I have finished the 1380cc kent instal in a Marlin i intend to trial later this year. It as a few mods twin dhla 40s a four branch exhaust and an A2 cam rebuilt engine etc.
I have covered 1500 miles in the car and yesterday i drove down from north lincolnshire to kidiminster then up the m6 to manchester and back over the pennines home. A great day spoiled by heavy rain near warington .
Never missed a beat and apart from a cable thinking about sawing a hole in a heater hose all looks good. I could see no issues with the car but as to be expected from a small crossflow it felt a little low on torque compared to the old 1800 MGB engine it used to have installed. But the car for all that drives a lot better generally throttle response with the 4.6 diff ratio is reasonable but i need it to hold on to a pull a little longer than it does I asked a wile ago regarding torque improvements and Megajolt seemed to be the cure all for most ills in this respect do you think it will be worthwhile on this engine in this application.
This engine has a lightened flywheel i installed it because it came free on an 1300 i had given, was in good condition so i used it, in hindsight do you think fiting the standard 1300 flywheel would improve torque and throttle response or am i best to stay with the light flywheel.

All a heavier flywheel will do is slow the throttle response, flywheel weight has nothing to do with the torque in any way. What do you mean by lacking in torque? If you are after power throughout the rev range then you need a bigger engine. The trade off is smaller engines have a faster response, bigger engines have a flatter torque curve.

The only real way to improve low rev torque on an existing motor is to reduce high rev torque - ie milder cam and smaller inlet tract that moves the torque band down the rev scale other than judicious supercharging that is and always assuming that fuelling and timing is spot on.

Also increasing compression ratio will help too assuming you can get the right fuel octane.

I have a 1680 crossflow and just changed from twin 40s to bike cars,although not fully set up yet,has made a great improvement to thottle responce and revs(will not be going back to 40s)

Forgot to mention - a four into two branch exhaust manifold will help spread the torque curve somewhat compared to a four branch one.

Advancing the cam ~7degrees should give 10% improvement in mid range at the expence of 5% at the top.

Just use some offset dowels and a vernier to set up.

Regards Mark

TBH the reply you probably dont want to hear is switch the Xflo out for the B engine, as that has the torque you want and can be tuned for more power, or a 1.8 Zetec. In fact I've seen a zetec head grafted onto a B bottom end!
If you want to stick with the Xflo then you'll need a small bore 4-2-1 ehxaust with long primary's, GT inlet manifold with a 28/36DCD, stock cam (not even the GT one just the boggo stock cam) and source some aftermarket rockers with different operating ratios to increase valve lift. The Xflo suffers from a shortage of valve lift anyway. For trialling the stock flywheel (1.3 Xflo was the lightest stock flywheel) may be a better bet especially with a stock cam.

Did you pick the Xflo up in this spec or did you spend lots of money building it to this spec?
Have you tried it on any trials yet? - I would be tempted to do a trial or two to see how it performs before making a decision on changing anything.

C

[Edited on 15/4/12 by chillis]

Lots of food for thought there, the offset dowel idea sounds a good one and a trade off i am more than prepared to take.
MY Engine? it cost me very little to assemble i had stockpiled many parts for this engine and what work i did outwork to others was minimal. I Have no experience in classic trials whatsoever, the car was tackled as a technical exercise as much as anything else. I asked a few questions on here regarding the ford engines and picked a few brains insprint and hillclimbing circles and came up with a plan for this crosflow.
I did a few u turns initially on actual engine choice and the old B series nearly stayed at home, but her weight problem made me evict the old lady in favor of a old but much more lithe replacement. The pinto was suggested from the engines eligible but it is tall and fat never a good match.

Just a thought as I know nothing at all about trials cars but from what I understand traction and lugging ability is important.

If the above is true then the less cylinders you have the less torque peaks you have per revolution as a twin cylinder only fires once every two revs and not once a rev as per a four cylinder so the less chance there is of breaking traction - I would think a large Harley motor would be ideal for the job so go BEC. (This is basically why off road bikes are single or twin cylinders and not four)

I understand exactly where you are coming from ivan , But so do the ACTC/ MSA car derived engines only, and on the class 7 list for the marlins, it is a grim choice. A series B serieso series the push rod Triumphs 4s and 6s the kent engines the pinto the fiat lancia twin cams and technically the alfa twin cams the old nord type alfas that is spider gtas etc.
The best is obviously the alfa then the fiat but rare and a bit porky, the A series performs quite well but i think out that lot the small kent as to be the right choice. Raw HP is all well and good but just how much HP do you need to spin a 750+ kilo car to a smoking standstill on a dirt track hill on a wet autumn day. Engine placement is pre set in the rules so basically you play the game with the cards you are given for your chosen car in your chosen class. You can dream up a car and have more radical options open to you by running in class 8. I have watched these classes and trials generally, and worked out what i think will work in this car, i think it will deliver more than its driver is capable of delivering.

[Edited on 17/4/12 by deep blue]