I also make 75deg cut into valve seat ( I do not have 70deg mill head, and also do not know why my cutters have 46-31deg and not 45-30deg). On ex. valve was also made 30deg back cut. Chambers are cc-ed, all 4 are around 24ccm, what will give us 10,7:1 CR (with top regrind block-piston look 0,8mm out of engine block).

I have also worked on chambers, like I later see and here read, on wrong side, because of hot spots and detonation. Also have been made three cuts, witch I see on some Nisan and Honda heads.( I make this for experiment, if something was different with better ignition of mixture). In this time we use this head and cam, because time is runing, but nex time we start with new head, cam and other things.

A lot of useful information for instaling valves and other work I found on your site, so many thanks, that you sharing knowledge with us.

Only one question. I look punto 1,4 GT turbo head. I do not understand, what is gain if this head have bigger ex valves-33mm, but valve seat and
diameter of valve seat is same that on heads with 31mm ex valves? Only change is, that GT punto have 3 locks on valve steams, and I think stronger springs.

I have some questions Guy, for jeting carb witch we have: The carb is Weber 34DMCP fully mechanical, with 24/24 venturies. The carb does not have main jets, only two iddle jets, two emulsion tubes with air corectors on top, and one start jet I think. I think that this jets are not good. I found on net that carb like that have original some FSO Polonez 1500, so jets maybee is not good for 1300cc engine. What do you think Guy, are air correctors too big?

jets are:
1) 45 (0,45mm)-primary
2) Emulzion tube F35, jet on top 230-primary
3) Emulzion tube F35, jet on top 200-sec.
4) Write on bottom of jet 130F1, jet on top 220
5) 100 (idle jet)-sec
Best regards, and thanks for answers.

Hello again. Engine at the moment runs great with 100 octane gasoline. The ignition timing is 12deg at idle. But engine is not runing so great, when second throtle on carb is open. So I thing that we must change jets on this carb. Guy, one question: What is good way to see if A/F ratio is ok? Is using CO exaust analyser good way?

In one post back, I attached picture with jets, that we have now.
many thanks for your time Guy.

Best regards