1300ccm twin port high rev engine

[samotorsport]

Here we go,
I need to build a new engine for my 67 bug as his "old" engine is going to move to the bay.
What I have:
AS41 engine case 1300ccm
stock crank and con rods
1300 ccm twinport heads with standard valves springs etc.... ( can be reworked )
2 x Weber 36 idf

I could go and modify it to 1600 ccm but that s not my plan, I wanna build a high rev 1300 ccm engine ,
Does anybody has some experiences with such a project and tell me how much power I can pull out of it for "daily use" ?
What C/R are you running , what camshaft would be a good deal for this

I would like to bring it to 5500-6000 rpm , 65 bhp
Thanks for any link to a build thread or what ever you know about it.
Thanks in advance
Best regards
Sam

[Marc]

When I started circletrack racing it was in a class that was limited to an original displacement of 1300cc and stock stroke; bore could be .040" oversize. We could use any carburetion that'd bolt to unaltered stock manifolds (fortunately for the Beetles, they were allowed to use DP Type III intakes so Solex 35PDSITs could be fit).
Never had any of those motors on a dyno but I think 65HP DIN would be dreaming, I doubt if they made an honest 65HP SAE. And I ran a static compression of over 12½:1 - the heads were flycut to the sparkplug hole, necessitating the removal of two fins (and the notching of the piston tops for the sparkplug electrodes to clear).
This is definitely more radical than you'd want in a daily driver so there's not much worth comparing, but I bring it up because there is one salient concern: 35.5mm intake valves DO NOT FIT inside 77mm cylinders. Cylinders bored 1mm oversize will work, but 78mm pistons and rings were hard to find even in 1978 - to run any serious valve lift with heads flycut that far the cylinderwalls had to be ground away for clearance. Either way, you're talking about some major valve shrouding so the intake flow patterns were lousy.
It's just not worth the effort IMO to try to get "1600" power from an ACVW 1300. With stock gearing, raising the power band that far is going to demand short tires so you'd probably end up having to buy tires (and most likely rims as well) which will cost you more than just replacing the pistons/cylinders and opening up the heads. Also, if you aren't aware, at ~5500 RPM the stock crank starts flexing which beats the hell out of the center main bearing and engine case, so it's really not wise to set out for 6000 without a counterweighted crankshaft.

If you're determined to build something using 77mm pistons, you might consider putting in a 76mm crank to get the displacement up enough that it could make enough torque to live with at more reasonable RPM (a smaller cam and/or lower C.R. will avoid the valve/cylinder clearance issue - the shrouding will still be there but it's not quite as critical at lower RPM). Now you've got a wider package and may need custom-length pushrods, but it should be worth it for the 130cc gain. 1415cc is still a far cry from 1585/1641/etc. though.

[samotorsport]

As I mentioned in the other topic I got a good case for building up my new engine, this one also has the needed attachments for the rear engine mount in the bay.
So basicaly I am back to square one.
I ve got a good case , and a set of 36 idf Weber with 30 venturies .
A camshaft I do not have yet, as the case is open anyhow I wanna change it straight away

I fully agree with the rpm crankshaft problem, so I stay under 5000 .

What do you think would be the perfect size engine for the 36 idf ? Still keeping in mind to stay with the thicker cylinders .
So I would be thankfull for a good "buildup guidelines" for an engine with the parts I have.
Thanks in advance
Best regards
Sam

[Sqrbckguy38]

I would say the 36s should be good in a twin setup to even an 1835. As far as a cam, go with a W100 or a W110 if your staying below am 1835.

[samotorsport]

Thanks for the tip, I ordered the 1776 thick wall cylinders for my project engine, I think this suits the dual 36 setup pretty well.
I gonna use the twin port 1300 ccm cylinderheads with stock valves.
I just gonna open them up for the bigger pistons.
I just have to find out how the chamber volume changes when I gonna rework the heads

[Marc]

I've only had my hands on a few 1300DP heads (that engine was never offered in the US) but IIRC the chamber CCs were ~4 less than 1600DP....let's say they're 48cc after the valve job & flycutting, if the piston deck height is .050" your static C.R. will be about 8.9:1. Personally I wouldn't go that high, but I understand you have better pump fuel available over there.
Is the crank a stock item (no counterweights)? If so, design the engine to stay below 5500 RPM. You WILL want to 8-dowel the flywheel/crank; a lightened flywheel would make it more responsive, but the ubiquitous 12½-pounder which works well for a street 1775 is a bit light IMO for a stock crank, if you have the 'wheel lightened keep it at least a couple pounds heavier than that.
I would use a mild cam (W-100 or W-110, or something in that range) with an entry-level set of HD single springs and "solid" rocker shafts; you could probably get away with stock pushrods & adjusters - assuming the geometry is OK - but many folks opt to go with steel/CrMo p'rods and swivel-foot adjusters even at this level for added peace of mind.

[E_bug]

I would say it all comes down to the Budget you have..

If you dont go the rpm way go to the boosted venue.

Up to 5000rpm small turbo , efi , (or not) will keep you happy with a 1.3

[Slow 1200]

are those 1300DP heads used? most of them are cracked pretty bad these days....make sure you have them checked

[samotorsport]

As always it is a budget thing
I gonna stay under 5500 rpm for sure, the heads I gonna use are used once but without any crack !
I gonna open them to the desired 98 mm to take the bigger cylinders and measure the cc volume , as of there I gonna adjust the deck clearence and calculate the C/R , would like to come to 9:1