Jenvey 45's and 438 cams

[mikekean]

Hi Guys,

Ive already got ITB's on my rally car but im going to be taking the head off soon to fit some uprated valves and though about adding a set of cams to get a bit more poke at the same time.

What sort of power would I be looking at with 438's and a head skim? I dont want to go for anything to lairy as i want to keep some low/mid rpm torque.

Cheers

Mike

 

[Cub.]

If you do go for 438's I have a set coming out of mine soon, PM if interested. Will be looking for £325ish.

 

[Chip-mk1]

438 timing doesnt seem to work as well on bodies as the 421 timing does.

On 421 though, 210bhp is pretty realistic generally.

 

[mikekean]

Thanks for the offer Cub but I want new cams really.

What sort peak revs would I be seeing with 421's, Don't really want to rev it past 7.5k if I can help it. Do the badly effect low down power when running them with ITB's? Are they running on the limits of valve to piston clearance or can I get away with a bit of a skim off the head as well?

 

[Fred@BTM]

i did a 438 car high comp with a skimmed head etc, just squeezed 211bhp and 180lbs

 

[Dan519]

I did 209 and 175 on stock bottom end and 421s
https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-ash3/6642_440095929377567_1937322143_n.jpg

 

[Dan519]

Thanks for the offer Cub but I want new cams really.

What sort peak revs would I be seeing with 421's, Don't really want to rev it past 7.5k if I can help it. Do the badly effect low down power when running them with ITB's? Are they running on the limits of valve to piston clearance or can I get away with a bit of a skim off the head as well?

use the longest induction length you can. You'll push the power and torque band down the revs nicely. I never enjoyed taking mine past 6.5k really

 

[mikekean]

Was that with high comp pistons Fred or just a head skim?

Danny I've got 90mm trumpets atm, would you recommend 120mm trumpets instead?

So what's the general consensus, 438's or 421's?

 

[Ph1 Tom]

Longest you can fit whilst keeping a filter. Trim under the bonnet if you need to.

421, if you've already got itbs and you're getting new cams it's a no brainer. Although the engine dynamics cams have a longer duration maybe worth a look as people have had good results with them. I went with the pipers, about £250 cheaper than the 438 and an equivalent imo.

 

[The Russian.]

If you do go for 438's I have a set coming out of mine soon, PM if interested. Will be looking for £325ish.

I could be interested

 

[Cub.]

The Russian. - afraid they've already been sold Jacob bud. Not even out of the engine yet! Lol!

If the sale falls through, I'll PM you chap

 

[The Russian.]

The Russian. - afraid they've already been sold Jacob bud. Not even out of the engine yet! Lol!

If the sale falls through, I'll PM you chap

No worries chap. That would be great thanks.

 

[Meek_racing]

Twas mine, that was with 120mm trumpets too. both head skimmed and high comp. If you are running aftermarket ECU and cams, why not get wilder cams than these?

Was that with high comp pistons Fred or just a head skim?

Danny I've got 90mm trumpets atm, would you recommend 120mm trumpets instead?

So what's the general consensus, 438's or 421's?

 

[mikekean]

I don't really want to go any wilder as that will mean revving the motor more which decreases reliability and you loose low end power.

Its all well and good having lots of power but when you don't finish a rally because your engine has blown all the power you had was useless. I want to keep the engine as standard as I can internally to keep it cheap if one blows/wears out. I can just replace it for another standard engine and swap the parts over. It's still early days for the F4R tuning wise IMO, so I'm going to wait a couple of years and see what the likes of Sandy Brown etc can come up with. At that point I'll purchase a proper race engine.

So 421's look the route to go, how much can I skim off the head before I get clearance issues? Wasn't going to go mad like 0.5-0.8 mm

 

[Ph1 Tom]

With the lift on the 421 I'm not sure, you'd have to dry build and get some plasticine on the pistons.

Someone might know though. However I'd imagine a 0.5mm skim (which is a fair bit) won't cause any trouble.

Have you already got Supertech valves?

 

[mikekean]

That's what I was trying to avoid lol, was just going to see what people had done before and subtract a bit off for a safety margin. If it comes down to it I'll have to do a dry build.

I haven't yet no, will order everything I need at the same time. If the valve seats are in good condition can I just lap the super techs in or do I need the seats recut?

 

[Chip-mk1]

Just lapping is fine.

The problem with a dry build, is you will need to make yourself a solid lifter to ensure you get the correct valve opening.

Slight variations in cam timing will alter how much you can safely skim, so make sure the cam timing when you dry build and plastigauge it is EXACTLY the same as when you do the final build!